Abstrict
The present invention relates to a heat storage element having
a latent heat storage material sealed in the container under a reduced
pressure. This heat storage element permits effective reduction
of air in the heat storage element, and therefore, heat is smoothly
transferred from outside to the latent heat storage material through
the wall of the container. Accordingly, a heat storage element which
has a very high heat storage characteristic is realized. Furthermore,
this heat storage element, having almost no air sealed in, has a
large heat storage density. When this heat storage element is used
in combination with an electric heater element, heat will be uniformly
transferred from the electric heater element to the latent heat
storage material, involving a very small risk of part of the electric
heater element being overheated.
Claims
What we claim is:
1. A heat storage element comprising a latent heat storage material
and a flexible container for housing this heat storage material,
said heat storage material being hermetically sealed in the flexible
container under a reduced pressure and said heat storage material
closely contacting the inner surface of said container.
2. The heat storage element of claim 1, wherein air pressure under
which said latent heat storage material is hermetically sealed in
the container falls within the range between 1 mmHg and 200 mmHg.
3. The heat storage element of claim 1, wherein said container
is formed of a metal-plastic plastic laminate film having at least
one layer of metal and a fusing layer.
4. The heat storage element of claim 1, wherein said latent heat
storage material is a mixture of sodium acetate trihydrate and sodium
pyrophosphate.
5. The heat storage element of claim 1, wherein said latent heat
storage material is a mixture of sodium acetate trihydrate and lithium
fluoride.
6. The heat storage element of claim 1, wherein said latent heat
sotrage material is sealed in a flexible gas-permeable bag, said
bag being hermetically sealed in the container under a reduced pressure.
7. The heat storage element of claim 6, wherein said gas-permeable
bag is formed of paper or cloth having a fusing layer.
8. An electric heater comprising a latent heat storage material
a flexible container for housing this heat storage material and
said heat storage material closely contacting the inner surface
of said container, and an electric heater element arranged in close
contact with said container having this heat storage material hermetically
sealed therein, said electric heater being designed to have said
heat storage material hermetically sealed in the container under
a reduced pressure.
9. The electric heater of claim 8, wherein said electric heater
element is a plane configured positive temperature coefficient electric
heater element.
10. The electric heater of claim 8, wherein said electric heater
element is bonded on the outside surface of the heat storage element.
11. The heat storage element of claim 8, wherein said latent heat
storage material is a mixture of sodium acetate trihydrate and sodium
pyrophosphate.
12. The heat storage element of claim 8, wherein said latent heat
storage material is a mixture of sodium acetate trihydrate and lithium
fluoride.
13. A heat storage element comprising a latent heat storage material
which is either one of a mixture of sodium acetate trihydrate and
sodium pyrophosphate, and a mixture of sodium acetate trihydrate
and lithium fluoride, and a container formed of a laminate film
for housing said storage material, said heat storage material being
hermetically sealed in the container under a reduced pressure.
14. The heat storage element of claim 13 further comprising an
electric heater element arranged in close contact with the container
having the heat storage material hermetically sealed therein.
Description BACKGROUND OF THE INVENTION
The present invention relates to a heat storage element for use
in heating apparatuses, etc., and an electric heater using the same.
Heretofore, when using a latent heat storage material hermetically
sealed in a flexible container, the mouth of the container was sealed
under atmospheric pressure, after a solid or liquid latent heat
storage material had been filled in the container.
When such a sealing method is utilized and if the latent heat storage
material is in granular shape, more than 33% of the volume of the
container is occupied by air which is sealed in together therewith.
Moreover, as this element is heated, the air inside the container
will expand and its proportion will further increase. If any air
exists inside the heat storage element, the heat is transferred
from outside to the heat storage material through this air layer;
therefore, the heat transfer becomes harder than when the air layer
does not exist, resulting a longer time being taken before the storing
of heat has been accomplished. It is only natural that if the heat
storage material and air are concurrently sealed in the heat storage
element, the heat storage density per unit volume of the heat storage
element will diminish. If the latent heat storage material in liquid
state is sealed in a flexible container and the container is to
be hermetically sealed, with the air content down, the liquid will
come up to the fusing part (the mouth of the container) as the fusing
layers are brought together, to be adhering thereon, thus detracting
from proper sealing. Although the sealing for housing appears to
be proper, the housings are easily opened by a small external pressure.
Then it is inevitable concurrently to seal into the container a
large amount of air in order to ensure the sealing; as a consequence,
the heat storage characteristic is affected, with reduced heat storage
density, as in the case of heat storage element having a granular
latent heat storage material sealed in. Besides, when this heat
storage element and an electric heater element are used in combination,
because of the existence of air in the heat storage element, almost
no heat is transferred to the heat storage material from the electric
heater element part in the neighborhood of the air. Therefore, the
temperature of the electric heater element at that part rises very
high, sometimes with a risk of burning.
SUMMARY OF THE INVENTION
A first object of this invention is to provide a heat storage element
which requires only a short time for storing heat.
A second object of this invention is to provide a heat storage
element having a high heat storage density per unit volume.
A third object of this invention is to provide a heat storage element
which permits easy hermetic sealing.
A fourth object of this invention is to provide an electric heater
which permits heat transfer from the electric heater element to
the heat storage element at a high efficiency.
A fifth object of this invention is to manufacture a safe electric
heater in which the electric heater element does not arouse local
abnormal heating.
These and other objects are accomplished by a heat storage element
which comprises a latent heat storage material and a container housing
this storage material; the heat storage material is hermetically
sealed in the container under a reduced pressure.
In a specific embodiment, the air pressure under which the latent
heat storage material is hermetically sealed in the container should
fall within the range of from 1 mmHg to 200 mmHg. The container
is formed of a metal-plastics laminate film having at least one
metal layer and a fusing layer. The latent heat storage material
is sealed in a gas-permeable flexible bag and this bag is hermetically
sealed in this container at a reduced pressure. The gas-permeable
bag is made of paper or cloth having a fusing layer. Further, the
aforementioned latent heat storage material is formed of a mixture
of sodium acetate trihydrate and sodium pyrophosphate. The container
is formed of a laminate film. In another specific embodiment, the
latent heat storage material is formed of mixture of sodium acetate
trihydrate and lithium fluoride.
This invention also relates to an electric heater which comprises
a latent heat storage material and a container housing this heat
storage material, which is designed to have the heat storage material
hermetically sealed in this container and which comprises an electric
heater element arranged in close contact with the container having
this storage material sealed therein.
In a specific embodiment, the electric heater element is a plane
electric heater element. 0n the outside surface of the heat storage
element, an electric heater element is bonded.
This invention has various advantages, among which are as follows:
(1) It provides a heat storage element which permits smooth transfer
of heat from outside to the latent heat storage material through
the wall of the container.
(2) It provides a heat storage element which gives a very high
heat storage characteristic.
(3) It provides a heat storage element which has a large heat storage
density.
(4) It provides an electric heater which can afford proper heat
transfer from its electric heater element, when the heat storage
element is used in combination with the electric heater element.
(5) It provides an electric heater in which part of the electric
heater element may not be abnormally overheated because the heater
element is in uniform contact with the latent heat storage material,
thereby permitting uniform transfer of heat.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front sectional view of a heat storage element of a
first embodiment of this invention;
FIG. 2 is a graph showing the heat storage characteristic of this
heat storage element;
FIG. 3 is a front sectional view of a heat storage element of a
second embodiment of this invention;
FIG. 4 is a front sectional view of a heat storage type electric
heater embodying this invention; and
FIG. 5 is a graph showing the heat storage characteristic of this
heat storage type electric heater.
DETAILED DESCRIPTION OF THE INVENTION
The heat storage element and the electric heater using the same
of this invention are described hereunder in connection with a few
preferred embodiments and by reference to the accompanying drawings:
(EXAMPLE 1)
A heat storage element as shown in FIG. 1 was manufactured for
trial. Employed as the latent heat storage material is a system
of sodium acetate trihydrate with the addition of 2 percent by weight
of sodium pyrophosphate as the anti-supercooling agent and used
as the flexible container is a laminate film of a metal and plastics
which involves no problem of causing evaporation of part of the
component of the heat storage material (mainly water content) at
the time of storing heat. According to a preferred embodiment of
this invention, taking into account the strength, etc., of the container,
a laminate film composed of 4 layers--from the outside, 12 .mu.m
polyester layer, 15 .mu.m drawn nylon layer, 9 .mu.m aluminum foil
layer, and 80 .mu.m polyethylene layer--was utilized. In the case
of this laminate film, it was the innermost layer which was fused.
Two such laminate films were put together and fused at necessary
parts and therewith, a container having internal dimensions of 40
mm.times.60 mm was formed. In this container, 8 g of a granular
latent heat storage material is hermetically sealed under various
air pressures, as shown in Table 1 below:
TABLE 1 ______________________________________ Time required for
Sample Air pressure at accomplishing the No. the sealing time storing
of heat ______________________________________ 1 0.1 mmHg 16 min.
2 1.0 16 min. 3 10 16 min. 4 50 16 min. 5 100 16 min. 6 300 20 min.
7 500 23 min. 8* 760 35 min. ______________________________________
*Sample 8 is presented as an example which is used for being compared
wit the embodiments of the invention.
With the heat storage element manufactured in this way placed horizontally
and a heating plate containing a heater and subjected to temperature
control at 70.degree. C. placed thereon, the temperature at the
bottom of the container is measured, using a thermocouple. The temperature
change of Sample 2 is depicted in FIG. 2. In this graph, the ordinate
represents the temperature at the bottom of the container, while
the abscissa gives the passage of time after the heating plate was
placed. And used as the measure of the time required for accomplishing
the storing of heat was the passage of time taken before the temperature
at the top of the container had risen over the transition temperature
(58.degree. C.) and reached 60.degree. C. This time is indicated
by an arrow mark in the drawing. The times required for accomplishing
the storing of heat are listed in Table 1, together with the air
pressures at the sealing time.
This table shows that when the air pressure at sealing time was
lower than 100 mmHg, the time required for accomplishing the storing
of heat was always 16 minutes. When it was 300 mmHg, the time required
was 20 minutes, a little longer than the above. And under 760 mmHg,
as long as 35 minutes is taken before accomplishing the storing
of heat, which is longer about 120%, as compared with the time taken
by the heat storage element which was hermetically sealed under
a pressure lower than 100 mmHg.
For reduction of pressure, a vacuum pump is necessary and in order
to elevate the degree of vacuum, long duration suction is necessary.
To obtain a degree of vacuum of the order of 1 mmHg, an ordinary
rotary pump is adequate, but to further elevate the degree of vacuum,
a very long period of suction with a rotary pump or joint use of
other vacuum pump is necessary. In that way, naturally the cost
of the heat storage element is too high for it to be practically
usable. As a final point, the desirable pressure range should fall
within the range of between 1 mmHg and 200 mmHg.
It should be noted that lithium fluoride may be added as the anti-supercooling
agent.
(EXAMPLE 2)
A heat storage element as shown in FIG. 3 was manufactured for
trial. The latent heat storage material 1 and the flexible container
2 used were similar as those of Example 1. According to this embodiment,
in order to prevent imperfect hermetic sealing resulting from adherence
on the sealing mouth of the soaring-up powder of the heat storage
material, the latent heat storage material was preliminarily sealed
in a gas-permeable bag and was, thereafter, hermetically sealed
in a flexible container under a reduced pressure. As the gas-permeable
bag, one formed of paper or cloth having a fusing layer was considered
to be suitable from the standpoint of mass-production. According
to this embodiment, a bag made of a nonwoven cloth having a thermally
fused layer of polyethylene on the inside was employed.
When the hermetic sealing was made under the similar air pressure
condition as in Example 1, the heat storage element obtained gave
a heat storage characteristic barely distinguishable from that in
Example 1.
It should be appreciated that when a person having a body weight
of approx. 60 kg had trampled the heat storage element of this example
after heat has been stored therein, no leakage of heat storage material
from the container was found at all.
(EXAMPLE 3)
A heat storage type electric heater (An electric heater using a
heat storage element) as shown in FIG. 4 was manufactured for trial.
The latent heat storage material 1 and the flexible housing container
material used were similar to those in Example 1.
Two laminate films were put together with necessary parts thermally
fused and therewith a container of 100 mm.times.100 mm in internal
dimensions was formed. In this container, 40 g of a granular latent
heat storage material was filled and hermetically sealed under various
air pressure as shown in Table 2 below. On one surface of the heat
storage element manufactured in this way, a plane configured positive
temperature coefficient electric heater element 4 (control temperature:
approx. 80.degree. C.) was pasted by use of an adhesive tape. This
heat storage type electric heater was held between approx. 1 cm
heat insulating material of expanded polyurethane and so installed
as to bring the heater surface to the bottom. Evaluation of the
heat storage characteristic was made by measuring with a thermocouple
the temperature of the central part of the heat storage element
on opposite side of the electric heater element. FIG. 5 exhibits
the heat storage characteristic of Sample 2. In this graph, the
ordinate gives the temperature at the center of the heat storage
element on opposite side of the electric heater element, while the
abscissa represents the time elapsed after the energization has
begun. And used as the measure of the time required for accomplishing
the storing of heat was the time elapsed before the temperature
of the heat storage element has risen over the transition temperature
of the heat storage material (58.degree. C.) and reached 60.degree.
C., just as in the case of Example 1. This time is indicated by
an arrow mark in the graph. The times required for accomplishing
the storing of heat which were measured in this manner are indicated
in Table 2 along with the air pressures at the sealing time.
This table shows that when the air pressure at the sealing time
is lower than 100 mmHg, the time required before accomplishing the
storing of heat is nearly constant and within 23 minutes, but under
an air pressure of 300 mmHg, 29 minutes is required. And under 760
mmHg (atmospheric pressure), as long as 62 minutes are taken before
the storing of heat has been accomplished. Thus approx. 170% more
time is required, as compared with that when the sealing is done
under a pressure of below 100 mmHg.
TABLE 2 ______________________________________ Time required for
Sample Air pressure at accomplishing the No. the sealing time storing
of heat ______________________________________ 1 0.1 mmHg 22 min
2 1.0 22 min 3 10 22 min 4 50 22 min 5 100 23 min 6 300 29 min 7
500 40 min 8* 760 62 min ______________________________________
*Sample 8 is presented as an example which is used for being compared
wit the embodiments of the invention.
(EXAMPLE 4)
Used as a latent heat storage material was a system of sodium acetate
trihydrate with addition of 2 percent by weight of lithium fluoride
as the anti-supercooling agent, and utilized as the container material,
a laminate fiim formed of 4 layers--from outside, 12 .mu.m polyester
layer, 40 .mu.m polyethylene layer, 9 .mu.m aluminum foil layer
and 150 .mu.m polyethylene layer. Such a laminate film is folded
in two and thermally fused at necessary parts. Forty grams of a
latent heat storage material was sealed in a gas-permeable bag made
of a similar material at that of Example 2 and this bag was hermetically
sealed in a flexible container made of the laminate film under an
air pressure of 10 mmHg. The electric heater element used was arranged
in a plane with a linear pyrogen normally electrically insulated
at its surface held between laminate films formed of 3 layers--from
the outside, 12 .mu.m polyester layer, 20 .mu.m aluminum foil layer
and 80 .mu.m polyethylene layer. This electric heater element and
the heat storage element were patched together, using an epoxy base
adhesive, whereby the heat storage type electric heater of this
embodiment was obtained.
On this heat storing electric heater, a bimetal type temperature
control which was set to operate at 80.degree. C. was mounted and
its heat storing characteristic was measured. The time required
for storing of heat was 25 minutes, which was an equivalent characteristic
to that of Example 1. A product of the same construction but in
which its heat storage material was sealed under atmospheric pressure
took as long a time as 70 minutes before accomplishing the storing
of heat.
While specific embodiments of the invention have been illustrated
and described herein, it is realized that modifications and changes
will occur to those skilled in the art. It is therefore to be understood
that the appended claims are intended to cover all modifications
and changes as fall within the true spirit and scope of the invention. |