Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF THE INVFNTIO~
Field Of The Invention
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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
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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
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~ co~ling have created a great need for some means of eficiently
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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
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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
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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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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
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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
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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
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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
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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
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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.
.
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
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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
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; ; 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
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~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
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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
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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~ -
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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
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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.
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; 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
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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
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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
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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
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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
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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,
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-~' 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
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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 ~.
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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
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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
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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
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'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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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
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passage of heat transfer fluid 52 from discharge head ~8r as
~ indicated~by directional arrows B.
;~ - Finally, Fig. 9 illustrates the preferred physical
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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
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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
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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
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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,~
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