JP3273361B2 - Solar heat collector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vacuum type solar heat collecting apparatus, and more particularly, to a vacuum type flat plate type solar heat collecting apparatus at 100.degree.
The present invention relates to a solar heat collecting apparatus capable of producing a high-temperature heat output exceeding the maximum.

[0002]

2. Description of the Related Art A conventional flat plate type solar heat collecting apparatus has a heat loss through a heat insulator supporting a heat absorbing plate for absorbing sunlight energy, or air around the heat absorbing plate, and an infrared ray from the heat absorbing plate. Since the radiation loss due to radiation is large, 80
It was difficult to efficiently obtain a high temperature of not less than ° C.

In a conventional flat plate type solar heat collecting apparatus,
To reduce the heat that escapes from the back of the heat sink, the back was covered with a solid thermal insulator. However, the best thermal insulator is a vacuum, and it is best to place the heat sink in a vacuum. Nevertheless, the reason why there was no flat type and no vacuum type was that the atmospheric pressure applied to the flat window and the housing was so large that it could not be supported economically. Therefore, the vacuum type flat plate type is not commercially available, and the vacuum type ones are all glass double tube type.

Conventionally, there was no flat plate vacuum type.
Particularly problematic when the vacuum, the measures for reducing the heat loss due to thermal radiation from the back of the heat absorbing plate has not been made. On the other hand, the drawback of the vacuum glass double tube method is that the radiation area of the glass tube when lost from the glass tube heated by sunlight to the outside due to the secondary radiation of infrared rays is smaller than the area of the incident sunlight. , Π / 2 times ≒ 1.6 times. In the case of a flat plate type, this ratio is 1: 1. The loss due to secondary radiation from the back that does not face sunlight is 1.6 times that of a flat glass tube.

[0005]

The problem to be solved by the present invention is to provide a solar heat collecting apparatus which has been used in the past.
In order to be able to use it as a heat source with a temperature much higher than 100 ° C, such as 200 ° C, instead of a heat source below 100 ° C, or to obtain a solar heat collecting device that is much more efficient than conventional products in the region below 100 ° C How to greatly reduce the heat loss from the heat absorbing plate of the solar heat collecting device.

One of the heat losses is mainly caused by infrared radiation emitted from the heated endothermic plate. When the temperature of the heat absorbing plate is high, the radiation loss is large. For example, a heat absorbing plate having an emissivity of 0.9 at 150 ° C. has an emissivity of 0.3 at 30 ° C.
The energy radiated to the gray radiator around 9 reaches about 1 kW / square meter even from only one side of the heat absorbing plate. The radiation loss from the heat absorbing plate is one from the surface of the heat absorbing plate toward the window, and the other from the back of the heat absorbing plate toward the housing. Therefore, the radiation loss of the 1 square rice heat absorbing plate reaches about 2 kW for both sides. On the other hand, the energy received from the sun from the heat absorbing plate is about 800 W / sq. In the case of the glass double tube system, since the radiation area is larger than that of the flat plate system, the problem of the radiation loss is further serious.

That is, a high temperature such as 200 ° C. cannot be obtained by a solar heat collecting apparatus which does not converge sunlight unless special measures are taken. When the temperature at which the radiation loss from the heat absorbing plate under the same conditions as described above becomes about 800 W / square meter is roughly calculated, it is about 80 to 90 ° C. Since the radiation loss is large, reducing this loss is essential for obtaining a high-temperature solar collector.

Another loss is due to heat conduction of air around the heat absorbing plate, heat transfer by convection of air, and heat conduction through a thermal insulator supporting the heat absorbing plate. When the heat absorbing plate is placed at atmospheric pressure, the loss due to air conduction and convection has a large loss almost equal to the loss due to radiation. That is, heat loss is caused by radiation and heat conduction. These two losses occur from both sides of the heat absorbing plate. In order to reduce these two losses, it is necessary to provide a means for maintaining the degree of vacuum around the heat absorbing plate at a level close to vacuum, and a means for reducing the loss due to radiation from the bottom of the heat absorbing plate to the housing, particularly of the loss due to radiation. It is an object of the present invention.

[0009]

In order to reduce the loss due to air, the air pressure in the housing including the heat absorbing plate is reduced to a degree of vacuum such that the heat conduction by the residual air in the housing becomes heat conduction under free molecular conditions. I do.

In order to reduce radiation loss from the back of the heat absorbing plate, a flat heat absorbing plate is used, and the area of the heat absorbing plate is made almost the same as the area of the housing, so that the rear surface of the heat absorbing plate is made to be a space close to a closed space. Then, the view factor relating to radiation is brought to a state close to 1. Then, the emission ratio of the back surface of the heat absorbing plate and the bottom surface of the housing facing the heat absorbing plate is reduced. Although these measures reduce the radiation loss, the present invention provides a means of further reducing the loss, by making the degree of vacuum in the housing, as described above, heat transfer under free molecular conditions, In addition, one or more partition walls having a metal reflecting surface are provided between the heat absorbing plate and the housing in parallel with the heat absorbing plate.

[0011] In this case, both the heat transfer by the residual air and the heat transfer by the radiation are reduced. Thermal insulation called so-called super insulation is performed. For this purpose, the degree of vacuum is set such that the mean free path of the air molecules is considerably larger than the distance between the partition and the partition, or between the partition and the heat absorbing plate, or between the partition and the housing. Specifically, in the case of the present solar heat collecting apparatus, since the interval is about 5 to 10 mm, the vacuum is set to about 0.1 Pascal or less at which the mean free path of air becomes about 6 cm, and then the partition wall is formed as described above. Is adopted.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a simplified structural view showing the outline of the structure of a solar heat collecting apparatus according to an embodiment of the present invention, where (a) is a plan view and (b) is AB in FIG. It is the cross section cut.

In FIG. 1, 1 is a solar heat collecting device, 2 is a housing, 3
Is a window for taking in sunlight, 4 is a heat absorbing plate, 5 is a selective absorbing film provided on the surface of the heat absorbing plate 4, 6 is a selective filter provided between the window 3 and the heat absorbing plate 4, and 7 is a heat absorbing plate. , A reflecting film provided on the bottom surface of the housing 2, and a metal reflecting surface 9 provided between the reflecting film 8 and the heat absorbing plate 4 in parallel with the heat absorbing plate 4. The partition wall 10 is a pillar connecting the bottom of the housing 2 and the window 3 to support the window 3, 11 is a hole formed in the partition wall 9 so that the pillar 10 does not touch the partition wall 9, and 12 is a pillar 1
0 is a hole formed in the heat absorbing plate 4 so as not to touch the heat absorbing plate 4, 13 is a pipe for passing a heat medium through which the heat absorbed by the heat absorbing plate 4 is taken out, and 14 is a column supporting the heat absorbing plate 4. is there.

The housing 2 is shaped like a flat box-like container, the top is covered with a window 3 made of transparent glass or a composite material of glass and plastic, and the bottom of the housing 2 is flat. It is formed so as to be substantially parallel to the window 3. A closed space is formed by the housing 2 and the window 3,
The inside is kept in a vacuum, and a heat absorbing plate 4 which receives sunlight and converts it into heat energy is provided at an intermediate position between the window and the window 3 in substantially the same area as the window 3. The partition wall 9 is installed in parallel with the back surface of the heat absorbing plate 4 so as not to touch the heat absorbing plate 4.

A large number of pillars 10 are arranged almost uniformly over the entire area of the window 3 for receiving sunlight, and the inside of the housing 3 and the atmospheric pressure received by the window 3 from above and below in FIG. Support. Since the atmospheric pressure is dispersed and received by many pillars 10, the window 3 can be made of thin glass or plastic.

When the temperature of the heat-absorbing plate 4 rises due to the absorption of sunlight, the heat-absorbing plate 4 emits radiation to an object having a temperature lower than that temperature in proportion to the difference between the absolute powers of the fourth power. Do. The temperature of the heat absorbing plate 4 that can be used is at most 300 ° C
Since it is of the lower order, its emission occurs almost at the wavelength in the infrared region. In a solar heat collecting apparatus employing vacuum heat insulation, heat loss occurs due to heat transfer by residual air and radiation from the heat absorbing plate 4. In order to reduce this loss, a partition 9 is provided. In order to prevent heat from being wastefully escaping to the housing 2 or the like by the heat conduction from the partition 9 where the column 10 touches the partition 9 and the temperature of which rises from the partition 9, the column 10 does not touch the partition 9. A hole 11 sized to penetrate the partition 9 is provided.

In order to reduce the heat transfer loss, the pressure in the housing is reduced to a degree of vacuum at which the molecules of the remaining air become free molecular conditions. Assuming that the mean free path of the air molecule is λ, λ is approximately expressed by Equation 1. λ = 0.66 / p [Pa] m (1) According to Equation 1, the mean free path of air molecules under a pressure of 0.1 Pascal is about 6.6 cm. As shown in Equation 1, the value of the mean free path is inversely proportional to the atmospheric pressure.

Assuming that the distance between the two surfaces performing the heat transfer is d,
When the condition of d と き λ is established between d and the mean free path λ of the air molecule, it is said that the free molecule condition is satisfied. When the pressure is low and the free molecular condition is satisfied, as is well known, the flow of thermal energy by air molecules does not depend on the temperature gradient, but depends on the temperature difference between the hot surface and the cold surface as the boundary condition. It is proportional and does not depend on the distance between these two surfaces. It is proportional to pressure. Since the flow of thermal energy by air molecules does not depend on the distance between the two surfaces, thermal insulation is improved by providing a large number of partition walls 9 perpendicular to the flow of heat. This is a thermal insulation method called super insulation. At this time, the material for forming the partition wall 9 may be metal, glass, paper, or plastic, and there is almost no difference in the effect.

The loss due to the radiation mainly composed of infrared rays from the back surface of the heat absorbing plate 4 is suppressed by increasing the reflectivity of the infrared rays on the surface, in other words, reducing the emission rate of the infrared rays. The partition walls 9 are similarly treated to reduce the emission rate of infrared rays in order to reflect radiation from the heat absorbing plate 4 and reduce loss due to radiation. The emission rate of the back surface of the heat absorbing plate 4 and the surface of the partition wall 9 does not need wavelength dependency unlike the selective absorption film 5 of the surface of the heat absorbing plate 4 and may be any as long as the emission rate is small at a wavelength in the infrared region. The magnitude of the emission rate in the visible light region is not a problem, and may be the same as in the infrared light region.

A typical good method for reducing the infrared radiation is to use a metal having good electrical conductivity such as gold, silver, copper, or aluminum as the reflection surface. These metal plates may be used as reflectors as they are, but vacuum-deposited films made by rapidly vapor-depositing these metals in a high vacuum have a very high reflectivity and are suitable for infrared rays with wavelengths longer than 1 micron. On the other hand, the reflectivity is around 98%. A metal film formed by sputtering or chemical plating instead of vapor deposition reflects infrared rays well, though not as much as a vacuum vapor deposited film. If the partition 9 itself is a good metal conductor, its surface can be mechanically or chemically polished so that the surface reflects infrared rays well.

The best of these reflecting surfaces is
Silver, copper, or gold is vacuum-deposited and has a reflectance of 98% or more to infrared rays. Among them, silver has the best characteristics and a reflectance close to 99%.

As a substrate on which these metals are deposited or plated, a metal foil or a metal plate, glass, a plastic film or the like is suitable. Since the partition wall 9 used in the solar heat collecting apparatus having a high temperature output is used at a temperature around 200 ° C., when a plastic film is used as a substrate, a material that can withstand high temperatures such as a polyimide film is used.

As in the solar heat collecting apparatus 1 of the present invention, the back surface of the heat absorbing plate 4 which is a radiation surface and the bottom surface of the housing 2 which is a reflection surface,
The area of the three members of the partition 9 is almost the same and almost in a closed state,
If the view factor for radiation is considered to be approximately one, then the heat transfer by radiation, like the heat transfer by residual air,
It is determined by the reflectance of the two surfaces and the temperature difference between the two surfaces without depending on the distance between the two surfaces related to radiation.

When the partition 9 is provided between the heat absorbing plate 4 and the housing 2, the temperature of the partition 9 becomes an intermediate temperature between the temperature of the heat absorbing plate 4 and the temperature of the housing 2, and the temperature difference between the two surfaces is divided. Therefore, the radiation loss from the heat absorbing plate 4 can be reduced by the above-described principle.

That is, by sufficiently lowering the air pressure inside the housing and providing the partition wall 9 having a metal surface having a good infrared reflectance, the loss due to the heat transfer due to the remaining air, the heat absorption plate 4 and the housing 2
Between the two radiation losses can be reduced at the same time. For example, when one partition 9 is provided, the loss is reduced to half, and when two partitions are provided, the loss is reduced to about 1/3.

According to the present invention, the atmospheric pressure in the housing is reduced to free molecular conditions, and a metal reflecting surface having a low infrared emission rate is provided between the surface of the heat absorbing plate and the housing surface facing the heat absorbing plate. heat by providing the partition, escaping in vain from the heat absorption plate heated to a high temperature by the sun energy entering shines to the external space with, i.e., the loss of heat transfer due to the residual air
And reduce radiation loss from the heat absorbing plate to the housing.
it can. Therefore, it is possible to obtain a solar heat collecting device having a high output temperature without converging sunlight with a lens or the like, and it is possible to apply solar energy to a wide range of uses, and the industrial effect is great.

[Brief description of the drawings]

FIG. 1 is a schematic structural diagram showing the structure of a solar heat collecting device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Solar heat collection apparatus 2 Housing 3 Window 4 Heat absorption plate 9 Partition wall 10 Hole

Claims (3)

(57) [Claims] 1. A flat panel that receives sunlight and converts it into heat energy.
Comprising a heat absorbing plate of the plate, the solar collector device of the vacuum plate type in which the inside of the housing to a high degree of vacuum, and the back surface of the heat absorbing plate between the bottom of the housing opposite to the back surface, the of approximately the same area as the area of the heat absorption plate, the partition walls have a good metal surface reflectance infrared solar collector device, characterized in that provided in parallel with the heat absorbing plate. 2. A solar heat collecting apparatus according to claim 1, characterized in that the air pressure inside of the casing below 0.1 Pascal. 3. The method according to claim 1, wherein the partition is made of metal, glass, plastic, or the like.
請 characterized the kite forms any of a click of a material by depositing metal having excellent electrical conductivity on the surface thereof as a base material
The solar heat collection device according to claim 1 or 2 .