CA1146158A - Phase change material heat exchanger - Google Patents

Abstract

PHASE CHANGE MATERIAL HEAT EXCHANGER

ABSTRACT OF THE DISCLOSURE
A phase change material heat exchanger wherein the latent heat of a substance as its physical state changes from solid to liquid, and vice versa, is utilized as a heat storage medium. Structure is also disclosed whereby a heat transfer fluid is intimately associated with the phase change material so as to accomplish the desired hear exchange between the phase change material and the heat transfer fluid. As a result of the construction utilized for the heat exchanger, the addition of homogenizing agents to the phase change material is not required.

Description

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BACKGROUND OF THE INVFNTIO~
Field Of The Invention . .
The present invention relates to a phase change material heat exchanger wherein a phase change material com- -prising a salt selected for its relatively high latent heat is utilized as a heat storage medium. The heat exchanger of the invention comprises a substantially c:Losed container into which the phase change material is placed. Then, using a system of conduits and discharge heads, a heat transfer fluid is passed through the phase change material 50 as to allow a heat energy exchange therebetween. This heat transfer takes ~`~ place substantiaLly at the heat of fusion of the phase chan~e material so as to make optimum use of the material's latent heat. B~ virtue of the construction o~ the phase change material heat exahanger the use of homogenizing agents in combination with the phase change ma~erial is not necessary. In a preferred ~ , embodiment the phase change~material heat exchanger is utili~ed as a heat storage facility in combination with a solar heat collector o state of the art construction~ Solar heat is ~absorbed by the heat transfer fluid and stored by the phase change material placed within the heat exchanger. If solar heat is not currently available, heat previously stored could be used to raise the temperature of the heat transfer fluid.
Descriptlon of the Prior Art Recent developments in the art of solar heatin~ and ,, ~ ~ . .
~ co~ling have created a great need for some means of eficiently "~:
storing the energy obtained from the sun for later use, such as at night or on cloudy days. ~ similar need has also been recognized with regard to the efficient operation of liquid-to-,'1 30 ~ air heat pump systems. Such heat stora~e facilities are oo~r~lyreferred to as heat sinks, and the prior art teaches numerous~
devices~for the~construction and operation of such heat storaqe facilities. ;

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Perhaps the simplest of such devices consists essentially of a large holding tank into which the fluid which has been heated by the sun is collected for subsequent usage, such as a hc~e's hot water supply.
Other devices teach the stora~e of heat within rocks placed inside a container through which the heated fluid is allo~ed to ~lcw. Most state of the art heat pumps utilize the at~osphere as a heat sink, either expelling waste heat to the air or extracting heat from the atmosphere, dependin~ upon the mode of operation of the heat pump.
Each of the state of ~he art devi oe s is relatively inefficient, and this inefficiency has become a primary con oe rn because of the high energy associated with operating devices using these primary types of heat storage facilities. ~t least in partial solution of these pro~lems, the current state of the art does teach what may be termed as secondary, or second generation, heat storage facilities.' m ese second generation heat storage facilities basically teach the use of a heat stora~e medium ccmprising a phase chan~e material having ~ . .
a heat of fusion of more than 50 BTU per pound. By 'Iphase change material"
is meant a material which undergces a physical change, such as fron a crystal to a liquid or fram an hydrated crystal to a dehydrated crystal, at a functional temperatore. me bulk of the prior art teaches the use of salt hydrates as the phase change material, and it ls the latent heat absorbed or expelled in accc~plishing the phase change which is capable of being sbored by the phase change material.
~ ccordingly, ik is clear that there is a great need in the art for a heat exchanger conskru~tion wherein a phase change makerial may be ef~iciently utllized for the purpose of alternately storing and releasiny .
heat energy~ Such a heat exchanger device should be suitahle for use in ; ~ combination wi~h existing heaking and oooling systems and should be of relati~ely simple conskruction so as to provi~e long lasking, maintenan oe -free operation. For purposed of efficlency, it wculd also be desirable to utilize the phase ch~ange material in an unadulberabed form without the ne oessity of ino~rForating nucleating and homogenizin~ agentsO

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5~3 According to the present invention there is provided a phase change material heat exchanger, the heat exchanger including container means defining a substantially closed volume and heat transfer fluid inlet means disposed in fluid communicating relation with the interior of the container means, the inlet means including a plurality of discharge head serially connected to the inlet means by a corresponding plurality of discharge conduits, the inlet means furher including N-l check valve means, wherein N
equals the number of the plurality of discharge heads. One of the check valve means is disposed in fluid flow regulating position upstream of each of the plurality of discharge heads other than the one of the plurality of discharge heads positioned in closest proximity to the bottom of the interior.
Each of the check valve means includes adjustment means whereby each of the valve means is adjustable to open at a predetermined pressure. A phase change material ~s placed :~' within the container means, the phase change material being ~, utili~ed in sufficient quantity to fill at least most of the container means. Heat transfer fluid outlet means is disposed .~ :
in fluid communicating relation with the interior of the container means. The outlet means is in spaced apart relation to the inlet means, and a heat transfer fluid flows from the . ~ .
inlet means through the phase change material to the outlet means. The settings of the adjustments are graduated so that the heat transfer fluid will flow from but one of the discharge heads depending upon the physical state of the phase change ; material so that exchange of heat energy may take place between the phase change material and the heat transfer material.
It may be seen, therefore, that the present invention relates to a phase change material heat exchanger sb/Jo ~ .

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wherein the latent heat of fusion of a phase change material is utilized as a heat storage medium. With the advent of solar-based heating and cooling systems, it has been determined that the use of a phase change material as the heat storage facility offers a predictable, relatively narrow band of operating temperature which permits radically improved efficiency in both cooling and heating modes. As will be set forth in greater detail below, the present invention utilizes such a phase change material in combination with 7lnique mechanical structures whereby heat exchange between the phase change material and a heat transfer fluid may be efficient]y conducted ~ without deleteriously affecting the heat storage capabilities ; of the phase change material. Briefly stated, the heat exchange takes place by passing a fluid into intimate contact with the phase change material. Dependent upon the operating condition of the system to which the heat exchanger is connected, heat will pass from the phàse change material into the heat transfer fluid, or from the heat transfer fluid into the phase change material. For example, the phase change material could be utilized to store heat ` energy absorbed by the heat transfer fluid as it passed through a solar collector. Conversely, latent heat of fusion from the phase change material could be utilized to warm the heat transfer fluid for subsequent extraction from that 1uid by a heating system.
In a specific embodiment of the phase change material heat exchanger the phase change material is placed directly into the heat exchanger container in the form of a supersaturated solution containing an excess of phase change material crystals. The inlet means is provided for the introduction of the heat transfer fluid into the sb/J,~
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4~Si5 container containing the encapuslated phase change material. This inlet means basically comprises a conduit extending from the top to a point substantially adjacent the bottom of the container.

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The dischar~e means o~ this embodiment comprlses a plurality of discharge heads serially connected to the inlet means by a corresponding plurality o~ discharge conduits. Each of the discharge heads comprises a plurality of radially extending spokes having apertures formed therethrough. The discharge heads are arranged in a spaced apart, stacked array from the top t~ the bottom of the container. ~urthermore, the apertures formed in the spokes of each discharge head are oriented toward the bottom of the container so that the heat transfer -fluid i5 discharged in a relatively downward direction. At this point it should also be noted that inasmuch as the heat transfer fluid will directly contact the phase change material, the heattransfer fluid must be selected from a class consisting of materials which are not only inert with regard to the phase change material but also are not solvents therefore. While a more detailed discussion of the~heat transfer fluid will be presented below, it is sufficient to note at this point that relatively low viscosity oils are contemplated for use in this second embodiment.
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The 1uid inlet means of this embodiment further com- ;
prises a SQrieS of check valves so as to regulate! in predeter-mined fashion, through which of the plurality of discharge heads the heat transfer fluid will flow. In order to obtain maximum interface between the heat transfer ~luid and the phase change material, it is preferred that the heat transfer fluid be discharged from one discharge head disposed in closest proximity to the bottom of the container in which the phase change material has been placed. However, owing to the nature of the phase change ma~erial and the wide variety o~
operating conditions which might be encountered, it is known ~ .
that part, or all of the phase change material may "freeze,"

presenting a block of material through which the hPat transfer ~ .

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fluid simply cannot flow. Ac~ordingly, the check valves include adjustment means whereby each of the check valves is adjustable to open at a pxedetermined pressure of the heat transfer fluid.
No check valve is provided adjacent the discharge head closest to the bottom of the container. That is to say that this individual discharge head will always present the least flow resistance and the heat transfer fluid wil:l pass thexethrough presuming total fluidity of the phase change material. Each of the remaining discharge heads does include a check va]ve operatively connected thereto, and these check valves are - adjusted so as to require greater fluid pressure to o~en them , ; ; as they progress from the bottom of the container to ~he top of the container.
A segregator means in the nature of a perforated screen is provided ~ithin the container at a position below the discharge head most proximate the container's top. The primary : ~ .
~functl~on~o the segregator means is to prevent passage of the phase change material from the container into the outlet means whiah Wl11 be descrlbed below. Accardingly, substantially all of the phase change materi~al is retained within the container ; belQw ~the segregatar means. Of course, lt shauld be abviaus ;; that the segregator~means is permeable to the heat transfer ~luid but is relatively impermeable to the phase change ~ material. A second, important function is acaomplished by the ; segregator means~
Inasmuch as virtually all the phase change material is retained below the seyregator means~ even if the entire mass of phase change material were to "fxeeze" the discharge head positioned above the segregator means would still be ~ 30 available for the flow of heat transfer fluid therethrough.
;~ In such~a situatian~ this flow onto the top of the "fraze~

mass of~phase change material would ~end to melt tha~ material cg/~C~

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as its heat of fusion was obtained. Then, owing to the serial construction of discharge heads and corresponding check valves, successively lower dischar~e heads would open, eventually resulting in a fluid phase change material bed from top to bottom.
As the heat transfer fluid passes from the inlet means, through the phase change material, and back to the top of the container, the heat transfer fluid is removed from the heat exchanger by fluid outlet means comprising a conduit dis-posed in fluid commun1ca~ing relation to the heat transferfluid substantially adjacent the top o~ the container. As a precautionary measure the end of the outlet means within the container is provided with a filter to prevent any phase change material from entering the system to which the heat exchanger is connected.
` Having thus set forth the basic construction for the phase change material heat exchanger of this invention, atten-tion is invited to certain considerations with regard to the phase change material and the heat transfer fluid. As stated above,in the Description of the Prior Art, the use of phase change material as heat sinks is known in the prior art. Of course, a particular phase change material is chosen with primary regard to the operating conditions which the system will encounter. It is therefore intended that the scope o the present invention does include any phase change material , possessing a latent heat of fusion appropriate for the operating conditions of the heat exchanger. Nevertheless, prime consideration in the development of this invention has been given to salts and salt hydrates such as, for example, calcium chloride and sodlum sulfate decahydrate.
With regard to the heat txansfer fluid, reference is a~ain made to the parameters set forth in the preceding brief description~ -~ 7 ~
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In -tl~e prcferrecl embodiment wherein the heat transfer :tluid in-timately contacts the phase change material itself, water as the heat trasnfer -fluid is not acceptable.
In this embodiment experimenta~ion has shown hydrocarbon and silicon oils to be mos~ effi.cacious.
The invention accordingly comprises the features of construction, combinations of elemen-ts, and arrangement of parts which will be exempli:Eied in the constructions hereinafter set forth 7 and the scope of the inven~ion will be indicated in the claims.

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Brief Description of the Drawings For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:
FIG~ 1 is an elevational view, in sectionl of a first embodiment for the phase change material heat exchanger.
F~G. 2 is a detail view, partially in section, of the phase change material.
FIG. 3 is a sectional view taken along line 3-3 of Fig. 1.
FIG~. 4 is a sectional view taken along line ~-4 of Fig. 1.
FIG. 5 is a sectional view taken along line 5-5 of , ' .
Fig. 1.
FIG. 6 is an elevational view, in section, of a second embodiment of the phase ch~nge material heat exchanger - showing its operation when the entire mass of phase change material is frozen.
~, , ; 20 ~ FIG. 7 is a sectional view similar to that of Fig. 6 showing the operation o the phase change material heat exchanger when only a portion of the phase change material is in a fluid state.
FIG. 8 is a sectional view similar to that o Fig. 6 showing the preferred mode oi operation for this embodiment of the phase change material heat exchanger.
FIG. 9 is a sectional view taken along line 9-9 of ~ig. 8.
Similar reference character~ refer to similar parts throughout the several views of the drawings.
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Detailed Description ~ ~ ;
; ~ The present lnvention relates to a construction for a ., . :
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phase change material heat exchanger, a primary embodiment of said heat exchanger being generally indicated as 10 in the view of Fig. 1. As shown therein heat exchanger 10 comprises a container means including top 12, side 14 and bot~om 16 to define a substantially closed volume. A heat transfer fluid inlet means comprising an inlet conduit 18 is disposed in fluid coll~Nnica~ng relation with the lnterior o~ the container means and includes a discharge means generally indicated as 20 disPosed on the interior end of inlet oonduit 18. As~st clearly seen in the view of Fi~. 5, discharge means 20 comprises a discharge head 22 includin~ a plurality of radially extending spoke means 24 disposed thereon~
Each of the spoke means 24 further includes a plurality of inlet apertures 26 formed therethrough so as to allow passage of a heat transer fluid. This flow of heat transfer fluid is indicated schematically in the view of ~igO 1 by directional .
arrows A through inlet conduit 18, B from inlet apertures 26, and C through the interior of the container means. As fu~ther shown in the view of Fig. 1, heat transfer fluid 28 substantially fills the interior of the container means.
Phase change material heat exchanger 10 further comprises a phase change material ~enerally indicated as 30 placed within the container means and surrounded by heat transfer fluid 28. Notwithstanding the partial representation of Fig.~l, it is to be understood that phase chan~e material . . .
30 is placecl within the container means so as to substantially fill its closed volume. With particular regard to the detailed view of Fig. 2, it can be seen that phase change material 30 comprises a salt 32, a predetermined quantity of which is ;~~
enclosed by capsule means 34. In this prefe~rred embodiment salt 32 c~nsists essentially o calcium chloride, and capsule means 34 is formed from a plastic material. Inasmuch as salt 32 is enclosed by the plurality of capsule means 34, heat .;
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transfer fluid 28 of this embodiment may comprise water~
of course, virtually any relatively low viscosity fluid may be utili~ed as heat transfer fluid 28 so long as the particular fluid chosen is substantially inert with regard to capsule means 34~
As best seen in the views of Figs ~ 1 and 4, phase chanye material 30 is maintained in a fixed, spaced apart relation with regard to discharge means 20 by a capsule support means 36. As shown in those views capsule support means 36 comprises a plate including a plurality of heat transfer fluid apertures formed there~hrough. Capsule support means 36 is maintained in the position shown in Fig. 1 by its placement around inlet conduit 18 onto support ledge 40 formed on the interior of side 1~.
A heat transfer fluid outlet means generally indicated as 42 is formed substantially adjacent top 12 of heat exchanger lO and in fluid communicating relation to heat transfer fluid 8~ As most clearly seen in the view of Figuxe 1~ heat transfer fluid outlet means 42 comprises overflow well means ~20 44 into which the warm or cool fluid 28 will flow, and outlet conduit 46 one end 48 of ~hich is in fluid communicatin~
relation to fluid 28 with end~well means 44.~ Accordingly, fluid 28 i5 removed from well means 44 through conduit 46 as indicated by directional arrows D.
In operation, phase change material heat exchanger 10 is operatively connected to a work unit, such as r for example, a heat pump, during the operation of which an exchange ~.
of heat energy is desired. In this example wherein phase ; change material 30 comprises calcium chloride salt 32, the heat transfer fluid 28 utilized is water. Calcium chloxide has ; ~ a melting point of about 81F and a latent heat of fusion equivalent to approximately 8,774 BTU per cubic foot. Dependent - cg/~

5~3 upon the mode of operation and, therefore, the temperature of incoming transfer ~luid 28, heat energy is stored in or absorbed from calcium chloride salt 32. ~his heat transfer is accom-plished with extreme efficiency for ~he reason that Eluid 28 is intimately contacts each of the capsules 34 including salt 32 placed therein. This intimate contact also has a stirring or mixing effect on the phase change material 30 so as to provide for truly reversible physical state changes of salt 32 from crystal to liquid and vice versa. Presuming that phase change material 30 is in an operating mode for the collection of hea~ energy, salt 32 within each of the capsules -34 absorbs heat from the heat transfer fluid 28 passing therearound, and the cooled fluid 28 then exits through outlet means 42 to begin ano-ther cycle.
It is, of course, to be understood that by virtu~
of the fact that phase change material heat exchanger 10 is ~ , preferably operated at the heat of fusion of salt 32, relati-vely large quantities of heat may be retained and~or rejected owing to the salt's latent heat o fusion.
Attention is now invited to the views of Figs. 6-9, ~ , .
-~' inclusive, wherein a second embodiment of the phase change ` material heat exchanger is generally indicated as SOO Inasmuch as many structural elements of this second embodiment 50 are identical to those of the primary embodiment 10, similar reerence numerals have been utilized where appropriate.
;1 A~ seen in the view of Fig. 6, this embodiment of phase change material heat exchanger 50 also comprises a l container means ha~ing a top 12, sides 14, and a bottom 16 ;, ~ to define a substantlally closed vblume. An inlet conduit 1 30 18 is provided for the introduction o a heat transfer fluid, herein designated as 52, into the container means. Discharge , . . .
means 20 of this emhodiment comprises a plurality of dicharge heads identified as 54, 56, 58, 60 and 62. As most clearly -,:::: , : :
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. ~,, seen in the view of Fig. 9, discharge head 62 comprises a plurality of radially extending spoke means 64, each of said spoke means 64 further comprising a plurality of orifices 66 formed therethrough and oriented in the direction of bottom 16.
The remaining discharge heads 54, 56, 58 and 60 are similarly constructed as indicated in the views of Figfi. 6, 7 and 8.
Those figures also illustrate the fact that each of.the discharge heads54-62 is interconnected in fluid communicating relation to inlet conduit 18 by a corresponding plurality of discharge conduits 68, 70, 72, 74 and 76, In order to regulate the open/close ~ondition of each of the discharge heads 54-60, adjustable check valves 78, 8Q, 82 and 84 are disposed in fluid flow regulating position in corresponding discharge conduits 68-74. Each of the check valves 78-84 is adjusted so as to open only upon reachin~ a predetermined pressure of heat transfer fluid 52u Of course, it should ~e obvious that discharge head 62 is always in an .
open position, for no check valve is provided. Check valve 84 requires relatively less pressure to open than does check .
valve 82. Similarly, check valve 82 requires less pressure to open than does check valve 80, and check valve 78 requires the greatest pressure to open. By virtue~of this construction~
heat trans~er~fluid 52 will be discharged from only one bf the discharge means 20 at any given operating condition, and this will be explained in g.reater detail below.
Now with particular attention to the view of Fig. 6, it can be seen that the interior of the phase change material heat exchanger S0 is substantially filled with phase change material 86 illustrated in the view of Fig. 6 in its substan tially solid or "frozen" state. A segregator means 88 is dis-posed at the top of phase change material 86 and supported.in that position by segregator ledge 90. As will be described ~.
' : -cg/~ ~ -below, segregator means 88 is permeable to heat transfer fluid 52, but substantially impermeable to phase change material 86, which in this embodiment comprises sodium sulfate decahydrate salt. Inasmuch as heat transfer fluid 52 will contact the phase change material 86 intimately, it is to be understood that heat transfer fluid 52 and phase change material 86 are immiscible. Again, with specific regard to the embodiment o Figs. 6-9, the heat transfer fluid 52 comprises a low viscosity .. ,~ . .
hydrocarbon oil. Of course, silicon-~ype fluids could also ' ~' 10 be utilized.
- Finally, with regar~ to structural elemen~s, phase change material heat exchanger 50 further comprises'heat trans-fer fluid outlet means generally indicated as 42 and comprising an outlet conduit 46 disposed in fluid communicating xelation to the interior o~ the container means. As shown in the views of Fig.s. 6, 7 and 8, and 92 of outlet conduit 46 disposed within heat transfer fluid 52 is'provided with a filter means - 94. FlLter means 94 is primarily intended as a precautionary device to preclude entry of phase change material 86 into the !
system serviced by phase change material heat exchanger 50.
Having thus set forth the structural elements of thls second'embodiment and their relationships to each-other, ;~ attention is now inyited to the following description of the operation of phase change material heat exchanger S0 as shown in Figs. 6, 7 and 8.
` ' The view of Fig. 6 illustrates the heat exchanger 50 ~1 .
'l~ ; wherein virtually all of the sodium sulfate decahydrate phase ; change material 86 is in a solid state. Accordingly, orifices 66 of discharge heads 62, 60, 58 and 56 are closed. The ' 30 pressure of heat transfer fluid 52 will rise to the point where check valve 78 opens, and heat transfer fluid 52 will be discharged from dischar~e head~54 as indicated by arrows A.

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;~ S8 The relatively warmer heat transfer fluid 52 will pass through segregator means 88 and, in effect, thaw phase change material 86 by raising its temperature to its heat of fusion, which for sodium sulate decahydrate is about 87F. This action will create a slurry, or fluidized bed, designated by the numeral 96 in Fi~s. 7 and 8 and comprising a supersaturated sol~tion of sodium sulfate decahydrate plus heat transfer fluid 52. It is within this slurry 96 that the most efEicient hea~ exchange takes place, utilizing the latent heat of fusion o the phase change material 86.
Then, as more of the phase change material 86 "melts"
successively lower discharge heads open. As illustra~ed in the vie~ of Fig~ 7, slurry 96 has formed so as to permit ,, passage of heat transfer fluid 52 from discharge head ~8r as ~ indicated~by directional arrows B.

;~ - Finally, Fig. 9 illustrates the preferred physical . .
condition of heat exchanger SO whexein substantially all of the phase chanye material 86 is contained within slurry 96, so that heat transfer fluid 5~ flows rom discharge head 62 as indicated by directional arrows C. This i~ preferred for the reason that substantially all of the phase chan~e material 86 is being utilized for heat transfer at thelatent heat level.

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~ Furthermore, inasmuch as heat transfer fluid 52 enters at the .
bottom o the container means, slurry 96 is in a relatively constant state of agitation thereby prov1ding for efficient, reversible transition of the sodium sulfate decahydrate back and foxth from its solid to liquid stages without the creation of free water.
~ The heat transfer cycle is concluded by the removal of either the heated or warmed trans~er fluid 52 throu~h outlet means 42 as indicated hy directional arrow B.
It is to be understood that there are numerous phase .
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change materials which lend themselves to various useful tem-perature plateaus. The example illustrated in the views of Figs. 6-9 utilizes sodium sulfate decahydrate as the phase change material for use in conjunction with a heat pump for heating and cooling a homeO As previously stated, the melting -~
point of sodium sulfate decahydrate is approximately 87F~
This material is relatively inexpensive, commercially available, and has a storage capacity in excess of 10,000 BTU per cubic ~oot. Because this salt hydrate is slightly basic, it has the additional advantage of being relatively non-corrosive to the metals normally utilized in such systems. It should also be noted that dehydration of the salt hydrate does not occur due : . :
to the light layer of heat transfer fluid covering and sealing the material, even when the salt i6 "frozen,'l above the ` ~ segregator means 88. ~s laten~ heat is removed from the liquid salt hydrate crystallization begins due to the seeding effect of the aupersaturated solution. However only very sma11 crystals ~ -~
orm,~and these small crystals are interlarded with the . ;., .
immiscible heat transmitting fluid. The crystals of the phase change material then are maintained in a slurry, or fluidized bed, and remain so during the normal upward movement of the hea~ transfer liquid.
It will thus be seen that the objects set forth above, amang those made~apparent fram the preceding descriction, are efficiently attained and since oertain changes may be made in the above construction without departing ~rom the scope of the invention, it is intended that all matter contained in;the above descrip~on or shown in the acco~nying drawings shall be interpret~ed has illustrative and not in a limi~nq sense.

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It lS also to be unders~x~ that the following claims are intended to cover all of the generic and specific fea~res of the invention hereLn described, and all statemerlts of the so~ of~the nventlon which, as a matter of language, might be said to~fall therebetween. :
- Now that thè invention~has been described,~

Claims (17)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A phase change material heat exchanger, said heat exchanger comprising: container means defining a substantially closed volume; heat transfer fluid inlet means disposed in fluid communicating relation with the interior of said con-tainer means, said inlet means comprising a plurality of dis-charge heads serially connected to said inlet means by a corresponding plurality of discharge conduits, said inlet means further comprising N-1 check valve means, wherein N equals the number of said plurality of discharge heads, one of said check valve means being disposed in fluid flow regulating position upstream of each of said plurality of discharge heads other than the one of said plurality of discharge heads posi-tioned in closest proximity to the bottom of said interior, each of said check valve means including adjustment means whereby each of said valve means is adjustable to open at a predetermined pressure; a phase change material placed within said container means, said phase change material being utilized in sufficient quantity to fill at least most of said container means; heat transfer fluid outlet means disposed in fluid communicating relation with the interior of said container means, said outlet means being in spaced apart relation to said inlet means; and a heat transfer fluid flowing from said inlet means through said phase change material to said outlet means, the settings of said adjustment means being graduated so that said heat transfer fluid will flow from but one of said discharge heads dependent upon the physical state of said phase change material, whereby an exchange of heat energy may take place between said phase change material and said heat transfer fluid.

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2. A phase change material heat exchanger as in claim 1 wherein said phase change material comprises calcium chloride.

3. A phase change material heat exchanger as in claim 1 wherein said phase change material comprises sodium sulfate decahydrate.

4. A phase change material heat exchanger as in claim 1 wherein said heat transfer fluid comprises a liquid.

5. A phase change material heat exchanger as in claim 4 wherein said liquid comprises water.

6. A phase change material heat exchanger as in claim 4 wherein said liquid comprises a hydrocarbon oil.

7. A phase change material heat exchanger as in claim 4 wherein said liquid comprises a silicon oil.

8. A phase change material heat exchanger as in claim 1 wherein each one of said plurality of discharge heads com-prises a plurality of radially extending spoke means.

9. A phase change material heat exchanger as in claim a wherein each one of said plurality of discharge heads further comprises a plurality of orifices formed through a wall of each of said plurality of spoke means, each of said plurality of orifices communicating with said interior and being oriented toward the bottom of said interior.

10. A phase change material heat exchanger as in claim 1 wherein said adjustment means are set so that the one of said check valve means most remote from said one discharge head in closest proximity to said bottom requires the greatest heat transfer fluid pressure to open and the one of said check valve means adjacent the discharge head closest to said one discharge head requires the least heat transfer fluid pressure to open, intermediate ones of said check valve means being serially graduated therebetween.

11. A phase change material heat exchanger as in claim cg/

10 wherein said phase change material comprises sodium sulfate decahydrate.

12. A phase change material heat exchanger as in claim 10 wherein said heat transfer fluid comprises a liquid.

13. A phase change material heat exchanger as in claim 12 wherein said liquid comprises a hydrocarbon oil.

14. A phase change material heat exchanger as in claim 12 wherein said liquid comprises a silicon oil.

15. A phase change material heat exchanger as in claim 1 further comprising segregator means disposed within said interior above the level of said phase change material and below at least one of said discharge heads, said segregator means being permeable to said heat transfer fluid and imper-meable to said phase change material.

16. A phase change material heat exchanger as in claim 15 wherein said heat transfer fluid outlet means is disposed above said segregator means in fluid communicating relation to said heat transfer fluid.

17. A phase change material heat exchanger as in claim 16 wherein said heat transfer fluid outlet means comprises filter means disposed thereon, whereby said heat transfer fluid is filtered as it enters said outlet means.

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