A heat-storing vessel filled with a heat-storing material of latent heat type is provided with a fluid flow passage in thermal contact with the heat-storing material for passing a fluid for storing and releasing heat. By passing a hot fluid through the fluid flow passage, the heat-storing material in the heat-storing vessel is melted to store heat. By passing a cold fluid through the fluid flow passage, the heat-storing material in the heat-storing vessel is solidified to release heat. The heat-storing material contains a gelling agent to suppress a phase separation phenomenon. A low temperature part is provided at a part of the heat-storing vessel and the heat-storing material containing the gelling agent is retained in a solid state at the low temperature part to prevent supercooling of the heat-storing material.

THE BACKGROUND OF THE INVENTION 
1. The Field of the Invention 
This invention relates to a heat-storing apparatus, which comprises a 
heat-storing material of latent heat type placed in a heat-storing vessel, 
where heat is stored or released by a phase change of the heat-storing 
material of latent heat type, and more particularly to a heat-storing 
apparatus, which stores solar heat, waste heat, heat generated by use of 
midnight electric power, etc. and releases the stored heat, when required. 
2. The Prior Art 
The conventional heat-storing apparatus uses a heat storing material of 
sensible heat type such as water, stone fragments, etc. as a heat-storing 
material, but such heat-storing material has a low heat-storing capacity, 
so that the heat-storing apparatus must have a considerably large size. 
Thus, attempts have been recently made to make the heat-storing apparatus 
smaller in size but larger in capacity by using a heat-storing material of 
latent heat type which utilizes the latent heat appearing at 
solidification and melting of inorganic hydrated salts such as sodium 
thiosulfate pentahydrate and calcium chloride hexahydrate. Various 
inorganic hydrated salts are available for desired temperature ranges, and 
for a temperature range of 40.degree. to 50.degree. C. , sodium 
thiosulfate pentahydrate (Na.sub.2 S.sub.2 O.sub.3. 5H.sub.2 O) is a 
promising heat-storing material because it has a melting point of 
48.degree. C., a solidification point of 45.degree. C. and a high latent 
heat such as 82 cal/cm/.sup.3, and is also cheap. However, when the 
inorganic hydrated salts are subjected to repetitions of solidification 
and melting, a phenomenon of separating the salt into a salt having a high 
melting point and a salt having a low melting point (phase separation 
phenomenon) takes place due to the nature of the salt, that is, the 
melting point corresponding to a peritectic point, and consequently the 
salt will not release the latent heat at the desired temperature (melting 
point) in the end. 
Sometimes, the salt undergoes supercooling and fails to undergo 
solidification at a temperature by 20.degree. to 30.degree. C. lower than 
the melting point and thus the stored heat is not released at the desired 
temperature (supercooling phenomenon). 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a heat-storing apparatus 
free from a phase separation phenomenon and a supercooling phenomenon. 
According to the present invention, a heat-storing apparatus is provided, 
which comprises a heat-storing material containing a gelling agent being 
placed in a heat-storing vessel, a low temperature section being provided 
at a part of the heat-storing vessel, and the heat-storing material 
containing the gelling agent being provided in a solid state in the low 
temperature section.

DETAILED DESCRIPTION OF THE INVENTION 
In FIG. 1, one embodiment of a heat-storing apparatus according to the 
present invention is shown, where a housing 1 is provided with a fluid 
inlet pipe 2 at the lower part and a fluid outlet pipe 3 at the upper 
part, and further with a plurality of heat-storing vessels 4 of 
polyethylene, copper, aluminum, or the like therein in a vertical state. 
Each of the heat-storing vessels 4 is filled with a heat-storing material 
5 of latent heat type comprising sodium thiosulfate pentahydrate or 
calcium chloride hexahydrate as the main component. The heat-storing 
material 5 undergoes volume change at the solidification and melting, and 
thus there must be a small space in the heat-storing vessel 4 when filled 
with the heat-storing material 5. It is also preferable that the liquid 
surface 5a of heat-storing material 5 is a little higher than the level of 
wall 1a of housing 1. Furthermore, one end of heat-storing vessel 4 is 
projected from the wall 1a of housing 1 to come in contact with a low 
temperature fluid 7 i.e. air, and thus is at a lower temperature than the 
melting point of heat-storing material 5 in the heat-storing vessel 4. The 
outwardly projected part will be hereinafter referred to as "low 
temperature part 4a". 
The heat-storing material 5' is deposited on the inner wall of low 
temperature part 4a of heat-storing vessel 4, i.e. inner wall in the space 
6 of heat-storing vessel 4. 
A fluid, i.e. water, oil, air or the like is introduced into the housing 1 
through the fluid inlet pipe 2 to pass through the space 8 in the housing 
1 and then is withdrawn therefrom to the outside through the fluid outlet 
pipe 3. When the temperature of the fluid is higher than the melting point 
of heat-storing material 5, 5', heat is transferred to the heat-storing 
material 5 from the fluid through the heat-storing vessels 4 to melt the 
heat-storing material 5, and is stored therein. 
When the temperature of the fluid is lower than the melting point of 
heat-storing material 5, heat is transferred to the fluid from the 
heat-storing material 5 through the heat-storing vessels 4 to solidify the 
heat-storing material 5, and is released. 
When the heat-storing material 5 undergoes repetitions of such heat cycle, 
a phase separation phenomenon gradually appears, so that it is separated 
into materials having different melting points. That is, a material having 
a high melting point deposits as a lower layer in the heat-storing vessel 
5 and a material having a low melting point as an upper layer, so that no 
phase change occurs at the desired tempererature. 
In FIG. 2, heat-releasing characteristics of sodium thiosulfate 
pentahydrate as a heat-storing material after several ten repetitions of 
heating-cooling cycle are shown, where the time (minute) from the start of 
heat release is plotted on the axis of abscissa, and the temperature 
(.degree.C.) of the heat-storing material is plotted on the axis of 
ordinate. Curve 9 shows a temperature change of heat-storing material. In 
the lower layer in the heat-storing vessel 5 sodium thiosulfate dihydrate 
having a high melting point deposits, as shown by dotted line 9a, so that 
no phase change takes place and thus there is no region of small 
temperature change at the solidification. In the upper layer in the 
heat-storing vessel 5 a material that undergoes phase change at a lower 
temperature, for example, 32.degree. C., than the solidification point 
45.degree. C. of sodium thiosulfate pentahydrate deposits, as shown by 
full line 9b. The round mark "O" on the curve 9 shows the solidification 
point of sodium thiosulfate pentahydrate. 
To suppress occurrence of the phase separation phenomenon, a gelling agent 
such as starch, gelatin, glass powder, alumina powder, etc. is added to 
the heat-storing material 5 according to the present invention. The 
gelling agent is also added to the heat-storing material deposited on the 
inner wall of the low temperature part 4a in the heat-storing vessel 4 
(the inner wall in the space 6 in the heat-storing vessel 4). 
For example, starch as a gelling agent is hygroscopic particles having 
particle sizes of 0.002 to 0.2 mm and is not soluble in cold water but 
swells in warm water so that the surrounding films of starch particles are 
broken to allow the starch substance to flow into the warm water and to 
turn it to a viscous liquid. The surrounding films of starch particles are 
broken at a temperature of 55.degree. to 70.degree. C., whereas the 
melting point of sodium thiosulfate pentahydrate is 48.degree. C., and the 
application temperature range of heat-storing material is 20.degree. to 
70.degree. C. 
That is, a viscous mixture prepared by adding starch to sodium thiosulfate 
pentahydrate is in a very suitable temperature range. The starch turns 
colloid by liquefaction to a viscous state, and the resulting viscous 
starch colloid encloses sodium thiosulfate pentahydrate to suppress 
occurrence of the phase separation phenomenon. 
In the structure shown in FIG. 1, the vicinity of low temperature part 4a 
in the heat-storing vessel 4 is at a lower temperature than the melting 
point of heat-storing material 5, and thus the heat-storing material 5' 
containing the gelling agent deposited on the inner wall of low 
temperature part 4a and the vicinity of the liquid surface 5a of 
heat-storing material 5 is solidified. When the heat-storing material 5 
releases heat, crystals grow around the solidified parts without any 
supercooling. Furthermore, the heat-storing material 5 contains the 
gelling agent, and thus occurrence of phase separation phenomenon of 
separating the heat-storing material into a material having a high melting 
point and a material having a low melting point can be suppressed. The 
heat-storing material 5' on the inner wall of low temperature part 4a 
contains the gelling agent, where the gelling agent in the heat-storing 
material 5' works as a kind of paste at the deposition and solidification, 
so that the heat-storing material 5' is secured to the inner wall of low 
temperature part 4a without peeling off to fall down. 
In FIG. 3, another embodiment of a heat-storing apparatus according to the 
present invention is shown, and in FIG. 4, a cross-sectional view along 
line IV--IV of FIG. 3 is shown. According to this embodiment, heat-storing 
vessels 4 are horizontally arranged in the housing 1, where the 
heat-storing material 5' containing a gelling agent is also deposited and 
solidified on the inner wall of low temperature part 4a in the 
heat-storing vessels 4. In the present embodiment, a cover 10 is provided 
over the low temperature parts 4a of the heat-storing vessels 4 to form a 
fluid passage 11 between the wall 1c of housing 1 and the cover 10. Air as 
a fluid is forced to enter the fluid passage 11 by a fan 12 through an 
inlet 13 and vented through an outlet 14. The low temperature parts 4a of 
heat-storing vessels 4 are much more cooled than by spontaneous cooling 
according to the embodiment of FIG. 1. For much better cooling, the fluid 
passage 11 is made liquid-tight, and water is forced to enter the fluid 
passage 11 by a pump to cool the low temperature parts 4a of heat-storing 
vessels 4. 
In FIG. 5, still another embodiment of a heat-storing apparatus according 
to the present invention is shown and in FIG. 6 a cross-sectional view 
along line VI--VI of FIG. 5 is shown. This embodiment differs in the shape 
of heat-storing vessel 4 from the foregoing embodiment. A heat-storing 
vessel 4 consists of a pipe part 4' and cap parts 4" welded to both ends 
of pipe part 4'. It is preferable that the cap parts 4" have a larger 
thickness than that of the pipe part 4', because the heat of a fluid 
having a high temperature is hard to transfer to the heat-storing material 
5' deposited and solidified on the inner wall of cap parts 4" when the 
fluid is allowed to pass through the space 8 in the housing 1, so that the 
heat-storing material 5' will not be molten. 
In FIGS. 7 to 13, heat-storing vessel sections of still other embodiments 
of heat-storing apparatuses according to the present invention are shown. 
According to the embodiment of FIG. 7, the inner wall of low temperature 
part 4a in the heat-storing vessel is lined with a porous material 15 of 
glass wool, Moltopren (trademark of polymethane foam made by Bayer, 
Germany), metal fibers, metal nettings, sintered metal, or the like, and 
then the porous material 15 is impregnated with a heat-storing material 
containing a gelling agent, and solidified. In this case, it is preferable 
to extend a part of the porous material 15 downwards across the liquid 
surface 5a of the heat-storing material 5 to dip therein. With this 
structure the heat-storing material containing the gelling agent is firmly 
secured to the inner wall of low temperature part 4a in the heat-storing 
vessel 4. 
According to the embodiment of FIG. 8, a heat-storing vessel 4 is inclined, 
and a block of porous material 15 is impregnated with a heat-storing 
material containing a gelling agent. 
According to the embodiment of FIG. 9, one end of porous material 15 is 
further extended downwards across the liquid surface 5a of heat-storing 
material 5 to dip therein. 
According to the embodiments of FIGS. 10 and 11, the inner wall of low 
temperature part 4a in the heat-storing vessel 4 is lined with a porous 
material 15 and at the same time, a porous material is provided at the 
center of space 6 in the heat-storing vessel 4 so that its tip end can be 
dipped in the heat-storing material 5. According to the embodiment of FIG. 
10, the tip end extends to the vicinity of liquid surface 5a of 
heat-storing material 5, whereas according to the embodiment of FIG. 11, 
the tip end extends deeply through the heat-storing material 5 to the 
vicinity of the bottom of heat-storing vessel 4. With these structures, 
the surface tension of heat-storing material 5 is increased, and the 
heat-storing material 5 is pulled upwards by the capillary force of porous 
material 15, so that the heat-storing material containing a gelling agent 
can be retained in all the porous material 15 in the space 4a in the 
heat-storing vessel 4. 
In FIG. 12, still another embodiment of a heat-storing apparatus according 
to the present invention is shown, and in FIG. 13 a cross-sectional view 
along the line XII--XIII of FIG. 12 is shown. A heat-storing vessel 14 is 
horizontally arranged, and the space 6 of heat-storing vessel 4 not only 
exists at the low temperature part 4a, but also horizontally extends in 
the space in the heat-storing vessel 4 at the left side of wall surface 1a 
of housing 1 (high temperature part). The porous material 15 is secured to 
all or parts of the upper wall in the space 6 in the heat-storing vessel 
4. With such a structure, the heat-storing material existing in the porous 
material 15 lined on the inner wall of heat-storing vessel at the space 
side 8 of housing 1 can melt when a high temperature fluid passes through 
the space 8 of housing 1, whereas the porous material 15 at the low 
temperature side 4a in the heat-storing vessel 4 can keep to retain the 
heat-storing material containing the gelling agent by the capillary force. 
In FIGS. 14 and 15, still further embodiments of heat-storing apparatuses 
according to the present invention are shown, which are to store or 
release heat by means of heater 16 and cooler 17 provided in the 
heat-storing material 5 in a large heat-storing vessel 4 as being 
different from the embodiments shown in FIGS. 1-13. That is, the 
heat-storing material 5 is made to melt and store heat by passing a high 
temperature fluid through the heater 16, and is also made to release heat 
by passing a low temperature fluid through the cooler 17 while solidifying 
the heat-storing material 5. 
According to the embodiment of FIG. 14, the low temperature part 4a in the 
heat-storing vessel 4 is lined with the porous material 15, and its 
function and effect are the same as those of the structure of FIG. 7 or 
FIG. 12. 
According to the embodiment of FIG. 15, a small pipe 18 is projected from 
the heat-storing vessel 4 at one side, and the projected end of small pipe 
18 is sealed with a cap 19. Porous material 15 is placed on the liquid 
surface 5a of heat-storing material 5 and one end of the porous material 
15 is extended into the small pipe 18. Other members are the same as in 
FIG. 14. In this embodiment, the small pipe 18 serves the low temperature 
part 4a in the heat-storing vessel 4. In this embodiment, nucleation is 
further assured by providing an appropriate number of a heat-storing 
material 5' containing a gelling agent in a solid state on the porous 
material 15 in the heat-storing vessel 4 and the small pipe 18. 
In the embodiments of FIGS. 14 and 15, the housing that forms a fluid 
passage for storing or releasing heat can be omitted. 
In the foregoing embodiments, the nucleation can be much more effectively 
attained and the super-cooling phenomenon can be more effectively 
suppressed by adding a nucleating agent that can facilitate nucleation to 
the heat-storing agent 5 containing the gelling agent, or to the 
heat-storing agent 5' containing the gelling agent deposited and solidifed 
on the inner wall of the low temperature part 4a in the heat-storing 
vessel 4 or to the porous material 15. 
Generally, a phase change from a liquid phase to a solid phase can be 
divided into two stages, i.e. a stage of generating crystal nuclei and a 
stage of making the crystals to grow at the nuclei. A large energy is 
required for the generation of nuclei, and it is known that the 
supercooling phenomenon appears owing to the presence of a barrier to such 
energy. To prevent such supercooling, a nucleating agent is added thereto. 
It is also known that the nucleating agent should be insoluble in a liquid 
phase and have a small.sup.2 interfacial energy with newly generated 
crystals on the interface and a nucleus size larger than a given critical 
radius ranging between 1 and 100 .mu.m. It is also known that the crystals 
are more liable to grow on a crystal face of low molecular density, for 
example, facet 100 or 110 in a cubic system. It is also known that such 
nucleating agent having a marked nucleating effect includes, for example, 
barium hydroxide and strontium for hydroxide calcium hydroxide 
hexahydrate. However, neither barium hydroxide nor strontium hydroxide as 
an alkaline material is applicable to sodium thiosulfate, for sodium 
thiosulfate is decomposed at an alkaline side. 
As a result of various experimental studies of a nucleating agent for 
sodium thiosulfate on such theoretical basis, it has been found that 
naphthalene has a remarkable nucleating action, as compared with other 
substances. Naphthalene has a low solubility in water (0.04 g in 100 g of 
water and less than 0.01 g in 100 g of sodium thiosulfate), can exist as 
nuclei in water, and has the same crystal form (monoclinic form) as sodium 
thiosulfate. From the viewpoint of said interfacial energy, it seems that 
the crystal of sodium thiosulfate pentahydrate is liable to grow on the 
naphthalene. Even a very small amount of the nucleating agent has some 
effect, but practically at least 0.01% by weight thereof must be added 
thereto on the basis of sodium thiosulfate. There is no upper limit 
thereto particularly in view of its function and effect, but a larger 
amount will reduce the heat-storing density, and thus a practical upper 
limit is about 10% by weight. 
FIG. 16 shows a model of heat-storing apparatus built up for determining 
the effect of a nucleating agent, where numeral 20 is a heat-storing 
vessel, numeral 21 a lid, and sodium thiosulfate pentahydrate is placed as 
a heat-storing material 5 in a heat-storing vessel 20. A heater 22 and a 
cooler is dipped in the heat-storing material 5. Numeral 24 is a 
nucleating agent added to the heat-storing material 5. When sodium 
thiosulfate pentahydrate is used as the heat-storing material 5, a 
nucleating material 24 is preferably naphthalene. The nucleating material 
24 has a smaller specific gravity than sodium thiosulfate (naphthalene has 
a specific gravity of 1.14 g/cm.sup.3, whereas sodium thiosulfate has a 
specific gravity of 1.73 g/cm.sup.3), and thus floats on the heat-storing 
material. 
In a test, hot water at 70.degree. C. is passed through the heater 22 to 
uniformly heat the heat-storing material 5 at about 70.degree. C., and 
then cold water at 20.degree. C. is passed through the cooler 23. 
FIG. 17 shows the test results, where the axis of abscissa shows time (min) 
from the start to pass cold water, whereas the axis of ordinate shows a 
heat release rate (Kcal/min) and the temperature (.degree.C. ) of 
heat-storing material 5 in the heat-storing vessel 20. In FIG. 17, a curve 
25 of full line shows the heat release rate, whereas a curve 26 of 
alternate long and short dash line show the temperature of heat-storing 
material. When no naphthalene is added to sodium thiosulfate pentahydrate 
as the heat-storing material, no solidification takes place, even if the 
temperature of heat-storing material is lower than the solidification 
temperature of 45.degree. C., as shown by curve 26a. That is, the 
temperature is continuously lowered. In that case, the heat release rate 
is also continuously lowered as shown by curve 25a, and reaches 
substantially zero after 50 minutes. On the other hand, when naphthalene 
is added thereto, supercooling by about 2.degree. C. takes place, as shown 
by curve 26b, but the lowered temperature is soon recovered to a 
solidification temperature of 45.degree. C. In that case, the heat release 
rate is kept substantially constant and higher than that of curve 25a 
after the start of solidification, as shown by curve 25b. 
As described above, supercooling can be effectively prevented by addition 
of naphthalene as a nucleating agent when sodium thiosulfate is used as a 
heat-storing material, and the nucleation effect can be further increased 
by further addition of at least one of phthalic anhydride, fumaric acid, 
benzoic acid, chlorobenzoic acid, ammonium thiosulfate, and naphthol to 
naphthalene. 
When sodium thiosulfate pentahydrate is used as a heat-storing material 
together with naphthalene as a nucleating agent and starch as a gelling 
agent for suppressing the phase separation phenomenon, starch turns into a 
colloidal state through liquefaction and the heat-storing material turns 
viscous material as described before, and encloses sodium thiosulfate 
pentahydrate to suppress the phase separation phenomenon. At the same 
time, starch encloses naphthalene to suppress such phenomena as floating 
of naphthalene as the upper layer in the heat-storing vessel or 
sublimation. 
Tests were conducted by changing mixing ratios of starch to sodium 
thiosulfate pentahydrate, and it was found that there is an optimum mixing 
ratio. In a smaller mixing ratio of starch, the phase separation is liable 
to occur, whereas in a larger mixing ratio no substantial nucleation 
supercooling is liable to take place. Supercooling is liable to take place 
in a smaller mixing ratio of starch due to the fact that starch cannot 
enclose the naphthalene as the nucleating agent completely due to the 
smaller amount of starch, and the naphthalene tends to float or sublimate. 
No substantial nucleation takes place in a larger mixing ratio of starch 
due to the fact that a larger amount of starch inhibits contacting of 
naphthalene with sodium thiosulfate pentahydrate. 
FIG. 18 shows the results of optimum mixing ratio of starch, where the axis 
of abscissa shows a mixing ratio .epsilon.(%) and the axis of ordinate 
shows a nucleation ratio .phi.(%). Nucleation ratio .phi. is a numerical 
value that represents how many times the solidification takes place at the 
specific temperature (solidification temperature: 45.degree. C.) through 
several tens of repetitions of solidification-melting cycle. It is seen 
from FIG. 18 that the nucleation ratio .phi. is substantially 100% at a 
mixing ratio .epsilon. of 1 to 4% by weight. Above a mixing ratio of 4% by 
weight, the viscous mixture tends to take air bubbles in, and the air 
bubbles are retained therein even by repetitions of heating and cooling. 
The thermal conductivity of heat-storing material becomes very low in such 
a state, and it is hard to release the heat from the heat-storing 
material. Thus, it is preferable that the mixing ratio .epsilon. does not 
exceed 4% by weight. When starch is added to sodium thiosulfate 
pentahydrate, the heat-storing material turns viscous through liquefaction 
of starch, and separation into two phases can be prevented, but the 
viscosity of heat-storing material is increased. Thus, the convection 
hardly takes place when the heat-storing material stores the heat, and 
thus the heat resistance becomes large, so that it takes much time in heat 
storing. To overcome such trouble, it is preferable to add metallic fibers 
or metallic cutting powders to a heat-storing material. The metallic 
fibers also serve to enclose masses of naphthalene as a nucleating agent 
to prevent them from floating as an upper layer. 
When naphthalene is added to the heat-storing material 5 as a nucleating 
agent in the heat-storing vessel with the porous material 15 provided on 
the inner wall at the low temperature part 4a, naphthalene undergoes 
sublimation through the heat cycle, and the sublimated naphthalene 
crystallizes porous material 15 on the inner wall at the low temperature 
part 4a in the heat-storing vessel 4. The crystals grow to a needle-like 
form and contact the liquid surface 5a of heat-storing material 5 to act 
again as the nucleating agent. 
In the embodiments shown in FIGS. 14 and 15, sublimation of naphthalene can 
be prevented by the porous material 15 on the liquid surface 5a of 
heat-storing material 5 when naphthalene is added to the heat-storing 
material 5 as the nucleating agent, and the reduction of the nucleating 
effect can be prevented. 
As described above, the phase separation phenomenon of heat-storing 
material can be suppressed, and supercooling can be prevented in the 
present invention, and thus heat storing and release can be effectively 
carried out.