WO1989000670A1

WO1989000670A1 - Heat and cold storage containers, systems and processes

Info

Publication number: WO1989000670A1
Application number: PCT/US1988/002482
Authority: WO
Inventors: William C. Whitman
Original assignee: WESTECH PRODUCTS Inc
Current assignee: WESTECH PRODUCTS Inc
Priority date: 1987-07-20
Filing date: 1988-07-20
Publication date: 1989-01-26
Anticipated expiration: 1990-01-20
Also published as: AU2253988A; KR890701972A

Abstract

This invention relates to novel heat storage tube containers (20) and tubesheets which are adapted to store and release heat and to cool by means of phase change material (''PCM'') (22) housed within storage tubes (20). Chemical materials which have high latent heat fusion (high BTU capacity) such as Glauber's salt (sodium sulfate decahydrate), can be used in the storage of heat, such as heat generated from solar units. The PCM is housed in storage tube containers (20) with flexible wall structure such as made from two films of material, for example, polymeric sheets (11, 12) as by heat welding (13, 14). Heat or cold storage systems can be provided by forming an array of the container tubes (20) or tubesheets within an enclosure having an inlet and outlet for air or other media to be heated or cooled. Processes for heating and cooling air or other fluid by using the systems are also provided.

Description

HEAT AND COLD STORAGE CONTAINERS, SYSTEMS AND PROCESSES

FIELD OF THE INVENTION

This invention relates to novel heat storage tube containers and tubesheets which are adapted to store and release heat and to cool by means of phase change material

("PCM") housed within storage tubes. Chemical materials which have high latent heat of fusion (high BTU capacity) such as Glauber's salt (sodium sulfate decahydrate), can be used in the storage of heat, such as heat generated from solar units. Glauber's salt, for example, can be used also for cool storage by combining it with other salts such as potassium chloride, ammonium chloride, sodium chloride, or the like. Sodium sulfate decahydrate is a solid below its transition temperature of approximately 89° F (31° C). At its transition temperature, it can be solid or liquid, depending on its BTU content. Glauber's salt is a preferred

PCM because it has a high latent heat value, approximately

100 BTU per pound, and is low in cost. The PCM is housed in storage tube containers such as made from two sheets of material, for example, polymeric sheets as by heat welding.

Heat or cold storage systems can be provided by forming an array of the container tubes or tubesheets within an enclosure having an inlet and outlet for air or other media to be heated or cooled. Processes for heating and cooling air or other media by using the systems are also provided. BACKGROUND ART

Various chemical substances which are capable of forming hydrates have been used in the storage of heat energy. These materials have been placed in various tubes or containers, which in turn are exposed to an environment which requires heating or requires removal of heat to provide cooling or air conditioning. Such tube containers have generally been rigid in construction to provide adequate strength to hold the weight of the contained PCM and with- stand pressures of expansion occurring during phase changes of the PCM. Tubes or containers of lighter or flexible construction have resulted in fractures or breakage of the walls of the tubes or containers, thereby causing leaks.

When rigid tubes or containers are used, the required thickness of the walls have resulted in inadequate heat transfer in order to provide desired heating or cooling of the environment. Additionally, in the case of rigid tubes or containers, contact of the housed PCM, as the PCM changes from liquid phase to solid phase, the volume of the PCM shrinks, resulting in gaps developing between the PCM and the walls of the tubes or containers. Therefore, the desired intimate contact of the PCM with the internal walls of the storage tubes or containers is reduced. Thus, the heat transfer process through the walls of the tube or container and into or out of the PCM is inefficient. For example, a 1 mm gap between the PCM and a container wall reduces heat transfer by about 70 percent. It is desired that heat storage tubes and tubesheets be provided which are adapted to house PCM and which have high strength and a flexibility to provide tube containers which may assume a non-circular or elliptical cross-sectional shape when filled with heat storage PCM and suspended horizontally from the top edge thereof in the environment to be heated or cooled. Such tube containers having such flexibility would assume a shape to provide an intimate contact with the housed PCM as it changes physical state from liquid to solid or solid to liquid.

SUMMARY OF INVENTION

Flexible heat storage tube containers are provided by this invention which provide some or all of the desired properties in the field of flexible tube containers adapted for heat or cold storage. Essentially parallel series of such heat storage tube containers are also provided, as from two sheets of selected flexible film, which are referred to as heat storage tubesheets. The tube containers and tubesheets are relatively thin-walled and are flexible. The tube containers are ordinarily supported in a horizontally disposed position within a insulated enclosure. Various arrangements or arrays of such supported tube containers or tubesheets can be made for efficient and economic use. The walls of the tube container and tubesheets are flexible so that when the respective tube containers are filled with PCM and suspended in a horizontal orientation from top thereof, the tubes are sufficiently flexible so that the cross section of the tube container is not circular or essentially circular but rather is asymmetrical in shape, such as elliptical and can flex and adjust in shape in response to the expansion and contraction of the PCM to retain a high degree of intimate contact. A typical tube container when filled in a vertical position, will have a circular cross sectional configuration. The walls of the tube containers have a low MVTR (moisture vapor transmission rate), such as below about 0.01 gram. The tube container walls have a high heat transfer coefficient of at least 5 BTU, preferably at least 8 BTU. The tube container walls have sufficient wall strength to contain the PCM with substantial absence of rupture and a dimensional condition which is substantially stable. The tube container has a stability to the operating temperature cycle range of the PCM employed, such as within the range from about 0° to about 250°F or higher, depending on the application. The tube containers will be filled with a PCM. Illustratively, the PCM can comprise Glauber's salt. The PCM can also include a suspending agent, nucleating agent, agents providing for altering the PCM, such as its phase change temperature, and the like.

Provided by this invention is also a process of storing or releasing heat by contacting the above filled tube containers or tubesheets with a heating or cooling air or other media.

Also provided by this invention are heat or cold storage systems which have an array of the tube containers or tubesheets within a confinement having an inlet and outlet for air or media to be heated or cooled.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a front elevational view of an unfilled tubesheet adapted to be filled with PCM and sealed to form heat or cold storage tubesheets made in accordance with the present invention.

FIG. 2 is a cross-sectional view of the tubesheet shown in FIG. 1 taken at phase 2-2 to show the cross-sectional configuration of the final sealed tubesheet after filling with PCM and suspended in a horizontal position from the top thereof by a suspending device 21 present in channel 19.

FIG. 3 is an section of the tubesheet wall 12 shown in

FIG. 2.

PETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EM BODI MENTS

Referring to FIGS. 1, 2, and 3, the tubesheet is made by contacting two plastic sheets 11 and 12. Sheets 11 and

12 are welded together as by heat sealing at terminal locations to form seals 13 and 13A and at intermediate locations to form seals 14 in the formation of the individual tube containers 20. The left hand margin of the contiguous sheets 11 and 12 are welded to form seal 15, which becomes one end of the tube containers. The right hand seal is partially formed as seal 17 leaving unsealed segments 18 to provide openings through which the PCM composition can be filled into the container tubes 20. Seal 13 and first seal

14 form channel tube 16, which receives a rod, rope or other suspending device through channel 19 for suspending the finally filled tubesheet as desired in an insulated enclosure or other thermal bank device. After the container tubes 20 are each filled with the PCM composition, the unsealed portion 21 of the right margin is carefully cleaned to remove any PCM composition or any other matter and is sealed to form a right hand seal corresponding to left hand seal 15.

FIG. 2 is a cross-sectional view taken at line 2 - 2 in

FIG. 1 after the individual container tubes are filled with the PCM composition 22 and the right hand seal corresponding to left hand seal 15 is formed. Channel 16 is shown formed by seal 13 and first seal 14 a nd having a suspending means

21 in place.

FIG. 3 is an expanded, partial sectional view of the wall of sheet 12. Layer 30 is made of a film-forming poly propylene; layer 31 is an aluminum foil; and layer 32 is made of nylon 6. The layers are adhered one to the other with adhesive.

The completed and filled tubesheet 10 is suspended and held in a vertical position with the tube containers horizontally disposed, by suspending element 21. It is noted that the tube containers have an elliptical cross section.

It will be suggested to those skilled in the art to make modifications to that cross-sectional shape. The tubesheet is made as by placing two films of flexible materials which provide the proper characteristics in contact. If the films are laminates having different materials on the two sides of the film, the two films are placed one on top of the other so that the sides having the same sealable material will be facing each other. If the films are to be welded together as by heat sealing, the sides having the materials which are readily heat welded and provide other desired properties are placed in contact with each other. The size of the films is selected to provide desirable dimensions in the final heat storage tube containers depending upon the capacity desired in the tube container, the cycle time desired, the size and the location of the enclosure or other storage structure used for positioning the tubesheets to function in heat or cold storage, and other factors.

In the tubesheet as shown in FIG.1, the dimensions of the starting films used in constructing the tubesheets can vary. It has been found suitable in many applications such as home use, for example, that the dimensions of the original films are about 24 in. by about 36 in. The tube containers can desirably be about 8 in. by about 24 in. The tubes can have a smaller or larger width. For example, it has been found that 10 to 12 in. width tube containers can be effectively used. Tubes with wider width carry a heavier load per in. of seal, assuming the final tubesheets in operation are suspended from the top thereof so that the tube containers are in a horizontal position. Therefore, in the use of increasing width container tubes, one must be certain that the seal strength of the container tubes is sufficiently high to withstand rupture.

The width of the seals made to form the tube container can vary in width so long as they are sufficiently wide to provide the strength to hold the PCM composition placed into the final tube container. In tubesheets made using, heat sealing or welding, it has been found using preferred starting sheets that a heat seal width of about 3/8 in. is sufficient. The width can suitably be varied such as within the range of from about 1/4 in. to about 1 in. so long as sufficient strength is provided to contain the stored PCM composition over a long term period. Unnecessarily wide seals should be avoided for economic reasons and for efficiency of operation of the tubesheets. The seals can be multiple such as double with an unsealed spacing between the seals, such as about 1/4 to about 1/2 inch, or more if desired, to produce desired configurations or characteristics. It has been found desirable to use laminated films to form preferred heat storage tubesheets of this invention, which are formed by laminating (1) a polyamide film, suitably nylon 6 (polycaprolactam) (2) an aluminum foil and (3) a polypropylene, suitably an isotactic polypropylene having a film-forming molecular weight. The films used in making the laminated film can vary in thickness. It has been found for many purposes that polyamide films and aluminum foils of about 0.5 mil function well. The films can be increased in thickness as required up to about 2 mil or more so long as the final laminated film provides the required flexibility and other required properties. The nylon film layer can be an oriented film to provide greater strength. The aluminum foil desirably is the core laminated layer. The polypropylene film suitably has a thickness of about 3 mil, desirably in the range of about 1 to about 5 mil. However, the thickness can be varied depending upon the width of the final tube containers, the weight which the tube containers must hold, seal strength required and sealing conditions, temperature used and other factors. The final laminated films used to make the tube containers and tube sheets should not exceed what provides satisfactory properties. Suitable adhesives known to the art are used in the lamination, e.g., urethane adhesives. Other films can be substituted and yet retain the required characteristics of the final, filled tube containers and tubesheets and such substitution will be suggested to those skilled in the art to whom this disclosure is directed with the benefit of this disclosure. The PCM used can be widely varied. It has been found desirable to use sodium sulfate and sufficient water to form the sodium sulfate decahydrate, also called Glauber's salt.

Other PCM components can be used so long as the phase change occurs at an appropriate temperature. Other materials which can be used are calcium chloride, sodium thiosulfate, sodium chloride, ammonium chloride, potassium chloride, and others which are known to those skilled in the art.

Certain materials can be added to the PCM composition.

For example, an amount of a nucleating agent can be used. A suitable nucleating agent is borax. A presently desirably amount of borax as the nucleating agent is about 2 to 5 percent of the total PCM composition. The amount can be varied widely so l ong as desired nucl eation is provided.

Other suitable nucleating agents can be used.

Suspending agents are also desirably used. It is presently preferred to use certain starch derivative suspending agents such as sold under the designation J-400 and J-500

The starch derivative suspending agents can, for example, be polyacrylonitrile-starch graft copolymers formed as by graft copolymerization of acrylonitr ile with a suitable starch.

The graft polyacrylonitrile starch copolymers can be saponified with suitable aqueous bases. It is understood that J-

400 and J-500 are starch graft copolymers coming within the

PAA(Na⁺) type. The starch graft copolymer suspending agents can be cross linked to a degree so long as the crosslinking does not interfere with the suspending action. The graft starch copolymers desirably used are called in the art superabsorbent polymers. It is presently believed that presently preferred graft starch copolymer suspending agents, such as polyacrylonitrile-starch graft copolymer superabsorbent suspending agent become more fluid as the PCM changes to the liquid phase and in turn becomes more viscous during the conversion of the PCM to the solid phase. The amount or suspending agent will vary depending upon the PCM and other factors. It has been found suitable to employ an effective amount, such as in the range of about 0.5 to 5 percent based on the weight of the PCM composition. About 1 to 2 percent of J-400 and J-500 has been found satisfactory in Glauber's salt PCM compositions.

Other suspending agents can also be effectively used. The role of the suspending agent is to prevent precipitation of the solid components of the PCM compositions, such as the solid components after the phase change component has been converted to non-hydrated entities or to prevent heterogeneous formation when the phase change composition converts gradually to the hydrated crystalline form upon release of heat.

Combinations of phase change components can be used it desired, depending upon the phase change tempera tur es desired, economic f actors and other considerations. Su ch combinations can be used to lower the transition tempe r atures of the PCM and are desired for certain end uses, such as cold storage.

The polymer films used to form the tube containe r s o r tubesheets can be sealed using conventional heating seal ing equipment using platens of the proper configuration to provide the seal s, or welds , such as shown in FIG. 1. Af ter filling the individual tube containers, the final sealing is made on the filling side on the tubesheets such as shown in FIG. 1, using a sealing bar to close the filling openings and to widen the seal as applicable along the entire filling side of the tubesheet. The platens and sealing bars are heated to provide a suitable heat sealing temperature.

The unsealed tubesheets as shown in FIG. 1 are filled as by forming a slurry of the anhydrous form of the PCM and feeding the slurry into. the openings of the respective tube containers of the tubesheet while the tube containers are held in a vertical position. The tubesheet is desirably rotated prior to filling so that its sealed left hand side is placed on the floor, scale or other horizontal surface. The slurry is added until the tube container is full, desirably about 2 inches from the partial seal of the filling side of the container or as full as possible and yet permit the completion of the seal of the respective filled container and the final sealing of the filling side of the tubesheet. It is desirable after filling to remove the remaining air at the top of the tube container with vacuum insofar as practicable. The filling openings and any other unsealed portions of the filling side of the tubesheet are cleaned to remove residual PCM composition deposited on the film surfaces during filling, and any other matter present on the surfaces which interfere with ffective sealing. A stream of air or other gas, appropriate wiping, or other procedures or combinations can be used for the cleaning. As expressed above, the PCM slurry used in filling the. tube containers is made using an anhydrous form of the PCM material, such as anhydrous sodium sulfate. The theoretical amount of water is added to form the desired hydrate. In the case of sodium sulfate, the desired hydrate is the decahydrate. In addition, other ingredients desired in the final PCM composition are added and the composition is mixed and heated suitably to about 120°F to form a homogeneous mixture, preferably in a vacuum to minimize the amount of air present in the final sealed tube. Such other ingredients as desired, such as nucleating agents, suspending agents and any others are added in forming the PCM homogeneous composition.

The filled and sealed heat or cold storage tubesheets are used in the systems of this invention for heating and cooling. The tubesheets are suspended as by passing a rod, cord or other suspending device through the channel at the top of the tubesheet. The suspending device can be adapted at the ends thereof for engagement with the walls of an insulated enclosure used for operation. If the suspending device is a cord of sufficient, strength, such as polypropylene or nylon, it can suitably have loops at the ends thereof for e agement with suspending hooks appropriately placed on the internal wall of the storage enclosure. Normally, a series or array of the filled tubesheets will be placed in a close, nesting relationship with controlled spacing in such an enclosure. The enclosure will be a closed system with inlet, and outlet passages for flow of air or other media including water, over the surfaces of the tube or tubesheets, desirably the flow being in a serpentine pattern. The inlet can introduce a heated air which is used to convert a cooled PCM material in the hydrate phase to a non-hydrated or less hydrated stage, with the stored heat energy required to convert from the hydrate to a non- hydrated or less hydrated stage. Or, the air or other medium, which is cold, can be passed through an inlet enclosure, to contact the tube containers or tubesheets to cause the PCM material to yield gradually its stored energy in conversion from a fluid non-hydrate form to a solid, crystalline hydrated form and to heat the passing air or other media. The warmed air can be used, e.g. to heat the interior of a dwelling. Some specific heat can also be available for heating and cooling. The change in phase of the PCM composition desirably occurs in residential heating uses during about a 10-hour period so that a complete cycle can occur diurnally. For example, during the sunlight hours, the hydrate phase can be converted to the non-hydrate phase as by heat generated by solar collectors, by heat from the rooms of the dwelling which is removed by passing a flow of air from the rooms over the surfaces of the filled container tubes or tube- sheets of this invention. During the night hours, the cooled air of the dwelling can be passed through the heat storage enclosure to convert gradually the non-hydrate phase to the hydrate phase.

The tubesheets desirably are placed in a relationship so that a. maximum contact of the walls of the tube containers or tubesheets with the flow of air or other media is made. Desirably, the flow is in a serpentine direction between the suspended containers. The tube containers ar rangement wherein the tube containers of adjacent tubesheets are appropriately higher or lower than the adjacent tube containers provide a nesting relationship and a serpentine flow.

The tube containers or the tubesheets of this invention have the following properties:

1) a flexibility to provide intimate contact of the inner wall of said storage tube with the contained phase change material during all phases thereof due to flex- ing permitting by design and support means used;

2) a low MVTR bel ow about 0.01 g;

3) a high heat transf er coeffi cient of at l east about 5 , preferably about. 8 , BTU per sq. ft./hr./°F;

4) a tensile wall strength and seal strength sufficient to contain said phase change material in said storage tube and to maintain said storage tube in dimensiona l ly stabl e condition ;

5) seal strength per l inear inch being at l east about 2 times the force of the l oad applied to the seal ;

6) stabl e to the heat or co l d conditions of the storage process used.

The following are in i llustration of the films and PCM compositions which can be used in carrying out the invention (TABLE I) ; the properties of the tubesheets formed (TABLE II) , and the conditions used in making the tubesheets. The isotactic polypropyl ene exter io r l ayers of the respective l aminate fi lms are pl aced in contact in making the tubesheets (TABLE III) .

J-400 superabsorbent suspending agent can be substituted in PCM 2 for the J-500 superabsorbent suspending agent.

*Sealing condition: 344.74 kPa, gauge, 204 C and 2 s;

Material direction is not applicable.

1 - numbers in parentheses are values expressed in lb/in.

2 - numbers in parentheses are values expressed in lb/in.²

1 - values in the parentheses are expressed in °F. 2 - values in the parentheses are expressed in lb/in.

It will be suggested to those skilled in the art to make variations in polymers, PCM, the devices and processes disclosed herein and the same are intended to be covered by the following claims insofar as they are within the spirit of the invention disclosed herein.

Claims

WHAT IS CLAIMED IS :

1. A heat or cold storage tube container for ho.using PCM, said tube container when fil led with PCM is adapted to store and to rel ease heat or to cool by phase change action of said PCM, said storage tube container comprising a closed tube having a wal l which has

1) a f l exibil ity to provide intimate contact of the inne r wal l surf aces of said storage tube f i l l ed with the PCM during the sol id and l iquid phases and changes between said phases when said storage tube container is hor izontal ly disposed and is supported from the top thereof; 2) a low MVTR below about 0..01 g;

3) a high heat transfer coefficient of at least about

5 BTU per sq. f t./hr. ° F;

4) a tensile wall strength and seal strength sufficient to contain said PCM in said storage tube container without rupture during said phase change actions of said PCM and to maintain said storage tube in dimensional ly stable condition; and

5) stability to heat and cold conditions of said phase change actions.

2. A storage tube container of claim 1 which is filled with PCM.

3. A storage tube container of claim 2 which is filled with Glauber's salt.

4. A s torage tube container of claim 2 wherein said PCM has an effective amount of a nucleating or suspending agent or both.

5. A storage tube container of claim 4 in which the nucleating agent is an effective amount of borax.

6. A storage tube container of claim 4 in which the suspending agent is an effective amount of a superabsorbent starch graft copolymer.

7. A storage tube container of claim 6 wherein the super- absorbent graft starch copolymer is a starch-poly- acrylonitrile graft copolymer.

8. A storage tube container of claim 1 in which the flexible wall is made of a laminate film of multiple layers.

9. A storage tube container of claim 8 in which an internal layer of said laminate film is an aluminum foil layer.

10. A storage tube container of claim 9 wherein said internal layer of aluminum has adhered on both sides polymer film layers of the same or different polymer films.

11. A storage tube container of claim 10 wherein the inside surface layer of said laminate film is a polypropylene film layer.

12. A storage tube container of claim 10 wherein the outside surface layer of said laminate film is a nylon film layer.

13 . A storage tube container of claim 9 wherein the inside surface l ayer is a polypropylene film and the external sur f ace l ay e r is a ny l on 6 f i lm l ayer .

14. A storage tube container of claim 2 wherein the cross section of said storage tube container is elliptical when said storage tube container is horizontally disposed and is supported from the top thereof.

15. A storage tube container of claim 4 wherein the PCM is

Glauber's salt having an effective amount of a nucleating agent or suspending agent.

16. A heat or cold storage tube container tubesheet having two or more storage tube containers, said storage tube containers being defined in accordance with claim 2.

17. A heat or cold storage tube container tubesheet in accordance with claim 16 wherein said storage tube containers are filled with PCM.

18. A heat or cold storage tube container tubesheet in accordance with claim 16 wherein the wall of said storage tube containers are made of a flexible laminate film in which an internal layer is an aluminum foil.

19. A heat or cold storage tube container tubesheet in accordance with claim 18 wherein the internal surface layer is a polypropylene film or the outside surface layer is a nylon 6 film layer or both.

20. A heating or cooling system having an array of tube- sheets suspended within an insulated enclosure with inlet and outlet ports, said tubesheets are as defined in claim 17.

21. A heating or cooling system of claim 20 wherein the tubesheets are as defined in claim 18.

22. A heating or cooling system of claim 20 wherein the tubesheets are as defined in claim 19.

23. A heating or cooling system of claim 22 wherein the contained PCM is Glauber's salt having an effective amount of a nucleating agent or suspending agent or both.

24. A process of heating or cooling by passing air or other medium through the system as defined in claim 20.