A swappable modular metal hyride system with 1KG hydrogen storage capacity for vehicular applications

Abstract

The present invention discloses a modular multi-tubular metal hydride (MH) based hydrogen (H2) storage system for storing 1kg hydrogen for vehicular applications. The present invention aims on developing least energy intensive hydrogen storage system wherein primarily utilizes high velocity ambient air due to vehicle motion as heat transfer fluid to desorb hydrogen. The present invention also discloses the impact of different profiles of artificial surface roughness over MH tubes which improves reaction performance due to improvement in heat transfer coefficient during fluid flow. It also proposes the use of water and PCM as an energy storage medium to store heat energy released during absorption and supply the same to desorb hydrogen from MH. The MH based hydrogen storage system in the present invention is compact, portable and swappable unit which can be attached in multiple units for higher hydrogen capacity and swapped with other unit to refuel similar to battery swapping.

Description

[0001]A SWAPPABLE MODULAR METAL HYRIDE SYSTEM WITH 1KG HYDROGEN STORAGE CAPACITY FOR VEHICULAR APPLICATIONS TECHNICAL FIELD The present disclosure relates to hydrogen storage system, metal hydride-based hydrogen storage, multi-tubular metal hydride system for hydrogen storage. More particularly, the invention relates to a portable, least energy intensive, swappable and compact modular multi tubular metal hydride (MH) system of 1 kg hydrogen (H2) storage capacity for vehicular applications. BACKGROUND The dire need to mitigate the consequences arising due to extreme use of fossil fuels for sustainable life on planet earth have led to far reaching transitions globally for decarbonization of energy landscape. Thereafter the adoption of alternatives as well as green energy technologies have gained an unprecedented momentum worldwide with major focus on decarbonization. Hydrogen being an energy carrier has also been viewed as a potential medium to decarbonize the energy sector along with renewable energy technologies. The gravimetric energy density and ability of producing hydrogen using renewable technology as a green hydrogen makes it a vital fuel for the decarbonizing energy sector. However, irrespective of numerous advantages, the primary challenge in the deployment of hydrogen technology remains the storage of hydrogen. In the present scenario, the commercially matured technologies such as compressed hydrogen storage (350 bar & 700 bar) and liquified hydrogen storage are utilized as probable technologies to store hydrogen. However, these matured technologies are energy intensive, cost intensive and possess safety issues in terms of their infrastructure development, large scale deployment and public acceptance. The solid-state hydrogen storage specifically in metal hydrides is among one of the potential technologies in order to overcome the limitations associated with compressed and liquified hydrogen storage technologies. The hydrogen storage in the form of metal hydrides offers higher volumetric energy density as compared to mature technologies, safety, long-term hydrogen storage is possible at lower pressure (<100 bar) and near ambient temperature using different classes of metal hydrides. The material properties of several class of metal hydrides can be tailored to accomplish required thermodynamic as well as kinetic properties which makes them favorable to use in many applications such as hydrogen storage, thermal energy storage, hydrogen purification, stationary power generation, nickel metal hydride batteries, vehicular application, refrigeration and air conditioning etc. However, the hydrogen charging process in metal hydride is an exothermic reaction while discharging process is an endothermic reaction. Thus, the energy transfer to or from the metal hydride is limited by heat transfer wherein removal of energy from MH bed during absorption process and supply of heat during desorption becomes crucial for this form of hydrogen storage. Several efforts have been made in the past to improve heat transfer issues associated with metal hydride system having smaller hydrogen storage capacity up to few hundred grams. Further, there is dearth on large capacity hydrogen storage systems based on metal hydride and very few have been reported in context of vehicular applications. The studies by large concentrates on improving absorption performance and not much attention has been given to desorption performance. Also, the poor system gravimetric capacity due to usage of complex and energy intensive heat augmentation techniques have restricted its use in vehicular applications. There exists an opportunity / demand for development of compact, least energy intensive, and portable metal hydride-based hydrogen energy storage systems for vehicular applications. The present invention addresses the above challenges and concentrates on the development of 1 kg metal hydride-based hydrogen storage system. Considering the heat transfer challenges, the 1 kg MH based hydrogen storage system in the present invention is a modular multi tubular arrangement comprising of optimum number of MH tubes in conformable limit. The present invention utilizes light weight heat augmentation techniques such as Al-foam or hexagonally perforated longitudinal metal fins mounted over cylindrical rings to enhance heat transfer from core of MH to surrounding. The present invention also investigates and proposes the incorporation of a U-tube or Finned U-tube within each MH tube also called as tube in tube heat exchanger as one of the heat augmentation solution. This arrangement imparts additional heat transfer surface area and additionally meant to utilize waste energy of high temperature fluid from liquid cooled fuel cell stack to desorb hydrogen and simultaneously cooling fuel cell stack. The present invention primarily aims to develop least energy intensive system using high velocity air available due to vehicle motion as heat transfer fluid to desorb hydrogen for vehicle propulsion. It is noteworthy that this invention introduces novel concept of different forms of surface roughness over external surface of MH tubes to improve system performance. Reference is being made to some of the prior arts and patent literature listed below: US2006228960A1 discloses utilizing the space between inner hull and outer hull structure of underwater marine vessel for hydrogen storage in one or more hollow tubes or has a honeycomb structure. The hydrogen storage can be either in metal hydride or compressed or in liquefied form. The onboard power generation may be obtained by means of regenerative fuel cell or pulse detonation engine utilizing hydrogen. US11525402B2 discloses development of solid-state hydrogen unit for propulsion of vehicle operated by means of gas turbine engine such as used in aircraft. The solid-state hydrogen storage system comprises one or more modular metal hydride-based canisters. The metal hydride primarily disclosed in patent is AlH3 but extends to usage other form of metal hydrides. The class of hydrides are distributed as such wherein hydrogen desorption caters the higher flow rate hydrogen requirement during takeoff or landings and units to cater cruising need of aircraft. CN213576788U discloses a utility model having metal hydride-based heat storage and supply system for electric vehicle. The heat storage and supply system consist of one or more hydrogen storage tanks / modules having low temperature metal hydride and high temperature metal hydride. The high temperature heat released during hydrogen storage in high temperature metal hydride is recovered by means of heat transfer fluid and heat exchange device. The recovered heat is then utilized to supply heat to the electric automobile for passengers’ comfort and battery operation in winter seasons in north regions. Johnson, T. A., Kanouff, M. P., Dedrick, D. E., Evans, G. H., & Jorgensen, S. W. (2012). Model-based design of an automotive-scale, metal hydride hydrogen storage system. International Journal of Hydrogen Energy, 37(3), 2835–2849. Johnson et al. discloses a complex metal hydride hydrogen storage system for automotive application. In this study, the hydrogen storage system consists of four identical modules wherein each module contains 12 cylindrical tubes made up of SS316L arranged in 4 x 3 staggered manner cascaded within a cuboidal shell. Each MH tube consist of 1.79 kg mass of sodium alanate and graphite mixture to store hydrogen. In this work, each module having 12 tubes contains 21.5 kg of sodium alanate and graphite mixture and stores 0.75 kg of hydrogen. The total hydrogen storage capacity of the entire 4 modules is 3 kg. The energy required to desorb hydrogen is met by circulating high temperature (100 to 220-degree C) oil as heat transfer fluid at a higher flow rate of approximately 114 LPM. The temperature of oil was raised with the help of hydrogen catalytic heater wherein at peak hydrogen flow rate requirement, 10% hydrogen and air mixture were used to heat the catalytic combustor to heat the oil flowing in shell to a temperature of 100 to 220-degree C. The vessels were designed for a maximum working pressure of 2000psi (13.8 MPa). The heat exchanger is divided into sections by the baffles. This is provided for fluid flow across the tube bank for cooling and heating. Lototskyy, M. V., Tolj, I., Davids, M. W., Klochko, Y. V., Parsons, A., Swanepoel, D., Ehlers, R., Louw, G., van der Westhuizen, B., Smith, F., Pollet, B. G., Sita, C., & Linkov, V. (2016). Metal hydride hydrogen storage and supply systems for electric forklift with low-temperature proton exchange membrane fuel cell power module. International Journal of Hydrogen Energy, 41(31), 13831–13842. Lototskyy, M. V., Tolj, I., Parsons, A., Smith, F., Sita, C., & Linkov, V. (2016). Performance of electric forklift with low-temperature polymer exchange membrane fuel cell power module and metal hydride hydrogen storage extension tank. Journal of Power Sources, 316, 239–250. These prior arts disclose a distributed hydrogen system having a liquid-heated- cooled MH extension tank which is thermally integrated with fuel cell module and compressed hydrogen composite cylinder to power 3 tonne electric forklift and tested the entire hydrogen storage system integrated with low temperature fuel cell for its performance onboard on an electric forklift in terms of light duty and heavy-duty operation. The MH extension tank comprises of 20 cylindrical MH tubes storing 3.2 kg of metal hydride in each tube. The 20 MH tubes stores 0.9 kg hydrogen in total 64 kg of MH. The MH material is a combination of main AB2 type alloy, a small amount of AB5 alloy for easier activation of AB2 type metal hydride and further expanded natural graphite (ENG) was used in order to enhance the thermal conductivity of MH bed. The MH tubes presented in the study by Lototskyy et. Al. incorporates perforated transverse copper fins of 0.5 mm thickness and a pitch of 5 mm across the entire length of tube to enhance heat transfer from the core of MH bed. The entire assembly of 20 MH tubes is assembled and cascaded into a cuboidal tank of dimension 950 mm (L) × 120 mm (W) × 700 mm (H) containing 50:50 water- glycol coolant for heat transfer which flows across the shell in thermal integration with fuel cell to desorb hydrogen. H. Buchner and R. Povel, “The daimler-benz hydride vehicle project,” Int. J. Hydrogen Energy, vol.7, no.3, pp.259–266, 1982 The Mercedes Benz T model were fitted with low multi tubular low temperature MH having 280 kg Ti-Cr-Mn alloys for storing 5 kg hydrogen. The MH system were used to power 2.3 litre SI engine wherein energy required to desorb hydrogen was supplied using water in thermal integration with high temperature exhaust gas obtained from engine operation. Further, the Mercedes Benz delivery van were fitted with high and low temperature MH combination hydrogen storage unit to reduce entire system weight for handling higher payload with increased energy efficiency. The Mg-based hydride was high temperature metal hydride whereas Ti-Cr-Mn forms the low temperature hydride. The HT-LT combined MH system was used to store 5.4 kg hydrogen to power IC engine wherein energy required for desorption was supplied using water in thermal integration high temperature exhaust gas. However, these documents do not disclose a compact and least energy intensive modular multi-tubular metal hydride system for hydrogen storage capacity by improving effective thermal conductivity of MH bed with the use of light weight heat augmented techniques. The present invention analyses the impact of various type of surface roughness developed on the surface of MH tubes in enhancing systems performance which is a novel concept and have not been disclosed in the cited prior arts. Therefore, there is a need for an efficient development of modular multi tubular metal hydride-based hydrogen storage reactor for storing 1 kg hydrogen for vehicular applications. The present invention proposed system consists of 16 MH tubes arranged in staggered or aligned manner that stores 75 kg of LaNi5 alloy and considered the impact of tube surface roughness on MH system’s performance. The present invention proposes utilization of high velocity air available during vehicle motion as heat transfer to desorb hydrogen flowing in cross flow within shell across MH tube tank. SUMMARY OF THE INVENTION The following disclosure presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key / critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later. An object of the present invention is to address and remove all the above limitations. Another object of the present invention is to provide a modular multi-tubular metal hydride system of 1 kg hydrogen storage capacity for vehicular application by involving use of water and PCM housed within cuboidal shell of system as an energy storage / supply medium to store waste heat released during absorption and use the stored energy to desorb hydrogen on-board. Yet another object of the present invention is to provide a modular multi-tubular metal hydride-based hydrogen system having 16 MH tubes capable of storing 1 kg hydrogen within 75 kg of LaNi5 alloy. Yet another object of the present invention is to improve effective thermal conductivity of MH bed wherein the invention proposes use of light weight heat augmentation techniques within MH bed such as Al-foam or perforated longitudinal fins. Yet another object of the present invention is to analyse the impact of various type of surface roughness developed on the surface of MH tubes in enhancing systems performance. Yet another object of the present invention is to incorporate a U tube or Finned U- tube within MH tube also called as tube in tube heat exchanger to provide additional heat transfer surface area and simultaneously harnessing waste energy of high temperature fluid from liquid cooled fuel cell stack for desorbing hydrogen from MH bed. Yet another object of the present invention is to provide a system to be arranged in multiple units or scaled in different dimensions to meet the higher hydrogen storage capacity. First aspect of the present invention is to provide a multi-tubular metal hydride (MH) system (2400) for H2storage capacity, the system comprising a plurality of metal hydride (MH) tubes optimized for length to diameter ratio (L / D) to develop compact hydrogen storage system wherein L / D ratio varies from 1 to 10 and the plurality of tubes varies from 1 to 20, one or more predefined shaped shell for cascading MH tubes in an aligned or staggered tube arrangement having different longitudinal pitch, diagonal pitch, transverse pitch wherein the MH tubes analyzed in depth for charging and / or discharging performances, at least one metal foam medium and a finned tube heater to transfer internal heat from or to a MH bed in process of absorption and / or desorption of hydrogen, at least four hexagonal perforated longitudinal fins mounted on a cylindrical ring housed within the MH tube to enhance heat transfer from core to the MH bed and allow uniform distribution of alloy within MH tubes, at least incorporating a U-tube or finned U- tube namely tube in tube heat exchanger within each MH tube to desorb hydrogen using high temperature fluid from liquid cooled fuel cell stack in addition to extended heat transfer surface area provided by such arrangements, at least 75 kg of LaNi5alloy as a metal hydride hydrogen storage medium distributed equally in 16 MH tubes and at least one disc filters fitted on one end of the cylindrical MH tube to separate alloy and / or gas circuit in process of charging and / or discharging of hydrogen in the system to utilize waste heat from the fuel cell as an energy medium to desorb hydrogen (H2) wherein the multi tubular MH system described herein forming at least 1kg hydrogen (H2) storage capacity system is compact, modular, portable and swappable which can be attached in multiple units to meet net hydrogen storage demand in vehicular applications. Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The above and other aspects, features and advantages of the embodiments of the present disclosure will be more apparent in the following description taken in conjunction with the accompanying drawings, in which: Figure 1 illustrates the graphical presentation of the validation of mathematical model with the experimental result of similar study within literature in accordance with the present invention. 1.a. validation of mathematical model for metal hydride; 1.b. validation of mathematical model for thermal energy storage considering gravity effect and boussinesq approximation Figure 2 illustrates the graphical presentation of the grid independence test results in accordance with the present invention. Figure 3 illustrates the graphical presentation of the time step independence test result in accordance with the present invention. Figure 4 illustrates the plot of reaction fraction at 21600s for selection of no. of MH tubes and L / D ratio in accordance with the present invention. Figure 5 illustrates the velocity profile of different shell and tube arrangements - (a) Cuboidal Shell Aligned MH Tubes; (b) Cuboidal Shell Staggered MH tubes; (c) Cylindrical Shell Aligned MH tubes; (d) Cylindrical Shell Staggered MH tubes; (e) Trapezoidal Shell Staggered Tube arrangement in accordance with the present invention. Figure 6 illustrates the desorption reaction fraction profile for different shell and tube arrangements in accordance with the present invention. Figure 7 illustrates the 2D CAD image of 16 MH Tube model in accordance with the present invention. Figure 8 illustrates the desorption reaction fraction and average MH bed temperature evolution at different vehicle velocities (kMHBED = 0.1 W / m-K) in accordance with the present invention. Figure 9 illustrates the desorption reaction fraction and average MH bed temperature evolution at 10 km / h with inclusion of Al-foam in accordance with the present invention. Figure 10 illustrates the velocity profile of air flowing through shell of MH system with (a) 1 inlet, (b) 2 inlet aligned tube arrangement; and (c) complete inlet staggered tube arrangement in accordance with the present invention. Figure 11 illustrates the comparison of desorption reaction fraction and average bed temperature evolution for MH system having aligned MH tube single inlet, 2 inlets and staggered MH tubes complete inlet for air flow in accordance with the present invention. Figure 12 illustrates the desorption reaction fraction evolution profile a) 10 km / h, b) 20 km / h, c) 30 km / h; d) 10% Al-foam, e) 15% Al-foam, f) 20% Al-foam with 10 km / h; g) 2I / 1O without Al-foam; h) 2I / 1O with 10% Al-foam at 10 km / h in accordance with the present invention. Figure 13 illustrates the CAD layout and model of different internal heat transfer arrangement within each MH tube to enhance system performance wherein Figure 13(a) illustrates the CAD layout of hexagonal perforated Cu fins in accordance with the present invention, Figure 13(b) illustrates the incorporation of U-tube within MH tube and Figure 13(c) illustrates the incorporation of finned U-tube embedded in MH tube in accordance within present invention. Figure 14 illustrates the desorption reaction fraction for different internal heat transfer arrangements in accordance with the present invention. Figure 15 illustrates the different types of surface roughness developed on external surface of MH tube in accordance with the present invention. Figure 16 illustrates the comparison of absorption reaction fraction and average MH bed temperature for different types of surface roughness in accordance with the present invention. Figure 17 illustrates the reaction fraction evolution during absorption, stratification and desorption studies on using water as an energy storage and supply medium in accordance with the present invention. Figure 18 illustrates the cuboidal shell and aligned MH tube arrangement considered for water and PCM related studies in accordance with the present invention. Figure 19 illustrates the average MH bed temperature and average shell water temperature during absorption, stratification and desorption studies on using water as an energy storage and supply medium in accordance with the present invention. Figure 20 illustrates the reaction fraction evolution during absorption and desorption study on using PCM (i.e. paraffin wax RT35HC) as an energy storage and supply medium in accordance with the present invention. Figure 21 illustrates the average MH bed temperature and PCM temperature during absorption and desorption study on using PCM (i.e. paraffin wax RT35HC) as an energy storage and supply medium in accordance with the present invention. Figure 22 illustrates the PCM phase transformation during absorption and desorption study in accordance with the present invention. Figure 23 illustrates the comparison of reaction fraction evolution during absorption and desorption study on using water and PCM as an energy storage and supply medium in accordance with the present invention. Figure 24 illustrates the integration of metal hydride based 1kg hydrogen storage system for vehicular applications in accordance with the present invention. Figure 25 illustrates the different possible arrangements of 1 kg hydrogen system for testing and their application in vehicular applications wherein Figure 25(a) and (b) depicts the 3-D assembly and side view of 16 MH tubes with 4 perforated longitudinal Cu fins inside each tube to be tested using air as HTF for hydrogen absorption and desorption performance; Figure 25(c) and 25(d) depicts the 3-D assembly and side view of 16 MH tubes having different surface roughness on outer surface of MH tubes; Figure 25(d) is a 3-D assembly of 16 MH tubes within a closed cuboidal shell considered for onboard thermal energy storage and supply using water and PCM; Figure 25(e) is a 3-D assembly of 16 MH tubes within a cuboidal shell having an inlet and outlet for heat transfer fluid flow to assess the charging and discharging performance. Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may not have been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures. DETAILED DESCRIPTION The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of various embodiments of the present disclosure as defined by the claims and their equivalents. It includes various specific details to assist in that understanding, but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the various embodiments described herein can be made without departing from the scope and spirit of the present disclosure. In addition, descriptions of well-known functions and constructions may be omitted for clarity and conciseness. The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the present disclosure. Accordingly, it should be apparent to those skilled in the art that the following description of various embodiments of the present disclosure is provided for illustration purpose only and not for the purpose of limiting the present disclosure as defined by the appended claims and their equivalents. It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, a reference to “a component surface” includes a reference to one or more of such surfaces. All terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which various embodiments belong. Further, the meaning of terms or words used in the specification and the claims should not be limited to the literal or commonly employed sense but should be construed in accordance with the spirit of the disclosure to most properly describe the present disclosure. The terminology used herein is for the purpose of describing particular various embodiments only and is not intended to be limiting of various embodiments. As used herein it is understood that the terms “comprises” and / or “comprising” used herein specify the presence of stated features, integers, steps, operations, members, components, and / or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, members, components, and / or groups thereof. Also, expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. The present invention will now be described more fully with reference to the accompanying drawings, in which various embodiments of the present disclosure are shown. The present disclosure may, however, be embodied in many different forms and should not be construed as being limited to the various embodiments set forth herein, rather, these various embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the present disclosure. Furthermore, a detailed description of other parts will not be provided not to make the present disclosure unclear. Like reference numerals in the drawings refer to like elements throughout. Embodiments discloses a modular multi-tubular metal hydride-based hydrogen storage system for different scales of vehicular applications. In a non-limiting embodiment of the present invention discloses to develop a compact, easy to manufacture and low energy intensive solution for the large-scale hydrogen storage systems involving an analysis of the desorption behavior of large-scale multi-tubular metal hydride-based hydrogen storage systems using air as heat transfer fluid flowing across the multi-tubular bank of metal hydride considering vehicular velocities and poor thermal conductivity of metal hydride (MH). The embodiments disclose the present system comprising LaNi5 as a reference metal hydride due to its easier activation, low susceptibility to impurities, good reversibility, good cyclic ability and ease of availability. The present invention discloses a compact and modular multi-tubular metal hydride (MH) based hydrogen (H2) storage system for storing 1 kg hydrogen for light / heavy duty vehicular applications using LaNi5 as a reference alloy. The present invention also discloses the possible inclusion of intermetallic compounds such as AB, A2B, AB2, AB5, BCC alloys and high entropy alloys. It further discloses the impact of different profiles of artificial surface roughness over MH tubes which improves reaction performance due to improvement in heat transfer coefficient during fluid flow. The invention incorporates 10 to 20 vol. % Al-foam or 4 internal longitudinal perforated Cu fins mounted over cylindrical rings to enhance heat transfer from the MH. The invention also discusses about the inclusion of tube in tube heat exchanger in the form of U-tube and finned U-tube heater to improve heat transfer to MH bed by means of extended surface and utilization of waste energy from liquid cooled fuel cell stack. Moreover, the present system may be integrated with fuel cell as well as internal combustion engine to propel vehicle. The present invention also proposes the use of water and PCM as an energy storage medium to store heat energy released during absorption and supply the same to desorb hydrogen from MH. A modular multi-tubular metal hydride-based hydrogen storage system for storing 1 kg hydrogen for light / heavy duty vehicular application have been developed. The objective behind the proposed metal hydride-based hydrogen system within the study is to develop a compact, easy to manufacture and low energy intensive solution for large scale hydrogen storage systems specifically in terms of vehicular applications. The study primarily analyses the desorption behavior of such large-scale multi-tubular metal hydride-based hydrogen storage systems using air as heat transfer fluid flowing across the multi-tubular bank of metal hydride considering vehicular velocities and poor thermal conductivity of metal hydride. There exists various class of metal hydrides such as AB5(e.g. LaNi5, MmNi5, etc.), AB2 (e.g. TiMn2, etc.), AB (e.g. TiFe), A2B (Mg2Ni), BCC alloys, High Entropy alloys which can be utilized within the scope of the present invention catering to primary objective as well as various other applications. LaNi5 was selected as a reference metal hydride for the present study due to its easier activation, low susceptibility to impurities, good reversibility, good cyclic ability and ease of availability. The desorption equilibrium pressure of LaNi5at 298 K is 1.8 bar which is higher than the required inlet pressure of fuel cell i.e.0.5 to 0.6 bar for considered scale of vehicular application within the scope of invention. The amount of LaNi5 required to store 1 kg hydrogen was 74.63 kg, computed considering gravimetric capacity 1.34 wt.% experimentally obtained in the laboratory. The total volume required to store the 74.63 kg LaNi5 was calculated considering density of LaNi5 as 8400 kg / m3, porosity of 0.5 and 20% expansion volume, which was obtained as 0.02132 m3. In order to enhance the heat transfer, the prime step taken was to reduce MH bed thickness by distributing the metal hydride alloy into multiple tubes. The reduction in bed radius will reduce the conduction pathway or thermal resistance to heat flow to the system. The challenges associated with internal heat transfer from MH bed core to surrounding medium have been addressed by inclusion of internal heat transfer augmentation techniques such as light weight Al-foam, hexagonal perforated longitudinal copper fins and tube in tube heat exchanger (U-tube and Finned U-tube) inside MH tubes have been examined and proposed in the present invention. Initially a 2-D mathematical model was solved using the parametric sweep feature in COMSOL Multiphysics 5.5 for obtaining the optimal bed radius or number of MH tubes within the conformable limit. The aspect ratio or L / D ratio varied from 1 to 10 and the number of MH tubes varied from 1 to 20. The thickness of the tubes was calculated using ASME pressure vessel code VIII for SS316L considering working pressure as 50 bar and factor of safety 2. After obtaining the optimum number of tubes and L / D ratio, the tubes were arranged in different configurations of tube arrangements and shell geometry. The MH tubes are analyzed for aligned and staggered arrangements with different transverse, longitudinal pitch and their distribution in shell. The shell geometry considered are cuboidal, cylindrical and trapezoidal cross section as shown in Figure 5. The different possible arrangements were analyzed for their desorption performance. Among all the possible configurations, the system having MH tubes arranged in aligned configuration of 4 rows and 4 columns with a pitch equal to 1.25 times the outer diameter of standard tube dimension within a cuboidal shell having one inlet and one outlet was considered for development due to ease of manufacturing, handling and also yields maximum desorption reaction fraction in comparison to other arrangements and equivalent reaction fraction to trapezoidal arrangement. The other arrangements were either having similar desorption or lesser than above considered arrangements. The multi-tubular MH system was then studied for desorption at different vehicle velocities of 10 km / h, 20 km / h and 30 km / h considering air as HTF and thermal conductivity of MH bed as 0.1 W / m-K. In order to enhance the heat, transfer from the MH bed, the effect on the hydrogen desorption with air as HTF on inclusion of 10%, 15% and 20% Al-foam by volume of metal hydride was analyzed at a 10 km / h vehicle velocity. Also, the effect of multiple and varying inlet length was analyzed on the discharging performance with or without Al foam at 10 km / h and compared with single inlet system. The entire study was studied for duration of 6 hours (21600s). The parameters considered for desorption study are listed in Table 1. Table .1 Parameters considered for the numerical studies Metal Hydride and Hydrogen Saturated density of MH, ^^sat8512.56 kg / m3External temperature, Tex303.15 K Density of MH, ^^emp8400 kg / m3Absorption Reaction constant, Ca 59 s-1Desorption Reaction constant, Cd 9.5 s-1Activation Energy for absorption, Ea21179.6 J / mol Activation energy for desorption, Ed16473 J / mol Initial Temperature, Ti 303.15 K Permeability, κ 10-8m2Enthalpy of formation, ^^^^ 30800 J / mol Universal gas constant, R 8.314 J / mol / K Molecular weight of H2, Mg 2×10-3kg / mol Specific heat for hydrogen gas, Cpg 14890 J / kg / K Specific heat of MH, Cps419 J / kg / K Porosity, ^^ 0.5 Entropy, ^^S 108 J / mol / K Air Thermal conductivity, kair26.3×10-3W / m / K Viscosity, μair 184.6×10-7Pa*s Specific heat of air, Cpair 1007 J / kg-K Gas Constant, Rair287 J / kg-K Density of air, ρair 1.1614 kg / m3Water Density, 1000 kg / m3Specific heat, Cp,water 4184 J / kg-K Thermal conductivity, kwater 0.6 W / m-K Dynamic viscosity, µwater0.00098 Pa-s PCM PCM RT35HC Properties Solid Phase Liquid Phase Density [kg / m3] 880 760 Specific heat, Cp [J / Kg-K] 1800 2400 Thermal conductivity, k [W / m-K] 0.2 0.2 Latent Heat of PCM [kJ / kg] 240 Melting Temperature [K] 308 Further, in order to increase heat transfer coefficient during cross flow of air across MH tubes, a novel study considering the effect of surface roughness on absorption reaction fraction have been analyzed within the research domain of metal hydride storage system development. The different form of surface roughness was considered such as v-rib, v-rib with gap, wire mesh and dimple shaped roughness as shown in Figure 15. The effect of various type of surface roughness was analyzed based on 3D mathematical model of a single MH tube developed using SOLIDWORKS and COMSOL Multiphysics software. Furthermore, considering the scalability of such MH systems for storing larger quantity of hydrogen to propel heavy duty and material handling mobility vehicle segments, the energy dissipation during charging and energy supply from or to MH bed will possess significant challenge for large scale metal hydride-based hydrogen storage system. In order to overcome the above challenges, the solution of onboard energy storage and supply was analyzed in the present invention. The thermal energy storage medium considered for this study are water and PCM. Water has higher specific heat capacity in terms of heat transfer fluid (HTF), economical, easily available, and safe due to which it finds its significant application as sensible thermal energy storage medium and heat transfer fluid in various energy generation and storage domains. It is to be noted that depending on the constraints such as space, system weight and deployment of MH system within a vehicle having fuel cell greater than 5-kilowatt, water can also be circulated as heat transfer fluid in thermal integration with fuel cell to meet the hydrogen flow rate for powering vehicle. Phase Change Material (PCM) such as paraffin wax are economical, non-reactive and capable of storing higher amount of thermal energy as latent energy apart from sensible energy. The charging and discharging performance of present MH system have been analyzed and compared for both the energy storage medium. The energy released by MH bed during absorption will be stored either in water or PCM and this stored energy will be utilized during desorption to meet the end use hydrogen demand. The hydrogen supply pressure of 35 bar is considered for charging the MH storage unit so that such system can be directly integrated with an electrolyzer unit generating hydrogen within a pressure range of 30 to 35 bar eliminating demand of hydrogen compression. The hydrogen stored within metal hydride-based hydrogen storage medium in present application can be utilized to power vehicles either using internal combustion engines or integrating it with fuel cell-an energy conversion device. However, the present invention is not limited to vehicular application and it can be extended to various applications such as thermal energy storage, hydrogen purification, stationary power generation, hydrogen compression, space heating and cooling. 2. Data Reduction 2.1. Calculations related to MH reactor dimension Amount of hydrogen to be stored = 1 kg Metal hydride (MH) alloy considered for study is LaNi5 Gravimetric capacity of LaNi5= 1.34 wt.% Mass of LaNi5required to store 1 kg hydrogen = = 74.63 kg Empty Density of LaNi5= 8400 kg / m3MH porosity = 0.5 Expansion volume = 20% Total volume required to store 74.63 kg LaNi53 = 0.02132 m ………(1) Working pressure (Pw) = 50 bar Factor of safety = 2 Design pressure (Pd) = 100 bar Material for reactor fabrication = SS316L Allowable stress (S) = 16700 psi = 1151.4245 bar Thickness of MH Actual Design pressure = ….…………………………………(3) Where, Longitudinal weld joint quality factor, E = 0.85, Di= inner diameter L / D ratio varied from 1 to 10 No. of MH tubes varied from 1 to 20 Based on 2D axisymmetric numerical simulations, the optimum no. of MH tube and L / D ratio selected is 16 and 9 respectively. The MH tubes are arranged in aligned arrangement (4 x 4) Table 2. Calculation of dimension of MH tube and cuboidal shell No. of MH tubes MH mass per tube [kg] Volume per tube [m3] 16 4.66 0.001333 Dimensions (in inches) The extended length (Lex) of MH tubes due to inclusion of different volume fraction of Al-foam was computed in order to keep the mass of metal hydride same within each tube as mentioned in Table 3 calculated using equation 4 to 6. As per 16 MH tube division, volume of MH per tube (V1) = 0.001333 m3The inclusion of 10%, 15% and 20% Al-foam by volume of metal hydride were considered. Volume of Al-foam referred as …….............................................(4) Total volume of MH tube, Vtotal = V1 + V2 ……………………………………...(5) Extended length of MH tube, ..………………………………...(6) Table 3. Extended length of MH tubes on addition of Al-foam (in inches) Extended length Schedule 10S Schedule 40S L (No Al foam) 14.913 16.985 Lex (10% Al foam) 16.404 18.684 Lex (15% Al foam) 17.149 19.533 Lex(20% Al foam) 17.895 20.382 2.2. Calculation of effective thermal conductivity of MH bed: Thermal conductivity of metal hydride (kMHBED) = 0.1 W / m-K Thermal conductivity of Al-foam (kAlfoam) = 10.9 W / m-K Thermal conductivity of hydrogen gas (kH2) = 0.127 W / m-K Inclusion of Al-foam within MH bed having 90%, 85%, 80% porosity. Where, E1= volume fraction of MH, E2= volume fraction of Al-foam and E3= volume fraction of hydrogen The effective thermal conductivity on inclusion of different volume fractions of Al-foam are listed in Table 4. Table 4. Effective thermal conductivity of MH tubes on addition of Al-foam keff(10% Al foam) 1.1908 W / m-K keff (15% Al-foam) 1.7294 W / m-K keff(20% Al-foam) 2.2681 W / m-K 2.3. Calculation of Heat Transfer Coefficient: The heat transfer coefficient was calculated using Zukauskas correlation formulated for flow across the bank of tubes. The correlation is defined for no. of Where, all the properties are evaluated at mean of inlet and outlet heat transfer fluid temperatures , constants C and m for aligned arrangement having St / Sl > 0.7 in the range 103to 2 × 105are 0.27 and 0.63 respectively. The Reynolds for the given correlations is based on the maximum fluid velocity occurring within the tube bank. For the aligned arrangement of MH tubes, maximum fluid is calculated as; The corrected Nusselt number for number of tube row, NL < 20, is given as follows: Wherein C2 for NL = 4 in aligned arrangement is 0.9 Table 5. Heat transfer coefficient calculation of MH system for different velocity Aligned arrangement of MH tubes Velocity [km / h] Vmax ReDmax corrected Nu h [W / m2-K] 10 14 m / s 64320.55 228.39 82.26 20 28 m / s 128647.98 353.46 127.30 30 41.65 m / s 191353.63 453.92 163.48 3. Mathematical modelling: 3.1. The following assumptions have been considered in developing the mathematical model for the present study: 1. The solid and gas are in local thermal equilibrium 2. Hydrogen behaves as an ideal gas 3. MH is isotropic and has uniform porosity 4. The pressure inside the MH tubes is uniform throughout Mathematical modelling is carried out in COMSOL Multiphysics 5.5a with the governing differential equations given below. 3.2. Governing equation for metal hydride bed and hydrogen: …...…………………………………………………………………..(13) The ideal gas equation is valid for hydrogen gas and its density is defined as : Darcy’s Law The velocity of hydrogen gas is determined by Darcy’s law: The first term on the left-hand side denotes the change of heat energy with time inside the reactor. The second term on the left-hand side is the measure of advection by hydrogen gas through a metal hydride bed. The velocity of hydrogen gas is negligible inside the bed and hence making the second term negligible. However, to make the study comprehensive, this term was included in the study. The first term in the right-hand side denotes the heat conduction inside the bed and the second term denotes the heat generation. Effective thermal conductivity is defined as: Effective volumetric heat capacity is expressed as follows: Reaction Kinetics For absorption process: ………………………………(19) For desorption process: ………………………………….(20) The equilibrium pressure of metal hydride is given by: 3.3. Governing equation for air as heat transfer fluid: The Continuity equation for heat transfer fluid is defined as: Momentum equation for the heat transfer fluid (air) The flow of fluid inside the cuboidal shell is defined by Naiver stokes equation as: …..(24) In this equation the first term on the left-hand side is the inertial force term. The first term in the right-hand side denotes the pressure force, the second term denotes the viscous force and the third term denotes the applied force. 3.4. Governing equation for water as a sensible energy storage medium in shell: Momentum equation: The Boussinesq approximation is applied in momentum equation to incorporate the effect of buoyancy. The applied force in the equation is the force due to gravity applied in y-direction as follows: 3.5. Governing equations for PCM as energy storage medium in shell: 3.6. Initial and Boundary Conditions Initially (at t=0), hydride density concentration is assumed to be constant as: ρs(x,y,t=0) =ρemp(for absorption)......………………………………………………..(34) ρs(x,y,t=0) =ρsat (for desorption)..........……………………………………………...(35) The temperature of metal hydride bed, the HTF inside the shell and the supply temperature of HTF entering inside shell is assumed to be constant as: T(x,y,t=0) = Ti = Ts = 303 K……..……………………………………………..(36) Pressure inside the metal hydride bed reaches the supply pressure during absorption and outlet pressure during desorption almost instantaneously as the process is started. Hence, it is considered that the during absorption reaction, pressure is uniform throughout the bed equivalent to supply pressure and as desorption reaction begins throughout the reactor at desorption pressure (Pd). All the simulations in this study are done at a supply pressure (Ps) of 35 bar and desorption reaction at initial outlet pressure of 1 bar. P(x,y,t=0) = P0= Ps= 35 bar (for absorption)….……………………………... (37) P(x,y,t=0) = P0= Pd= 1 bar (for desorption)…………………………………...(38) The velocity of heat transfer fluid (air) at the inlet of shell is defined as: u = v = Uin ...……………………………………………………………………(39) The no slip condition is assumed at the inner wall of shell and outer wall of MH tubes: u = v = 0 ………………………………………………………………………(40) The outlet boundary of heat transfer fluid (air) is defined as: Pf = 0 …..……………………………………………………………………….(41) The temperature condition at the outlet of heat transfer fluid is defined as: The boundary walls of the shell are assumed to be thermally insulated and hence the energy equations for these walls are: where, n is the unit normal vector out of the walls. The amount of hydrogen desorbed is given by a dimensionless number and is described as: (for absorption) ……………………………………………..(44) (for desorption) ………………………………………….....(45) 3.7. Model validation and grid independence test: The mathematical model for metal hydride developed for the present work is validated with the experimental result reported by Laurencelle and Goyette for metal hydride and the results are shown in Figure 1.a. The mathematical model is also validated with experimental study performed by Khurana et. Al. for thermal energy storage in water considering boussinesq approximation and gravity effect as shown in Figure 1.b. Further, the grid independence test was performed using extremely coarse (7431 elements), extra coarse (7544 elements), coarser (9175 elements), coarse (10735 elements) and normal (11731 elements) meshes as shown in Figure 2. So, the normal mesh is used in this numerical study. The time step independence test was also performed for the step size of 3, and 5 to 25 seconds in the step of 5 seconds. The result as represented in the Figure 3 indicates that the reaction fraction curve at all-time step was overlapping and smooth in nature as compared. However, the time step of 10 seconds was used to simulate the entire study. 4. Results and Discussions: 4.1. Study of the present invention of MH Hydrogen storage reactor using air as heat transfer fluid: 4.1.1. Selection of number of MH tubes and L / D ratio: The 1 kg-H2modular MH based hydrogen storage system in this study is intended to be used in a vehicular application. In vehicular application, space and conformability limit of device both remains as a constraint along with heat transfer issue associated with MH based hydrogen storage system. In order to accommodate the H2storage system within a limited space available in the vehicle, the aspect ratio or L / D ratio was varied from 1 to 10 and the number of MH tubes were varied from 1 to 20 tubes. In order to store 1 kg of H2 in LaNi5, the total mass of LaNi5required is 74.63 kg considering the gravimetric capacity of 1.34 wt.% which was obtained experimentally for the available alloy. The total volume required to store 74.63 kg LaNi5 is 0.02132 m3including 20 percent expansion volume and porosity of LaNi5as 0.5. The number of tube divisions are based on the division of total volume. The development of multi-tubular systems would be also advantageous in terms of heat transfer from the MH bed. The reduction in the bed radius will reduce the conduction pathway leading to better heat transfer from the core to or from the surrounding resulting in enhanced heat and mass transfer. The dimensions for each tube division and L / D ratio was calculated considering the volume required to store MH in each tube, and ASME 8 pressure vessel code for SS316L for working pressure of 50 bar and design pressure of 100 bar with factor of safety = 2. The MH systems are advantageous in terms of storing hydrogen at lower pressure of less than 100 bar, hence the design pressure of the present MH system is limited to 100 bar which will also lead to reduction in the system weight. The effect of number of tubes and L / D ratio were analyzed simultaneously for desorption behavior using 2D axisymmetric model with parametric sweep feature in COMSOL Multiphysics 5.5. The values of the parameters used for this analysis are listed in Table 1. It is important to note that the present analysis was performed considering thermal conductivity of MH bed as 0.1 W / m-K and constant heat flux condition with heat transfer coefficient of 250 W / m2-K. In the extended scope of the present invention, it is to be noted that in case of scaling or depending on the amount of hydrogen to be stored, process conditions and class of applications, the no. of MH tubes, related dimensions and selection of standard schedule pipe size may differ. 4.1.2. Comparison of different shell and tube geometries on MH reactor performance: The parameters associated with orientation of bank of tubes influences the heat transfer behavior as overall heat transfer coefficient is affected by shell and tube geometry. In this analysis, shell geometry compared are trapezoidal, cuboidal and cylindrical whereas the tube arrangements considered are aligned and staggered as shown in Figure 5. The cuboidal and cylindrical arrangements having fixed inlet and outlet opening of 3.59 inches equivalent to 1.25Dowhereas trapezoidal cross section smaller parallel side as outlet of 3.59 inch and larger parallel side as an inlet as shown in Figure 5. The longitudinal (SL) and transverse (ST) pitch for various arrangements and shell dimensions are given in Table 6. The performance in terms of desorption reaction fraction for a duration of 6 hours was studied considering air velocity of 10 km / h, effective thermal conductivity of metal hydride bed as 1.027 W / m-K, and initial temperature = 303 K. Table 6: MH tube and shell pitch and geometry description 4.1.3. Effect of different vehicle velocity on desorption of hydrogen from MH hydrogen storage system with air as heat transfer medium: The present system was analyzed for its desorption which is crucial for propelling a vehicle on integration with fuel cell using a 2D mathematical model. The thermal conductivity of MH was considered to be 0.1 W / m-K. The effect of air as HTF for different vehicle velocity cruising at a speed of 10 km / h, 20 km / h and 30 km / h on desorption of hydrogen from MH system is analyzed at an ambient temperature of 303 K and initial outlet pressure of 1 bar. The heat transfer coefficient for each velocity was computed using Zukauskas correlation described in section, wherein it was found to be 82.26 W / m2-K, 127.3 W / m2-K and 163.48 W / m2-K for air as HTF at vehicle velocity of 10 km / h, 20 km / h and 30 km / h respectively. The MH system was observed to desorb 34.63%, 38.64% and 40.95% of stored hydrogen in the duration of 6 hours as shown in Figure 8. The lower desorption fraction is attributed to poor thermal conductivity of MH bed and air being an HTF has lower specific heat capacity along with lower heat transfer coefficient limits the energy required to desorb hydrogen even at higher velocities. 4.1.4. Effect of improvement in effective thermal conductivity of MH bed. In order to improve the desorption from MH bed, the heat transfer enhancement is accomplished by adding Al-foam to MH bed. The Al-foam have been examined in literature as one of the light weight heat transfer enhancement solution for increasing the effective thermal conductivity of MH bed (kAl-foam = 10.9 W / m-K) which in turn leads to better energy supply to / from surrounding to MH bed. Also, Al-foam has low mass density i.e.2700 kg / m3which reduces the system mass and helps in improving system gravimetric capacity. In the present case, 10%, 15% and 20% Al foam by volume of MH were incorporated within each tube. The extended length in each case was computed based on increase in volume due to Al-foam keeping the mass of MH in each tube and diameter the same. The extended tube lengths are mentioned in Table 3. The thermal conductivity of MH bed was considered to be 0.1 W / m-K, for hydrogen gas was taken as 0.127 W / m- K and of Al foam was taken as 10.9 W / m-K as mentioned in the references. The effective thermal conductivity was then calculated and are found to be 1.1908 W / m-K, 1.7294 W / m-K and 2.2681 W / m-K for 10%, 15% and 20% porous Al- foam respectively compared to 0.1135 W / m-K for system without Al-foam. The 2-D mathematical model was studied for desorption with air as HTF for vehicle velocity at 10 km / h, initial temperature of 303 K and outlet pressure of 1 bar. 4.1.5. Comparison of varying inlets with single inlet, with and without heat transfer enhancements: In the above cases it was observed that the desorption of hydrogen from upper diagonal MH tubes is higher as compared to the lower diagonal tubes as shown in figure 12(a) to 12(f). This behavior was due to non-uniform flow of air from inlet to outlet. The air velocity near the tubes in the lower diagonal tubes are below than the inlet velocity of air resulting in lower desorption fraction from these tubes which in turn affects the overall desorption of hydrogen to application. In order to overcome this issue, the system was analyzed with aligned arrangement two air inlets and one outlet and staggered arrangement having complete air cross flow as shown in the Figure 10. The two inlets and one outlet MH system and staggered arrangement complete cross air flow system was initially simulated for desorption performance with 10% Al-foam and further compared with that of one inlet and one outlet system respectively at vehicle velocity of 10 km / h. The maximum air velocity achieved within the shell for both the system is 9 m / s as compared to 6 m / s in the 1 inlet system. 4.2. Comparison of internal heat transfer enhancement techniques within MH tubes The poor thermal conductivity (i.e. kMH = 0.1 to 0.3 W / m-K) of metal hydride alloy and exothermic / endothermic behavior during charging / discharging reactions for storing hydrogen in metal hydride leads to major bottleneck of heat transfer from / to the core of MH bed for efficient performance of the hydrogen storage system. There exists significant literature on improving heat transfer from core of the MH bed by means of metal foams, expanded natural graphite, fins (e.g. transverse, longitudinal, internal, external, spiral, plate, pin, etc.) and cooling tubes (e.g. straight, and helical) depending on various applications. The present invention primarily concentrates on vehicular applications. The fuel efficiency of vehicle depends on payload wherein increased mass of vehicle may affect the vehicle performance. Metal hydride-based hydrogen storage primarily suffers from low system gravimetric capacity due to inclusion of large mass of metal alloy for storing higher amount of hydrogen. In such case, it will be an advantageous to have low weight heat augmentation solution to enhance heat transfer simultaneously increasing vehicles’ fuel efficiency. In the present study, Al-foam, hexagonal perforated longitudinal Cu fins, tube in tube heat exchanger (i.e. U-tube and finned U-tube) fabricated using SS316L and Cu have been analyzed as solution to be incorporated within MH bed for improving heat transfer. Al-foam are considered to be effective light weight solution but inclusion of foam affects its uniform distribution along with metal hydride alloy across the length of reactor. The non-uniform distribution of foam and alloy will affect the heat and mass transfer for large scale metal hydride hydrogen storage system. In order to overcome the issue associated with metal foam, internal fins or embedded tubes can be used within MH tubes. In the present work, perforated Cu fins have been developed, analyzed and compared with MH tube with and without Al-foam. The 3D CAD model of single MH tube with fins was developed in SOLIDWORKS and imported in COMSOL Multiphysics software to numerically analyze its desorption performance subjecting to air velocity of 10 km / h flowing across cylinder and initial temperature of 303 K. Further, a tube in tube heat exchanger in the form of U-tube and Finned U-tube heat exchanger arrangement fabricated with either SS316L or Cu as fabrication material were developed in COMSOL Multiphysics 5.5 and analyzed for hydrogen desorption from MH at water flow rate of 1 LPM, 303 K and heat flux imparted by cross flow of air at 10 km / h over outer surface of cylinder. The considered U-tube and Finned U-tube heat exchanger provides extended heat transfer surface area and can be utilized to regulate the fluid flow in thermal integration with higher capacity water cooled fuel cell stack (>5 kW) for desorbing hydrogen from MH bed. The hot fluid from fuel cell can be circulated within U-tube embedded inside the MH tube that leads to utilization of waste energy from fuel cell to desorb hydrogen and simultaneously supplying low temperature fluid from outlet of U-tube to cool the fuel cell stack. In the scope of this proposed solution for heat transfer enhancement within MH bed, the fin can be manufactured also using aluminum, the fin design can be modified (e.g. impeller, spiral, etc.) and an optimum number of fins can be arranged in transverse manner. 4.3. Effect of surface roughness on performance of metal hydride tube: The heat transfer coefficient is also one of the vital parameters in terms of heat transfer when multi tubular system is subjected to flow of external heat transfer fluid such as air and water. The heat transfer coefficient is majorly influenced by nature of HTF, HTF velocity, surrounding and fluid temperature, thermal conductivity of HTF, geometry / orientation of system and surface roughness. There exist many literatures that concentrates on enhancing heat transfer coefficient using embedded cooling tubes (spiral, straight, finned tubes), external fins, heat transfer fluid with higher specific heat and velocity. In this study, effect of wire mesh, v-rib, v-rib with gap, and dimple shaped artificial surface roughness developed over external surface of single MH tube have been analyzed numerically for hydrogen absorption using 3-D mathematical model in COMSOL Multiphysics software. The application of such concept is novel in the domain of metal hydride system research. The single MH tube considered for the present study have internal diameter of 2.469-inch, outer diameter of 2.875 inch and length of 16.985 inch. The MH tube considered for this particular study have been examined for its absorption performance at a supply pressure of 35 bar, thermal conductivity of MH as 0.1 W / m-K, initial temperature of 303 K and subjected to cross flow of air over MH tube at velocity of 2.8 m / s (10 km / h). 4.4. Onboard thermal energy storage and supply using water and PCM The energy storage in the form of hydrogen within metal hydride is an exothermic process wherein waste heat is being released from MH bed. Generally, this heat is dissipated into the surrounding by means of any heat transfer fluid. In this process of heat dissipation, the thermal energy released from MH bed is wasted. The hydrogen desorption process from MH is an endothermic process wherein energy needs to be supplied by means of high temperature HTF or electric heating. In this case, the external energy that needs to be supplied are associated with different forms of work and their associated losses such as pump work, resistance heating, etc which reduces the efficiency of overall process. This reduced efficiency in turn impacts the economics of the hydrogen storage system and may also result in increased system weight due to complex balance of plant (BOP) to deliver the necessary energy to deliver hydrogen to the end use. In large scale onboard hydrogen storage such as vehicular applications, the increased hydrogen storage system with complex BOP will affect the range of the vehicle leading to reduced fuel economy and operational challenges. Herein, storing the energy released from MH bed while charging the metal hydride reactor in appropriate energy storage medium either in sensible or latent form will result in saving waste energy released during absorption as useful energy that can be utilized to desorb hydrogen to propel vehicle. The literature studies in terms of thermal energy storage utilizes water and phase change material. However, the literature related to vehicular applications by large have considered circulation of high temperature heat transfer fluid (e.g. water, ethyl glycol-water, oil) in thermal integration with fuel cell. In the present analysis, a 2D mathematical model of 16 MH tubes cascaded in cuboidal shell is developed in COMSOL Multiphysics software to study water and PCM as energy storage and supply medium during hydrogen absorption and desorption respectively as represented in section 3. The absorption studies are performed at a hydrogen supply pressure of 35 bar and surrounding / outlet pressure of 1 bar is considered for hydrogen desorption at initial / ambient temperature of 303 K. 4.4.1. Water The mathematical model and related governing equations have been explained in detail in the section 3 and the parameters used within study are listed in table 1. The boussinesq approximation was applied to momentum equation to consider the effect of buoyancy wherein density variation gives rise to stratification effect within fluid medium. The absorption study is for 6 hrs. followed by 3 hrs. stratification and considering the final state after stratification as initial condition desorption study is considered for 6 hrs. The MH system in the present invention was analyzed for 4 different cases comparing the effect of inclusion of 10%, 15% and 20% Al-foam with system without any Al-foam (keff = 0.1 W / m-K) on overall process. The inclusion of Al-foam leads to increment in length of MH tubes and accordingly shell length has also been increased by same length in this study. The increase in shell length leads to increase in shell volume and thereby increased mass of water within shell. The mass of water within shell varies as 39.37 kg, 43.68 kg, 46.25 kg and 49.14 kg for system without foam, 10%, 15% and 20% Al- foam respectively. In terms of hydrogen absorption, it takes 1800s (30 min), 3400s (57 min), 7200s (120 min) for MH reactor with 20%, 15% and 10% Al- foam respectively whereas reactor without Al-foam absorbs 74.35% of hydrogen storage capacity in 21600 (360 min). The peak average MH bed temperature during absorption rises to 399.18 K in 20 seconds, 389.33 K, 388.13 K, 387.39 K in 10 seconds from beginning of the reaction for system with no foam, 10%, 15%, and 20% Al-foam respectively. The average water temperature in the shell rises to 370.92 K, 362.66 K, 354.51 K, 346.51 K at the end of 6 hrs for cases with no foam, 10%, 15%, 20% Al-foam by volume of MH respectively and attains thermal equilibrium with MH bed temperature except system without no foam as shown in Figure 19. The temperature decrement in shell HTF after complete reaction duration of 6 hrs. is associated with increasing thermal mass and water mass for each case. The effect of stratification is not that prominent within the present invention with respect to the results obtained as energy release and its distribution is uniform in all direction due to MH tube orientation within aligned arrangement. However, the temperature distribution seems to have lower temperature near the wall as compared to the center region of shell due to the no slip condition at the wall. In case of desorption study, the MH reactor without no foam takes 305 min (5 hrs) to desorb 74.35% of absorbed hydrogen whereas the reactor with 10%, 15% and 20% Al-foam of metal hydride volume takes 84.2 min, 57.5 min and 39.2 min respectively to desorb 90% of hydrogen storage capacity utilizing the energy stored within water during absorption. The shell HTF temperature attains equilibrium with MH bed temperature after reaction completion except the system without Al foam. 4.4.2. PCM In this study, paraffin wax RT35HC have been considered as phase change material. The melting temperature of this PCM is 308 K which is within operational range of low temperature LaNi5 and have higher latent heat capacity of 240 kJ / kg. The detailed properties are listed in table 1. Similar to the case of water, the extended length due to inclusion of foam leads to increase in shell volume and thereby increase in the mass of PCM. The mass of the PCM varies as 34.65 kg, 38.44 kg, 40.70 kg, and 43.24 kg respectively for the MH system with no foam, 10%, 15%, and 20% Al-foam of metal hydride volume respectively. The duration of absorption study considered herein is 6 hours followed by 6 hrs of desorption. The final state of absorption study has been considered as the initial state for the hydrogen desorption from MH bed. 4.5. Integration of Metal hydride based 1 kg Hydrogen storage system for vehicular applications: The 1 kg hydrogen storage system described herein this document having 16 MH tubes with L / D ratio = 9 have been studied for its end use primarily in vehicular applications. The vehicular application as stated can be light duty or heavy-duty vehicular applications, such as two-three-wheeler passenger or good carrying vehicles, buses, heavy duty trucks carrying payload greater than 30 tons, locomotives, marine applications. These systems are also useful for material handling mobility devices such as forklifts. The energy required for desorption can be met using air, water, nanofluids, coolants (mixture of ethyl glycol and water in appropriate proportion) as heat transfer fluid flowing through shell. The shell can be housed with water, PCM and reversible thermochemical energy storage medium that reacts with air / oxygen and water (e.g. cobalt oxide (Co3O4), manganese oxide (Mn2O3), etc.), to store energy released during hydrogen absorption and utilize this as useful energy during desorption of hydrogen from MH bed. Further, each MH tube can be embedded with finned tube electric heaters to raise the temperature of MH bed to desorb hydrogen. The modular MH system in the present invention can be thermally integrated with fuel cell in case of fuel cell powered vehicle and combustion exhaust air of internal combustion engine utilizing waste heat from such sources to desorb hydrogen. LaNi5 is considered as reference material for laying the foundation of this invention. However, different class of metal hydrides belonging to AB5, AB2, A2B, AB, BCC and High Entropy Alloys having higher gravimetric capacity can be used tailoring their properties as per the end use requirements. The multi tubular arrangement may house single type of metal hydride alloy as well as combinations of hydride such as one with low temperature operation for initiation of the vehicle or any stated application and other form of hydride will later to aid operation once sufficient energy source is available to desorb hydrogen at higher temperature. The internal heat transfer enhancement as disclosed in the present invention in the form of Al-foam, hexagonal perforated longitudinal Cu fins, and tube in tube heat exchanger (e.g. U-tube and finned U-tube within MH tube) can be further supplemented with other form of arrangements such as transverse fins having impeller geometry with perforations, fins with non-uniform cross section such as nature aspired leaves having higher heat transfer surface area within MH core and lesser area towards surface. These MH tubes can be cascaded into cuboidal as well as cylindrical shell based on end use requirement. The present system as discussed will have a buffer hydrogen storage volume either in rectangular or elliptical cross section attached to the hydrogen inlet. This buffer volume would help in desorption process in bridging the gap between initial faster reaction and continuous supply to fuel cell. The primary application of the present invention is intended towards vehicular application. However, the scope of the present invention can be extended to many other applications such as stationary power generation based on different electric demand such as back-up power to residential / commercial buildings, remote villages, hilly regions as well as emergency back-up power unit to hospitals, hydrogen energy storage, thermal energy storage, hydrogen purification and hydrogen compression. The 1 kg hydrogen MH unit can be scaled or attached in multiple units for different applications. The present invention is about the design and development of swappable, portable and compact metal hydride based 1 kg H2storage capacity system for vehicular applications. The MH system disclosed in the present invention stores 1 kg hydrogen. In a non-limiting embodiment, the present invention provides a multi-tubular metal hydride (MH) system (2400) for 1 kg H2storage capacity, the system comprising a plurality of metal hydride (MH) tubes optimized for length to diameter ratio (L / D) to develop compact hydrogen storage system wherein L / D ration varies from 1 to 10 and the plurality of tubes varies from 1 to 20, one or more predefined shaped shell for cascading MH tubes in an aligned tube arrangement having different longitudinal pitch, diagonal pitch, transverse pitch wherein the MH tubes analyzed in depth for charging and / or discharging performances, at least one metal foam medium and a finned tube heater to transfer internal heat from or to a MH bed in process of absorption and / or desorption of hydrogen, at least four longitudinal fins mounted on a cylindrical ring of the MH tube to enhance heat transfer from core to the MH bed, at least one tube in tube heat exchanger in the form of U-tube or a Finned U-tube heat exchanger embedded within MH tubes having extended heat transfer surface area to utilize waste energy of high temperature fluid of fuel cell stack to desorb hydrogen, at least one disc filters fitted on one end of the cylindrical MH tube to separate alloy and / or gas circuit in process of charging and / or discharging of hydrogen in the system and at least one fuel cell thermally integrated into the MH system to utilize waste heat from the fuel cell as an energy medium to desorb hydrogen (H2) wherein the multi tubular MH system described herein forming at least 1 kg hydrogen (H2) storage capacity system is compact, modular, portable and swappable which can be attached in multiple units to meet net hydrogen storage demand in vehicular applications. The MH system thermally integrated with internal combustion engine of a vehicle wherein combustion exhaust air of internal combustion engine can be utilized to desorb hydrogen from the MH tubes forming at least 1kg of MH hydrogen (H2) storage capacity system attached in multiple units to meet net hydrogen storage demand in vehicular applications. Further, the multi tubular metal hydride-based hydrogen storage system have been optimized for number of tubes and length to diameter ratio (L / D) in view of developing compact hydrogen storage system within conformable limits pertaining to easier installation and use within vehicular application. The number of tubes has been varied from 1 to 20 and L / D ratio 1 to 10. In a non-limiting embodiment, the present MH system have 16 no. of MH tubes. In case of vehicular applications, such system may be scaled in multiple units to be utilized in 2 wheelers, 3 wheelers, golf-cart, light duty vehicles, heavy duty vehicles, material handling vehicles, locomotives, construction equipment and marine applications. The MH system primarily developed as part of this work can be extended to its utilization in various other applications such as hydrogen storage, stationary backup power generation in residential and commercial buildings, hospitals, remote villages, thermal energy storage, heating and cooling, hydrogen purification, and hydrogen compression. Furthermore, the metal hydride (MH) system uses high velocity ambient air due to vehicle motion as a heat transfer fluid flowing in a cross flow across bank of MH tubes housed in a cuboidal shell to desorb hydrogen onboard. The predefined shell may be housed with water, phase change materials and reversible thermochemical energy storage material to store the waste heat released during hydrogen absorption and utilize the same stored energy to desorb hydrogen onboard for propulsion of vehicle. The MH system power fuel cell-based hydrogen powered vehicles on integration with fuel cell and thermally integrated with fuel cell to utilize waste heat from the fuel cell as an energy supply medium to desorb hydrogen (H2), the MH system can power vehicle using internal combustion engine that uses hydrogen as a fuel wherein combustion exhaust air of internal combustion engine can be utilized to desorb hydrogen from the MH tubes. In a non-limiting embodiment, the present invention provides a multi-tubular metal hydride (MH) system (2400) for 1 kg H2storage capacity wherein the perforated longitudinal Cu fins have hexagonal shape perforations wherein four perforated longitudinal fins having hexagonal shape perforations fabricated using copper (Cu) material supported over the cylindrical rings coaxially placed in each MH tube to improve the heat transfer. The perforated fins supported over the cylindrical rings coaxially placed in each MH tube to improve the heat transfer and to allow uniform distribution of alloy within MH tubes. The MH tube in the present invention have at least four internal copper longitudinal fins with hexagonal perforations mounted over a cylindrical ring. The hexagonal perforated fins provide conduction pathway, helps in uniform distribution of alloy throughout the length of MH tube and also reduces weight of internal heat augmentation medium. In a non-limiting embodiment, the present invention provides a multi-tubular metal hydride (MH) system (2400) for 1 kg hydrogen storage wherein a tube in tube heat exchanger have been incorporated to enhance heat transfer from core of MH bed simultaneously utilizing waste heat from fuel cell stack. The tube in tube heat exchanger discussed herein is a U-tube and Finned U-tube embedded within each MH tube that primarily offers additional heat transfer surface area improving the heat transfer capability of MH system during charging and discharging performance. The U-tube or Finned U-tube can be used to circulate heat transfer fluid carrying waste heat during liquid cooled fuel cell stack operation in onboard vehicle to desorb hydrogen and simultaneously supplying relatively low temperature fluid to fuel cell due to endothermic nature of hydrogen desorption. In a non-limiting embodiment, the present invention provides a multi-tubular metal hydride (MH) system (2400) for H2 storage wherein MH tubes with various surface roughness such as v-rib, v-rib with gap, wiremesh and / or dimple shaped protrusions enhance the MH system performance in fluid flowing medium. The surface roughness on outer surface of tubes enhances heat transfer coefficient leading to better charging and discharging performance. Further, the various artificial surface roughness over MH tubes such as v-rib, v-rib with gap, wire mesh and dimple shaped protrusions have been designed on the external surface of MH tubes and analyzed for its effect on hydrogen absorption with air flowing in cross flow. The incorporation of roughness has enhanced performance over tube without surface roughness. In a non-limiting embodiment, the present invention provides a multi-tubular metal hydride (MH) system (2400) for H2storage wherein the shell comprising inlet and outlet of shell to dissipate and / or supply heat from the MH bed involving heat transfer fluid such as water, coolant, nanofluids, oil as flowing medium between inlet and outlet of shell. The MH system having at least 16 MH tubes, thermally integrated with fuel cell as well as engine exhaust of internal combustion engine to utilize the waste heat to desorb hydrogen. In a non-limiting embodiment, the present invention provides a multi-tubular metal hydride (MH) system (2400) for H2storage wherein the among the different class of metal hydrides (MH) comprising AB2, AB5, A2B, AB, BCC and high entropy alloys the present development involves LaNi5 alloy as a reference material to analyze and develop hydrogen storage unit for hydrogen powered vehicular applications. Further, the present study considers LaNi5 alloy as a reference material to analyze and develop hydrogen powered vehicular applications. The present invention has scope of using various class of metal hydrides such as AB2, AB5, A2B, AB, BCC and high entropy alloys for storing hydrogen. The 16 MH tubes forming a MH hydrogen storage system are modular in nature. These tubes are portable, easy to handle and can be safely detached or replaced during charging as well as in case of any mechanical damage. In another non-limiting embodiment, the present invention a multi-tubular metal hydride (MH) system (2400) for H2storage wherein incorporation of metal foam within MH tube are A1 foam and / or copper foam having 10 to 20% by volume of metal hydride to increment effective thermal conductivity of MH by 10 to 20 times improving the overall performance of the MH system. In a non-limiting embodiment, the present invention provides a multi-tubular metal hydride (MH) system (2400) for H2 storage wherein the MH system utilized for thermal energy storage having one or more upper and / or lower diagonal group of tubes filled with low temperature metal hydride and the other group with high temperature metal hydride. In a non-limiting embodiment, the present invention provides a multi-tubular metal hydride (MH) system (2400) for H2 storage capacity wherein MH tube embedded with finned tube heaters inside to rise the temperature of metal hydride to desorb hydrogen. The inclusion of internal fins inspired from nature such as different forms of leaves. The leaves generally have higher surface area in the bottom and it decreases towards the top. The inclusion of such fins enhances heat transfer from the core of metal hydride bed with lesser addition to the system weight. Further, the MH tube within present invention may also have optimum number of transverse fin arrangement having impeller type geometry with perforations in the impeller blades. The fin material can be of copper and aluminum. The absorption and desorption performance analysis of the MH system have shown significant improvement. In a non-limiting embodiment, the present invention provides a multi-tubular metal hydride (MH) system (2400) for H2 storage capacity wherein programmed electric heating enables controlled dynamic desorption by supplying sufficient amount of energy based on end use hydrogen flow rate requirement. The MH system in the present invention have been analyzed for its desorption performance using air as a heat transfer fluid medium for a vehicle speed of 10 to 30 km / h which can be further extended depending on road condition and vehicle motion to higher speeds. In a non-limiting embodiment, the present invention provides a multi-tubular metal hydride (MH) system (2400) for H2storage capacity wherein two or more hydrogen storage alloy among different class of metal hydrides stored within separate tubes to accomplish higher volumetric energy density and dynamic desorption by means of programmed layer by layer or tube by tube switching depending on vehicle torque and power requirement on acceleration and constant speed cruising. In a non-limiting embodiment, the present invention provides a multi-tubular metal hydride (MH) system (2400) for 1 kg H2storage capacity wherein hydrogen supply pressure increased upto 80 bar or more depending upon the hydrogen storage capacity involving the alloy material used in MH system and the end use application. Further, the 16 MH tubes with L / D ratio = 9 is developed in the present invention. The MH system for larger scale hydrogen storage for more than 1 kg hydrogen storage, depending on the application number of MH tubes and its related dimensions can be varied. Also, multiple units of such MH system of 1 kg hydrogen storage can be connected in series to stack them to achieve 2,3,4 or higher kg of hydrogen storage. In a non-limiting embodiment, the present invention provides a multi-tubular metal hydride (MH) system (2400) for H2 storage wherein the MH system having swappable, portable characteristic after usage with other unit such as battery swapping technology. The 16 MH tubes forming a MH hydrogen storage system are modular in nature. These tubes are portable, easy to handle and can be safely detached or replaced during charging as well as in case of any mechanical damage. In a non-limiting embodiment, the present invention provides a multi-tubular metal hydride (MH) system (2400) for H2 storage capacity wherein the optimization of MH system in terms of shell and tubes arrangement is based on different alignments such as aligned, staggered with different transverse, longitudinal and diagonal pitch. In a non-limiting embodiment, the present invention provides a multi-tubular metal hydride (MH) system (2400) for H2 storage capacity wherein the shell geometry shape comprising both cuboidal, cylindrical and trapezoidal shaped based on end user requirements. In a non-limiting embodiment, the present invention provides a multi-tubular metal hydride (MH) system (2400) for H2 storage wherein MH system incorporated with water, Phase Change Material (PCM), thermochemical heat storage material in the shell to store energy released by the MH bed during absorption and further desorb hydrogen on-board and / or off-board from MH system. Further, such inclusions are useful in the onboard application which will prove helpful in increasing system’s overall efficiency and will eliminate the requirement of complex balance of plant to power vehicle and reduce the energy required. In a non-limiting embodiment, the present invention provides a multi-tubular metal hydride (MH) system (2400) for H2 storage wherein the MH tube fabricated using SS316L, aluminum and / or low weight material having resistance to hydrogen embrittlement. The MH tubes can be entirely filled with single type of alloy as well as different combinations of hydrides where a one class of hydride will operate at lower temperature to supply hydrogen to fuel cell vehicle initially and further supplemented with alloy having higher gravimetric capacity and operational temperature which will be beneficial when integrated with IC engine. In a non-limiting embodiment, the present invention provides a multi-tubular metal hydride (MH) system (2400) for H2storage wherein 16 MH tubes with L / D ratio = 9 have been developed in the present invention. The MH system for larger scale hydrogen storage (>1 kg hydrogen storage) and depending on the application, number of MH tubes and its related dimensions can be varied. In a non-limiting embodiment, the present invention provides a multi-tubular metal hydride (MH) system (2400) for H2 storage wherein fins of non-uniform cross section such as nature aspired leaves or impeller blade structure fabricated using high thermal conductivity material to improve heat transfer from core of MH bed with lesser addition of parasitic weight to the system thereby improving system gravimetric capacity In a non-limiting embodiment, the present invention provides a multi-tubular metal hydride (MH) system (2400) for H2 storage wherein primarily developed for vehicular applications as part of this work can be extended to its utilization in various other applications such as hydrogen storage, stationary backup power generation in residential and commercial buildings, hospitals, remote villages, thermal energy storage, heating and cooling, hydrogen purification, and hydrogen compression. Referring to the brief description of the drawings stated above. Figure 1 illustrates the graphical presentation of the validation of experimental result developed by mathematical model in accordance with the present invention. In a non-limiting embodiment, the Figure 1.a. discloses a mathematical model developed for the present work is validated with the experimental result reported by Laurencelle and Goyette and the results. It was observed that in terms of results there was not much deviation in the results of the reaction fraction In a non-limiting embodiment, the Figure 1.b. discloses a validation of mathematical model in present work with the experimental results of H. Khurana et. Al. for thermal energy storage. The mathematical model validates the implication of gravity effect and boussinesq approximation applied in thermal energy storage related studies in close agreement with the experimental results as shown in figure 1.b. Figure 2 illustrates the graphical presentation of the grid independence test results in accordance with the present invention. The figure 2 disclose the grid independence test was performed using extremely coarse (7431 elements), extra coarse (7544 elements), coarser (9175 elements), coarse (10735 elements) and normal (11731 elements) meshes. However, the results of grid independence show that normal and coarse mesh were overlapping with each other. The normal mesh is used in this numerical study for higher accuracy. Figure 3 illustrates the graphical presentation of the time step independence test result in accordance with the present invention. The time step independence test was performed for the step size of 3, and 5 to 25 seconds in the step of 5 seconds. The figure 3 discloses that the reaction fraction curve at all-time step was overlapping and smooth in nature as compared. However, the time step of 10 seconds was used to simulate the entire study. Figure 4 illustrates the plot of reaction fraction at 21600s for selection of no. of MH tubes and L / D ratio in accordance with the present invention. It can be observed from the figure 4 that for the given conditions reducing the bed radius results in higher desorption fraction, wherein the 16 number of tubes with L / D ratio of 9 is desorbing 55% of the hydrogen stored in 6 hours as compared to number of tubes in the range 1 to 15. Increasing number of tubes beyond 16 i.e. from 17 to 20, had variation of just 3% in reaction fraction. So, 16 tubes with L / D ratio = 9 were selected for further study. The MH tube dimensions theoretically calculated for the 16 tubes and L / D ratio of 9 are internal diameter = 2.25-inch, thickness = 0.1228-inch, outer diameter = 2.46 inch and length = 20.32 inch. Based on the ASME standards, the SS316L pipe of Schedule 10 nominal size was selected with internal diameter = 2.635-inch, thickness = 0.12 inches, outer diameter = 2.875 inches and length = 14.913 inch have been selected for developing the actual experimental MH system. The selection of the Schedule 10 pipe for development of MH tubes yields design pressure of 84.5 bar and reduces system weight by approximately 30 kg as compared to manufacturing MH tubes using Schedule 40 pipe. Figure 5 illustrates the velocity profile of different shell and tube arrangements - (a) Cuboidal Shell Aligned MH Tubes; (b) Cuboidal Shell Staggered MH tubes; (c) Cylindrical Shell Aligned MH tubes; (d) Cylindrical Shell Staggered MH tubes; (e) Trapezoidal shell Staggered Tube arrangement in accordance with the present invention. In this analysis, shell geometry compared are trapezoidal, cuboidal and cylindrical whereas the tube arrangements considered are aligned and staggered as shown in Figure 5. The cuboidal and cylindrical arrangements having fixed inlet and outlet opening of 3.59 inches equivalent to 1.25Do whereas trapezoidal cross section smaller parallel side as outlet of 3.59 inch and larger parallel side as an inlet as shown in Figure 5. The longitudinal (SL) and transverse (ST) pitch for various arrangements and shell dimensions are given in table 6. The performance in terms of desorption reaction fraction for a duration of 6 hours was studied considering air velocity of 10 km / h, effective thermal conductivity of metal hydride bed as 1.027 W / m-K, and initial temperature = 303 K. Figure 6 illustrates the desorption reaction fraction profile for different shell and tube arrangements in accordance with the present invention. It was observed that 16 MH tubes arranged in trapezoidal shell staggered MH tubes having longitudinal and diagonal pitch equal to 1.25Do and cuboidal shell aligned MH tubes arrangement with transverse and longitudinal pitch equal to 1.25Do results into maximum desorption fraction of 64.84 and 64.33% respectively as compared to 61.45%, 60.5% and 57.41% for cylindrical shell staggered tubes, cuboidal shell staggered tubes and cylindrical shell aligned tubes arrangements respectively as shown in Figure 6. The trapezoidal shell staggered MH tubes arrangement has better rate kinetics as compared to cuboidal shell aligned MH tubes arrangement. However, the scope of invention has to be economical, easier to manufacture and use, so cuboidal arrangement is preferred over trapezoidal for further analysis. The cuboidal shell aligned MH tubes arrangement was considered for further analysis as this arrangement also results into higher heat transfer coefficient of 82.26 W / m2-K compared to other considered arrangements at air velocity of 10 km / h. Figure 7 illustrates the 2D CAD image of 16 MH Tube model in accordance with the present invention. The 16 MH tubes having internal diameter and outer diameter of 2.469 inch and 2.875 inch respectively with L / D = 9 are arranged in aligned arrangement within 4 rows and 4 columns as shown in figure 7. The transverse and longitudinal pitch is equal to 1.25 times of outer diameter. The tube bundle is then cascaded into a cuboidal shell of dimensions 15.66 inch (L) × 15.66 inch (H) × 16.985 inch (W) having an air inlet and air outlet of 3.59 inches in length and spread across the entire width of the system. The arrangement can be considered as tube bundles in cross flow having heat transfer fluid as air. Figure 8 illustrates the desorption reaction fraction and average MH bed temperature evolution at different vehicle velocities considering keff-MHBED = 0.1 W / m-K in accordance with the present invention. The heat transfer coefficient for each velocity was computed using Zukauskas correlation described in section, wherein it was found to be 82.26 W / m2-K, 127.3 W / m2-K and 163.48 W / m2-K for air as HTF at vehicle velocity of 10 km / h, 20 km / h and 30 km / h respectively. The MH system was observed to desorb 34.63%, 38.64% and 40.95% of stored hydrogen in the duration of 6 hours as shown in Figure 8. Figure 9 illustrates the desorption reaction fraction and average MH bed temperature evolution at 10 km / h with inclusion of Al-foam in accordance with the present invention. The figure 9 discloses the effect of addition of Al foam in different volume fraction of MH on reaction fraction and average MH bed temperature as compared to MH bed without Al-foam. It can be observed that after inclusion of Al-foam the reaction fraction improves drastically wherein MH bed desorbs 85%, 93.2% and 97.71% of stored hydrogen for system with 10%, 15% and 20% Al-foam by MH volume respectively within system as compared to the 34.63% of reaction completion for system without Al-foam in the duration of 6 hours. It can be seen that thermal conductivity is one of the important parameters in terms of enhancing the performance of large-scale MH based hydrogen system. The average MH bed temperature drops to 285 K in all cases of Al-foam due to endothermic behavior wherein the MH bed meets the initial energy required to desorb hydrogen from its own stored sensible energy. However, after 6 hours, the average bed temperature for 90%, 85% and 80% Al foam are 291.47 K, 294. 69 K and 297.81 K which also signifies the extent of completion of reaction fraction. Figure 10 illustrates the velocity profile of air flowing through shell of MH system with (a) 1 inlet, (b) 2 inlet aligned tube arrangement; and c) staggered tube arrangement with complete inlet in accordance with the present invention. In the above cases it was observed that the desorption of hydrogen from upper diagonal MH tubes is higher as compared to the lower diagonal tubes. This behavior was due to non-uniform flow of air from inlet to outlet. The air velocity near the tubes in the lower diagonal are below than the inlet velocity of air resulting in lower desorption fraction from these tubes which in turn affects the overall desorption of hydrogen to application. In order to overcome this issue, the system was analyzed with aligned arrangement two air inlets and one outlet and staggered arrangement having complete air cross flow as shown in the Figure 10. The two inlets and one outlet MH system and staggered arrangement complete cross air flow system was initially simulated for desorption performance with 10% Al-foam and further compared with that of one inlet and one outlet system respectively at vehicle velocity of 10 kmph. The maximum air velocity achieved within the shell for both the system is 9 m / s as compared to 6 m / s in the 1 inlet system. It is also evident from the velocity profile that the flow of air in later MH system effectively supplies energy to MH tubes in the lower diagonal of MH system overcoming the limitations of 1 inlet system. Figure 11 illustrates the comparison of desorption reaction fraction and average bed temperature evolution for MH system with single inlet and 2 inlets in accordance with the present invention. In terms of desorption reaction fraction for the duration of 6 hours as shown in Figure 11, it is observed that 2 inlet system with 10% Al-foam desorbs 98% which is 60% increase over the system without any heat transfer enhancement. The MH system with staggered MH tubes having complete cross flow of air across tubes desorbs 94% hydrogen. Further, if we compare the system with 2 inlets aligned and staggered full inlet MH systems seem to desorb hydrogen completely in 6 hours yielding a reaction fraction of 98% and 94% respectively as compared to 85% of 1 inlet system. In overall context, it can be concluded that the poor thermal conductivity plays a major role in the MH based hydrogen system affecting its usage in onboard application. The inclusion of just 10 vol.% Al-foam and increased mass flow of air within the system leads to significant improvement of 10 to 15% in the desorption of hydrogen from MH system for a given time period as compared to single inlet and outlet MH system. Figure 12 illustrates the desorption reaction fraction evolution profile a) 10 km / h, b) 20 km / h, c) 30 km / h without Al-foam; d) 10% Al-foam, e) 15% Al-foam, f) 20% Al-foam with 10 km / h; g) 2 Inlet / 1Outlet without Al-foam; h) 2Inlet / 1 Outlet with 10% Al-foam at 10 km / h in accordance with the present invention. Figure 12(a)-(c) represents the reacted fraction after 6 hours wherein it can be observed that desorption of hydrogen is near the reactor surface whereas desorption of the core remains a major bottleneck even at higher velocities of 30 km / h. It can be concluded that even forced convection of air is not sufficient enough to desorb hydrogen completely from the MH based hydrogen system. In order to improve the desorption further, a heat transfer enhancement need to be incorporated to desorb hydrogen. Figure 13 illustrates the CAD layout and model of different internal heat transfer arrangement within each MH tube to enhance system performance wherein Figure 13(a) illustrates the CAD layout model of hexagonal perforated Cu fins in accordance with the present invention. The Cu fins developed within the scope of the present invention have hexagonal perforations over its cross section as shown in Figure 13. The perforations will allow the distribution and movement of powdered alloy during cycling and also reduces the weight. In the present work, 4 longitudinal hexagonal perforated Cu fins mounted over a cylindrical ring amounting to 10 to 15% of volume of MH have been incorporated within each MH tube to provide heat conduction pathway from / to the core of MH bed and surrounding medium. The effective thermal conductivity of metal hydride bed on inclusion of Cu fins 10% by metal hydride volume is 38.6 W / m-K compared to 1.19 W / m-K on inclusion of 10% by metal hydride volume of Al-foam. Figure 13(b) illustrates the CAD layout of tube in tube heat exchanger embedded within MH tube. The tube in tube heat exchanger mentioned herein is a U-tube inside a MH tube. The material of fabrication for U-tube is considered either SS316L or Cu. The inner and outer diameter of U-tube is 8 and 11 mm respectively. The major radius and length of U-tube is 18 mm and 379 mm respectively. Figure 13(c) illustrates the CAD layout of another form of tube in tube heat exchanger in the form of Finned U-tube arrangement within each MH tube wherein circular cross section fins made of either SS316L or Cu having 24 mm diameter, and 0.5 mm thickness are mounted over length of U-tube with 5 mm fin pitch. The inclusion of such arrangement within MH tubes primarily offers extended heat transfer surface area to aid heat transfer from or to MH bed during hydrogen charging and discharging respectively. Further, the considered tube in tube heat exchanger arrangement (i.e. U-tube and Finned U-tube) can be utilized to regulate the high temperature fluid flow carrying waste heat from higher capacity water cooled fuel cell stack (>5 kW). The hot fluid from fuel cell can be circulated within U-tube embedded inside the MH tube that leads to utilization of waste energy from fuel cell to desorb hydrogen improving overall heat transfer coefficient of process and simultaneously supplying low temperature fluid from outlet of U-tube to cool the fuel cell stack. The heat transfer fluid considered within the U-tube embodiment is water flowing at flow rate of 1 LPM and 303 K temperature. The considered Finned U-tube arrangement occupies only 7.5% of total volume of metal hydride. Figure 14 illustrates the desorption reaction fraction for different internal heat transfer arrangements in accordance with the present invention. As observed from the Figure 14, it takes 15050s (4.2 hrs) and 17810s (4.95 hrs) to desorb 80% of hydrogen using perforated Cu fins and Al-foam within MH bed respectively. The inclusion of Cu-fins and Al-foam improves the desorption performance by 48% compared to reactor without any heat transfer enhancement medium. However, the reaction kinetics behavior on using perforated Cu fins and Al-foam is almost similar generally due to the assumption that Al-foam is uniformly distributed within MH bed throughout the length of MH bed. Further, U-tube and Finned U- tube embedded within MH bed as shown in the Figure 13(b) and 13(c) respectively are analyzed for impact on desorption behavior. The HTF considered is water flowing at 1 LPM at 303K within U-tube and air flowing past MH tube at 10 km / h. The desorption reaction fraction completion is 65.7% and 72.69% for simple SS and Cu U-tube respectively. Considering Finned U-tube heat augmentation technique imparting extended surface area along with fluid flow desorbs 79% of hydrogen for both finned U-tube made of Cu and SS. In the overall context, the perforated Cu fins yields maximum desorption fraction of 91% as compared to any other heat augmentation techniques considered within the study as shown in Figure 14. Figure 15 illustrates the different types of surface roughness developed on external surface of MH tube in accordance with the present invention. The present invention explores the novel study on effect of surface roughness developed over MH tubes on their performance as shown in the Figure 15. In this study, effect of wire mesh, v-rib, v-rib with gap, and dimple shaped artificial surface roughness on hydrogen absorption in single MH tube have been analyzed numerically using 3D model in COMSOL Multiphysics 5.5 software. This concept of such different forms of artificial surface roughness have been extensively used in improving the performance of solar air heaters. Further, in order to increase heat transfer coefficient during cross flow of air across MH tubes, a novel study considering the effect of surface roughness on absorption reaction fraction have been analyzed within the research domain of metal hydride storage system development. Figure 16 illustrates the comparison of absorption reaction fraction and average MH bed temperature for different types of surface roughness in accordance with the present invention. It was observed from Figure 16 that MH tubes absorbs 91%, 90.67%, 87.26%, and 82.38 of hydrogen in 3 hours (10800s) for MH tubes having v-rib, v-rib with gap, wire mesh, and dimple shaped surface roughness respectively. The MH tube without surface roughness absorbs 82% for the considered duration. The inclusion of surface roughness improves the hydrogen absorption performance by almost 10% compared to MH tube without any surface roughness. Figure 17 illustrates the cuboidal shell and aligned MH tube arrangement considered for water and PCM related studies in accordance with the present invention. In the present invention as shown in Figure 17, 16 MH tubes in aligned arrangement are cascaded in cuboidal shell. In order to store released thermal energy during absorption process, water and phase change material within shell have been considered as an energy storage medium. The energy storage medium can be extended to thermochemical heat storage material on usage of high temperature metal hydride alloy. The organic PCM such as paraffin wax are economical, extensively used in many long-term thermal energy storage applications as it offers increased energy storage efficiency due to latent form of energy storage. However, PCM suffers from poor thermal conductivity affecting energy supply at higher rate to end use. On the other hand, a much cheaper and easily available resource – water, a sensible energy storage medium can also be used to store thermal energy. Water have higher specific heat capacity and thermal conductivity compared to PCM. However, its utilization is limited due to temperature range on energy storage. The different class and types of PCM offers wide temperature range and latent heat capacity for thermal energy storage. Figure 18 shows the combined results of absorption, stratification and desorption reaction fraction profile on using water as an energy storage medium. The mathematical model and related governing equations have been explained in detail in the section 3 and the parameters used within study are listed in table 1. The boussinesq approximation was applied to momentum equation to consider the effect of buoyancy wherein density variation gives rise to stratification effect within fluid medium. The absorption study is for 6 hrs followed by 3 hrs stratification and considering the final state after stratification as initial condition desorption study is considered for 6 hrs. The MH system in the present invention was analyzed for 4 different cases comparing the effect of inclusion of 10%, 15% and 20% Al-foam with system without any Al-foam (keff = 0.1 W / m-K) on overall process. In terms of hydrogen absorption, it takes 1800s (30 min), 3400s (57 min), 7200s (120 min) for MH reactor with 20%, 15% and 10% Al-foam respectively whereas reactor without Al-foam absorbs 74.35% of hydrogen storage capacity in 21600 (360 min). In case of desorption study, the MH reactor without no foam takes 305 min (5 hrs) to desorb 74.35% of absorbed hydrogen whereas the reactor with 10%, 15% and 20% Al-foam of metal hydride volume takes 84.2 min, 57.5 min and 39.2 min respectively to desorb 90% of hydrogen storage capacity utilizing the energy stored within water during absorption. Figure 19 illustrates the average MH bed temperature and average shell water temperature during absorption, stratification and desorption studies on using water as an energy storage and supply medium in accordance with the present invention. It is to be noted that inclusion of Al foam in different vol.% leads to increase in tube volume and its length, in similar manner the shell length also increases that leads to increased shell volume and thereby increased mass of water within shell. The mass of water within shell varies as 39.37 kg, 43.68 kg, 46.25 kg and 49.14 kg for system without foam, 10%, 15% and 20% Al-foam respectively. The peak average MH bed temperature during absorption rises to 399.18 K in 20 seconds, 389.33 K, 388.13 K, 387.39 K in 10 seconds from beginning of the reaction for system with no foam, 10%, 15%, and 20% Al-foam respectively. The average water temperature in the shell rises to 370.92 K, 362.66 K, 354.51 K, 346.51 K at the end of 6 hrs for cases with no foam, 10%, 15%, 20% Al-foam by volume of MH respectively and attains thermal equilibrium with MH bed temperature except system without no foam as shown in Figure 19. The temperature decrement in shell HTF after complete reaction duration of 6 hrs is associated with increasing thermal mass and water mass for each case. The effect of stratification is not that prominent within the present invention with respect to the results obtained as energy release and its distribution is uniform in all direction due to MH tube orientation within aligned arrangement. However, the temperature distribution seems to have lower temperature near the wall as compared to the center region of shell due to the no slip condition at the wall. The shell HTF temperature attains equilibrium with MH bed temperature after desorption reaction completion except the system without Al foam. Figure 20 illustrates the reaction fraction evolution during absorption and desorption study on using PCM (i.e. paraffin wax RT35HC) as an energy storage and supply medium in accordance with the present invention. It was observed that it takes 114.5 min, 46.17 min, and 23 min for complete hydrogen absorption with MH system having 10%, 15% and 20% Al-foam of metal hydride volume respectively whereas MH reactor without foam stores 80.75% of total hydrogen storage capacity in 6 hrs. The inclusion of 10 to 20% Al-foam leads to 68.2% to 93.6% reduction in reaction time as compared to 6 hrs absorption in system without foam. In case of hydrogen desorption, the MH system with 10%, 15% and 20% Al-foam desorbs 100% hydrogen in 4.7 hrs, 5.6 hrs and 5.7 hrs respectively whereas system without foam desorbs only 70.74% of 80.75% absorbed hydrogen within 6 hrs. Figure 21 illustrates the average MH bed temperature and PCM temperature during absorption and desorption study on using PCM (i.e. paraffin wax RT35HC) as an energy storage and supply medium in accordance with the present invention. The peak average MH bed temperature during absorption observed was 392.76 K in 20s, 388.66 K in 260s, 387.46 K in 160s, 384.78 K in 70s from the beginning of reaction for MH system with no foam, 10%, 15%, and 20% Al-foam of metal hydride volume respectively. The average temperature of PCM within shell measured are 356.15 K, 350.35 K, 333.55 K and 320.28 K for 6 hrs. absorption duration wherein PCM temperature tends to attain thermal equilibrium with MH bed temperature as indicated by figure 21. The average MH bed temperature and PCM temperature drops and attains thermal equilibrium during endothermic desorption reaction due to energy supply from PCM to MH bed as shown in Figure 21. Figure 22 illustrates the PCM phase transformation during absorption and desorption study in accordance with the present invention. Figure 22 indicates the phase transition of paraffin wax from solid to liquid and vice versa during hydrogen absorption and desorption respectively. It was observed that for 50% phase transformation from solid to liquid during absorption reaction it takes nearly 45.5 min, 22.17 min, 22 min, 23 min whereas it takes 271 min, 88.33 min, 68.67 min and 46.17 min for liquid to solid transformation during desorption reaction for MH reactor with no foam, 10%, 15% and 20% Al-foam respectively. Figure 23 illustrates the comparison of reaction fraction evolution during absorption and desorption study on using water and PCM as an energy storage and supply medium in accordance with the present invention. In terms of comparing the MH system performance with respect to use of water and PCM as an energy storage medium. It is observed that MH system performance majorly differs during hydrogen desorption. The time required to desorb 90% hydrogen using energy stored in PCM is 174 min, 171 min and 160 min for MH system with 10%, 15% and 20% Al-foam respectively whereas this time reduces to 84.2 min, 57.5 min and 39.2 min respectively on using water as an energy supply medium. The poor thermal conductivity of PCM leads to higher desorption time wherein water having comparatively higher thermal conductivity leads to effective energy supply to desorb hydrogen. Figure 24 illustrates 3D CAD layout of metal hydride based 1kg hydrogen storage system for vehicular applications in accordance with the present invention. The 1 kg hydrogen storage system described herein this document having 16 MH tubes with L / D ratio = 9 have been studied for its end use primarily in vehicular applications. In case of large amount of hydrogen storage, the present invention can be attached in multiple units to meet the end use demand. However, depending on the space and quantity of hydrogen storage, number of metal hydride tubes, related dimensions of tubes and their arrangement may vary to meet the end use application demand. The MH tubes or entire system can be fabricated either using SS316L, Aluminum or any weight reducing material having good resistant towards hydrogen embrittlement. The figure 24 discloses modular multi tubular metal hydride system storing 1 kg hydrogen can be either integrated with fuel cell or internal combustion engine to power given vehicle. In terms of vehicular applications, the end product can also work similar to battery swap technology in terms of usage. Figure 25 illustrates the different possible arrangements of 1 kg hydrogen system for testing and their application in vehicular applications wherein Figure 25(a) and (b) depicts the 3-D assembly and side view of 16 MH tubes with 4 perforated longitudinal Cu fins inside each tube to be tested using air as HTF for hydrogen absorption and desorption performance; Figure 25(c) and 25(d) depicts the 3-D assembly and side view of 16 MH tubes having different surface roughness on outer surface of MH tubes; Figure 25(d) is a 3-D assembly of 16 MH tubes within a closed cuboidal shell considered for onboard thermal energy storage and supply using water and PCM; Figure 25(e) is a 3-D assembly of 16 MH tubes within a cuboidal shell having an inlet and outlet for heat transfer fluid flow to assess the charging and discharging performance. As used herein, Phase Change Material (PCM) refers to a phase-change material (PCM) is a substance which releases / absorbs sufficient energy at phase transition to provide useful heat or cooling. Generally, the transition will be from one of the first two fundamental states of matter - solid and liquid - to the other. The solid / liquid phase change materials that PCM Products supply can be most simply divided into four categories: eutectics, salt hydrates, organic materials, and high temperature salts. As used herein, heat transfer fluid (HTF) refers as an intermediate fluid to transfer heat from a heat source to other heat demands (or cold streams). Single heater can provide heat to any number of cold streams through HTF. As used herein, desorption refers when a substance detaches from or through a surface. Desorption pertains to a phenomenon wherein a hydrogen is released from another, either from or through the surface. The process of hydrogen absorption (or desorption) by metals is reversible and involves the surface and the bulk of the material, through several steps. As used herein, 3D CAD refers to a (3-dimensional computer-aided design) is a technology that engineers, product developers and designers use to create functional, virtual prototypes of three-dimensional objects. With 3D CAD, designers can dynamically create and modify every detail of a product, part or assembly. As used herein, Boussinesq approximation refers to assumes a constant kinematic viscosity and can be used for both turbulent and laminar flows. The approximation assumes a linear change in density that is dependent on temperature. It is very accurate for natural convection flows at relatively low- temperature differences from ambient. Henceforth, the present invention proposes a metal hydride (MH) -based hydrogen storage system for storing 1 kg of hydrogen for vehicular applications. This system comprises of optimized 16 tubes having LaNi5 as a reference MH material of AB5 type is used for developing the hydrogen storage system. The present invention introduces the concept of developing artificial surface roughness over surface of MH tubes to enhance heat transfer coefficient during fluid flow across MH tubes. The present invention offers multiple technical advantages out of which few have been enumerated below for ease of understanding: • The present invention provides a compact and modular multi-tubular metal hydride-based system for 1 kg hydrogen storage capacity for vehicular applications. • The present invention provides a development of artificial surface roughness over external surface of MH tubes to increase heat transfer coefficient which in turn increases system’s performance. • The present invention provides an inclusion of light weight heat augmentation techniques such as internal hexagonal perforated longitudinal Cu plate fins or Al foam to improve effective thermal conductivity and heat transfer from / to core of MH bed. • The present invention utilizes high speed air due to vehicle motion as heat transfer fluid to desorb hydrogen from MH bed for proposed arrangements of MH tubes. Further also proposes the use of water and PCM within shell as an energy storage and supply medium to utilize waste heat released during absorption to desorb hydrogen. • The present invention proposes inclusion of tube in tube heat exchanger in the form of a U-tube or a Finned U-tube arrangement embedded within each MH tubes that offers higher extended heat transfer surface area and can be utilized to regulate the waste energy carried by high temperature fluid flow in thermal integration with higher capacity water cooled fuel cell stack (>5 kW) to improve system’s performance. The hot fluid from fuel cell can be circulated within U-tube embedded inside the MH tube that leads to utilization of waste energy from fuel cell to desorb hydrogen and simultaneously supplying low temperature fluid from outlet of U-tube to cool the fuel cell stack. • The present invention provides a multi-tubular modular MH system capable of storing 1 kg hydrogen within 16 MH tubes having LaNi5 as a hydrogen storage alloy arranged in aligned or staggered manner housed in a cuboidal shell. • The present invention provides a compact and modular multi-tubular metal hydride-based hydrogen storage system wherein the multitubular configuration will be helpful in regulating or accomplishing a dynamic or controlled desorption. This controlled desorption can be achieved by means of controlled energy supply to desorb hydrogen using electric heating or switching desorption from one MH tubes layer to another MH tube layer desorption as per the demand. This will lead to efficient utilization of total stored energy and eliminate the requirement of additional buffer volume. • The 16 MH tubes forming a unit to store 1 kg hydrogen are cascaded in compact dimension approximately 16 in x 16 in x 18 in cuboidal shell. This compact and modular arrangement will be swappable like battery swapping or multiple such portable units can be assembled within vehicle to have higher amount of hydrogen as a fuel to propel vehicle over a larger range. • The present invention with multi tubular configuration can be developed using different class of hydrides having higher gravimetric capacity but different operating conditions to accomplish higher volumetric energy density and system gravimetric capacity. • The present invention is designed as such that it can be integrated both with fuel cell as well as internal combustion engine to power vehicle. • The present invention primarily developed for vehicular applications as part of this work can be extended to its utilization in various other applications such as hydrogen storage, stationary backup power generation in residential and commercial buildings, hospitals, remote villages, high altitude regions, thermal energy storage, heating and cooling, hydrogen purification, and hydrogen compression. The foregoing description of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form or forms disclosed, and other modifications and variations may be possible in light of the above teachings wherein those of skill in the art will recognize certain modifications, permutations, additions and sub combinations thereof.

Claims

CLAIMS:

1. A multi-tubular metal hydride (MH) system (2400) for 1 kg H2storage, the system comprising: - a plurality of metal hydride (MH) tubes optimized for length to diameter ratio (L / D) to develop compact hydrogen storage system, wherein L / D ratio varies from 1 to 10 and the plurality of tubes varies from 1 to 20; - one or more predefined shaped shell for cascading MH tubes in an aligned tube arrangement having different longitudinal pitch, diagonal pitch, transverse pitch, wherein the MH tubes analyzed in depth for charging and / or discharging performances; - at least one metal foam medium or a finned tube heater to transfer internal heat from or to a MH bed in process of absorption and / or desorption of hydrogen; - at least four hexagonal perforated longitudinal fins mounted on a cylindrical ring of the MH tube to enhance heat transfer from core to the MH bed and allow uniform distribution of alloy within MH tubes; - at least one tube in tube heat exchanger in the form of U-tube or finned U-tube embedded within each MH tube as a heat exchanger offering higher heat transfer surface area and utilizing high temperature fluid from liquid cooled fuel cell stack to desorb hydrogen and simultaneously supplying low temperature fluid (due to endothermic nature of hydrogen desorption from MH) to cool fuel cell stack; - at least 75 kg of LaNi5alloy as a metal hydride hydrogen storage medium distributed equally in 16 MH tubes; and - at least one-disc filters fitted on one end of the cylindrical MH tube to separate alloy and / or gas circuit in process of charging and / or discharging of hydrogen in the system to utilize waste heat from the fuel cell as an energy medium to desorb hydrogen (H2), wherein the multi tubular MH system forming at least 1kg hydrogen (H2) storage capacity system is compact, modular, portable and swappableattached in multiple units to meet net hydrogen storage demand in vehicular applications.

2. The system (2400) as claimed in claim 1, wherein four perforated longitudinal fins having hexagonal shape perforations fabricated using copper (Cu) material supported over the cylindrical rings coaxially placed in each MH tube to improve the heat transfer.

3. The system (2400) as claimed in claim 1, wherein MH tubes with various surface roughness such as v-rib, v-rib with gap, wiremesh and / or dimple shaped protrusions enhance the MH system performance in fluid flowing medium.

4. The system (2400) as claimed in claim 1, contains a tube in tube heat exchanger in the form of U-tube or finned U-tube embedded within each MH tube as a heat exchanger having an extended surface area for heat transfer and utilizes waste energy in the form of high temperature fluid from liquid cooled fuel cell stack to desorb hydrogen and simultaneously supplying low temperature fluid to cool fuel cell stack thereby enhancing overall system’s performance.

5. The system (2400) as claimed in claim 1, wherein the shell comprising inlet and outlet of shell to dissipate and / or supply heat from the MH bed involving heat transfer fluid such as water, coolant, nanofluids, oil as flowing medium between inlet and outlet of shell.

6. The system (2400) as claimed in claim 1, wherein the different class of metal hydrides (MH) comprising selectively AB2, AB5, A2B, AB, BCC and high entropy alloys adapted to store hydrogen in present invention.

7. The system (2400) as claimed in claim 1, wherein incorporation of metal foam within MH tube are Al foam and / or copper foam having 10 to 20%by volume of metal hydride to increment effective thermal conductivity of MH by 10 to 20 times improving the overall performance of the MH system.

8. The system (2400) as claimed in claim 1, wherein the MH system utilized for thermal energy storage having one or more upper and / or lower diagonal group of tubes filled with low temperature metal hydride and the other group with high temperature metal hydride.

9. The system (2400) as claimed in claim 1, wherein MH tube embedded with finned tube heaters inside to rise the temperature of metal hydride to desorb hydrogen.

10. The system (2400) as claimed in claim 1, wherein programmed electric heating enables controlled dynamic desorption by supplying sufficient amount of energy based on end use hydrogen flow rate requirement.

11. The system (2400) as claimed in claim 1, wherein two or more hydrogen storage alloy among different class of metal hydrides stored within separate tubes to accomplish higher volumetric energy density and dynamic desorption by means of programmed layer by layer or tube by tube switching depending on vehicle torque and power requirement on acceleration and constant speed cruising.

12. The system (2400) as claimed in claim 1, wherein hydrogen supply pressure increased upto 80 bar or more depending upon the hydrogen storage capacity involving the alloy material used in MH system and the end use application.

13. The system (2400) as claimed in claim 1, wherein the MH system having swappable, portable characteristic after usage with other unit such as battery swapping technology.

14. The system (2400) as claimed in claim 1, wherein the optimization of MH system in terms of shell and tubes arrangement is based on different alignments such as aligned, staggered with different transverse, longitudinal and diagonal pitch.

15. The system (2400) as claimed in claim 1, wherein the shell geometry shape comprising both cuboidal, cylindrical and trapezoidal shaped based on end user requirements.

16. The system (2400) as claimed in claim 1, wherein MH system incorporated with water, Phase Change Material (PCM), thermochemical heat storage material in the shell to store energy released by the MH bed during absorption and further desorb hydrogen on-board and / or off-board from MH system.

17. The system (2400) as claimed in claim 1, wherein the MH tube fabricated using SS316L, aluminum and / or low weight material having resistance to hydrogen embrittlement.

18. The system (2400) as claimed in claim 1, 16 MH tubes with L / D ratio = 9 have been developed in the present invention. The MH system for larger scale hydrogen storage (>1 kg hydrogen storage) and depending on the application, number of MH tubes and its related dimensions can be varied.

19. The system (2400) as claimed in claim1, wherein fins of non-uniform cross section such as nature aspired leaves or impeller blade structure fabricated using high thermal conductivity material to improve heat transfer from core of MH bed with lesser addition of parasitic weight to the system thereby improving system gravimetric capacity.

20. The system (2400) as claimed in claim 1, primarily developed for vehicular applications as part of this work can be extended to its utilization in various other applications such as hydrogen storage, stationary backuppower generation in residential and commercial buildings, hospitals, remote villages, thermal energy storage, heating and cooling, hydrogen purification, and hydrogen compression.

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