Systems and methods for fabrication of a hydrogel-coated FIN-tube heat exchanger

Abstract

Systems and processes for a full-scale heat exchanger having a hydrogel coating is provided. In some embodiments, the heat exchanger can be a fin-tube heat exchanger, such as a hygroscopic hydrogel coated heat exchanger / Absorbent Bed Unit (ABU) device, which exhibits high-performance with precise plate-to-plate spacing, which would allow for optimization and maximization of thermal performance. After assembly, the heat exchanger can be subsequently molded with a hydrogel layer of optimized, yet adaptable thickness, allowing for flexibility in application. The hydrogel layer can capture atmospheric moisture and facilitate its release using low-grade heat sources, making them particularly suited for renewable-powered applications and waste heat recovery.

Description

Attorney Docket No.: MIT 26047 PCT | 88212-429428SYSTEMS AND METHODS FOR FABRICATION OF A HYDROGEL-COATED FIN-TUBE HEAT EXCHANGERGOVERNMENT RIGHTS

[0001] This invention was made with government support under DE-EE0009679 awarded by the U.S. Department of Energy. The government has certain rights in the invention.CROSS REFERENCE TO RELATED APPLICATION(S)

[0002] The present disclosure claims priority to and the benefit of U.S. Provisional Application No. 63 / 751,834, entitled “Systems and Methods for Fabrication of a Hydrogel-Coated Fin-Tube Heat Exchanger,” filed on January 30, 2025, the content of which is incorporated by reference herein in its entirety.FIELD

[0003] The present disclosure relates to systems and methods for fabrication of hygroscopic hydrogel-coated heat exchangers / Absorbent Bed Unit (ABU) devices and manufacturing processes for fin-tube heat exchanger / ABU devices, and more particularly relates to systems and methods for in-situ synthesis and molding of hydrogel coatings onto fin-tube heat exchanger (HX) structures using modular mold assemblies with leak-tight sealing mechanisms.BACKGROUND

[0004] Hygroscopic hydrogel-coated heat exchangers represent a transformative opportunity in the pursuit of energy-efficient and sustainable solutions across industries. Hygroscopic hydrogels, with their exceptional ability to absorb and release moisture, can offer unparalleled performance when integrated with heat exchangers, enabling novel functionalities such as simultaneous humidity control, water harvesting, and enhanced thermal management. Use of hydrogels has increased in recent years and stems from their potential to address critical global challenges, including water scarcity, energy inefficiency, and climate control in diverse sectors.

[0005] Conventionally, there are several challenges to the use of hydrogels in heat exchangers known to one skilled in the art. For example, the hydrogel is typically a stiff material that has high shear forces, making application of the hydrogel to the surface of theAttorney Docket No.: MIT 26047 PCT | 88212-429428heat exchanger difficult. Further, hydrogels can be challenging to work with due to biocompatibility concerns with contamination and degradations of the gel during application. That is, hydrogels can lose their ability to absorb and / or release moisture when manipulated to coat various surfaces. Moreover, molding hydrogels in their pre-gelated liquid state directly onto a heat exchanger has been shown to add another layer of complexity. For example, it is exceedingly difficult to create an environment that is both leak-tight and conducive to gelation while ensuring the hydrogel adheres securely to the heat exchanger surface. Any leakage during this process can compromise the uniformity of the gel and the integrity of the final product. Further still, during demolding, it is challenging to avoid damaging or ripping the gel from the heat exchanger surface due, for example, to the adhesive and mechanical properties of the hydrogel. These combined factors contribute to the significant technical hurdles in using hydrogels within heat exchanger systems.

[0006] Accordingly, there is a need for systems and methods for coating heat exchangers with hydrogels that do not degrade the performance of said hydrogels.SUMMARY

[0007] The present disclosure is directed to systems and methods for a scalable and repeatable manufacturing process for a full-scale hygroscopic hydrogel coated heat exchanger / Absorbent Bed Unit (ABU). The device can include a fin-tube heat exchanger that is coated with one or more hydrogel and / or hydrogel / salt compounds that can obviate the challenges with application and performance of hydrogels in moisture rich environments following manipulation of the compound. The fabrication set-up can include ultra-smooth 3D printed PLA panels, laser-cut acrylic, and / or rubber gaskets with brass screw inserts to ensure a water-tight seal, which is important for the integrity of the hydrogel during gelation. Surface ironing or smoothing can be used to prepare 3D printed parts for hydrogel coating, thereby enhancing surface smoothness and water-tightness, which can prevent hydrogel adhesion on systems parts like ABU vapor spacers and hairpins. The other parts then can be put together to form the mold for gelation and the hydrogel can be introduced to the mold. In some embodiments, the systems and methods may utilize a specific lithium chloride-polyacrylamide (LiCl-PAM) hydrogel composition with particular component ratios, applied to a fin-tube style heat exchanger architecture for sorption-based energy storage and water harvesting applications, combined with a controlled processing window that prevents premature gelation while ensuring good infiltration and adhesion on the heatAttorney Docket No.: MIT 26047 PCT | 88212-429428exchanger surfaces. The combination of the specific hydrogel composition, the fin-tube heat exchanger geometry, and the precisely controlled timing window for hydrogel introduction and curing may enable successful fabrication of hygroscopic hydrogel-coated heat exchangers with uniform coverage and strong adhesion. In some embodiments, the systems and methods of the present embodiments can form a heat exchanger, which can be used in simultaneous humidity control, water harvesting, and / or enhanced thermal management.

[0008] In an aspect, embodiments relate to a method of applying a hydrogel to a device. The method comprises forming a mold by assembling one or more gaskets and one or more panels around one or more components of the device. The method further comprises introducing a hydrogel mixture into a cavity of the mold to fill a designated space between the one or more panels, the hydrogel mixture being formed by adding a hydrogel initiator to a mixture and stirring for approximately in the range of about 10 seconds to about 15 seconds to form a mixture before introducing the mixture into the mold. The method also comprises allowing the hydrogel mixture to cure and bond to form a hydrogel coating on the heat exchanger, wherein the hydrogel mixture comprises deionized water, acrylamide, lithium chloride, ammonium persulfate, N,N'-methylenebisacrylamide, and tetramethylethylenediamine (TEMED).

[0009] One or more of the following features can be included. The hydrogel mixture can be cured and bonded over a period of about 24 hours. The hydrogel mixture can be introduced within approximately 20 seconds after addition of the TEMED to prevent premature gelation. The method can further comprise preparing at least one of an inner surface of the one or more gaskets or the one or more panels to enhance surface smoothness and water tightness thereof prior to forming the mold. The device can comprise a heat exchanger. The one or more components of the device can comprise a U-bend pipe structure of the heat exchanger to enclose the U-bend pipe structure. The heat exchanger can comprise one or more fins and one or more vapor spacers positioned between the fins, and consistent vapor gaps can be maintained across the one or more fins during the hydrogel coating process. Enclosing the U-bend structure can further comprise placing one or more fins and one or more spacers on top of one another in sequence to align holes of the fin with the U-tube structure. The method can further comprise adding an anti-corrosion coating onto at least one of the one or more gaskets and panels prior to introducing the hydrogel. The method can further comprise removing the one or more spacers prior to adding the anticorrosion coating. The method can further comprise demolding by removing the one or more panels from the mold. The hydrogel mixture can comprise deionized water at a ratio approximately in a range of about 9 grams per 1 gram of acrylamide to about 12.5 grams perAttorney Docket No.: MIT 26047 PCT | 88212-4294281 gram of acrylamide. The hydrogel mixture can comprise lithium chloride at a ratio approximately in a range of about 3.4 grams per 1 gram of acrylamide to about 4.7 grams per 1 gram of acrylamide. The hydrogel mixture can comprise ammonium persulfate at a ratio approximately in a range of about 0.0029 grams per 1 gram of acrylamide to about 0.004 grams per 1 gram of acrylamide, and N,N'-methylenebisacrylamide at a ratio approximately in a range of about 0.0051 grams per 1 gram of acrylamide to about 0.007 grams per 1 gram of acrylamide. The hydrogel mixture can comprise TEMED at a ratio approximately in a range of about 2.45 pL per 1 gram of acrylamide to about 3.4 pL per 1 gram of acrylamide.

[0010] In another aspect, embodiments relate to a method of fabricating a hydrogel-coated fin-tube heat exchanger. The method comprises assembling a fin-tube heat exchanger comprising one or more U-bend pipes and a plurality of fins. The method further comprises positioning vapor spacers between adjacent fins to maintain vapor gaps. The method also comprises forming a leak-tight mold around the fin-tube heat exchanger using ultra-smooth panels and gaskets. The method additionally comprises preparing a lithium chloridepolyacrylamide hydrogel mixture by dissolving lithium chloride in deionized water. The method further comprises pouring the hydrogel mixture into the mold within approximately 20 seconds of TEMED addition. The method also comprises allowing the hydrogel to cure in situ for a period sufficient to achieve crosslinking. The method additionally comprises removing the mold to reveal the hydrogel-coated fin-tube heat exchanger with preserved vapor gaps between the fins.

[0011] One or more of the following features can be included. Preparing the lithium chloride-polyacrylamide hydrogel mixture can further comprise adding acrylamide at a ratio of approximately 4.0 g lithium chloride per 1 g acrylamide, adding ammonium persulfate and N,N'-methylenebisacrylamide, and adding TEMED catalyst before pouring. The method can further comprise applying an anti-corrosion coating to the fin-tube heat exchanger prior to forming the leak-tight mold. The ultra-smooth panels can comprise 3D printed PLA panels that have been surface treated to enhance smoothness and water-tightness. The hydrogel can be allowed to cure for approximately 40 to approximately 60 minutes to achieve full crosslinking and mechanical stabilization before demolding. The hydrogel mixture can comprise approximately 10.69 grams of deionized water per 1 gram of acrylamide. The ammonium persulfate can be added at approximately 0.0034 grams per 1 gram of acrylamide and the N,N'-methylenebisacrylamide can be added at approximately 0.0060 grams per 1Attorney Docket No.: MIT 26047 PCT | 88212-429428gram of acrylamide. The TEMED catalyst can be added at approximately 2.9 microliters per 1 gram of acrylamide.

[0012] In yet another aspect, embodiments relate to a heat exchanger. The heat exchanger comprises one or more U-bend pipes. The heat exchanger further comprises a first panel and a second panel, each having inserts that include a gasket therein, each of the gaskets being configured to be placed around each bend of the U-bend pipes. The heat exchanger also comprises a hairpin placed on one or more of the first panel or the second panel. The heat exchanger additionally comprises one or more heat exchanger fins. The heat exchanger further comprises one or more vapor spacers evenly placed between the heat exchanger fins. The heat exchanger also comprises a hydrogel coating that coats the one or more U-bend pipes.BRIEF DESCRIPTION OF DRAWINGS

[0013] This disclosure will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0014] FIG. 1A is a schematic illustration of a heat exchanger (HX) molding process for a HX of the present embodiments;

[0015] FIG. IB is an exploded view of a fastening assembly showing an inset (i) with screws engaged with brass screw inserts used in the mold construction;

[0016] FIG. 2A is a magnified perspective view of the heat exchanger mold of the present embodiments;

[0017] FIG. 2B is a perspective view of the heat exchanger of FIG. 2A;

[0018] FIG. 2C is a magnified perspective view of an interior surface of the heat exchanger of FIG. 2A;

[0019] FIG. 3A is a perspective view of a 3D printer that prints mold panels for fabricating a hydrogel-coated heat exchanger of the present embodiments;

[0020] FIG. 3B is a top view of the 3D printer of FIG. 3A;

[0021] FIG. 3C is a perspective view of a completed mold of the present embodiments;Attorney Docket No.: MIT 26047 PCT | 88212-429428

[0022] FIG. 3D is a perspective view of an interior of the mold of FIG. 3C;

[0023] FIG. 3E is a top view of the interior of the mold of FIG. 3C showing a panel being coupled thereto;

[0024] FIG. 3F is a perspective view of an anti-corrosion coating being applied to the mold of FIG. 3C;

[0025] FIG. 3G is a top view of the mold following application of the anti-corrosion coating of FIG. 3F;

[0026] FIG. 3H is a perspective view of a protective film cover being applied to the mold of FIG. 3G;

[0027] FIG. 31 is a perspective view of various stages of the hydrogel-coated heat exchanger fabrication and demolding process;

[0028] FIG. 3J is a perspective view of various stages of the hydrogel-coated heat exchanger fabrication and demolding process;

[0029] FIG. 3K is a perspective view of various stages of the hydrogel-coated heat exchanger fabrication and demolding process;

[0030] FIG. 3L is a perspective view of various stages of the hydrogel-coated heat exchanger fabrication and demolding process; and

[0031] FIG. 4 is an exploded view of a full-scale hydrogel-coated heat exchanger assemblyDETAILED DESCRIPTION|0032| Certain embodiments will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the systems, devices, related components (e.g., ultra-smooth 3D printed PLA panels, laser-cut acrylic gaskets, rubber gaskets, brass screw inserts, vapor spacers, hairpin tubes, U-bend pipes, heat exchanger fins, hydrogel mixtures, and mold assemblies), and methods disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those skilled in the art will understand that the devices and methods specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments and thatAttorney Docket No.: MIT 26047 PCT | 88212-429428the scope of the present disclosure is defined solely by the claims. The features illustrated or described in connection with one exemplary embodiment may be combined with the features of other embodiments. Such modifications and variations are intended to be included within the scope of the present disclosure. Further, to the extent features, components, panels, steps, or the like are described as being "first," "second," "third," etc., and / or "front," "back," "side," "top," "bottom," etc., such numerical and / or location ordering / identification is generally arbitrary, and thus such numbering can be interchangeable unless indicated or otherwise understood by those skilled in the art to not be interchangeable.

[0033] The figures provided herein are not necessarily to scale, although a person skilled in the art will recognize instances where the figures are to scale and / or what a typical size is when the drawings are not to scale. Further, to the extent that linear or circular dimensions or shapes are used or described herein, such dimensions are not intended to limit the types of shapes or sizes of such devices, components, etc. A person skilled in the art will recognize that an equivalent to such linear and / or circular dimensions or shapes can be easily determined for any geometric shape (e.g., references to widths and diameters being easily adaptable for circular and linear dimensions, respectively, by a person skilled in the art). While in some embodiments movement of one component is described with respect to another, a person skilled in the art will recognize that other movements are possible. Further, to the extent arrows are used to describe a direction a component can expand or move, these arrows are illustrative and in no way limit the direction the respective component can expand or move. A person skilled in the art will recognize other ways and directions for creating the desired tension or movement.

[0034] Still further, in the present disclosure, like-numbered components of various embodiments generally have similar features when those components are of a similar nature and / or serve a similar purpose, unless otherwise noted or otherwise understood by a person skilled in the art. To the extent the present disclosure includes prototypes, mock-ups, bench models, or the like, a person skilled in the art will recognize how to rely upon the present disclosure to integrate the techniques, systems, devices, and methods into a product, such as hygroscopic hydrogel-coated heat exchangers, Absorbent Bed Unit (ABU) devices, HVAC systems, water harvesting systems, and thermal management systems. A number of terms may be used throughout the disclosure interchangeably but will be understood by a person skilled in the art. By way of non-limiting example, the terms "hydrogel mixture," "hydrogelAttorney Docket No.: MIT 26047 PCT | 88212-429428precursor," "pre-gelated liquid," "mold," "mold assembly," "mold cavity," "heat exchanger," "fin-tube heat exchanger," "ABU," and "Absorbent Bed Unit" may be used interchangeably with one another. Moreover, it will be appreciated that although features may be discussed with respect to one embodiment within the present disclosure, these features can be applied to every embodiment of the present disclosure where such feature would be supported.

[0035] To the extent terms like "approximately," "about," and "substantially" are used herein, a person skilled in the art will appreciate the scope those words convey in the context of their usage. In the context of hydrogel coating fabrication and heat exchanger manufacturing, obtaining a certain degree of spacing precision, coating thickness uniformity, vapor gap consistency, and / or gelation timing control, among other dimensional and process parameters may be difficult, and thus use of terms like "approximately," "about," and "substantially" is intended to address this difficulty. A person skilled in the art will understand what constitutes how close a particular dimension or placement should be to still fall within the spirit of the quantification and description provided for herein. Even in instances where such terminology is not used, and a dimension or spacing / thickness just includes the number or term (e.g., "parallel" is used instead of "substantially parallel"), a person skilled in the art will appreciate that, unless explicitly indicated otherwise, terms like "approximately," "about," and "substantially" are applicable to those dimensions and terms as well. The foregoing notwithstanding, a person skilled in the art will appreciate that terms like "approximately," "about," and "substantially" at least encompass dimensions, quantities, timing parameters, and spacing measurements that are ±10%, 10°, etc. of the provided amount, or encompass dimensions that are ±5%, 5°, etc. of the provided amount, unless indicated otherwise or otherwise known to those skilled in the art. The present disclosure appreciates that a person skilled in the art, in view of the present disclosure, understands suitable placements for various features of the disclosed systems, devices, mold assemblies, and related components of any of the same, and thus to the extent a particular spacing, thickness, or timing parameter is described, unless it is explicitly indicated that spacing, thickness, or timing parameter, a person skilled in the art will appreciate other spacing, thickness, or timing parameters that are possible without impacting the overall system, device, or mold assembly.

[0036] Hydrogels excel in capturing atmospheric moisture and facilitating its release using low-grade heat sources, making them particularly suited for renewable-powered applicationsAttorney Docket No.: MIT 26047 PCT | 88212-429428and waste heat recovery. The performance of these hydrogels in combination with heat exchangers can unlock a wide array of benefits, including reduced energy consumption, improved system efficiency, and access to clean water in resource-scarce environments.

[0037] The present disclosure generally provides for a scalable and repeatable manufacturing system and process for a full-scale heat exchanger, focusing on preventing contamination and ensuring the integrity of hydrogels during fabrication. The heat exchanger can be a hygroscopic hydrogel coated heat exchanger / Absorbent Bed Unit (ABU) device that can exhibit high-performance with precise plate -to-plate spacing, which allows for optimization and maximization of thermal performance. After assembly, the heat exchanger can be subsequently molded with a hydrogel layer of optimized, yet adaptable thickness, allowing for flexibility in application. Hygroscopic hydrogels, from improving HVAC / air conditioning systems and industrial cooling processes to enabling water access in arid regions, can bridge the gap between performance and sustainability. Their ability to pull moisture from the air directly can reduce an HVACs latent load by eliminating energy intense dehumidification through condensation. Their application in agricultural irrigation, greenhouse climate control, and humidity regulation in sensitive environments, such as data centers and medical facilities, can demonstrate their versatility and impactpotential. Additionally, their compact and modular design allows for integration into existing infrastructure, further accelerating adoption and scaling opportunities.

[0038] Prior to the full scale-up of ABU mold fabrication, the mold design of the present embodiments can be validated by synthesizing 1 / 16thand l / 8thsized ABU units. To realize the full potential of these technologies, it can be important to transition from experimental validation to large-scale deployment. Demonstrating their feasibility in diverse real-world settings and optimizing system design for specific use cases will allow for driving market adoption. For example, with growing demands for efficient water, energy, and air conditioning systems, and an increasing focus on renewable technologies, the time is ripe to harness the capabilities of hygroscopic hydrogel-coated heat exchangers. Scaling their deployment will not only revolutionize heat exchanger applications but also contribute meaningfully to addressing some of the most pressing environmental and societal challenges. Therefore, it will be appreciated that while a subset or a fraction of the mold of the ABU is shown and / or described with respect to some steps of the present disclosure, theAttorney Docket No.: MIT 26047 PCT | 88212-429428disclosure is applicable to at least a full-scale ABU, which is shown in the accompanying figures and discussed below, as well as larger volumes of heat exchangers.

[0039] FIG. 1A illustrates an example embodiment of a heat exchanger (HX) molding process 1 for the HX 101 of the present embodiments. As shown, the molding process 1 can include one or more steps of a prior art molding process 10 (numbers 1 to 5 in box A) and further include a novel and inventive molding process 100 of the present embodiments (numbers 6 to 9 in box B). In particular, FIG. 1 A illustrates the refined series of steps involved in the fabrication of the fin-tube heat exchanger 101 of the present embodiments. As shown in steps (1) to (5) of FIG. 1 A, and as will be appreciated by one skilled in the art, the conventional HX molding process 10 may include (1) cutting of tubes 103, (2) fin fabrication 105 and insertion, (3) tube expansion 103A, (4) hairpin 102 brazing, and (5) application of a metal anti -corrosion coating 110, which aligns closely with conventional heat exchanger manufacturing techniques. This intentional alignment can be adopted to establish a scalable and cost-effective approach for ABU production, ensuring the method remains practical and economically viable for large-scale deployment. To ensure accurate spacing of fins 105 during the tube expansion process (3), in some embodiments, spacers 107, including spacers that can be about 8 millimeters in size, and caps, e.g., rubber caps 113, can be used. The spacers 107 and fins (arbitrarily 32 each) can be placed atop one another in sequence while ensuring the fin holes lined up (1-3). Thereafter, the pipes can be inserted through the fin's holes, and rubber caps can be added at either end of the ABU, ensuring that the spacers and fins did not move. It will be appreciated that while this embodiment uses rubber caps 113, larger embodiments of the heat exchanger, such as the full-scale ABU assembly 400 discussed in FIG. 4, can use silicone gaskets 413, as shown and discussed below, or other suitable components, as will be appreciated by a person skilled in the art in view of the present disclosures.

[0040] Steps (6)-(9) of FIG. 1 A illustrate fabrication steps for the molding process 100 of the present embodiments. Factors considered when making the present mold may include preventing hydrogel leakage, covering all surfaces while preserving vapor gaps, minimizing shear effects during demolding, and maintaining consistent dimensions of components. As shown in (6)-(9) of FIG. 1 A, a fabrication setup of the present embodiments can include surrounding the corrosion coated HX of (5) with one or more ultra-smooth 3D printed PUA panels 104, and laser-cut acrylic and robber gaskets 1 14 with brass screw inserts 116, whichAttorney Docket No.: MIT 26047 PCT | 88212-429428can be used to ensure a water-tight seal that prevents the leakage of hydrogel during gelation. A unique approach using surface ironing, or otherwise smoothing, to prepare 3D printed parts for hydrogel coating can be used, thereby enhancing surface smoothness and water-tightness and preventing hydrogel adhesion on parts like the ABU vapor spacers and hairpins. In some embodiments, "ultra-smooth" can refer to panels having high smoothness or a low coefficient of friction in the field of heat exchangers, as known to one skilled in the art.

[0041] The hydrogel mixture 112 can be poured into the mold cavity, as shown in (7) of FIG. 1 A, filling the designated space between the panels. The hydrogel can be allowed to set for a specified amount of time, e.g., overnight, to ensure proper curing and bonding. It will be appreciated that the method of applying a hydrogel to equipment may comprise forming a mold by assembling one or more gaskets 114 and one or more panels 104 around a U-bend pipe, or the hairpin 102, to enclose the U-bend pipe 104 while ensuring that the gaskets fit securely around each bend of the U-bend pipe 104. The unit 120 can then be demolded, as in (8) by removing the panels 104, leaving the ABU 120 with an intact hydrogel layer and correctly aligned U-bend components.

[0042] The heat exchanger 101 can be scaled to different sizes including but not limited to 1 / 16th, l / 8th, and full-scale (16 U) versions using the same modular design approach. The manufacturing process can align with conventional heat exchanger manufacturing techniques including tube cutting, fin fabrication and insertion, tube expansion, hairpin brazing, and anticorrosion coating before hydrogel application. The mold assembly includes brass screw inserts that are secured to gaskets using screws in designated locations to form a tight fit.

[0043] FIG. IB illustrates an exploded view of a fastening assembly used in the mold construction. The gaskets 114 and brass screw inserts 116 are illustrated in greater detail. As shown in FIG. IB and inset (i), the gaskets 114 may be strategically placed between the panel molds 104 to create a secure seal, ensuring that the hydrogel, in its pre-gelated liquid state, may remain contained within the mold. In particular, the threaded insert 116 may provide a robust anchoring point within the mold structure, while the specialized gasket 114 at the bottom may conform to the mating surfaces to prevent leakage of the hydrogel mixture during the gelation process. By maintaining a controlled environment, the gaskets 114 may play a role in ensuring consistent and reliable results during the gelation process. To create the seal, the brass screw inserts 116 may be secured to the gaskets 114 using screws 118 inAttorney Docket No.: MIT 26047 PCT | 88212-429428designated locations in the panel molds 104 to form a tight fit in the arrow directions shown. In some embodiments, the gaskets 114 may be treated with a two-step sealing process involving first a layer of flexible silicone rubber followed by a hard silicone epoxy coating for enhanced leak-tight integrity.

[0044] FIGS. 2A-2C illustrate an isometric view of the heat exchanger assembly 101 of the present embodiments encased within the panels 104 in more detail. The method may include placing one or more fins 105 and one or more spacers 107 on top of one another in sequence to align holes of the fin 105 with the U-tube structure 102, wherein the equipment comprises a heat exchanger (as shown in FIG. 2C). The spacers 107 can be received within inserts 111 positioned at regular intervals in the surface of the panels 104 to maintain the requisite gaps therebetween. In some embodiments, the assembly 101 can include multiple parallel vertical fins 105 arranged in such a spaced configuration, allowing the U-bend pipes 102 to extend through the fin assembly, creating a continuous flow path for thermal transfer fluid. As shown, the fins 105 can be positioned at regular intervals along the length of the pipes, forming channels or hydrogel gaps 109 between adjacent fin surfaces. The vapor spacers 107 may maintain consistent spacing between adjacent fins 105 to preserve vapor gaps that are useful for optimal thermal and moisture transfer performance. That is, the positioning of vapor spacers 107 evenly placed between the heat exchanger fins 105 may ensure uniform air flow patterns and consistent hydrogel coating thickness across the heat exchanger surface. The vapor gaps 109 can enable the exchange of moisture between the hydrogel-coated surfaces and the surrounding air during operation of the heat exchanger 101. This process may be repeated for both side panels 104 to maintain symmetrical spacing throughout the heat exchanger assembly.

[0045] The heat exchanger assembly 101 can include a base structure 122 that supports the fin-tube arrangement. One or more U-bend connections 102 can be visible at one end of the assembly 101, where the pipes 103 curve to create a return path for the working fluid. The U-bend sections 102 can be arranged in a parallel configuration, allowing for multiple flow circuits within the heat exchanger.

[0046] The assembly can demonstrate a modular construction approach, with the fin-tube heat exchanger 101 positioned to receive a hydrogel coating. The structure can be designed to accommodate the application of a hydrogel mixture that will coat the fin surfaces 105 while maintaining the vapor gaps 109 between adjacent fins 105. The arrangement ofAttorney Docket No.: MIT 26047 PCT | 88212-429428components can facilitate the molding process by providing accessible surfaces for hydrogel application. The modular design can allow for scalable manufacturing and can support efficient assembly and disassembly operations during the fabrication process. The heat exchanger assembly 101 can show the integration of conventional heat exchanger components with features designed to support hydrogel coating operations. The fin arrangement, pipe configuration, and spacing elements can work together to create a structure suitable for in-situ hydrogel synthesis and application. The assembly can provide the foundation for creating a hygroscopic hydrogel-coated heat exchanger capable of moisture absorption and release functions. The integration of these components can enable the heat exchanger assembly 101 to perform simultaneous thermal management and humidity control operations, expanding the functional capabilities beyond traditional heat exchanger applications.

[0047] Referring to FIGS. 3A-3L, a molding schematic for scale-up synthesis validation of the heat exchangers of the present embodiments is illustrated. The figures demonstrate the step-by-step assembly process or fabrication workflow 200 for preparing hydrogel-coated heat exchangers 201 at reduced scales to validate the manufacturing approach before full-scale production. In particular, FIGS. 3A-3L illustrate a synthesized 1 / 8thsized hydrogel mold ABU unit of the present embodiments 100, though it will be appreciated that 1 / 16thsized variants, as well as others, can also be constructed. The assembly process 200 may include multiple stages from initial component preparation through final demolding of the completed hydrogel-coated heat exchanger 201. It will be appreciated that the hydrogel-coated heat exchangers 201 made following the assembly process 200 can largely resemble the hydrogel-coated heat exchanger 101, and therefore a detailed description of the structure of the heat exchanger 201 can be omitted for the sake of brevity.

[0048] It will be appreciated that prior to full assembly, all PLA and acrylic parts may be coated with an anti-mold release coating and allowed to dry for about 10 minutes. The antimold release coating may enhance the surface properties of the mold components to facilitate subsequent demolding operations. The coating process may involve applying the anti-mold release coating to the inner surfaces of the gaskets 114 and panels 104 to enhance surface smoothness and water tightness thereof. In some embodiments, the surface preparation may include ironing an inner surface of the one or more gaskets 114 and the one or more panels 104 to enhance surface smoothness and water tightness thereof. With continued reference toAttorney Docket No.: MIT 26047 PCT | 88212-429428FIG. 3A-3J, food-grade gaskets may be placed over the brass insert surface of the parts following the coating and drying process. The gaskets may be positioned to create sealing interfaces around the U-bend pipes 102 and other components that have leak-tight containment during the hydrogel gelation process. The food-grade designation may ensure compatibility with the hydrogel materials and prevent contamination during the manufacturing process.

[0049] In particular, FIGS. 3A-3L is a series of photographs that document manufacturing mold components used in the hydrogel coating process 200. For example, the fabrication workflow 200 may include 3D printing of mold panels 204, handling and assembly of components, and positioning of molded parts during the assembly process. The photographs of FIGS. 3A-3L illustrate the progression from initial component manufacturing through final assembly preparation of the mold system.

[0050] As shown in FIG. 3A, a 3D printer 203 can print a white panel 204 on its build platform. The 3D printing process may be used to manufacture ultra-smooth 3D printed PLA panels 204 that form the structural components of the mold assembly. The printing environment may include cardboard boxes and equipment positioned in the background, indicating an active manufacturing workspace. The 3D printing process may provide precise dimensional control and surface finish characteristics suitable for hydrogel molding applications.

[0051] With reference to FIG. 3B, the manufacturing process 200 may involve sequential printing of multiple panel components to complete the full mold assembly. The 3D printed components may be fabricated from PLA material, which can provide the necessary structural properties and surface characteristics for effective mold performance. The printing process 200 may ensure consistent dimensional accuracy across multiple panel components.

[0052] FIG. 3C presents a completed mold panel 220 that has been removed from the 3D printer 203 following the printing process 200. As shown, the mold panel 220 can include panels 204 arranged in parallel ridged structures with a plurality of fins 205 extending therefrom. In particular, the parallel ridged structures may correspond to features designed to accommodate the heat exchanger fins 205 during the molding process. The handling of the component may demonstrate the structural integrity and dimensional stability achieved through the 3D printing process.Attorney Docket No.: MIT 26047 PCT | 88212-429428

[0053] As shown in FIGS. 3D and 3E, a panel 204 having one or more spacers 207 received within inserts 211 positioned at regular intervals in the surface of the panels 204 to maintain the requisite gaps 209. Moreover, the panels 204 can receive the tubes 213 and the hairpin on the bottom panel, with the acrylic vapor spacers 207 being evenly placed between the HEX fins 205. To finalize the mold before adding hydrogel, the panels 204 may be tightly fixed using screws. The panels 204 can then be fixed to another by M4 screws, for example. The screw fastening system may create the compression to activate the sealing properties of the gaskets 114 and ensure leak-tight performance during the hydrogel introduction and gelation phases. The tight assembly may prevent hydrogel leakage while maintaining the precise positioning of all internal components.

[0054] A high-quality anti -corrosion coating may be applied to ensure long-term durability by protecting the heat exchanger from environmental exposure, including moisture, corrosion, and degradation over time. The application of the coating may not only preserve the structural integrity of the device, but may also ensure optimal performance by preventing material breakdown that can interfere with heat and moisture transfer. In some embodiments, a heresite coating may be applied to the mold to ensure long-term durability by protecting the heat exchanger from environmental exposure, including moisture, corrosion, and degradation over time.

[0055] FIG. 3F illustrates application of an anti-corrosion coating 210 onto the mold or mold panels 220, though it will be appreciated that in some embodiments, the anti-corrosion coating can be added onto the final product 201 in addition to being added to the mold 220 and / or in lieu of being added to the mold 220. The anti-corrosion coating 210 can be applied to prevent hydrogel material for sticking to the mold. In some embodiments, one or more spacers 207 can be removed prior to adding the anti-corrosion coating 210. The spacers 207 may be removed to expose the underlying heat exchanger surfaces for subsequent coating operations. The method may further include adding the anti-corrosion coating onto at least one of the one or more gaskets 214 and panels 204 prior to introducing the hydrogel. The anti-corrosion coating may protect the metallic components of the heat exchanger from degradation while maintaining compatibility with the hydrogel material.

[0056] The anti-corrosion coating application process may involve several sequential steps to achieve uniform coverage and enhanced protection. In some embodiments, the heat exchanger 201 and / or the mold 220 may be securely mounted in a fume hood to ensureAttorney Docket No.: MIT 26047 PCT | 88212-429428stability during the coating process. This positioning may also allow for easy access to both sides of the unit, ensuring comprehensive coverage of all exposed surfaces. The controlled environment of the fume hood may provide proper ventilation and safety conditions during the spray application process.

[0057] As shown, a spray application technique may be used to apply a first uniform layer of heresite coating across the fins 205, tubes 203, and U-bends 202 of the heat exchanger. Care may be taken to ensure that all areas, including difficult-to-reach crevices, are coated evenly during the first coat application. The spray application method may provide consistent coverage across complex geometries and may allow the coating material to reach areas that might be inaccessible through other application methods. The heresite coating may be specifically selected for its industry-recognized corrosion resistance properties, which may be particularly effective for HVAC and heat exchanger components exposed to humid or corrosive environments.

[0058] After the initial layer is applied, the mold 220 and / or the heat exchanger 201 may be left undisturbed for several hours to allow the coating to cure and adhere uniformly to the surface. This drying period for the first layer may be necessary to achieve proper adhesion and to prepare the surface for the subsequent coating application. The curing time may allow the coating material to develop its protective properties and create a stable foundation for the second coat.

[0059] Once the first layer has dried, a second coat may be applied to further enhance the protection and ensure redundancy in the coverage. This additional layer may be applied using the same spray application technique to maintain consistency in the coating process. The second coat may be particularly important for preventing corrosion in high-moisture environments, especially around the U-bend 202 connections and fin 205 edges, which may be particularly vulnerable to degradation. The dual-layer application may provide enhanced barrier properties and may extend the service life of the heat exchanger in challenging operating conditions.

[0060] Following the application of both coating layers, the mold 220 may be left in the fume hood to cure for a full 24 hours. This extended curing period may ensure that the coating adheres completely and creates a durable, corrosion-resistant surface across the entire unit. During this curing time, periodic inspections may be conducted to verify the uniformityAttorney Docket No.: MIT 26047 PCT | 88212-429428of the coating and confirm that no gaps or inconsistencies are present in the protective layer. The completed anti -corrosion coating may ensure that the heat exchanger 201 will maintain its structural integrity over time, even in harsh environments with high humidity or moisture exposure, which may be particularly important for long-term performance in hygroscopic applications where the hydrogel coating interfaces with moisture-laden air.

[0061] The hydrogel can then be added, as shown in FIG. 3G, with the spacing 209 and alignment of the internal features, e.g., fins 205 and spacers 207 visible via the parallel internal structures maintained in the final heat exchanger assembly. The component orientation may facilitate inspection of the dimensional accuracy and structural integrity of the printed mold. The hydrogel may be formed by adding a hydrogel initiator to a mixture, as shown in FIG. 3G, and stirring for approximately in the range of about 10 seconds to about 15 seconds to form a mixture before pouring the mixture into the mold 220. The hydrogel mixture may be poured into the mold cavity while the mixture remains in a flowable state, allowing the material to conform to the complex geometry of the heat exchanger fins and tubes. The controlled timing window may ensure that the hydrogel mixture can adequately infiltrate all areas of the heat exchanger before gelation begins. That is, the timing of the stirring process may be controlled to prevent premature gelation while ensuring uniform distribution of the initiator throughout the hydrogel precursor mixture. A detailed discussion of the formulation, initiator / accelerator ratios, timing of pouring to prevent premature gelation, and so forth is discussed in greater detail below.

[0062] FIG. 3H shows the mold 220 having the hydrogel disposed therein being covered with a protective film cover 230, e.g., a polyurethane film, for gelation. The protective film cover 230 may serve multiple functions including shielding the mold from external contamination and creating a controlled environment by isolating the mold from ambient air. This isolation may be particularly important because the hydrogel contains salt, which is hygroscopic and readily absorbs moisture from the surrounding air. Any unregulated moisture absorption could alter the volume of the hydrogel, introducing variability into the manufacturing process. By using the protective film cover 230, the volume of the hydrogel may remain consistent and accurately reflect the specific relative humidity conditions under which the hydrogel was prepared.

[0063] Gelation can last about 24 hours to allow complete curing and bonding of the hydrogel material, though these times can vary. Referring to FIGS. 3I-3L, various stages ofAttorney Docket No.: MIT 26047 PCT | 88212-429428the hydrogel-coated heat exchanger fabrication and demolding process are illustrated. The method may further comprise setting the hydrogel by allowing the hydrogel to cure and bond, wherein the hydrogel is cured and bonded over a period of about 24 hours. During this curing period, the hydrogel may transition from a liquid precursor state to a solid, crosslinked network that adheres to the heat exchanger surfaces. The figures demonstrate the progression from mold preparation through final product completion, showing the transformation of the heat exchanger assembly as the hydrogel coating is applied and cured. In particular, after gelation, the screws 118 and the panels 204 can be removed, as shown in FIGS. 3I-3J.

[0064] The hydrogel mixture may flow around and between the heat exchanger fins 205 and tubes 213, conforming to the complex geometry of the internal components. The liquid state of the hydrogel mixture may allow complete infiltration of all accessible surfaces while maintaining the predetermined spacing between components. The filling process may ensure uniform coverage of the heat exchanger surfaces while preserving the vapor gaps 209 between adjacent fins 205. As shown in 3K-3L, the demolding process may reveal minimal adhesion of the hydrogel material to the mold components due to the smoothness of the surfaces combined with the anti-mold release coating. The smooth interior surfaces and antiadhesive properties of the mold components may facilitate clean separation of the cured hydrogel -coated heat exchanger from the mold assembly. The demolded heat exchanger 201 may illustrate the final coated product with the hydrogel layer intact on the heat exchanger surfaces. The vertical tube structures 213 may extend through the hydrogel matrix while maintaining their structural integrity and dimensional accuracy. The hydrogel coating may be adhered to the fin 205 surfaces, providing the hygroscopic properties needed for moisture absorption and release applications.

[0065] As further shown in FIG. 3L, the method may result in consistent vapor gaps 209 being maintained across the one or more fins 205 of the heat exchanger 201. The vapor gaps 209 may remain uniform and unobstructed following the hydrogel coating process, ensuring optimal air flow and moisture transfer performance. The preservation of consistent vapor gaps 209 may be achieved through the controlled positioning of vapor spacers during the mold assembly process and the precise timing of hydrogel introduction before gelation begins. The maintained vapor gaps 209 may facilitate the exchange of moisture between the hydrogel-coated surfaces and the surrounding air, enabling the heat exchanger to perform its intended hygroscopic functions.Attorney Docket No.: MIT 26047 PCT | 88212-429428

[0066] The demolding process illustrated in FIGS. 3I-3L may demonstrate the successful separation of the cured hydrogel-coated heat exchanger from the mold assembly. The smooth interior surfaces of the mold components may facilitate clean removal without damaging the hydrogel coating or disrupting the structural integrity of the heat exchanger. The final product 201 may exhibit uniform hydrogel coverage on the designated surfaces while maintaining the precise dimensional characteristics needed for thermal and moisture transfer applications.

[0067] FIG. 4 illustrates an example embodiment of a full-scale ABU assembly 400, and specifically a process for ensuring a leak-tight assembly of the hydrogel mold, capable of holding over 16 Liters of liquid without leakage. As shown, the modular, full-scale assembly 400 may be assembled using panel gaskets 413 specifically designed to create a tight seal between mold sections. The assembly 400 may include multiple panel components arranged to form a mold structure for hydrogel application. A side panel 404 with vapor insert slots 411 may be positioned on the left side of the assembly 400, featuring multiple parallel slots designed to accommodate vapor spacers 407. Adjacent to this may be a front panel 406 with vertical fin-like structures that provide spacing and support during the molding process.

[0068] The central portion 408 of the assembly 400 may show vapor insert slots 411 in a standalone configuration, displaying the spacing elements that maintain gaps 409 between heat exchanger fins 405. Silicone gaskets 413 may be positioned around the perimeter and at connection points to create a water-tight seal during the gelation process. These gaskets 413 may prevent hydrogel leakage while the material cures within the mold cavity. Additionally, specialized gaskets 413 may be fitted around the front and back ends of the piping to prevent any potential leakage at these interfaces.

[0069] A back panel 410 with silicone inserts may be shown on the right side, incorporating integrated sealing elements that interface with the piping connections. Below this, another side panel 404 with vapor insert slots 411 may mirror the configuration of the opposite side panel 404. At the bottom of the assembly 400, a base panel 416 with vapor insert slots 411 may provide the foundation for the structure, featuring corresponding slots that align with the vertical spacing elements.

[0070] To further enhance the leak-tight integrity of the assembly 400, the front and back-end pipe gaskets 413 may be treated with a two-step sealing process. First, the gaskets 413Attorney Docket No.: MIT 26047 PCT | 88212-429428may be coated with a layer of flexible silicone rubber, which may provide a conformal seal by adapting to surface irregularities. Once this layer has cured, the flexible silicone rubber may be overlaid with a hard silicone epoxy coating, which adds structural rigidity and longterm durability to the seal. This combination of materials and techniques may ensure that the mold is robust, reliable, and capable of maintaining a completely sealed environment during the gelation process and subsequent operations.

[0071] The exploded view demonstrates how the modular components fit together to enclose the heat exchanger structure while maintaining precise vapor gaps and uniform spacing throughout. The arrangement may allow for the introduction of hydrogel mixture into the cavity formed by the assembled panels 404, 406, 410, 412, 416, with the gaskets 413 ensuring containment during the gelation period. The design may facilitate subsequent demolding by providing smooth interior surfaces that minimize adhesion between the cured hydrogel and the mold components. The modular design may allow for scaling the ABU to different sizes and configurations based on future applications, while the simplified mold design may reduce production costs, making the approach feasible for large-scale deployment.

[0072] COMPOSITION

[0073] A particular challenge of fabrication of hydrogel coated systems such as heat exchangers involves achieving the right processing window to prevent premature gelation while ensuring good infiltration and adhesion on the heat exchanger surfaces. If the gelation process begins too early, the hydrogel mixture may not adequately flow into and coat all surfaces of the complex heat exchanger geometry, resulting in incomplete coverage and poor adhesion. Conversely, if the processing window is too long, the hydrogel may not cure properly or may be subject to contamination.

[0074] The hydrogel composition of the present embodiments may include specific ratios of components designed to achieve optimal performance characteristics for moisture absorption and release applications. The hydrogel mixture may include deionized water at a ratio approximately in a range of about 9 grams (g) per 1 gram (g) of acrylamide to about 12.5 g per 1 g of acrylamide, or at a ratio of approximately 10.69 g per 1 g of acrylamide, providing the aqueous medium for polymerization and hydration of the final gel network. The acrylamide monomer may serve as the primary building block for the polymerAttorney Docket No.: MIT 26047 PCT | 88212-429428backbone, while lithium chloride, or other salt, may be incorporated at a ratio approximately in a range of about 3.4 g per 1 g of acrylamide to about 4.7 g per 1 g of acrylamide, or at a ratio of approximately 4.0 g per 1 g of acrylamide, to provide hygroscopic properties that enable moisture capture from ambient air. The crosslinking agent N,N'-methylenebisacrylamide (MBA) may be included at a ratio approximately in a range of about 0.0051 g per 1 g of acrylamide to about 0.007 g per 1 g of acrylamide, or at a ratio of approximately 0.0060 g per 1 g of acrylamide, to create the three-dimensional network structure that gives the hydrogel its mechanical properties and dimensional stability. The polymerization initiator ammonium persulfate may be added at a ratio approximately in a range of about 0.0029 g per 1 g of acrylamide to about 0.004 g per 1 g of acrylamide, or at a ratio of approximately 0.0034 g per 1 g of acrylamide, to initiate the free radical polymerization process, while the tetramethylethylenediamine catalyst (TEMED) may be incorporated at a ratio approximately in a range of about 2.45 pL per 1 g of acrylamide to about 3.4 pL per 1 g of acrylamide, or at a ratio of approximately 2.9 pL per 1 g of acrylamide to accelerate the crosslinking reaction.

[0075] The processing parameters for the hydrogel synthesis may involve precise temperature control and timing to ensure successful gelation within the heat exchanger mold. In preparing the lithium chloride polyacrylamide (LiCl-PAM) hydrogel, the lithium chloride salt solution preparation may begin with gradual dissolution of LiCl in deionized water with stirring, where the solution may be gently heated if needed to achieve complete salt dissolution. Following dissolution, the LiCl solution may be allowed to cool to about 40-45°C before adding the acrylamide monomer. This temperature control step may be performed to avoid premature initiator decomposition and to keep the viscosity of the mixture manageable during subsequent processing steps. The acrylamide may be added at the specified ratio and the mixture may be stirred for about 5 to about 10 minutes until the monomer is fully dissolved in the salt solution.

[0076] The hydrogel mixture may undergo a degassing step to remove dissolved gases and minimize bubble formation in the final gel structure. The degassing process may be performed using a vacuum desiccator or similar method to extract dissolved air from the acrylamide / LiCl solution. This degassing step may prevent the formation of voids or bubbles that could compromise the structural integrity and performance of the curedhydrogel coating. Following degassing, the ammonium persulfate initiator and N,N'-Attorney Docket No.: MIT 26047 PCT | 88212-429428methylenebisacrylamide crosslinker may be added to the mixture and dissolved through mixing until both components are fully incorporated. In some embodiments, the initiator may be incorporated at approximately 0.34 wt% relative to the acrylamide monomer, while the crosslinker may be added at approximately 0.60 wt% relative to the acrylamide monomer. These specific initiator and crosslinker ratios may play a role in controlling the gelation timing and mechanical properties of the final hydrogel network. At this stage, minimal polymerization may occur since the TEMED catalyst has not yet been added to the mixture, providing a stable intermediate state that allows time for mold preparation and heat exchanger positioning before the rapid gelation phase begins.

[0077] The TEMED catalyst may be added immediately before casting the hydrogel mixture into the mold assembly. Once TEMED is incorporated into the mixture through quick mixing, gelation may start rapidly, creating a narrow processing window for successful mold filling. The pour window may be approximately 20 seconds from the time of TEMED addition to ensure uniform filling and coating of the heat exchanger surfaces before the gelation process progresses to a point where flow becomes restricted. This narrow timing window may be an important aspect of the fabrication process, as it prevents premature gelation while ensuring that the hydrogel mixture remains sufficiently fluid to infiltrate the complex geometry of the fin-tube heat exchanger and achieve good adhesion to all surfaces. If the hydrogel mixture is poured too late after TEMED addition, premature gelation may occur, resulting in incomplete filling of the mold cavity and poor coverage of the heat exchanger fins and tubes. Conversely, the rapid onset of gelation after TEMED addition may ensure that once the mixture is in place, it quickly solidifies to maintain its position and prevent settling or separation. This timing constraint may involve efficient coordination between the mixing process and the mold filling operation to achieve consistent results across the entire heat exchanger structure. The specific combination of initiator concentration (approximately 0.34 wt% APS relative to acrylamide), crosslinker concentration (approximately 0.60 wt% MBA relative to acrylamide), and catalyst amount (approximately 2.9 pL TEMED per gram of acrylamide) may work together to create this precisely controlled processing window that enables successful fabrication of the hydrogel-coated heat exchanger.

[0078] The gelation process may occur in situ within the mold and heat exchanger assembly, allowing the hydrogel to conform to the complex geometry of the fins and tubesAttorney Docket No.: MIT 26047 PCT | 88212-429428while curing in place. The system may sit undisturbed for approximately 40 minutes to approximately 60 minutes to allow full crosslinking and mechanical stabilization of the hydrogel network before demolding operations begin. During this stabilization period, the hydrogel may transition from a liquid precursor state to a solid, crosslinked polymer network that adheres to the heat exchanger surfaces while maintaining its hygroscopic properties. The curing time may be sufficient to achieve complete polymerization and develop the mechanical strength needed to withstand the demolding process without damage to the hydrogel coating. The in-situ gelation approach, combined with the controlled processing window, may enable the hydrogel to infiltrate all, or most of, accessible surfaces of the fin-tube heat exchanger, including narrow channels between fins and around tube bends, while forming strong adhesive bonds with the heat exchanger surfaces during the curing process. This combination of rapid gelation onset (triggered by TEMED addition) and sufficient working time (the approximately 20-second pour window) may distinguish the present fabrication method from conventional approaches and may enable successful coating of complex heat exchanger geometries with uniform hydrogel coverage.

[0079] The composite formulation may be designed with 50% relative humidity operating conditions in mind, optimizing the hydrogel composition for moisture absorption and release performance at this humidity level. The material sorption isotherm at 50% relative humidity may be used to estimate the equilibrium water loading of the LiCl-polyacrylamide network and to size the LiCl / polymer ratio accordingly. This design approach may ensure that the hydrogel coating can effectively capture and release moisture under typical operating conditions while maintaining its structural integrity and adhesion to the heat exchanger surfaces. The 50% relative humidity design point may represent a balance between moisture absorption capacity and practical operating conditions encountered in HVAC, water harvesting, and thermal management applications.

[0080] The combination of the specific lithium chloride -polyacrylamide (LiCl-PAM) hydrogel composition, the fin-tube heat exchanger architecture, and the controlled processing and timing window may work synergistically to achieve the desired hydrogel-coated heat exchanger performance. The specific component ratios in the hydrogel formulation discussed above — namely the approximately 10.69 g water per 1 g acrylamide, approximately 4.0 g lithium chloride per 1 g acrylamide, approximately 0.0034 g ammonium persulfate per 1 g acrylamide, approximately 0.0060 g N,N'-methylenebisacrylamide per 1 gAttorney Docket No.: MIT 26047 PCT | 88212-429428acrylamide, and approximately 2.9 pL TEMED per 1 g acrylamide — may provide the hygroscopic properties needed for moisture absorption while also enabling the controlled gelation timing that allows successful coating of the heat exchanger. The fin-tube heat exchanger architecture, with its parallel fins creating narrow vapor gaps and complex surface geometry, may present particular challenges for uniform hydrogel coating that are addressed by the rapid yet controlled gelation process. The processing window, particularly the approximately 20-second interval between TEMED addition and pouring into the mold, may be specifically tailored to the viscosity and flow characteristics of this particular hydrogel composition and the geometric constraints of the fin-tube heat exchanger. It will be appreciated that a different hydrogel composition might use a different processing window, while a different heat exchanger geometry might utilize adjustments to the gelation timing to ensure complete infiltration, both of which are within the scope of the present disclosure. The integration of these three elements — composition, architecture, and processing timing — may enable fabrication of hygroscopic hydrogel-coated heat exchangers of the present embodiments with uniform coverage, strong adhesion, and preserved vapor gaps that would be difficult to achieve through other fabrication approaches or with different combinations of materials and methods.

[0081] A representative, non-limiting formulation (scaled batch) that can be used to formulate a hydrogel of the present embodiments, that is in the scope of the present disclosure, can include (amounts may be approximate):• Deionized water: 219.924 g• Acrylamide (AM): 20.5656 g• Lithium chloride (LiCl): 82.2624 g• Ammonium persulfate (APS, initiator): 0.069864 g• N,N'-methylenebisacrylamide (MBA, crosslinker): 0.123 g• TEMED (catalyst): 59.04 pL

[0082] The hydrogel-coated heat exchanger system of the present embodiments may enable simultaneous humidity control, water harvesting, and enhanced thermal management through the hygroscopic properties of the hydrogel coating. The multi-functional capability may arise from the unique combination of conventional heat transfer mechanisms with moisture absorption and release properties provided by the lithium chloride-polyacrylamide hydrogel network. The system may operate by capturing atmospheric moisture through theAttorney Docket No.: MIT 26047 PCT | 88212-429428hygroscopic salt component while simultaneously facilitating heat transfer through the underlying fin-tube heat exchanger structure. This dual functionality may allow a single device to perform multiple environmental control functions that would traditionally use separate systems.

[0083] In HVAC applications, the hydrogel-coated heat exchanger may reduce the latent load on air conditioning systems by directly removing moisture from the air without requiring energy-intensive dehumidification through condensation. The hygroscopic hydrogel coating may absorb water vapor from humid air passing through the heat exchanger, reducing the moisture content of the air stream while the heat exchanger simultaneously provides thermal conditioning. This combined operation may result in improved energy efficiency compared to conventional HVAC systems that must separately address sensible and latent cooling loads. The system may be integrated into existing HVAC infrastructure to enhance performance while reducing overall energy consumption.

[0084] For industrial cooling processes, the hydrogel-coated heat exchanger may provide enhanced thermal management capabilities while simultaneously controlling humidity levels in manufacturing environments. The system may capture moisture from industrial processes that generate both heat and humidity, providing dual environmental control functions. The thermal management function may remove excess heat from industrial equipment or processes, while the humidity control function may maintain optimal moisture levels for product quality or worker comfort. This multi-functional approach may reduce the need for separate cooling and dehumidification equipment in industrial facilities.

[0085] In water harvesting applications, particularly in arid regions, the hydrogel-coated heat exchanger may extract moisture from ambient air to produce clean water while providing thermal regulation. The hygroscopic properties of the lithium chloride component may enable moisture capture even at relatively low humidity levels typical of arid environments. The captured moisture may be released from the hydrogel coating through thermal cycling, allowing water collection for potable use or irrigation purposes. The heat exchanger component may facilitate the thermal cycling process by providing controlled heating and cooling to drive moisture absorption and release cycles.

[0086] Agricultural irrigation systems may benefit from the water harvesting capability of the hydrogel-coated heat exchanger, particularly in regions with limited water resources. TheAttorney Docket No.: MIT 26047 PCT | 88212-429428system may extract moisture from ambient air during periods of high humidity and release the collected water for crop irrigation during drier periods. The thermal management capability may also provide climate control for agricultural facilities, maintaining optimal temperature conditions for plant growth while simultaneously producing irrigation water. This dual functionality may be particularly valuable in greenhouse operations where both temperature and humidity control are needed for optimal crop production.

[0087] In greenhouse climate control applications, the hydrogel-coated heat exchanger may maintain optimal growing conditions by simultaneously controlling temperature, humidity, and water availability. The system may remove excess moisture from the greenhouse atmosphere during periods of high humidity while providing thermal regulation to maintain optimal growing temperatures. The captured moisture may be recycled within the greenhouse system for irrigation purposes, creating a closed-loop water management system. This integrated approach may reduce external water needs while maintaining precise environmental control for optimal plant growth.

[0088] Sensitive environments such as data centers and medical facilities may benefit from the precise humidity regulation capabilities of the hydrogel-coated heat exchanger system. In data centers, the system may provide both thermal management for electronic equipment and humidity control to prevent condensation and static electricity issues. The hygroscopic hydrogel coating may maintain humidity levels within narrow operating ranges while the heat exchanger component removes excess heat generated by computing equipment. In medical facilities, the system may provide environmental control for sensitive equipment and patient comfort while maintaining sterile conditions through controlled humidity levels.

[0089] The compact and modular design of the hydrogel-coated heat exchanger may allow for integration into existing infrastructure across these various applications. The system may be retrofitted into conventional HVAC systems, industrial cooling circuits, or water treatment facilities without requiring extensive modifications to existing equipment. The modular construction approach may enable scaling of the system capacity to match specific application uses, from small residential units to large industrial installations. This flexibility may accelerate adoption across diverse market segments while providing consistent performance characteristics regardless of scale.

[0090] Examples of the above-described embodiments can include the following:Attorney Docket No.: MIT 26047 PCT | 88212-4294281. A method of applying a hydrogel to a device, comprising:forming a mold by assembling one or more gaskets and one or more panels around one or more components of the device;introducing a hydrogel mixture into a cavity of the mold to fill a designated space between the one or more panels, the hydrogel mixture being formed by adding a hydrogel initiator to a mixture and stirring for approximately in the range of about 10 seconds to about 15 seconds to form a mixture before introducing the mixture into the mold: and allowing the hydrogel mixture to cure and bond to form a hydrogel coating on the heat exchanger,wherein the hydrogel mixture comprises deionized water, acrylamide, lithium chloride, ammonium persulfate, N,N'-methylenebisacrylamide, andtetramethylethyl enediamine (TEMED) .2. The method of claim 1, wherein hydrogel mixture is cured and bonded over a period of about 24 hours.3. The method of claim 1 or claim 2, wherein the hydrogel mixture is introduced within approximately 20 seconds after addition of the TEMED to prevent premature gelation.4. The method of any of claims 1 to 3, further comprising preparing at least one of an inner surface of the one or more gaskets or the one or more panels to enhance surface smoothness and water tightness thereof prior to forming the mold.5. The method of any of claims 1 to 4, wherein the device comprises a heat exchanger.6. The method of claim 5, wherein the one or more components of the device comprise a U-bend pipe structure of the heat exchanger to enclose the U-bend pipe structure.7. The method of claim 5 or claim 6, wherein the heat exchanger comprises one or more fins and one or more vapor spacers positioned between the fins, and wherein consistent vapor gaps are maintained across the one or more fins during the hydrogel coating process.Attorney Docket No.: MIT 26047 PCT | 88212-4294288. The method of claim 6 or claim 7, wherein enclosing the U-bend structure further comprises placing one or more fins and one or more spacers on top of one another in sequence to align holes of the fin with the U-tube structure.9. The method of any of claims 1 to 8, further comprising adding an anti-corrosion coating onto at least one of the one or more gaskets and panels prior to introducing the hydrogel.10. The method of claim 9, further comprising removing the one or more spacers prior to adding the anti-corrosion coating.11. The method of any of claims 1 to 10, further comprising demolding by removing the one or more panels from the mold.12. The method of any of claims 1 to 11, wherein the hydrogel mixture comprises deionized water at a ratio approximately in a range of about 9 grams per 1 gram of acrylamide to about 12.5 grams per 1 gram of acrylamide.13. The method of any of claims 1 to 12, wherein the hydrogel mixture comprises lithium chloride at a ratio approximately in a range of about 3.4 grams per 1 gram of acrylamide to about 4.7 grams per 1 gram of acrylamide.14. The method of any of claims 1 to 13, wherein the hydrogel mixture comprises ammonium persulfate at a ratio approximately in a range of about 0.0029 grams per 1 gram of acrylamide to about 0.004 grams per 1 gram of acrylamide, and N,N'-methylenebisacrylamide at a ratio approximately in a range of about 0.0051 grams per 1 gram of acrylamide to about 0.007 grams per 1 gram of acrylamide.15. The method of any of claims 1 to 14, wherein the hydrogel mixture comprises TEMED at a ratio approximately in a range of about 2.45 pL per 1 gram of acrylamide to about 3.4 pL per 1 gram of acrylamide.16. A method of fabricating a hydrogel-coated fin-tube heat exchanger, comprising:Attorney Docket No.: MIT 26047 PCT | 88212-429428assembling a fin-tube heat exchanger comprising one or more U-bend pipes and a plurality of fins;positioning vapor spacers between adjacent fins to maintain vapor gaps; forming a leak-tight mold around the fin-tube heat exchanger using ultra-smooth panels and gaskets;preparing a lithium chloride-polyacrylamide hydrogel mixture by dissolving lithium chloride in deionized water;pouring the hydrogel mixture into the mold within approximately 20 seconds of TEMED addition;allowing the hydrogel to cure in situ for a period sufficient to achieve crosslinking; andremoving the mold to reveal the hydrogel -coated fin-tube heat exchanger with preserved vapor gaps between the fins.17. The method of claim 16, wherein preparing the lithium chloride-polyacrylamide hydrogel mixture further comprises adding acrylamide at a ratio of approximately 4.0 g lithium chloride per 1 g acrylamide, adding ammonium persulfate and N.N'-methylenebisacrylamide, and adding TEMED catalyst before pouring.18. The method of claim 16 or claim 17, further comprising applying an anti-corrosion coating to the fin-tube heat exchanger prior to forming the leak-tight mold.1 . The method of any of claims 16 to 18, wherein the ultra-smooth panels comprise 3D printed PLA panels that have been surface treated to enhance smoothness and watertightness.20. The method of any of claims 16 to 19, wherein the hydrogel is allowed to cure for approximately 40 to approximately 60 minutes to achieve full crosslinking and mechanical stabilization before demolding.21. The method of any of claims 16 to 20, wherein the hydrogel mixture comprises approximately 10.69 grams of deionized water per 1 gram of acrylamide.Attorney Docket No.: MIT 26047 PCT | 88212-42942822. The method of any of claims 16 to 21, wherein the ammonium persulfate is added at approximately 0.0034 grams per 1 gram of acrylamide and the N.N'-methylenebisacrylamide is added at approximately 0.0060 grams per 1 gram of acrylamide.23. The method of any of claims 16 to 22, wherein the TEMED catalyst is added at approximately 2.9 microliters per 1 gram of acrylamide.24. A heat exchanger, comprising:one or more U-bend pipes;a first panel and a second panel, each having inserts that include a gasket therein, each of the gaskets being configured to be placed around each bend of the U-bend pipes: a hairpin placed on one or more of the first panel or the second panel;one or more heat exchanger fins;one or more vapor spacers evenly placed between the heat exchanger fins; and a hydrogel coating that coats the one or more U-bend pipes.

[0001] One skilled in the art will appreciate further features and advantages of the disclosure based on the above-described embodiments. Accordingly, the disclosure is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. By way of example, the hydrogel-coated heat exchanger systems may be adapted for use in automotive thermal management, marine desalination systems, pharmaceutical manufacturing environments requiring precise humidity control, food processing facilities, and renewable energy storage applications where thermal cycling and moisture management are critical. A person skilled in the art, in view of the present disclosures, will be able to adapt some or all of the various systems, devices, and methods disclosed herein for different heat exchanger geometries, alternative hydrogel compositions with varying hygroscopic salts, scaled manufacturing processes for different production volumes, integration with smart building systems for automated environmental control, and hybrid applications combining multiple environmental control functions in a single integrated system. All publications and references cited herein are expressly incorporated herein by reference in their entirety.

Claims

Attorney Docket No.: MIT 26047 PCT | 88212-429428CLAIMSWhat is claimed is:

1. A method of applying a hydrogel to a device, comprising:forming a mold by assembling one or more gaskets and one or more panels around one or more components of the device;introducing a hydrogel mixture into a cavity of the mold to fill a designated space between the one or more panels, the hydrogel mixture being formed by adding a hydrogel initiator to a mixture and stirring for approximately in the range of about 10 seconds to about 15 seconds to form a mixture before introducing the mixture into the mold; and allowing the hydrogel mixture to cure and bond to form a hydrogel coating on the heat exchanger,wherein the hydrogel mixture comprises deionized water, acrylamide, lithium chloride, ammonium persulfate, N,N'-methylenebisacrylamide, and tetramethylethylenediamine (TEMED) .

2. The method of claim 1, wherein hydrogel mixture is cured and bonded over a period of about 24 hours.

3. The method of claim 1, wherein the hydrogel mixture is introduced within approximately 20 seconds after addition of the TEMED to prevent premature gelation.

4. The method of claim 1, further comprising preparing at least one of an inner surface of the one or more gaskets or the one or more panels to enhance surface smoothness and water tightness thereof prior to forming the mold.

5. The method of claim 1, wherein the device comprises a heat exchanger.

6. The method of claim 5, wherein the one or more components of the device comprise a U-bend pipe structure of the heat exchanger to enclose the U-bend pipe structure.

7. The method of claim 5, wherein the heat exchanger comprises one or more fins and one or more vapor spacers positioned between the fins, and wherein consistent vapor gaps are maintained across the one or more fins during the hydrogel coating process.Attorney Docket No.: MIT 26047 PCT | 88212-4294288. The method of claim 6, wherein enclosing the U-bend structure further comprises placing one or more fins and one or more spacers on top of one another in sequence to align holes of the fin with the U-tube structure.

9. The method of claim 1, further comprising adding an anti-corrosion coating onto at least one of the one or more gaskets and panels prior to introducing the hydrogel.

10. The method of claim 9, further comprising removing the one or more spacers prior to adding the anti-corrosion coating.

11. The method of claim 1 , wherein the hydrogel mixture comprises deionized water at a ratio approximately in a range of about 9 grams per 1 gram of acrylamide to about 12.5 grams per 1 gram of acrylamide.

12. The method of claim 1, wherein the hydrogel mixture comprises lithium chloride at a ratio approximately in a range of about 3.4 grams per 1 gram of acrylamide to about 4.7 grams per 1 gram of acrylamide.

13. The method of claim 1, wherein the hydrogel mixture comprises ammonium persulfate at a ratio approximately in a range of about 0.0029 grams per 1 gram of acrylamide to about 0.004 grams per 1 gram of acrylamide, and N,N'-methylenebisacrylamide at a ratio approximately in a range of about 0.0051 grams per 1 gram of acrylamide to about 0.007 grams per 1 gram of acrylamide.

14. The method of claim 1, wherein the hydrogel mixture comprises TEMED at a ratio approximately in a range of about 2.45 pL per 1 gram of acrylamide to about 3.4 pL per 1 gram of acrylamide.

15. A method of fabricating a hydrogel-coated fin-tube heat exchanger, comprising: assembling a fin-tube heat exchanger comprising one or more U-bend pipes and a plurality of fins;positioning vapor spacers between adjacent fins to maintain vapor gaps;Attorney Docket No.: MIT 26047 PCT | 88212-429428forming a leak-tight mold around the fin-tube heat exchanger using ultra-smooth panels and gaskets:preparing a lithium chloride-polyacrylamide hydrogel mixture by dissolving lithium chloride in deionized water;pouring the hydrogel mixture into the mold within approximately 20 seconds of TEMED addition;allowing the hydrogel to cure in situ for a period sufficient to achieve crosslinking; andremoving the mold to reveal the hydrogel-coated fin-tube heat exchanger with preserved vapor gaps between the fins.

16. The method of claim 15, wherein preparing the lithium chloride-polyacrylamide hydrogel mixture further comprises adding acrylamide at a ratio of approximately 4.0 g lithium chloride per 1 g acrylamide, adding ammonium persulfate and N,N'-methylenebisacrylamide, and adding TEMED catalyst before pouring.

17. The method of claim 15, further comprising applying an anti-corrosion coating to the fin-tube heat exchanger prior to forming the leak-tight mold.

18. The method of claim 15, wherein the ultra-smooth panels comprise 3D printed PLA panels that have been surface treated to enhance smoothness and water-tightness.

19. The method of claim 15, wherein the hydrogel is allowed to cure for approximately 40 to approximately 60 minutes to achieve full crosslinking and mechanical stabilization before demolding.

20. A heat exchanger, comprising:one or more U-bend pipes;a first panel and a second panel, each having inserts that include a gasket therein, each of the gaskets being configured to be placed around each bend of the U-bend pipes: a hairpin placed on one or more of the first panel or the second panel;one or more heat exchanger fins;one or more vapor spacers evenly placed between the heat exchanger fins; and a hydrogel coating that coats the one or more U-bend pipes.

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