Roof integrated solar powered desiccant atmospheric water generating device

Abstract

The present invention relates to a Flow Assisted Desiccant Solar Still (FADSS) device for extracting potable drinking water from atmospheric air The FADSS device comprises a desiccant box having silica gel as a desiccant material, for adsorbing water from atmospheric air. The FADSS device may further comprise a blower and a condenser. An inlet tube is positioned at bottom of one corner of the desiccant box, and an outlet tube is positioned on a side surface above the desiccant bed, in a diagonally opposite direction to the inlet tube. The inlet tube and the outlet tube are connected to a condenser. The blower forces ambient air across the desiccant box, for saturating the desiccant bed. The air is circulated in the desiccant box carries released vapour to the condenser. The vapour is condensed from circulated air and is removed from bottom of the condenser, in form of potable water.

Description

ROOF INTEGRATED SOLAR POWERED DESICCANT ATMOSPHERIC WATER GENERATING DEVICETECHNICAL FIELD

[0001] The present invention relates to a device for obtaining water from ambient air. In particular, the invention relates to a device for obtaining water from ambient air by regeneration of water from the adsorbed water vapour.BACKGROUND OF THE INVENTION

[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.

[0003] With growth in global population, demand for freshwater is growing at an alarming rate. Unfortunately, due to unsustainable growth of human population, there has been severely dwindling groundwater levels, erratic weather patterns, and widespread desertification. This has caused a looming crisis for human population to obtain potable water.

[0004] Many techniques are employed to obtain potable water. Desalination is currently one of the most widely used solutions to meet an ever-increasing demand for freshwater. The conventional desalination methods involve fuel burning activity for boiling and condensation have dire impact on environment. Also, desalination methods require high cost plants undertaking desalination mechanism. Further, desalination methods involves reverse osmosis mechanism leading to discharge of concentrated material in coastal seawater which impact marine species.

[0005] Other alternatives for obtaining freshwater are commercially available Atmospheric Water Generators (AWG) using electricity to produce water. The AWG use various cooling technologies to get air temperature below dew point, which starts the condensation process. The output of AWG devices are highly influenced by humidity andtemperature of the surrounding air. The effectiveness of AWG devices are based on Vapour Compression Refrigeration (VCR) under various temperature and humidity levels. But, the VCR-based system needs high amount of power consumption to produce 1 litre of water in humid and mild to dry environments. Another approach is to utilize Thermo-Electric Dehumidifier (TED) based AWG to produce water from the atmosphere. The TED AWG devices also lack power efficiency.

[0006] Another commonly used device for obtaining potable water is a desiccant solar still device. A desiccant solar still device is a promising substitute for electrically powered AWGs, requiring low maintenance and having a prolonged life span. These devices use direct solar radiation to evaporate water absorbed in a desiccant bed, and hot, moist air is released is condensed at colder surfaces. Unlike electrically powered AWGs, the desiccant solar still devices can operate in a wide range of humidity levels and temperatures, making them suitable for use in various environmental conditions, including arid and semi-arid regions. However, a conventional desiccant solar still device has a drawback as it depends upon natural airflow for adsorption, limiting the bed design and the amount of desiccant used in the given area. Also, the condensation of water vapour takes place under a glass cover during the desorption process, which is inefficient.

[0007] Thus, there is a need for a cost effective and power effective solution for exacting potable water.OBJECTS OF THE INVENTION

[0008] A general object of the present invention is to provide a cost-effective solution for extracting potable water.

[0009] Yet another object of the present invention is to extract potable water without using any external energy requirement but solar energy.

[0010] Still another object of the present invention is to provide a solution for exacting potable water from ambient air.

[0011] Another objective of the present invention is to provide a device for extracting potable water from ambient air which can be installed as a roofing system and reduces an overall cost of a building.

[0012] Another objective of the present invention is to provide a roof integrated water generating and the rainwater harvesting mechanism to provide drinking water all year round, even during cloudy weather or when sunlight is absent.SUMMARY OF THE INVENTION

[0013] The summary is provided to introduce aspects related to a device for obtaining water from air, and the aspects are further described below in the detailed description. This summary is not intended to identify essential features of the claimed subject matter nor is it intended for use in determining or limiting the scope of the claimed subject matter.

[0014] The present invention may relate to a device for obtaining water from air. The device may be a Flow Assisted Desiccant Solar Still (FADSS) device for extracting potable drinking water from atmospheric air. The FADSS device may comprise a desiccant box. The desiccant box may comprise a desiccant bed of silica gel as a desiccant material. As the air passes through the desiccant bed, water molecules in the air adhere to the desiccant material due to the van der Waals force of attraction. The FADSS device may comprise a blower and a condenser. An inlet tube may be positioned at bottom of one comer of the desiccant box, and an outlet tube may be positioned on a side surface above the desiccant bed, in a diagonally opposite direction to the inlet tube. The inlet tube and the outlet tube may be connected to a condenser. The condenser may further be connected to a water collecting jar for collecting potable water.

[0015] During the night (adsorption process), ambient air may be blown continuously through the desiccant bed, facilitating the silica bed to adsorb moisture. During the daytime (desorption process), heat energy may heat the silica bed, releasing the adsorbed water vapour to the circulating air, which carries it to the condenser. The blower may increase the rate of the adsorption process by allowing a larger volume of humid air to interact with the silica bed per unit of time. The moist air may then exit the box through the outlet tube. The warm, moisture-laden air may then be directed to the condenser and passed through copper tubes of the condenser, where it condenses on the colder surface. A resulting condensed water collects at the bottom of the heat exchanger and is discharged into the water collecting jar. During the night (adsorption process), ambient air is blown continuously through the bed, facilitating the silica bed to adsorb moisture. During the daytime (desorption process), solar energy heats the silica bed, releasing the adsorbed water vapour to the circulating air, which carries it to the condenser. The water vapour condenses in the condenser, and the air may return to the bed.

[0016] The FADSS device may force air circulation for better adsorption of desiccant material and regulate the condensation of water vapour using a condenser during the desorption period.

[0017] In one aspect, the FADSS device may include silica filled Evacuated Tube Collector (ETC) instead of the desiccant box. Evacuated tubes may be two concentric glass tubes that are fused and space in between the two tubes may be made vacuum using a pump, which facilitates it to store heat for a longer time and reduces the convection losses.

[0018] Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS

[0019] The accompanying drawings constitute a part of the description and are used to provide further understanding of the present invention. Such accompanying drawings illustrate the embodiments of the present invention which are used to describe the principles of the present invention. In the figures, similar components and / or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label with a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label.

[0020] The embodiments are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this invention are not necessarily to the same embodiment, and they mean at least one. In the drawings:

[0021] Fig. 1 illustrates a schematic diagram of a FADSS device, in accordance with an embodiment of the present invention;

[0022] Fig. 2 illustrates the pictorial view of FADSS device, in accordance with an embodiment of the present invention;

[0023] Fig. 3 illustrates a line diagram of a detailed view of an evacuated tube, in accordance with an embodiment of the present invention;

[0024] Figs. 4(a) and 4(b) illustrate individual silica filled Evacuated Tube Collector (ETC) and silica filled ETC tubes connected respectively, in accordance with an embodiment of the present invention.

[0025] Fig. 5 illustrates silica filled ETC tubes connected in parallel, in accordance with an embodiment of the present invention;

[0026] Fig. 6 illustrates a photographic image of the FADSS device having desiccant material (silica) filled ETC tubes, in accordance with an embodiment of the present invention;

[0027] Fig. 7 illustrates variation in measured outdoor solar radiation and a simulated radiative heat flux provided by the solar simulator every hour, in accordance with an embodiment of the present invention;

[0028] Fig. 8(a) to 8(d) illustrate a perspective view, sectional view and enlarged view of four configurations of desiccant bed in the FADSS device, in accordance with an embodiment of the present invention;

[0029] Fig. 9 illustrates a plot of variation of mean ambient temperature and relative humidity with time over a day, in accordance with an embodiment of the present invention;

[0030] Fig. 10 illustrates a plot of temporal variation of the desiccant bed temperature during the entire operational cycle of 24 hours, in accordance with an embodiment of the present invention;

[0031] Figs. 11(a) and 11(b) illustrate a plot of variation of inlet and outlet temperatures throughout the desorption process, including the soaking period of two hours respectively, in accordance with an embodiment of the present invention;

[0032] Fig. 12 illustrates water production per day from the FADSS device at different airflow rates, in accordance with an embodiment of the present invention;

[0033] Fig. 13 illustrates hourly water production during desorption process at different airflow rates, in accordance with an embodiment of the present invention;

[0034] Fig. 14 illustrates temporal variation of silica bed temperature in the FADSS device during desorption process including soaking across different desiccant bed designs, in accordance with an embodiment of the present invention;

[0035] Figs. 15(a) and 15(b) illustrates temporal variation of the inlet and outlet air temperature profiles of the desiccant box respectively, in accordance with an embodiment of the present invention;

[0036] Fig. 16 illustrates water production per day with different bed designs, in accordance with an embodiment of the present invention;

[0037] Fig. 17 illustrates hourly water production during desorption process with different desiccant bed designs, in accordance with an embodiment of the present invention;

[0038] Fig. 18 illustrates the variations of r|c(conversion efficiency) and r|sys(system efficiency) of the FADSS with airflow rate, in accordance with an embodiment of the present invention;

[0039] Fig. 19 illustrates a plot of variation of r|cand r|sysfor different desiccant bed designs, in accordance with an embodiment of the present invention; and

[0040] Fig. 20 illustrates front view and isometric view of ETC bed design, in accordance with an embodiment of the present invention.

[0041] Fig. 21 illustrates roof integrated atmospheric water generator, in accordance with an embodiment of the present invention.

[0042] Fig. 22 illustrates trimetric view of FADSS system with 1.5 m2surface area, in accordance with an embodiment of the present invention.

[0043] Fig. 23 illustrates FADSS without solar panel arrangement, in accordance with an embodiment of the present invention.

[0044] Fig. 24 illustrates Front view of FADSS with water filtration unit, in accordance with an embodiment of the present invention.

[0045] Fig. 25 illustrates detailed view of FADSS without water filtration unit, in accordance with an embodiment of the present invention.DETAILED DESCRIPTION OF THE INVENTION

[0046] The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments in which the present invention may be practiced. Each embodiment described in this disclosure is provided merely as an example or illustration of the present invention, and should not necessarily be construed as preferred or advantageous over other embodiments. The detailed description includes specific details for the purpose ofproviding a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details.

[0047] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.

[0048] If the specification states a component or feature “may”, “can”, “could”, or “might” be included or have a characteristic, that particular component or feature is not required to be included or have the characteristic.

[0049] The present invention relates to a device for obtaining water from ambient air. The device may be a Flow Assisted Desiccant Solar Still (FADSS) device for extracting potable drinking water from atmospheric air. The FADSS device may comprise a desiccant box. The desiccant box may comprise a desiccant bed of a desiccant material. The desiccant materials may be solid, liquid or composite. In one implementation, the desiccant material may be silica gel. The silica gel may adsorbs the moisture from surrounding air and when the silica gel regenerates, moisture may be released in form of water droplets. When the humid air passes through the silica gel, the water molecules attach to the surface of the silica gel due to the inter- molecular van der Waals force of attraction. These water molecules separate from the silica gel after receiving enough energy, called heat of desorption. The FADSS device may operate in two process cycles. A first process cycle may be an open cycle of operation of the FADSS device, occurring during night time. A second process cycle may be a closed cycle of operation of the FADSS device, occurring during day time. The desiccant material in the FADSS device, during the first process cycle, may adsorb moisture from the surrounding air. During the second process cycle, the FADSS device may receive a direct solar radiation and may heat the bed of the desiccant solar still, thereby releasing the absorbed water vapour from the desiccant material.

[0050] The FADSS device may further comprise a blower and a condenser. The blower may force ambient air across the desiccant box, thereby saturating the desiccant bed. The ambient air circulated in the desiccant box may carry released vapour to the condenser. Thevapour may be condensed from circulated air and may be removed from bottom of the condenser, in form of potable water. The circulated air may return to the desiccant bed and the first process cycle and the second process cycle may continue iteratively. The FADSS device may thus regulate condensation process by controlling the airflow rate and providing flexibility in designing structure of the desiccant bed.

[0051] Fig. 1 illustrates a schematic diagram of a FADSS device, in accordance with an embodiment of the present invention. The FADSS device 100 may comprise a desiccant box 102. The desiccant box 102 may be an insulated desiccant box. In one implementation, the desiccant box 102 may be made of mild steel and covered with Nitrile rubber to minimise heat loss. The desiccant box 102 may have dimensions of 0.5 m x 0.5 m x 0.15 m and covered with 9mm Nitrile rubber. The desiccant box 102 may be sealed with a 6 mm thick glass on top. The desiccant box 102 may comprise a desiccant bed 104 resting inside the desiccant box 102 with supporting structures. The desiccant bed 104 may consist of silica gel as desiccant material. Over the glass top of the desiccant box 102, a bulb holder setup 106 may be positioned for mounting one or more incandescent bulbs 108 for constructing a solar simulator. Four 250 W incandescent bulbs may be mounted diagonally opposite to each other on a plank measuring 0.5 x 0.5 m, with a distance of 17.5 cm between them to deliver a uniform heat flux as much as possible. A power regulator may govern bulb output and regulate heat flux as required. An inlet tube 110 may be positioned at bottom of one corner of the desiccant box 102, and an outlet tube 112 may be positioned on a side surface above the desiccant bed 104, in a diagonally opposite direction to the inlet tube 110. The inlet tube 110 and the outlet tube 112 may be connected to a condenser 114. The condenser 114 may further be connected to a water collecting jar 116 for collecting potable water. The condenser 114 may be connected to the water collecting jar 116 through a 1 / 4" narrow tube fixed at the bottom of the condenser 114. A centrifugal air blower 118 may be installed on the inlet tube 110 for circulating the air inside the desiccant box 102. Air in the inlet tube 110 may be regulated by a flow meter 120. An ambient sensor 122 may be used to measure ambient conditions.

[0052] Water production process in the FADSS device 100 involves two processes, i.e. adsorption and desorption. During adsorption, water may be adsorbed by surface of the silica gel in the desiccant bed 104. In contrast, during desorption, the adsorbed water is evaporated from the silica gel, followed by condensation. The adsorption process of FADSS is an open cycle that operates during the night. The desiccant box 102 and the condenser 114 may beconnected by a hosepipe, which remains open throughout the process of adsorption. Fresh air, rich in moisture and at low temperature, may be drawn into the desiccant box 102 by a blower through the inlet tube 110 located at the bottom of the desiccant box 102. As the air passes through the desiccant bed 104, water molecules in the air adhere to the desiccant material due to the van der Waals force of attraction. The blower 118 increases the rate of the adsorption process by allowing a larger volume of humid air to interact with the silica bed per unit of time. The moist air then exits the box through the outlet tube 112.

[0053] Further, the desorption process in the FADSS device 100 consists of two phases i.e. a soaking period and a desorption period. The soaking period lasts for two hours, during which the desiccant bed 104 is heated to a required temperature for a subsequent desorption period. The desorption period may run for a short period, and may involve the extraction of water vapour from the silica gel surface by blowing air into the desiccant box 102. In one implementation, the desorption period lasted six hours. The warm, moisture-laden air may then be directed to the condenser 114 and passed through copper tubes of the condenser 114, where it condenses on the colder surface. A resulting condensed water collects at the bottom of the heat exchanger and is discharged into the water collecting jar 116. Fig. 2 illustrates a photographic image of the FADSS device 100, in accordance with an embodiment of the present invention.

[0054] In another implementation, the FADSS device 100 may include desiccant material filled Evacuated Tube Collector (ETC) instead of the desiccant box 102. Evacuated tubes are two concentric glass tubes that are fused and space in between the two tubes may be made vacuum using a pump, which facilitates it to store heat for a longer time and does not allow conduction and convection losses. Fig. 3 illustrates a line diagram of a detailed view of an evacuated tube, in accordance with an embodiment of the present invention. The glass may be borosilicate. Silica gel may be filled inside the evacuated tubes. Figs. 4(a) and 4(b) illustrate individual silica filled ETC and silica filled ETC tubes connected respectively, in accordance with an embodiment of the present invention. A selective coating may be provided on an outer surface of inner tube to absorb most of impinging solar radiation, and the vacuum helps in retaining solar heat inside the evacuated tubes, thereby reducing convective losses. The evacuated tubes may be open at both ends for air inlet and outlet. Fig. 5 illustrates silica filled ETC tubes connected in parallel, in accordance with an embodiment of the present invention.A series of evacuated tubes may be connected together in parallel using an inlet and an outlet header tube. The silica filled ETC tubes may result in improvement in production of water. Fig. 6 illustrates a photographic image of the FADSS device having desiccant material (silica) filled ETC tubes, in accordance with an embodiment of the present invention.

[0055] Referring back to Fig. 1, The solar simulator delivers necessary heat instead of direct solar energy, for the process of desorption for heating the silica gel bed. The heat flux from the solar simulator may be regulated to ensure that the heat provided by the solar simulator is the same as the actual solar conditions during the day. In one implementation, an experimental setup of the FADDS device 100 was prepared and temperature readings were taken at different points using seven PtlOO (platinum resistance) thermal sensors. The desiccant bed temperature was measured by positioning three of thermal sensors at various locations in the desiccant bed, while one sensor was attached to the bottom of the glazing to indicate glass temperature. Two sensors were placed at the inlet and outlet of the desiccant box, and one sensor was used to measure ambient conditions. A 10 W blower was used to circulate air through the FADSS device 100. It was noted that a 30 W solar panel with a panel area of 0.22 m2and a 20 Ah energy storage system may be sufficient to run the blower all day at its total capacity. The condenser used in the study was a finned tube heat exchanger consisting of twenty * " copper tubes connecting two 1" (25.4 mm) copper tube manifolds at the entry and exit points. A 34970A data acquisition system from Keysight Technologies was used to collect data such as temperatures from the seven sensors and solar flux readings. The data was stored in a computer. The airflow rate was measured using an F1031V micro gas flow sensor from Winson Technologies. Accurate and reliable data were obtained for the analysis by using the experimental setup.

[0056] Fig. 7 illustrates variation in measured outdoor solar radiation and a simulated radiative heat flux provided by the solar simulator every hour, in accordance with an embodiment of the present invention. It was observed that the adsorption process takes 16 hours a day, followed by 2 hours of soaking and 6 hours of desorption process from 10 am to 4 pm Indian Standard Time (1ST). The airflow rate is fixed at 92.5 FPM for the adsorption process during all days of experimentation. Data were recorded every 15 minutes using a data logger to analyze the performance of the FADSS device. The water produced was collected and measured every hour during the desorption process.

[0057] In another implementation, an impact of airflow rates and bed designs on water production was studied to identify an optimal system for maximum water output. Four different desiccant bed designs were developed and constructed to use in the FADSS device. Fig. 8(a) to 8(d) illustrate a perspective view, sectional view and enlarged view of four configurations of desiccant bed in the FADSS device, in accordance with an embodiment of the present invention. As illustrated in Fig. 8(a), desiccant bed configuration 1 is a D-channel bed consisting of 18 D-shaped channels made of aluminium, each with a cross-sectional area of 2.5 x 5 cm. Uniformly sized holes, 2 mm in diameter, were provided at both the top and bottom of the channels to enable air to pass through the desiccant bed. As illustrated in Fig. 8(b), desiccant bed configuration 2 is an inclined fin bed consisting of 24 rectangular channels with a 2 x 7.5 cm cross-sectional area. Holes were only provided at the bottom of the channels, and the top surface of each channel was inclined and partially closed. A little space is left intentionally at the edges along the length to allow for effortless airflow. The length of both designs is 0.5 m. As illustrated in Fig. 8(c), desiccant bed configuration 3 is an open tray with dimensions of 0.5 x 0.5 m. Holes were only provided at the bottom and the top surface was kept open. The height of the tray is 7 cm. As illustrated in Fig. 8(d), desiccant bed configuration 4 is a square honeycomb bed having holes provided uniformly throughout the bottom of the tray, while the top surface was left open. An open square section with a cross-sectional area of 2 x 2 cm was uniformly arranged in 24 rows and columns. The height of the tray is 7.5 cm.

[0058] In one implementation, experiments were performed to investigate the impact of variation of configuration of the desiccant bed on yield of water in the FADSS device obtained from the desorption process. Four configurations of desiccant beds, as illustrated in Figs. 8(a) to 8(d). Silica gel of type A was used as desiccant material for the FADSS device. Properties of the silica gel are mentioned in below described Table 1:Table 1

[0059] Before the experiments, the silica gel was left open for several days to ensure complete adsorption. The saturated silica gel was then filled to a depth of 3 cm in the bed designs to facilitate desorption. An airflow rate of 30 LPM was maintained throughout the desorption period and all other parameters were also held constant for the duration of the experimentation. A thermal mass of configurations of desiccant beds, weight of silica gel used and theoretical volume of desiccant beds are described in below mentioned Table 2:Table 2

[0060] In another implementation, experiments were performed to investigate the impact of airflow rate on yield of water in in the FADSS device obtained from the desorption process. The velocity of air flowing through a heat exchanger may be crucial in optimizing use of solar energy by controlling the condensation process. A high airflow rate combined with a low flux of solar heat leads to unsaturated air reaching the condenser inlet during desorption, resulting in poor condensation. For analysing variations in the parameter affecting water production in the FADSS device, bed configuration 1 was selected as the baseline model. Experiments were conducted using six different airflow rates i.e. 10, 20, 30, 40, 50, and 60 Litre Per Minute (LPM) to study the impact of airflow rate (Q) on water production. The blower drew theambient air at its full capacity at 92.5 LPM during the adsorption process in all the experiments. All other parameters were kept constant during the experiments, with a denoting thickness of the silica bed set at 3 cm and an average solar flux of 760 W / m2during the desorption period.

[0061] As the experiments were conducted during the winter months, due to temperature gradient present between the heat exchanger and the surroundings, ambient conditions strongly affected the desorption process. Fig. 9 illustrates a plot of variation of mean ambient temperature and relative humidity with time over a day, in accordance with an embodiment of the present invention. The vertical bars in Fig. 9 represent the standard deviation of all the data for the entire study duration (all days of experiments). A maximum fluctuation of relative humidity (RH) were observed between 4 and 6 am, ranging from 75 to 95% on certain days of the experiment.

[0062] In another implementation, airflow rate of the FADSS device was optimised. The airflow rate (Q) is a critical factor affecting water production efficiency during the desorption process in the FADSS device. The airflow rate directly affects rate of heat loss at the condenser and moisture desorption from the desiccant bed. For analysing an impact of the airflow rate, configuration 1 of the desiccant bed and maintained a constant thickness of 3 cm throughout. Fig. 10 illustrates a plot of temporal variation of the desiccant bed temperature during the entire operational cycle of 24 hours, in accordance with an embodiment of the present invention. The desiccant bed temperature decreases rapidly during first two hours of the adsorption process. This is due to heat exchange between the ambient air and the silica bed at a relatively high- temperature post-desorption process. The desiccant bed temperature subsequently decreases gradually, stabilizing as the desiccant bed becomes saturated with moisture. Even though the airflow rate during the adsorption process is constant for all experiments, a slight deviation of less than 2% was be observed in first 16 hours of operation. It was due to variability in thermal characteristics of ambient air that is forced through the desiccant bed.

[0063] During soaking period, the desiccant bed temperature was observed to increase rapidly due to the sensible heating of the silica bed. Once the blower turns on at beginning of the desorption process, a sharp decrease in the desiccant bed temperature occurs. The circulating air cools the silica bed by transporting heat to the condenser. Observations suggested that the heat carried by the air from the desiccant bed is greater than the heat provided by solar flux to the bed at the beginning of the desorption process. The temperature graduallyincreases, peaks by 2 pm, and then decreases, coinciding with the simulated solar flux. A highest temperature of 75.12°C of the desiccant bed is achieved for Q = 20 LPM. The peak bed temperature is observed to decrease with an increase in airflow rate. An increase in the airflow rate appeared to increase the sensible heat loss from the desiccant bed. In contrast, at Q = 30 LPM, the desiccant bed temperature significantly decreased during the last three hours of desorption, suggesting that a large chunk of heat in form of latent energy is utilized in the evaporation of water vapour than sensible heating of silica bed. There appears to be a balance between the evaporation rate of water vapour and the rate of circulating air to carry them forward at this Q.

[0064] Figs. 11(a) and 11(b) illustrate a plot of variation of inlet and outlet temperatures throughout the desorption process, including the soaking period of two hours respectively, in accordance with an embodiment of the present invention. The inlet temperature may experience an abrupt rise at the onset of the desorption process, followed by a gradual increase, reaching its peak between 2 and 3 pm, and decreasing for the remaining period. The initial temperature surge may be caused by sudden heat exchange between the forced air passing through the FADSS and the silica bed. The inlet temperature during the rest of the desorption process is dependent on the effectiveness of the condenser for different values of Q. The highest recorded inlet temperature of 35 °C occurred when the FADSS device operates at a flow rate of Q = 60 LPM, and this value decreases as the airflow rate decreases.

[0065] Fig. 11(b) depicts temperature variation of the outlet air in the desiccant box during the desorption period. When the blower is switched on, the outlet temperature suddenly increases, followed by a drop due to the cooling of the bed at the beginning of the desorption process. A large temperature gradient between the initial circulating air and the heated silica bed causes the outlet temperature to rise rapidly at beginning of the desorption process. After the rapid increase, the temperature gradient decreases gradually in the first hour due to the initial cooling of the desiccant bed. The outlet temperature increases after that, reaches a peak, and decreases towards the completion of the desorption period. For the first three hours of the desorption period, the outlet temperature is higher for the airflow rate of Q that is 20 LPM and decreases with an increase in Q.

[0066] It is noted that an average solar flux is high during the first three hours of the desorption process, causing the higher outlet temperatures at lower Q due to more sensible heating of the saturated air as it moves up on the saturation curve. When value of Q is 60 LPM, a maximum outlet temperature of 71 °C during the last three hours of desorption was observed. This value decreases with a decrease in airflow rate as the process nears completion and the air leaves the bed unsaturated due to inadequate solar flux. As a result, much of the energy is spent on sensible heating of the bed and circulating air instead of evaporating water from the silica gel, resulting in warmer air at the desiccant box exit.

[0067] Fig. 12 illustrates water production per day from the FADSS device at different airflow rates, in accordance with an embodiment of the present invention. Different airflow rates were measured at glazing area of 0.25 m2, maximum water was produced at the airflow rate of 30 LPM (optimal) and it was 12% more than the 20 LPM. Water production from the 40 and 50 LPM cases was 9 and 6% lower than an optimal case. The yield of water harvested was lowest for airflow rate of 60 LPM, which was 21% less water than the optimal case. Fig. 8 illustrates hourly water production during desorption process at different airflow rates, in accordance with an embodiment of the present invention. Performance of the FADSS device for the airflow rate of 60 LPM may appear to be low towards the end of the desorption process. Even 50 and 40 LPM cases follow a slightly better but similar trend. Higher flow rates i.e. the airflow rate greater than 30 LPM yield less water towards the completion of desorption due to the inadequate solar energy available to maintain the evaporation rate of adsorbed water. Thus, the unsaturated air reaches the heat exchanger, resulting in a lower yield.

[0068] The FADSS device at the airflow rate of 30 LPM performed very well during most of the desorption period, as illustrated in Fig. 13. This means that the circulating air reaching the condenser inlet is saturated. Thus, there is efficient condensation of desorbed water vapour that air carries to the condenser. The findings suggest that there is an optimal balance between the evaporation rate of water vapour from silica and the condensation rate of this desorbed vapour in the condenser at this airflow rate.

[0069] Although the water production peaks at the airflow rate of 60 LPM in the first hour, it decreases significantly for the remainder of the desorption period. Thus, decline can be attributed to the circulating air leaving the desiccant box and reaching the condenser inlet in an unsaturated state, owing to its high moisture-carrying capacity. Consequently, there is adecrease in water production. The hourly water collection data suggests that water production at an optimal flow rate of 30 LPM performed significantly well during the last two hours of desorption.

[0070] To assess the influence of desiccant bed design on performance of the FADSS device, experiments were carried out on four distinct bed designs, depicted in Figs. 8(a) to 8(d) having configuration as depicted in Table 2. Among these designs, configuration 1 referred to as the D-channel bed, was fabricated using aluminium, while the remaining desiccant beds were constructed using galvanized iron. During the desorption phase, experiments were conducted with a consistent airflow rate of 30 LPM. A fixed bed thickness of 30 mm was maintained throughout all tests. The silica gel employed in the study was ensured to be saturated by being exposed to an open environment for several days. The desorption process, including the soaking period, was carried out for 8 hours, from 8 am to 4 pm. Temperature distribution in the FADSS device.

[0071] Fig. 14 illustrates temporal variation of silica bed temperature in the FADSS device during desorption process including soaking across different desiccant bed designs, in accordance with an embodiment of the present invention. It was evident that the desiccant bed temperature experiences a rapid rise during the initial two-hour soaking period, primarily attributed to the sensible heating of the desiccant bed in absence of circulating air. Notably, configuration desiccant bed design 3, namely the open tray desiccant bed, exhibits the highest bed temperature during soaking, while configuration desiccant bed design 4, the honeycomb bed, displays the lowest temperature. It was due to significant energy consumption involved in heating the silica within the open tray bed configuration. In contrast, the thermal mass of honeycomb bed consumes significant energy due to its large heat capacity during the soaking period.

[0072] As the desorption process commences, the desiccant bed temperature slightly decreases initially when the blower initiates air circulation. However, it subsequently increases gradually and reaches its peak around 2 pm, followed by a decline towards the end of the desorption process, corresponding to the decrease in solar radiation. Desiccant bed design 2 and 4 demonstrate a minimal reduction in bed temperature at onset of the desorption process, owing to their substantial heat-storing capacity. Among the different desiccant bed designs, the honeycomb bed exhibits the highest maximum temperature during desorption, followed by theinclined fin bed, open tray bed and the D -channel bed designs with minimum and maximum recorded temperatures of 67°C and 72°C for desiccant bed design 1 and 4, respectively.

[0073] Figs. 15(a) and 15(b) illustrates temporal variation of the inlet and outlet air temperature profiles of the desiccant box respectively, in accordance with an embodiment of the present invention. As illustrated in Fig. 15(b), the outlet air temperature indicates a sudden increase when the blower is activated and begins circulating the air throughout the FADDS device. Among the different bed designs during the desorption period, the inclined fin bed design exhibited the highest outlet temperature, followed by the honeycomb bed, open tray bed, and the D-channel bed design. Conversely, as shown in Fig. 15(a), the inclined fin bed design demonstrated the highest inlet temperature, followed by the open tray bed, D-channel bed and honeycomb bed. Notably, during the desorption period between 10 and 11:15 am, the outlet temperature of the inclined fin bed design is lower than that of the honeycomb and open tray beds.

[0074] The inclined fin bed design i.e. the desiccant bed design 2, exhibited an average outlet temperature of 57°C, with a maximum temperature of 66°C. In comparison, the honeycomb bed design achieves average and maximum outlet temperatures of 62 and 65°C, respectively. Although the inclined fin bed design attains a higher maximum outlet temperature than the honeycomb bed, the latter exhibits fewer fluctuations during the desorption period, as the average temperature data suggests. The indicates the significance of thermal mass in delivering stored energy to the silica gel during the evening when solar energy availability is lower. Fig. 15(a) shows that the honeycomb bed design has the lowest inlet temperature. This may be attributed to the improved condensation and water production from the system, as a significant amount of energy is lost in the heat exchanger before entering the desiccant box.

[0075] Fig. 16 illustrates water production per day with different bed designs, in accordance with an embodiment of the present invention. The honeycomb bed design, referred to as desiccant bed design 4, yields the maximum water production. The D-channel desiccant bed design produces 19% less water than the honeycomb bed, with an average bed temperature of 64°C, the lowest among the designs. Similarly, the open tray bed design results in 17% less water production compared to the optimal case. The average bed temperatures corresponding to designs 2 and 3 are 68 and 67°C, respectively. The inclined fin bed design produces 585 ml of water per day, 18% less than the honeycomb bed which is considered as the optimal case.

[0076] The daily water yield from the honeycomb bed exceeds the second-largest yield, the open tray bed, by 101 ml. The differences between the second-largest, third-largest, and fourth-largest water producer may be relatively smaller. The observation may imply that the honeycomb bed exhibits more efficient heat conduction through the silica gel than the other desiccant bed. The honeycomb bed design features small square sections, as depicted in Figs. 8(a) to 8(d), with each section containing a small quantity of silica gel, for an example 13 grams silica gel. Consequently, heat may penetrate through these square sections and conduct into the silica gel, which is confined within these smaller volumes, allowing for effective heat transfer. In addition, the large thermal mass of the honeycomb bed stores heat during the peak solar radiation hours and feeds it back to the silica gel when the solar flux availability is lower. Thus, enhancing the desorption of silica during the lower radiation period.

[0077] Fig. 17 illustrates hourly water production during desorption process with different desiccant bed designs, in accordance with an embodiment of the present invention. It was observed that the honeycomb desiccant bed yields the highest water production. However, as depicted in the Fig. 17, the initial water production during the desorption process exhibits lower values. This can be attributed to the characteristics of the honeycomb desiccant bed, which possesses a significant thermal mass and heat storage capacity. Consequently, a substantial portion of the heat is initially utilized to warm up the desiccant bed itself, leading to reduced water production in the first hour.

[0078] The FADSS device has two principal components i.e. the desiccant box and the condenser. The solar radiation falls upon the desiccant box and heats the silica bed and the air flowing through it. This hot and humid air, coming out of the desiccant box, flows through the condenser tubes, where the heat is released into the atmosphere. Thus, the solar energy conversion efficiency (r|c) of the FADSS device can be expressed as below mentioned Equation 1:Here, Qcondenser may denote the heat rejected to the ambient air at the condenser and Esoiar is the cumulative solar energy falling on the glazing surface of the desiccant box. The heat rejected at the condenser is equal to the sum of sensible heat loss across the condenser and the latentheat loss due to the condensation of water collected in the collecting jar.where, mamay denote the mass of air passed through the condenser, c may denote the specific heat, 0 may denote the average temperature difference between the inlet and outlet of the condenser, mwmay denote the mass of water produced at the end of the desorption process and L may denote the latent heat of condensation. The total solar energy may be given by the below mentioned Equation 3:where, A may denote the glazing area of the desiccant box and I(t) may be the instantaneous solar radiation.

[0079] The efficiency of the FADSS (rp^) is defined as the ratio of heat of condensation of water vapour to total solar energy used. The efficiency of the FADSS (r|jys) may be given by below mentioned Equation 4:

[0080] Fig. 18 illustrates the variations of rp (conversion efficiency) and qsys (system efficiency) of the FADSS with airflow rate, in accordance with an embodiment of the present invention. rp may represent the ability of the desiccant bed to capture and convert solar energy into heat. As illustrated in Fig. 18, the maximum rp may be achieved at an airflow rate (Q) of 60 FPM, reaching 36%, while the minimum rp of 26% may be observed at airflow rate of 20 LPM. At the airflow rate of 20 LPM, a higher bed temperature may be exhibited but lower r was observed due to its limited heat-carrying capacity. The airflow rate (Q) may directly impact rp as it influences the sensible cooling of warm air in the condenser during the desorption. Therefore, even though the airflow rate of 60 FPM results in lower water production, it yields the highest rp due to more efficient cooling. On the other hand, rpysmay represent the fraction of available solar energy utilized for water production. A maximum rpysof 21% may be achieved at the airflow rate of 30 FPM, attributed to the FADDS device improved yield of water, while the minimum rpysof 17% was observed at the airflow rate of 60 FPM. A differencebetween r|cand r|sysmay represent a total sensible heat loss from the condenser to the surrounding atmosphere.

[0081] Fig. 19 illustrates a plot of variation of r|cand r|sysfor different desiccant bed designs, in accordance with an embodiment of the present invention. The honeycomb bed, exhibited the highest values of r|cand r|sys, reaching 47 and 38%, respectively. The other bed designs showed comparable efficiencies. As the honeycomb bed design facilitates better heat penetration across the silica gel thickness. Its higher thermal mass plays a crucial role in storing and delivering heat energy to the silica gel during the later stages of the desorption process.

[0082] The honeycomb desiccant bed effectively utilizes approximately 38% of solar energy for water production in the FADSS device, while about 9% is lost due to sensible cooling of the air in the condenser. There are two areas of improvement to further enhance the performance of the FADSS device. Firstly, reducing convective heat loss from the desiccant box may be beneficial. This may be achieved by optimizing the design and insulating the desiccant box to minimize heat transfer through convection. Secondly, enhancing the thermal conductivity of the silica bed may contribute to improved system efficiency. By improving the heat conduction properties of the silica material, more effective heat transfer may be achieved, leading to increased water production and overall system performance.

[0083] The FADSS device as disclosed in the present invention thus yielded an increasing trend in water production with a maximum yield of 389 ml at the airflow rate of 30 LPM. The yield of water subsequently decreased with the other airflow rates. This observation suggests that the FADSS device achieves maximum water production efficiency (?sys= 21%) at an optimal airflow rate (30 LPM), striking a balance between the evaporation rate of water vapour from silica and the condensation rate of desorbed vapour in the condenser. This indicates an optimal utilization of available solar energy with minimal losses. It is noted that a high airflow rate, Q greater than 30 LPM, combined with a low flux of solar heat lead to unsaturated air reaching the condenser inlet during desorption, resulting in poor condensation. Conversely, at lower airflow rates (Q < 30 LPM), the circulating air could not transport the entire desorbed vapour from the silica gel to the condenser.

[0084] The honeycomb desiccant bed exhibited the highest water production of 694 ml / 0.25 m2glazing area using an airflow rate of 30 LPM, with system and conversionefficiencies of 38 and 47%, respectively. Notably, when solar energy availability was reduced, the honeycomb desiccant bed showed greater water yield during the later stages of the desorption process. This can be attributed to its higher thermal mass, enabling efficient heat storage and release as needed. Furthermore, a small sectional arrangement of the honeycomb desiccant bed improved thermal conductivity and heat penetration across the silica bed.

[0085] The honeycomb desiccant bed with 30 LPM airflow rate emerged as an optimal choice for use in the FADSS device for the maximum water production. A maximum water production of 2776 ml / m2glazing area, was observed. The FADSS device indicated a capacity to produce 1.85 times more water per m2(by scaling) of glazing area compared to traditional silica-based systems.

[0086] Further, in other implementations, thickness of desiccant bed may be optimized for effective utilization of available solar energy during the day and parabolic concentrators may be used with the FADSS device to enhance desorption during periods of lower solar radiation. Additionally, convective heat losses from the desiccant box may be reduced. Reduction in the heat losses may be achieved by optimizing the design of the desiccant box and insulating the desiccant box to minimize heat transfer through convection. Further, more effective heat transfer across the desiccant bed may be achieved by improving heat conduction properties of the silica material, resulting in increased water production and overall system performance.

[0087] In one implementation, the FADSS device may be installed as a standalone system, making potable water available to households even in remote, isolated, and arid regions. In another implementation, the FADSS device may further be expanded as an integrated hybrid system that would harvest atmospheric moisture using sunlight and function as roofing system that also functions as a complete rainwater harvesting system, which would be attractive, ensuring not only potable water on a sustainable basis but also providing a shelter for the self- reliance of the households. The FADSS device, as an integrated roof system, may be accommodated with roof integration and a rainwater harvesting mechanism that may reduce the overall cost of the building and provide additional water supply during cloudy weather or rainy seasons. This may ensure water supply all year round, making it the more reliable solution for all drinking water needs.

[0088] In another implementation, the desiccant box can be replaced with evacuated tube collector (ETC) tubes to reduce the overall weight of the device and enhance its efficiency. The ETC bed design, illustrated in Fig. 20, improves the thermal conductivity of the silica gel contained within the tubes by facilitating uniform heat distribution along the radial direction. The newly designed bed comprises a narrow solid rod that spans the length of the ETC tubes. Four thin fins are affixed circumferentially to the rod and are twisted by 180 degrees along its length. This specific twist angle ensures effective heat conduction across the radial direction, enabling uniform heating of the desiccant material during the desorption process. The newly designed bed is integrated within the desiccant (silica gel)-filled ETC tubes. Its uniform heating mechanism ensures that the entire desiccant material effectively releases the adsorbed water during the desorption process. This optimized thermal distribution not only increases water production but also enhances the utilization of solar energy absorbed by the ETC tubes, thereby significantly improving the overall efficiency of the system.

[0089] In another implementation, the Flow-Assisted Desiccant Solar Still (FADSS) system can be implemented as a roof-integrated solution, incorporating a rainwater harvesting mechanism to ensure a consistent supply of drinking water during cloudy or rainy conditions. As depicted in Fig. 21, the roof-integrated atmospheric water generator features an array of flatbed FADSS units as shown in Figs. 22, 23, 24, 25. This integrated system includes two storage tanks: one for rainwater collection and the other for potable water storage. Rainwater is directed into the storage tank via channels positioned along the sides of the FADSS units. The collected rainwater is then processed through multiple filtration units to meet potable water quality standards before being supplied for use. For enhanced productivity, the desiccant boxes in the FADSS system can be replaced with newly designed evacuated tube collector (ETC) tubes.

[0090] In another implementation, the FADSS system utilized in the roof-integrated atmospheric water generator can also function as a stand-alone system for potable water production. Furthermore, it can be customized to meet specific potable water requirements. A scaled-up version of the FADSS system with a surface area of 1.5 m2is illustrated in Figs. 22, 23, 24, 25. For improved productivity, the desiccant boxes in this flatbed FADSS system can be replaced with evacuated tube collector (ETC) tubes.

[0091] In another implementation, the scaled-up atmospheric water generation device of 1.5 m2 glazing area, is illustrated in Figs. 22, 23, 24, 25, providing multiple perspectives for enhanced comprehension. This system comprises six desiccant boxes, each packed with silica gel filled in a honeycomb structure to optimize performance. The six desiccant boxes are systematically divided into two groups, each consisting of three boxes. Within each group, the boxes are interconnected in series through a header pipe. A dedicated blower is assigned to each group to ensure effective air circulation.

[0092] In one implementation, a fin-and-tube condenser is integrated for the condensation of water vapor, with both groups connected in parallel to this condenser. To optimize airflow, an airflow sensor regulates the rate of air circulation within each group, dynamically adjusting based on solar energy availability to maximize water production. Additionally, a valve is positioned at the inlet of the condenser header tube, enabling the bypass of the condenser during night time operation. The entire system is powered by a solar panel, which not only drives the blowers during daylight hours but also stores excess solar energy to facilitate night time operation, as depicted in Fig. 22. To ensure the collected water meets human consumption standards, the device is equipped with a comprehensive water filtration system. This system consists of a water collection tray, a bottom storage tank, a pump, a pre-carbon filter, a mineral enrichment cylinder, a post-carbon filter, a UV light sterilization unit, and a potable water tank for final distribution.

[0093] In another implementation, the device operates in a two-phase cycle: adsorption during night time and desorption during daytime.

[0094] Adsorption Phase (Night time Operation): During the adsorption phase, the system operates in an open cycle. The blower draws moisture-rich ambient air and directs it into the desiccant boxes via the inlet header tube. Within each desiccant box, the air enters from the bottom, passes through the honeycomb- structured silica gel bed, and exits through an outlet header tube positioned diagonally opposite the inlet. As the air traverses the honeycomb bed, moisture from the air is effectively adsorbed onto the silica gel surface. A designated valvefacilitates the release of dry air exiting the desiccant boxes. This process continues throughout the night until the silica gel reaches saturation with adsorbed water.

[0095] Desorption Phase (Daytime Operation): During daylight hours, the desorption process occurs in a closed cycle. The condenser is engaged, and the valve remains shut throughout the process. Solar radiation heats the desiccant boxes, elevating the temperature of the silica gel and inducing the release of the adsorbed moisture in the form of water vapor. The blower circulates air within each group through the header tubes, ensuring the efficient transport of water vapor to the condenser inlet. The airflow rate is dynamically regulated by the airflow sensor to maintain optimal saturation conditions within the condenser, thereby maximizing condensation efficiency. Once the moisture-laden air enters the condenser tubes, it undergoes cooling, causing the water vapor to condense within the tubes. The condensed water is then collected through a designated narrow outlet tube positioned at one end of the condenser's outlet header tube. To enhance thermal efficiency, the thickness of the silica gel layer is meticulously optimized, ensuring minimal material usage per unit area while aligning with the available solar energy per unit glazing area. The integration of a pre-tested honeycomb bed structure significantly improves the thermal conductivity of the silica gel, facilitating uniform heat distribution across the bed. The honeycomb design consists of small square sections along its depth, enhancing heat penetration and ensuring effective desorption. Additionally, the honeycomb structure functions as a thermal energy reservoir, absorbing heat during peak solar radiation hours and gradually releasing it during periods of low solar intensity (typically in the evening), thereby improving overall water production efficiency.

[0096] In another implementation, the condensed water generated during the desorption phase is directed into a water collection tray situated beneath the condenser outlet tube. This tray channels the collected water into a storage tank for subsequent purification. The multistage water purification process is designed to ensure the highest quality of potable water. Initially, a coarse filter at the top of the storage tank removes large insoluble particles. The water then passes through a pre-carbon filter, which eliminates residual impurities. Next, a mineral enrichment cylinder replenishes essential minerals. Following this, a post-carbon filter removes any remaining harmful chemicals. Finally, a UV sterilization unit disinfects the water to ensure compliance with drinking water safety standards. The purified water is stored in a potable water tank, ready for distribution.This fully optimized atmospheric water generation device can be deployed as a standalone potable water production system. It is also adaptable for integration into residential or industrial settings as a hybrid rooftop system, ensuring a consistent supply of potable water throughout the year based on specific user requirements.

[0098] Although a form of the invention has been described herein, it will be obvious to those skilled in the art that variations may be made in the construction and relation of parts and method without departing from the spirit and scope of the invention described herein. While embodiments of the present disclosure have been illustrated and described, it will be clear that the disclosure is not limited to these embodiments only. Numerous modifications, changes, variations, substitutions, and equivalents will be apparent to those skilled in the art, without departing from the scope of the disclosure.

Claims

WE CLAIM:

1. A Flow Assisted Desiccant Solar Still (FADSS) device (100) for extracting potable drinking water from atmospheric air, comprising: an ambient sensor (122) to measure ambient conditions; a centrifugal air blower (118), wherein the blower (118) absorbs fresh air which is rich in moisture and has low temperature; a desiccant box (102), wherein the desiccant box receives the moisture rich air from the blower (118) through an inlet tube (110), wherein the desiccant box (102) is made of mild steel and covered with Nitrile rubber to minimise heat loss, wherein the desiccant box (102) have dimensions of 0.5 m x 0.5 m x 0.15 m and covered with 9mm Nitrile rubber, wherein the desiccant box (102) is sealed with a 6 mm thick glass on top, wherein the desiccant box (102) further comprises: a desiccant bed (104) resting inside the desiccant box (102) with supporting structures, wherein the desiccant bed (104) consist of silica gel as desiccant material, wherein the received air is passed in into the desiccant box (102) by the blower through the inlet tube (110) located at the bottom of the desiccant box (102), wherein water molecules in the air is adsorbed by the desiccant material in desiccant bed (104) during night time, wherein the water molecules in the desiccant material is desorbed and carried by circulating air in to the outlet tube during daytime; a solar source (108) for heating the desiccant material; the inlet tube (110) is positioned at bottom of one comer of the desiccant box (102), wherein the air in the inlet tube is controlled by a flow meter (120); an outlet tube (112) is positioned on a side surface above the desiccant bed (104), in a diagonally opposite direction to the inlet tube (110), wherein the moist air exits the desiccant box (102) through the outlet tube (112);a condenser (114), wherein the inlet tube (110) and the outlet tube (112) are connected to the condenser; wherein the condenser receives the saturated air from the outlet tube; and a water collecting jar (116) is connected with condenser for collecting potable water received from the condenser, wherein the condenser (114) is connected to the water collecting jar (116) through a 1 / 4" narrow tube fixed at the bottom of the condenser (114).

2. The FADSS device as claimed in claim 1, wherein the inlet tube (110) is located at the bottom of the desiccant box (102).

3. The FADSS device as claimed in claim 1, wherein the blower (118) increases the rate of the adsorption process by allowing a larger volume of humid air.

4. The FADSS device as claimed in claim 1, wherein the desiccant box (102) is an insulated desiccant box.

5. The FADSS device as claimed in claim 1, wherein the water molecule is adsorbed by surface of the silica gel in the desiccant bed (104).

6. The FADSS device as claimed in claim 1, wherein adsorption process of FADSS is an open cycle that operates during the night.

7. The FADSS device as claimed in claim 1, wherein desorption process of FADSS is closed cycle that operates during the night.

8. The FADSS device as claimed in claim 1, wherein the water molecules in the air adhere to the desiccant material due to the van der Waals force of attraction.

9. The FADSS device as claimed in claim 1, wherein during desorption, the adsorbed water is evaporated from the silica gel.

10. The FADSS device as claimed in claim 1, wherein the condenser comprises copper tubes.

11. The FADSS device as claimed in claim 1, wherein an Evacuated Tube Collector (ETC) can replace desiccant box.

12. The FADSS device as claimed in claim 1, wherein the desiccant material is filled in Evacuated Tube Collector (ETC).

13. The FADSS device as claimed in claim 10, wherein the Evacuated tubes are two concentric glass tubes that are fused and spaced in between the two tubes, wherein the space creates vacuum.

14. The FADSS device as claimed in claim 10, wherein the glass is made of borosilicate, wherein the silica gel is filled inside the evacuated tubes.

15. The FADSS device as claimed in claim 10, wherein a selective coating is provided on an outer surface of inner tube to absorb most of impinging solar radiation.

16. The FADSS device as claimed in claim 10, wherein the silica filled ETC tubes are connected in parallel.

17. The FADSS device as claimed in claim 10, wherein the ETC bed comprises a narrow solid rod that spans the length of the ETC tubes, wherein four thin fins are affixed circumferentially to the rod and are twisted by 180 degrees along its length.

18. The FADSS device as claimed in claim 16, wherein the specific twist angle ensures effective heat conduction across the radial direction, enabling uniform heating of the desiccant material during the desorption process.

19. A roof integrated system, comprising: a Flow-Assisted Desiccant Solar Still (FADSS) system, further comprising: an ambient sensor (122) to measure ambient conditions;a centrifugal air blower (118), wherein the blower (118) absorbs fresh air which is rich in moisture and has low temperature; a desiccant box (102), wherein the desiccant box receives the moisture rich air from the blower (118) through an inlet tube (110), wherein the desiccant box (102) is made of mild steel and covered with Nitrile rubber to minimise heat loss, wherein the desiccant box (102) have dimensions of 0.5 m x 0.5 m x 0.15 m and covered with 9 mm Nitrile rubber, wherein the desiccant box (102) is sealed with a 6 mm thick glass on top, wherein the desiccant box (102) further comprises: a desiccant bed (104) resting inside the desiccant box (102) with supporting structures, wherein the desiccant bed (104) consist of silica gel as desiccant material, wherein the received air is passed in into the desiccant box (102) by the blower through the inlet tube (110) located at the bottom of the desiccant box (102), wherein water molecules in the air is adsorbed by the desiccant material in desiccant bed (104) during night time, wherein the water molecules in the desiccant material is desorbed in to the outlet tube during daytime; a solar source (108) for heating the desiccant material; the inlet tube (110) is positioned at bottom of one comer of the desiccant box (102), wherein the air in the inlet tube is controlled by a flow meter (120); an outlet tube (112) is positioned on a side surface above the desiccant bed (104), in a diagonally opposite direction to the inlet tube (110), wherein the moist air exits the desiccant box (102) through the outlet tube (112); a condenser (114), wherein the inlet tube (110) and the outlet tube (112) are connected to the condenser; wherein the condenser receives the saturated air from the outlet tube; a water collecting jar (116) is connected with condenser for collecting potable water received from the condenser, wherein the condenser (114) is connected to thewater collecting jar (116) through a 1 / 4" narrow tube fixed at the bottom of the condenser (114); andTwo storage tanks, wherein the one tank is for rainwater collection and the other tank is for potable water storage, wherein the rainwater is directed into the storage tank via channels positioned along the sides of the FADSS units.

20. The roof integrated system as claimed in claim 18, wherein the desiccant boxes in the FADSS system can be replaced with newly designed evacuated tube collector (ETC) tubes.

21. The roof integrated system as claimed in claim 18, wherein the FADSS system is as a stand-alone system for potable water production.

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