Apparatus to passively transport bubbles for boiling without buoyancy

Abstract

The present disclosure pertains to an apparatus (100) to passively enhance boiling heat transfer in absence of buoyancy or gravity assisted bubble departure. The apparatus (100) includes a boiling chamber (104) configured to accommodate the liquid (110), a heater surface (106) immersed in the liquid (110) configured to generate and hold the bubble, one or more porous membranes (108) configured to absorb the bubble and a pipe (102) inside a boiling chamber (104) configured to transport the bubble. The generated bubble, due to the boiling of liquid (110), detaches from the heater surface (106) to be absorbed by the one or more porous membranes (108) and the pipe (102) transports the absorbed bubble to a pre-defined location. The apparatus (100) enhances heat transfer efficiency and critical heat flux (CHF) by preventing bubble accumulation on the heater surface (106).

Description

TECHNICAL FIELD

[0001] The present invention relates to the field of thermal systems. Inparticular, it relates to an apparatus to transport bubble s for sustaining orenhancing boiling heat transfer in the absence of buoyancy or gravity as well asagainst the buoyancy or gravityBACKGROUND

[0002] Background description includes information that may be useful inunderstanding the present disclosure. It is not an admission that any of theinformation provided herei n is prior art or relevant to the presently claimeddisclosure, or that any publication specifically or implicitly referenced is prior art.

[0003] Space based equipment need to dissipate large amount of heat throughsmall areas. Boiling heat transfer is of signif icance to the design of space basedhardware such as electronic equipment, cryogenic fuel storage, heat exchange r sand material processing. Boiling relies on the latent heat of vaporization and isvery efficient mode of heat transfer and the e bullition cycle that dictates heattransfer relies on gravity or buoyancy. The use of boiling in space basedapplications is limited due to the absence of buoyancy assisted ebullition cycleand the departure of bubble remains absent due to insufficient buoyancy. T heformation of a large dry patch underneath the big primary bubble significantlydeteriorates the heat transfer in surface tension dominated boiling regime. Thisresults in a very low critical heat flux (CHF) in comparison to the earth gravitycondition.

[0004] Existing technologies apply external body force to the bubble toartificially induce bubble removal from heater surface, such that the boilingprocess can be made viable in the absence of buoyancy. A body force is applied tothe bubble to remove it from th e heater surface so that the life cycle of nextbubble can be started. Absence of buoyancy (or gravity) assisted bubble departuremechanism limits the use of boiling based energy systems in zero gravity ofspace. These technologies utilize acoustic field o r electric field or flow to applyexternal body force on the bubble.

[0005] The presence of acoustic field creates circulation of the fluid,preventing formation of vapor film and enhancing performance of heat transfer inmicrogravity. The application of electric field remove s the bubbles away fromheater surface and is able to sustain boiling in microgravity in the absence ofbuoyancy. In the absence of gravity, the bubble is perfectly spherical, gr owsbigger and stay s on the heater surface. When electric field is applied, it resul ts inbubble detachment normal to the heated substrate. Liquid flow induced by a pumpis also used to remove bubbles from the heater surface. However, these techniquesinvolve energy consumption and the presence of additional com ponents mak ingthe system complicated, bulky, inefficient and less reliable. The energy to massratio of the system deteriorates leading to difficulties in space applications. Theselimitations have highlighted the need for efficient and reliable solution forsustaining boiling heat transfer in the absence of buoyancy or gravity.

[0006] There is, therefore a need to provide a n innovative solution that canovercome the limitations of existing devices, providing efficient, simple andreliable apparatus for boiling heat transfer in the absence of gravity or buoyancy.OBJECTS OF THE INVENTION

[0007] Some of the objects of the present disclosure, which at least oneembodiment herein satisfies are as listed herein below.

[0008] A general object of the present disclosure is to provide an apparatus totransport bubble s during boiling , enhancing performance of boiling heat transferin the absence of buoyancy assisted bubble departure and in zero gravity

[0009] Another object of the presen t disclosure is to provide efficiency byvapor transport, enabling effective and continuous heat transfer in microgravity.

[0010] Another object of the present disclosure is to provide adaptabilitywithout the requirement of additional components , making the app aratus simpleand compact for a wide range of use in space based applications.

[0011] Another object of the present disclosure is to provide reliability byusing passive bubble departure techniques without consumption of externalenergy.

[0012] Yet a nother object of the present disclosure is to provide optimizationby using porous membranes impermeable or repellent to the liqui d , for transportof bubble s from the surface immersed in various liquids.SUMMARY

[0013] Aspects of the present disclosure relate to an apparatus to transportbubble s for sustaining and enhancing boiling in absence of buoyancy or gravityassisted bubble departure . The apparatus provides continuous and efficient heattransfer by preventing bubble accumulation and enhancing thermal performancefor space based applications as well as earth based applications.

[0014] An aspect of the present disclosure pertains to an apparatus to enhanceboiling heat transfer without relying on buoyancy assisted bubble departure. Theapparatus includes a boiling chamber that accom modates the liquid , within whicha heater surface is positioned and immersed in the liquid to facilitate bubblegeneration and retention. One or more porous membranes impermeable orrepellent to the liqu id , are placed at a predefined distance from the hea ter surfacewhile ke eping inside the liquid to absorb and remove these bubbles from theheater surface . Additionally, a pipe is located inside the boiling chamber, with theporous membranes positioned at least at one end of the pipe, allowing it totransport the absorbed bubbles to a predefined location. As bubbles detach fromthe heater surface, they are captured by the porous membranes and carried awayby the pipe for efficient removal.

[0015] In an aspect, the apparatus is further capable of inducing pas sivebubble removal from an inverted or downward facing heated surface in earthgravity.

[0016] In an aspect, the apparatus is further capable of inducing passivebubble removal from the heated surface present in narrow gaps in earth gravity.

[0017] In an aspect, the l iqu id contained inside the boiling chamber is one ormore liquid with or with out additives.

[0018] In an aspect, the porous membranes are composed of a materialimpermeable or repellent to the liquid and have a contact angle greater than 120 °with the liquid .

[0019] I n an aspect, the porous membranes are attached to the pipe by afastening mean.

[0020] In an aspect, the heater surface is at least one of a heated surface of anelectronic device or a thermal / energy system.

[0021] In an aspect, the pipe is any of straight or bent.

[0022] In a n aspect, the pipe is at least one of hollow or filled with the porousmembranes.

[0023] In an aspect, the pipe is composed of polyvinylidene difluoride(PVDF) thermoplastic fluoropolymer or other material with suitable chemical andthermal stability

[0024] Various obj ects, features, aspects, and advantages of the inventivesubject matter will become more apparent from the following detailed descriptionof preferred embodiments, along with the accompanying drawing figures in whichlike numerals represent like componentsBRIEF DESCRIPTION OF DRAWINGS

[0025] The accompanying drawings are included to provide a furtherunderstanding of the present disclosure, and are incorporated in and constitute apart of this specification. The drawings illustrate exemplary embodiments of thepresent disclosure and, together with the description, serve to explain theprinciples of the present disclosure.

[0026] FIG. 1 A illustrates an exemplary view of the proposed apparatus topassively transport bubble from a surface during boiling in accordance wit h anembodiment of the present disclosure.

[0027] FIG s . 1B 1C illustrates exemplary view s of the proposed pipe indifferent configurations , in accordance with an embodiment of the presentdisclosure.

[0028] FIG. 2A illustrates an exemplary flow chart of process of fabri cationof the superhydrophobic porous membrane , in accordance with an embodiment ofthe present disclosure.

[0029] FIG s . 2B 2C illustrate exemplary views of porous membrane before and after modification using composite solution, in accordance with anembodiment of the present disclosure.

[0030] FIG. 2D illustrates an exemplary view of L shaped foam vaportransport pipe (VTP), in accordance with an embodiment of the presentdisclosure.

[0031] FIG. 2E illustrates an exemplary view of vapor transport pipe (VTP)with porous membranes at both ends, in accordance with an embodiment of thepresent disclosure.

[0032] FIG. 2F illustrates an exemplary view of vapor transport pipe (VTP)with super hydrophilic wick structure, in accordance with an embodiment of thepresent disclosure.

[0033] FIG. 3A illustrates an exemplary view of pool boiling setup with Ushaped VTP configuration, in accordance with an embodiment of the presentdisclosure.

[0034] FIG. 3B illustrates an exemplary view of the heater assembly, inaccordance with an embodiment of the prese nt disclosure.

[0035] FIG. 3C illustrates an exemplary view of pool boiling setup withstraight VTP configuration, in accordance with an embodiment of the presentdisclosure.

[0036] FIG. 3D illustrates an exemplary view of pool boiling setup with Lshaped foam VTP confi guration, in accordance with an embodiment of the presentdisclosure.

[0037] FIG s. 4A 4D illustrate exemplary view of bubble departuremechanism during boiling on an upward facing heater in earth gravity, inaccordance with an embodiment of the present disclosure.

[0038] FIG. 4E illustrates an exemplary view of bubble behaviour duringboiling on an upward facing heater in earth gravity, in accordance with anembodiment of the present disclosure.

[0039] FIG s . 4 F 4 G illustrate exemplary view s of similarity in bubblebehaviour in zero gravity and in downward facing heater in earth gravity , inaccordance with an embodiment of the present disclosure.

[0040] FIG. 4 H illustrates an exemplary view of VTP augmented ebullitioncycle during boiling under downward facing heater, in accordance with anembodiment of the present disclosure.

[0041] FIG. 4 I illustrates an exemplary schematic representation of bubbledetachment mechanism, in accordance with an embodiment of the presentdisclosure.

[0042] FIG. 4 J illustrates an exemplary view of bubble formed during bo ilingof water without side wall and with side wall, in accordance with an embodimentof the present disclosure.

[0043] FIG. 4 K illustrates an exemplary side view of the heate r surface andvapour transport pipe during boiling of water , in accordance with an embodimentof the present disclosure.

[0044] FIG. 5A illustrates an exemplary graphical representation of forcebalance model for bubble detachment in downward facing heater, in accordancewith an embodiment of the present disclosure.

[0045] FIG. 5B illustrates an exemp lary graphical representation of forcebalance model for bubble detachment in zero gravity, in accordance with anembodiment of the present disclosure.

[0046] FIG. 5C illustrates an exemplary graphical representation of poolboiling curve of water with and withou t VTP, in accordance with an embodimentof the present disclosure.DETAILED DESCRIPTION

[0047] The following is a detailed description of embodiments of thedisclosure depicted in the accompanying drawings. The embodiments are in suchdetail as to clearly communidetail as to clearly communicate the disclosure. However, the amount of detail cate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope ofalling within the spirit and scope of the present disclosure as defined by the f the present disclosure as defined by the appended claims.appended claims.

[0048] Embodiments of the present disclosure pertain to an apparatus to passively transport the bubbles for sustaining and enhancing boiling heat transfer in the absence of buoyancy or gravity assisted bubble departure. The apparatus provides continuous and efficient heat transfer by preventing bubble accumulationand enhancingthermal performance for space-based applications as well as earth-based applications where buoyancy assisted bubble departure is absent

[0049] In an embodiment, an apparatus to enhance boiling heat transfer without relying on buoyancy-assisted bubble departure is disclosed. The apparatus includes a boiling chamber that accommodates the liquid, within which a heatersurface is positioned and immersed in the liquid to facilitate bubble generation and retention. One or more porous membranes, repellent to the liquid, are placed at a predefined distance from the heater surface to absorb and remove these bubbles from the heater surface. Additionally, a pipe is located inside the boiling chamber, with the porous membranes positioned at least at one end of the pipe, allowing it to transport the absorbed bubbles to a predefined location. As bubbles detach from the heater surface, they are captured by the porous membranes and carried away by the pipe for efficient removal.

[0050] In an embodiment, the apparatus is further capable of inducing passive bubble removal from an inverted or downward facing heated surface in earthgravity.

[0051] In an embodiment, the apparatus is further capable of inducing passive bubble removal from the heated surface present in narrow gaps in earth gravity.

[0052] In an embodiment, the liquid contained inside the boiling chamber is one or more liquid with or without additives.

[0053] In an embodiment, one or more porous membranes are composed of a material impermeable or repellent to the liquid and have a contact angle greater than 120° with the liquid.

[0054] In an embodiment, the porous membranes are attached to the pipe by a fastening mean.

[0055] In an embodiment, the heater surface configured to generate and retain the bubbles is at least one of a heated surface of an electronic device or thermal / energy systems.

[0056] In an embodiment, the pipe is any of straight or bent.

[0057] In an embodiment, the pipe is at least one of hollow or filled with theporous membranes.

[0058] In an embodiment, the pipe is composed of polyvinylidene difluoride (PVDF) thermoplastic fluoropolymer or other chemically and thermally stable material.

[0059] Referring to FIGs. 1A to 1C, an apparatus 100 to passively transportbubbles for boiling heat transfer is disclosed. The apparatus 100 includes a boilingchamber 104 configured to accomodate the liquid 110. A heater surface 106 immersed inside the liquid 110 configured to generate and hold the bubbles during boiling. One or more porous membranes 108 positioned at a predefined distance from the heater surface 106 to absorb the bubbles. A pipe 102 positioned inside a boiling chamber 104 to transport the absorbed bubbles from the heater surface 106. The pipe 102 can be used as a vapor transport pipe (VTP) for transporting the bubbles generated during boiling. The diameter of the pipe 102 can be either 25 millimeter having a thickness of 2 millimeters or other dimensions depending on the size of the heater surface.

[0060] In an embodiment, the pipe 102 is any of straight or bent. The pipe 102 can have various configurations such as, U shape, straight or the like. This allows for various configurations, enabling versatile integration in different boiling chamber 104 designs.

[0061] In an embodiment, the pipe 102 is composed of polyvinylidene difluoride (PVDF) thermoplastic fluoropolymer. The PVDF is a non-reactive thermoplastic fluoropolymer. The PVDF has chemical resistance and thermal stability, making it suitable for conditions inside the boiling chamber 104. moreover, pipe of other suitable materials with chemical and thermal stability may also be used.

[0062] In an exemplary embodiment, the pipe 102 can be hollow, and in the hollow configuration, the pipe 102 provides a simple conduit for transporting bubbles from the heater surface 106 to a designated location. This allows absorbtion of bubbles by the porous membranes 108 to move through the pipe and be directed away from the heated surface. Alternatively, the pipe can be filled with the porous membranes 108. In this configuration, the porous membranes are integrated within the pipe, enabling them to directly interact with the bubbles as they move through the pipe. This setup helps to further absorb and transport bubbles efficiently, optimizing the removal process. Both configurations ensure effective bubble transport and removal, tailored to different operational needs and design preferences.

[0063] In an embodiment, the boiling chamber 104 is configured to hold one or more liquids or mixture of liquids with or without additives. The liquids can include, such as but not limited to, water, dielectric fluids, alcohols and other aqueous solutions.

[0064] In an embodiment, the apparatus 100 includes a heater surface 106 positioned inside the boiling chamber 104 and immersed inside the liquid 110 configured to hold the bubble. The heater surface 106 holds the bubble before the bubble detaches itself from the heater surface 106. The heater surface 106 allows generation of vapor bubbles consistently as it transfers the heat to the liquid inside the boiling chamber 104. The heater surface 106 promotes rapid bubble formation and VTP promotes its release.

[0065] In an exemplary embodiment, the heater surface 106 in the apparatus 100 can be any surface that is heated as part of its operational function. This includes but is not limited to, the heated surface of electronic devices, such as processors or power modules, where efficient heat dissipation is crucial to prevent overheating. Similarly, it can be part of an energy system, like a boiler or heatexchanger, where managing bubbles formed during heat transfer is essential for maintaining optimal performance. The apparatus is configured to effectively remove bubbles from these surfaces, enhancing heat transfer and operational efficiency in both contexts.

[0066] In an embodiment, the apparatus 100 includes one or more porous membranes 108, repellent to the liquid and contact angle more then 120°, positioned on at least one end of the pipe 102 configured to absorb the bubble. The porous membranes 108 are placed at a predefined distance from the heater surface 106. The porous membranes 108 is positioned at a distance of 3 millimeters from the heater surface 106. The superhydrophobic porous membranes 108 are fabricated from PU foam and the method is adopted from the literature. The porous membranes 108 has a diameter of 30 millimeters and thickness of 25 millimeters. The other types of porous membranes repellent to the liquid 110 can also be used such as superhydrophobic porous PTFE, superhydrophobic copper foam, and superomniphobic porous membrane or the like depending on the type of liquid 110. The porous membranes 108 repellent to the liquid 110 ensure that the bubbles are captured effectively while minimizing interference with the boiling process.

[0067] In an embodiment, the porous membranes 108 are composed of a super hydrophobic material. The hydrophobic material can repel water and rapidly absorb the bubbles generated during boiling, ensuring that the bubbles pass through the porous membranes 108 and into the pipe 102.

[0068] In an embodiment, the porous membranes 108 are composed of a material impermeable or repellent to the liquid and have a contact angle greater than 120° with the liquid.

[0069] In an embodiment, the porous membranes 108 are attached to the pipe 102 by a fastening mean. The porous membranes 108 can be attached to the pipe 102 using fastening means such as silicone paste, adhesives, welding or the like. This ensures a stable and secure connection to withstand the conditions inside the boiling chamber 104. The porous membranes 108 can be used as vapor transport pipe (VTP) directly for bubble transport in L shaped and straight configurations.

[0070] In an embodiment, the bubble detaches from the heater surface 106 to be absorbed by the porous membranes 108 and the pipe 102 transports the absorbed bubble to a pre-defined location. When the bubble is formed during boiling, it initially remains attached to the heater surface 106 due to upward acting buoyance and surface tension force. As the bubble grows, it touches the porous membranes 108 and gets detached from the heater surface 106. The detached bubble is absorbed by the porous membranes 108 and moves through the pipe 102 followed by the continuation of life cycle of the next bubble. The bubble is transported from the pipe 102 where it can be condensed or discharged into the liquid. The efficient heat transfer is maintained by preventing the accumulation of vapor bubbles on the heater surface 106, ensuring continuous contact between the liquid 110 and the heater surface 106 within the boiling chamber 104.

[0071] In an embodiment, the apparatus 100 enables passive removal of bubbles from a heated surface 106 positioned in an inverted or downward-facing orientation. Without buoyancy assistance, bubbles naturally accumulate on such surfaces. The porous membranes 108 are positioned near the surface to absorb these bubbles, which are then transported away through the pipe 102 to maintain efficient heat transfer.

[0072] In an embodiment, the apparatus 100 is also configured to remove bubbles passively from heated surfaces located in confined spaces. In narrow gaps, fluid movement is restricted, making it difficult for bubbles to escape. The porous membranes 108 absorb these bubbles, which are then directed through the pipe 102, ensuring that heat transfer efficiency is preserved even in tight spaces.

[0073] Referring to FIG. 2A, process of fabricating the one or more superhydrophobic porous membranes 108 is disclosed. The fabrication process is adopted from the literature. Prior to the start of the fabrication process, all the glassware used for fabrication is thoroughly cleaned with acetone and ethanol and washed with deionized (DI) water. A foam material such as PU foam is cut in the size having, diameter 30 millimeter and thickness of millimeter. At step 202, trichloromethane in 60 millimeter is taken in a beaker and 4 grams of hydrophobic fumed silica and 2 gram of polystyrene are added. At step 204, a nanoparticle / polymeric composite solution is prepared with the trichloromethane solution. At step 206, PU foam is immersed inside the prepared composite solution at room temperature for 3-5 minutes. During this process, a hydrophobic coating is developed on the PU foam. At step 208, PU foam is taken out and dried in the oven at a temperature of 80°C for 1 hour and is removed from the oven to be cooled. At step 210, the PU foam is rinsed with boiling water to remove any unbonded fumed silica from the sponge to form the superhydrophobic porous membrane. At step 212, the superhydrophobic porous membrane, impermeable to water is integrated with the pipe 102 with the aid of silicone paste. Any pipe, such as polyvinylidene difluoride (PVDF) thermoplastic fluoropolymer pipe, that can safely sustain the temperature of water without contaminating it, i.e., chemically and thermally stable, can be used in the pipe 102. The PU foam before and after modification and corresponding contact angle measurement is shown in FIG. 2B and 2C.

[0074] Referring to FIGs. 2D to 2F, various potential vapor transport pipe (VTP) configurations are depicted. An L-shaped foam VTP is fabricated (FIG. 2D), where the entire VTP is the superhydrophobic porous membrane. This is used to discharge the bubble in the bulk liquid itself. In another configuration, the superhydrophobic porous membrane can be present at both the end of the VTP (FIG. 2E). The pipe 102 can be U-shaped or straight and can be used to discharge the vapor bubble in the bulk liquid 110. The U-shaped pipe has length on one side as 170 millimeters, width of 70 millimeters and length on other side as 75 millimeters, while the straight pipe has a length of 250 millimeters (as shown step 212 of FIG. 2A). The VTP can be of other dimensions depending on the size of the boiling chamber. The presence of the superhydrophobic foam at the ends will prevent the flooding of the pipe when submerged in the bulk liquid 110. In another variation of the VTP, a super hydrophilic wick structure may be present inside the pipe 102 (FIG. 2F). The function of the wick structure inside the VTP would be to collect and condense water, if any, without blocking the passage for the vapor flow. This will also be helpful in returning the condensed liquid to the bulk in zero gravity of space.

[0075] In an exemplary implementation, referring to FIGs. 3A, 3C and 3D, a pool boiling setup with downward facing heater configuration is used to test and validate the different configurations of the pipe 102 used as vapor transport pipe (VTP). The setup consists of a glass pipe held in between the polytetrafluoroethylene (PTFE) plates 302-1, 302-2 with the help of four stainless steel threaded rods and nuts. The boiling liquid 110 is contained in a transparent glass enclosure 304 having diameter 150 millimeter and thickness of 4 millimeter. Silicone cloth heater 306 is mounted at the side of the enclosure to maintain the temperature of water at saturated condition (100°C). Silicone cloth heater 306 is connected to an AC power supply. The heater assembly 308 is attached to the top PTFE plate 302-1 in such a way that the heater surface 106 faces downward direction.

[0076] In the heater assembly 308 (FIG. 3B), a stepped copper block 324 with flat circular surface having diameter 14 mm is used. PTFE bush insulation 328 is placed all around the copper block 324 to minimize the heat loss. A cartridge heater 326 having diameter of 8 millimeters and length of 35 millimeters with 250 Watt and 230 Volt is inserted inside copper block 324 to act as a heat source. Three J-type thermocouples 310 (T1, T2 and T3) with probe diameter 1 millimeter, are inserted in the copper block 324 near the heater surface 106 to measure the heat flux and surface temperature. The spacing between the thermocouples 310 are 6 millimeters. The lowest thermocouple is 6 mm away from the heater surface 106. An aluminum foil 330 having thickness of 11 microns is placed at the bottom of the heater assembly 308 and act as the heater surface 106.

[0077] A U-shaped vapor transport pipe 102 (VTP) is placed closed to the heater surface 106 such that the distance between the porous membrane 108 and heater surface 106 is 3 millimeters (FIG. 3A). This distance may be of other dimensions less than 5 millimeter in earth gravity and in zero gravity of space it may be more or less than 5 millimeter. The other end of the U-shaped VTP is kept open to the vapor space 312 above the free surface level of liquid 110 inside the boiling chamber 104. The bulk liquid 110 temperature is controlled using silicone cloth heater 306. The temperature of the bulk liquid 110 is measured with another J-type thermocouple 310. A pressure sensor 314 is also attached at the top of the setup to monitor the pressure inside the boiling chamber 104. A data acquisition system such as Keysight, DAQm901A or the like connected to a computing device is used to record thermocouples 310 temperature data. A camera 316 is also used to visualize the boiling process from the side and bottom to get detailed insights about the bubble dynamics. A condenser 318 is connected to the top PTFE cover plate 302-1 of the boiling test rig which condense the vapor of the boiling fluid generated during boiling. Cooling water 320 is circulated with the help of a pump 322 through the condenser 318.

[0078] Before starting experiments, a 600-grit size sand paper is used to polish the heater surface 106. Heater assembly 308 and glass enclosure 304 are cleaned with acetone and rinsed with de-ionized (DI) water. DI water as a test liquid 110, is filled inside glass enclosure 304 and maintained at saturated condition. Heating of the test block is done using DC power supply and power is increased in steps. At each power input step, steady-state condition is reached before moving to the next step of power input. All the thermocouple data are captured using a data acquisition (DAQ). A camera 316 is used to capture the bubble images. All the experiments are repeated twice to ensure repeatability.

[0079] In the case of straight VTP (FIG. 3C), the open end is kept open to ambient conditions through the bottom of the boiling chamber 104. In the case of L-shaped foam VTP (FIG. 3D), the entire VTP is made up of superhydrophobic porous membrane. One end of the L-shaped foam VTP is placed near the heater surface 106 while other end is submerged inside the bulk liquid 110 itself. With this configuration the absorbed vapor bubble 322 is discharged in to the bulk liquid 110. However, due to the presence of hydrostatic pressure in earth gravity, the vapor can be discharged in the bulk liquid 110 through the other end of L-shaped foam VTP at elevations above the heater surface 106. In case of zero gravity of space, the hydrostatic pressure remains absent, consequently, the absorbed vapor can be discharged into any location inside the bulk liquid 110.

[0080] In an exemplary embodiment, the mechanism of the VTP augmented bubble departure and corresponding heat transfer includes various processes. The process of bubble nucleation, growth, departure and rewetting, constitute a cyclic process termed as ebullition cycle (FIGs. 4A to 4D), essentially dictates the heat transfer during boiling. The ebullition cycle strongly relies on the gravity (or buoyancy). Larger the gravity level, larger the frequency of ebullition cycle, hence better the heat transfer. The bubble departure behaviour during boiling in presence of gravity on an upward facing heater is shown in FIG. 4E, where the bubble is removed due to buoyancy from the heater surface 106 so that the life cycle of next bubble could be started. In the absence of buoyancy assisted bubble departure, such as microgravity of space and on an inverted heater in earth gravity, coalescence of small nucleating bubbles results in the formation of big bubble that blankets the heater surface (FIGs. 4F and 4G).

[0081] Through experimentation, to validate for zero gravity of space, boiling on downward facing heater in earth gravity can be used to mimic boiling in space conditions. Similar to the zero gravity of space, bubble departure remains absent under a downward facing heater. In fact, it is more adverse condition compared to zero gravity from the perspective of bubble departure, since the surface tension Fst and buoyancy Fb both act in the upward direction (FIG. 4G) to oppose departure of the bubbles from the heater surface. Similar to buoyancy induced ebullition cycle, the downward facing heater with VTP integrated also consisted of bubble nucleation, growth, absorption and rewetting as shown in FIG. 4H. When the bubble forms during boiling, initially it remains attached to the heater surface 106 due to the upward acting buoyancy (Fb) and surface tension force (Fst). During its growth, as soon the bubble touches the superhydrophobic membrane it gets detached and absorbed by the VTP followed by the continuation of life cycle of next bubble. This technique is so effective that despite upward acting buoyancy and surface tension, it still induced ebullition cycle resembling buoyancy-assisted ebullition cycle (FIG. 4A-4D).

[0082] The driving force for the detachment of the bubble is the unbalance capillary force that acts away from the heater surface 106 towards the VTP, in this case, in the downward direction (FIG. 4I). As the bubble touches the membrane, a capillary bridge is created that results in the formation of three-phase contact line (TCL) on the membrane as shown in FIG. 4I (II, point PQ). This generates a downward acting capillary force on the bubbles. The TCL grows continuously due to the Laplacian pressure difference, and tends to maintain the larger contact angle of 170° owing to the superhydrophobic nature of the membrane. Consequently, the downward acting capillary force also tend to vary with the propagation of the TCL. When the downward acting capillary force dominates over the upward acting surface tension and buoyancy, bubble detaches from the heated surface 106 and absorbed by the porous membrane 108.

[0083] The bottom view image of the bubble formed during boiling with pure water without deployment of VTP is shown in FIG. 4J. In the absence of buoyancy assisted bubble departure, the nucleating bubbles coalesce together to form big primary bubble that enveloped the heater surface (FIG. 4J (a)). When the bubble grows sufficiently bigger that it reaches the edge of the heater assembly, it results in sideway departure due to buoyancy (dotted circle). This sideway departure will not happen in zero gravity of space. Accordingly, a side wall is attached surrounding the heater assembly (FIG. 4J (b)) to prevent side way departure so that it can accurately mimic the bubble behavior in zero gravity of space. Consequently, big vapor bubble formed which envelopes the entire heater assembly. The mode of heat transfer quickly changes from efficient phase-change heat transfer to the poor heat conduction through the insulating vapor layer. This results in uncontrollable rise in temperature, often termed as thermal runaway, leading to the very small value of CHF (50 kW / m2).

[0084] With the deployment of VTP, bubble detachment is induced even against the upward acting buoyancy and surface tension force. Consequently, ebullition cycle is sustained and boiling heat transfer significantly improves. The side view of the boiling process at a heat flux of 500 kW / m2 with VTP is shown in FIG. 4K. As evident from the figure, all the bubbles are directly absorbed and transported by the VTP and no big bubbles are formed, as shown in FIG. 4K.

[0085] The plot of cumulative upward acting forces Fup and downward acting force Fdp versus bubble size is shown in the FIG. 5A.Equation 1:Equation 2:where pi is the liquid density, V is the volume of the bubble, g is acceleration due to gravity, R is the bubble radius, a is the surface tension of water and 6 is the contact angle of water with the heated surface. In the case of downward facing heater, the Fup increases more rapidly with the increase in bubble size in comparison to Fdp (FIG. 5A). This is due to the fact that buoyancy force FbkR3 whereas FstkR. Still the downward acting capillary force Fdp dominates over the upward acting force Fup for bubble size less than 2.5 millimeters in radius and capable enough of inducing bubble detachment from the boiling surface. Accordingly, a gap of 3 millimeter between the superhydrophobic porous membrane of VTP and the heater surface 106 is adopted. In case of zero gravity of space, the buoyancy will be absent and the capillary force induced by the superhydrophobic porous membrane Fst2 will always dominate over the surface tension force Fsti during propagation of TCL (FIG. 5B). Accordingly, bubble detachment would be much easier in case of zero gravity condition as compared to downward facing heater configuration.

[0086] The corresponding pool boiling curve with and without the augmentation of U-shaped VTP (FIG. 3A) during boiling of water is shown inFIG. 5C. The horizontal arrows indicate the thermal run-away, i.e., CHF. The VTP augmented bubble detachment results in improved heat transfer performance, hence significantly high value of CHF 780 kW / m2, as compared to without the VTp case. The VTp developed has huge implications for the design of not only boiling-based thermal systems but also for other technical processes, where multiphase flow and heat transfer are encountered, for space as well as earth-based applications.

[0087] Thus, the present disclosure introduces an apparatus to transport the bubbles from the heater surface for enhanced boiling heat transfer in the absence of buoyancy or gravity assisted bubble departure. By incorporating porous membranes, impermeable and repellent to the liquid, the apparatus provides continuous and efficient way of heat transfer by facilitating removal of bubbles and preventing bubble accumulation on the heater surface, thereby, enhancing thermal performance.

[0088] The technique introduced in the present disclosure can also be utilized in non-boiling process, such as, gas evolution reactions involved in hydrolysis and electrolysis or the like, where gas bubble forms on the electrode surface and its removal is critical to sustain chemical reactions. This technique can be used to remove and transport the gas bubbles, generated due to chemical reactions, from the surface or electrode submerged inside the liquid electrolyte to the other locations, thereby maintaining the efficient chemical reactions.

[0089] While the foregoing describes various embodiments of the disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof. The scope of the disclosure is determined by the claims that follow. The disclosure is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the disclosure when combined with information and knowledge available to the person having ordinary skill in the art.ADVANTAGES OF THE INVENTION

[0090] The present disclosure provides an apparatus to transport bubbles during boiling, enhancing performance of heat transfer in the absence of buoyancy or gravity assisted bubble departure.

[0091] The present disclosure provides efficiency by vapor transport, enabling effective and continuous heat transfer in microgravity.

[0092] The present disclosure provides adaptability without the requirement of additional components, making the apparatus simple and compact for a wide range of use in space-based applications.

[0093] The present disclosure provides reliability by using passive bubble departure techniques without consumption of external energy.

[0094] The present disclosure provides optimization by using porous membranes impermeable or repellent to the liquid, for transport of bubblesthrough various liquids.

Claims

1.An apparatus (100) for boiling heat transfer in the absence of buoyancy-assisted bubble departure, the apparatus (100) comprising: a boiling chamber (104) configured to accommodate liquid (110); a heater surface (106) positioned within the boiling chamber (104) and immersed in the liquid (110), configured to facilitate generation and retention of bubbles; one or more porous membranes (108) positioned at a predefined distance from the heater surface (106), configured to absorb and remove the bubbles from the heater surface (106); and a pipe (102) positioned inside a boiling chamber (104), with the porous membranes (108) positioned to at least at one end of the pipe (102), configured to transport the absorbed bubbles; wherein the generated bubbles, during boiling of liquid (110), detach from the heater surface (106) and are absorbed by the one or more porous membranes (108), and the pipe (102) transports the absorbed bubbles to a pre-defined location.2.The apparatus (100) as claimed in claim 1, further configured to induc e passive bubble removal from an inverted or downward facing heated surface in earth gravity.3.The apparatus (100) as claimed in claim 1, further configur ed to induce passive bubble removal from the heated surface present in narrow gaps in earth gravity.4.The apparatus (100) as claimed in claim 1, wherein the liquid (110) contained inside the boiling chamber (104) is one or more liquid with or without additives.5.The apparatus (100) as claimed in claim 1, wherein the one or more porous membranes (108) are composed of a material impermeable or repellent to the liquid (110) and comprises a contact angle greater than 120° with the liquid (110).6.The appar atus (100) as claimed in claim 1, wherein the one or more porous membranes (108) are attached to the pipe (102) by a fastening mean.7.The apparatus (100) as claimed in claim 1, wherein the heate r surface (106) is at least one of a heate d surface of an elec tronic device or any of thermal or energy system.8.The apparatus (100) as claimed in claim 1, wherein the pipe (102) is any of straight or bent.9.The apparatus (100) as claimed in claim 1, wherein the pipe (102) is at least one of hollow or filled with the one or more porous membranes (108).10.The apparatus (100) as claimed in claim 1, wherein the apparatus is further configured to passively remove and transport the bubbles generated due to the chemical reaction on the surface (106) immersed in the liquid ( 110), to other locations by the one or more porous membranes (108) and the pipe (102).