JPS5819014B2 - Heat pipe for solar collector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a solar thermal energy absorption structure and a thermal energy transfer structure in a solar collector.

There are various types of solar energy absorption and transfer structures in solar collectors, but all of them have advantages and disadvantages, such as poor thermal efficiency, complicated structures, and the possibility of collapse.

The most common type is a flat collector.

In this method, a solar heat absorption film is formed on one side of a flat metal plate, and a metal tube is formed or glued on the back side of the metal plate, and the heat energy absorbed from the absorption film surface is heated to the metal tube by thermal conduction.
It exchanges heat with a heat medium liquid such as water on its inner wall.

This is because the energy density of the light-receiving surface is low, so high temperatures cannot be obtained.

Therefore, even if heat is maintained using a heat insulating material, a large amount of energy is dissipated and dissipated from the back side of the light receiving surface.

A circulation device for circulating water or heat transfer fluid is essential.

The structure of the solar collector as a whole is complex, which causes problems such as frequent failures.

Another type of solar collector is the plastic tube type.

This system stores water in large-diameter pipes that have good solar heat absorption, and the energy absorbed on the surface of the plastic pipe is directly exchanged with the inner wall of the pipe to obtain hot water, which has the advantage of an extremely simple structure. Problems include that the response time from the start of light reception to the start of heat exchange is slow due to the poor thermal conductivity of plastic, and that high temperatures cannot be obtained because the heat absorption efficiency is low and the received light energy density is low.

Furthermore, there is a vacuum glass tube type receiver tube as a thermal energy absorbing structure of a solar collector.

This has a structure in which a metal tube with metal fins is enclosed in a vacuum glass tube, so there is no heat loss due to air convection, loss from the back side of the light receiving surface is extremely small, and heat is absorbed by re-reflection on the inner surface of the glass tube. It has the advantage of additional heat absorption from the back side.

This structure is more efficient than a normal flat collector, and because of the glass tube's lens effect and internal re-reflection, the received heat energy density is high and high temperatures can be obtained.

While hot water of about 60°C can be obtained with a normal flat light receiving surface, hot water of about 80°C can be obtained, so it can be used for air conditioning without the aid of a heat pump or the like.

However, the structure is complicated, and a circulation device for water or heat transfer fluid is also essential as in the flat plate type.

Another problem is that vacuum glass tubes require great care when transporting and installing them, and are always at risk of breakage even after the solar collector system is in operation.

If a flat collector has a structure with a protective glass plate, there is a risk of damage due to flying objects during strong winds, but damage to the protective glass does not pose a problem in system operation.

However, in the case of a vacuum tube type, damage to the vacuum glass tube means a decrease in the received light energy density and a drastic increase in convective heat loss, resulting in fatal damage to the system.

Vacuum glass tubes have no convection loss, so the fins that are the light-receiving surface are not provided with any kind of insulation and heat-retention means.
Most of the absorbed heat energy is dissipated due to the influence of wind from outside the collector.

In addition to complete damage to the vacuum glass tube, vibrations caused by strong winds,
Even a decrease in the degree of vacuum due to incorrect installation due to freezing may lead to a significant decrease in functionality.

A further improved structure of the vacuum glass tube thermal energy absorption method is a method in which a finned heat pipe is enclosed.

In this case, due to the excellent heat transfer ability of the heat pipe, the thermal efficiency is further improved compared to the usual vacuum tube type, and the circulation of water or heat medium liquid has the advantage that the device can be simplified.

However, it is similar to ordinary vacuum glass tube collectors in terms of vulnerability to strong winds, typhoons, etc.

Furthermore, as another type of solar heat collector, heat transfer liquid can be used as a solar heat collector.
There is a vacuum glass tube type collector that uses a solar light focusing method that uses a heat pipe to absorb and transfer heat energy and heat it to a high temperature of ℃ or higher and use it for solar power generation.

This is a structure in which a heat pipe is supported at the focal point of a reflective plate with an animal linear curved surface, and a heat-resistant solar heat absorbing film is formed on the entire surface of the heat pipe.

This method has the advantage of good thermal efficiency and can easily reach high temperatures, but the problem is that the diameter of the heat pipe is small compared to the light receiving area, so in order to concentrate sunlight on the surface of the heat pipe, it is necessary to use a parabolic curved surface. Since it is necessary to precisely manufacture the curved structure of the reflecting mirror or reflecting plate, the equipment cost is also high.

Another problem is that in order to effectively focus sunlight on the surface of the heat pipe, it is necessary to precisely track the direction of sunlight.

The heat pipe for a solar heat collector according to the present invention is intended to improve the problems of the solar heat absorption and transfer structure used in the conventional solar heat collector as described above, and to provide a highly efficient and simple structure.

As mentioned above, the flat plate type collector conducts the solar heat energy absorbed from the light receiving plane to the metal tube bonded to the back side of the light receiving plane, and exchanges heat with the water or heat transfer liquid circulating inside the metal tube on the inner wall of the metal tube. However, it required complicated piping, pressure pumps, and power for circulating water or heat transfer fluid.

In order to simplify this, by using a heat pipe instead of a metal tube, at least the back piping of the solar heat receiving plane can be greatly simplified.

That is, the heat pipe can transfer thermal energy from the heat absorbing section to the heat dissipating section extremely efficiently without requiring any power or the aid of any equipment due to the action of the working fluid in the container.

However, it is impossible to prevent radiation loss from the metal surface between the metal tubes or between the heat pipes on the back side of the light-receiving plane, and the same is true in both cases.

In order to prevent this loss, ordinary flat collectors are insulated with heat insulating material, but even if excellent heat insulating material is used, considerable loss is inevitable.

A vacuum tube type collector was devised to eliminate this loss, but as mentioned above, it still has some problems.

A new type of heat pipe, which is a solar heat absorption and transfer structure according to the present invention, will be described in detail below with reference to the drawings.

FIG. 1 is an external view of a heat pipe for a solar collector according to the present invention, and FIG. 2 is a sectional view thereof.

Reference numeral 1 denotes a heat absorbing portion of the heat pipe body, and in this embodiment, three heat absorbing fins 2 are welded to the outer periphery of the container.

The heat absorbing fins are provided in continuous motion over the entire length of the heat absorbing portion A of the heat pipe.

Furthermore, the tips of the heat absorbing fins 2 are hermetically welded to predetermined positions of adjacent fins, and the entire structure is formed into a hollow cylindrical structure 3 as shown in the drawings.

At both ends of the cylindrical structure, lids 9, 9' are hermetically welded and sealed.

Further, a solar heat absorbing film 4 is provided on the entire outer surface.

This absorption film may be provided by any method such as coating, baking, or forming on the surface by chemical treatment.

The absorbing film 4 may be a black paint with good solar heat absorption efficiency, but even better characteristics can be obtained if it is a selective absorbing film that absorbs most of the sunlight and emits almost no infrared rays.

1 is a ventilation hole, which is provided as a means to provide slight ventilation between the inside and outside in order to prevent deformation of the hollow columnar structure due to expansion and contraction of air within the hollow columnar structure during solar heat absorption operation and when the operation is stopped. It is something.

The ventilation holes 7 are not necessarily provided in the illustrated positions, but may be provided in the lids 9, 9', etc.

5 is a heat radiation part of the heat pipe main body, and 6 is a heat radiation fin.

8 is a heat insulating layer for preventing heat loss from the heat transfer section.

Although one embodiment of the heat pipe for a solar heat collector according to the present invention has been described above, its cross-sectional shape does not necessarily have to be a hollow cylindrical structure as shown in FIG.

Hollow columnar structures of various shapes may be employed depending on the design of the applied solar collector.

Figures 3a, b, c, and d show various cross-sectional shapes, respectively.

The features of c and d are that they have a special shape in which the tip of the heat absorbing fin and the welded part to the heat pipe body are not clearly distinguishable.

FIG. 4 is a sectional view of an embodiment in which the heat pipe according to the present invention is applied to a solar collector.

In the figure, 11 is a heat pipe according to the present invention, and 12 is a reflecting plate or reflecting mirror having a parabolic curved surface for reflecting sunlight into the hollow columnar structure of the heat pipe.

Since the hollow cylindrical structure occupies a sufficiently large external area compared to the area of the light-receiving plane of the collector, the parabolic curved surface does not need to be a precise curved surface.

For the same reason, another major feature is that even if the sunlight indicated by the arrow is not necessarily projected from the vertical direction, the reflected light is certainly reflected onto the surface of the hollow cylindrical structure.

13 is a heat insulating layer, 14 is a protective glass plate, and 15 is a collector protection plate.

The heat pipe for solar heat collector according to the present invention has the above-described structure and is used as shown in the usage example in Fig. 4.
It exhibits the following unique functions and effects.

For convenience of explanation, we will assume that a solar collector as shown in Figure 4 is applied to an air-conditioning, heating, and hot water supply system, and the heat pipe is a copper container water-operated type with a diameter of 13 m.
The operation will be explained assuming that the diameter of the hollow cylindrical structure is 50 m and the diameter of the sunlight receiving plane, that is, the entrance of the reflecting mirror is 300 rrrrn.

(1) Since the surface temperature does not become higher than necessary, radiation loss from the surface is extremely small.

1 if the heating medium is water in an operating air conditioning, heating, and hot water system.
Since the temperature is 00°C or less, and 150°C in the case of a heat transfer liquid, it is considered that a heating temperature of 200°C to 250°C for the heat pipe heat absorption section is sufficient.

It is said that the amount of heat radiated from sunlight to the earth's surface in outer space is 1.35 KW/h per square meter per year in terms of electric energy.

This amount of heat varies depending on the region and season before it reaches the earth's surface, but approximately 50% of it is absorbed by the atmosphere, dust, etc., and the amount of radiant heat from sunlight that reaches the solar collector is equivalent to the amount of electricity per square meter per year. ``It is estimated to be around 650w/h.

In a flat solar collector, the effective amount of solar heat absorption is generally considered to be about 300 W/h to 400 W/h per square meter.

This varies widely depending on the presence or absence of a reflector, the performance of the reflector, and the thermal efficiency of the collector itself.

In a normal flat plate type collector, the surface temperature of the flat plate is 80°C to 90°C when operating to obtain hot water of around 50°C to 65°C.
It is thought that the temperature will be around ℃.

(However, when the operation is stopped, the temperature reaches 180°C to 190°C.

) At a distance of 300 m from the sunlight receiving plane, the solar energy density when the heat pipe directly focuses and receives the light is 5 = 7.35 times, and the surface temperature is several 1
It is conceivable that the temperature will reach 00°C.

When a selective absorption film is formed on the surface of the heat pipe When the absorption film is a black oxide film formed on the surface of copper 10
At temperatures below 0°C, 90% of sunlight is absorbed and only 8% of infrared radiation is emitted (U.S. Energy Research and Development Agency), but as the temperature rises, radiation loss increases and reaches the break-even temperature at 450°C (the agency). ) That is, when the surface temperature reaches several 100 degrees Celsius, the radiation heat loss becomes greater and the solar light focusing effect is lost.

In order to prevent this, extremely expensive combinations such as nickel-black nickel are required as heat pipe particles and selective absorption membranes.

In addition, in terms of heat transfer performance as a heat pipe, in the case of a copper container water-operated heat pipe, it is most efficient and the amount of heat transfer is maximum at around 200°C, and above that it rapidly loses its ability, and it does not work at all at around 250°C. I won't.

This is due to the fact that it becomes a dry amplifier state and the movement of the hydraulic fluid becomes impossible.

Further, when the temperature reaches about 250° C., the vapor pressure of the working fluid increases, and there is a possibility that the life of the heat pipe will be rapidly reduced.

Therefore, it is desirable from all points of view that the temperature of the heat absorbing portion of the heat pipe is approximately 200° C. or less and 180° C. or less.

Therefore, as in the heat pipe having the structure according to the present invention, the tip of the fin is formed into a hollow cylindrical structure with a diameter of 501rrIr, and once sunlight is received on this surface, the heat pipe can be prevented from overheating. It is.

The degree of convergence of the solar thermal energy density on the selective absorption surface of the hollow cylindrical structure surface is 300 = 300 = 1.9 times5.
From 0π 157 , the solar thermal energy absorbed by the flat collector is about 1.9 times, and its surface temperature is considered to be about 170°C.

Therefore, at this temperature, heat radiation loss from the surface is extremely small.

(2) Compared to flat collectors, conductive heat loss is extremely low.

In a flat collector, heat conduction loss cannot be avoided from the back side of the light-receiving plane through the heat insulating material.

The entire surface of the hollow cylindrical structure of the heat pipe of the present invention is a heat absorption plane, that is, a light receiving surface, and there is no conductive heat loss.

(3) Convection heat loss is extremely low compared to flat collectors.

Compared to a flat plate type with the same surface area, the heat loss from the surface of the cylindrical body is smaller due to the smaller air flow rate.

Due to the effect of low heat loss in terms (2) and (3), (
The surface temperature of the hollow cylindrical structure described in item 1) is 170°C (the actual temperature of Inference 9 has been measured to exceed 200°C).

(4) Thermal energy absorbed by the selective absorption film of the hollow cylindrical structure is absorbed by the heat pipe extremely efficiently with almost no loss, and is transferred to the heat radiation section with almost no loss.

The thermal energy transfer takes place as follows.

[) Conducted directly to the heat pipe through the fins and absorbed.

11) The heat is directly absorbed by the heat pipe as radiant heat from the inner wall of the hollow columnar structure, or it is absorbed by the fins as radiant heat and then conducted to the heat pipe and absorbed.

Due to the intense air convection sealed between the inner wall of the hollow columnar structure and the outer periphery of the heat pipe, the thermal energy of the hollow columnar structure is rapidly absorbed into the A-column and the heat pipe.

iV) As mentioned above, the thermal energy absorbed by the heat absorption part of the heat pipe with almost no loss is due to the unique heat transfer characteristics of the heat pipe, and the copper container water hydraulic fluid exerts its maximum capacity and the heat of the copper is absorbed by the heat absorption part of the heat pipe with almost no loss. The heat is transferred to the heat sink at a speed several hundred times faster than the conduction speed.

This transfer does not require any power and therefore does not result in any mechanical losses.

Also, unlike the thin metal tubes for heat exchange on the back side of the flat collector, it is transferred over the shortest distance at a speed with almost no time for heat radiation loss.

This is because the inside of the heat pipe is in a high vacuum and the working fluid absorbs thermal energy and moves to the heat dissipation section at a speed close to the speed of sound.

Considering the above (1), (2), (3), and (4), the heat pipe for a solar collector according to the present invention exhibits extremely excellent efficiency as a collector thermal energy absorption and transfer structure. Most of the loss is due to absorption loss and radiation loss from the solar heat absorption film formed on the outer surface of the hollow columnar structure.Other losses include slight convection loss, which is only a few fractions of that of a flat collector, and reflection from the reflective plate. It is only the absorption loss of the mirror.

Therefore, if a selective absorption film and reflecting mirror with good characteristics are selected, it is possible to construct a collector that is far more efficient than a flat plate collector and comparable in efficiency to a vacuum glass tube collector. It is something.

The heat pipe according to the present invention further has the following effects.

(5) Since the focal point is larger than in the case of directly receiving focused sunlight on the outer surface of the heat pipe, high precision is not required for the reflective curved surface of the reflector or reflector, so manufacturing is easy and inexpensive.

(6) For the same reason as above, high accuracy is not required for the angle of incidence of the sun, so a simple tracking device may be used to track the direction of the sun.

(7) Vacuum glass tube type collectors have excellent properties as there is no risk of damage or property deterioration due to thermal expansion, contraction, other external shocks, freezing, etc. However, these points remain as problems. was.

This advantage also provides the advantage that there is no risk of damage during transportation.

As described above, when the heat pipe of the new structure according to the present invention is applied to a solar heat collector, it exhibits many outstanding effects in improving the performance of the collector, and is believed to greatly contribute to the improvement of solar heat utilization technology. .

The present invention is not necessarily limited to the structure described in claim 1.

In claim 1, a thin metal plate fin is welded to a heat pipe container, and the hollow columnar structure is formed by forming the tip of the fin, but other methods may be used in practice. A heat pipe with structural performance can be obtained.

That is, a hollow columnar structure is first manufactured by forming a thin metal plate, and then one or more circumferential, longitudinal, or spiral metal fins are placed continuously or discontinuously over the entire length of the outer periphery of the heat absorbing part. We produced a heat pipe formed in
A heat pipe that exhibits exactly the same performance and effect as the heat pipe according to claim 1 by press-fitting or inserting the heat pipe into the hollow columnar structure and then sealing both ends of the hollow columnar structure. can be obtained.

Needless to say, in this case as well, it is necessary to provide a slight amount of air permeability between the inside and outside of the hollow columnar structure by some means.

In this case, thermal resistance occurs between the inner wall of the hollow columnar structure and the outer edge of the fin, reducing the amount of heat conducted.

However, by the same amount of thermal energy, the thermal energy radiated from the inner wall of the hollow columnar structure and the amount of heat transfer due to the convection of the internal air are increased, and the overall heat pipe has the structure according to claim 1. They can exhibit exactly the same performance.

As another application example, the object of the present invention can still be achieved even if the metal fins are omitted and a heat pipe is inserted inside the hollow columnar structure as shown in FIGS. 3c and 3d. It is possible.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway side view illustrating an embodiment of the present invention;
Fig. 2 is a vertical front view, Fig. 3 a - d are sectional views explaining different structural examples of the heat pipe, Fig. 4 is a longitudinal side view showing a structural example when applied to a collector, and Fig. 5 is a longitudinal sectional view. It is a sectional view explaining other structural examples when applied to a collector. DESCRIPTION OF SYMBOLS 1...Heat pipe body, 2...Heat absorption fins, 3...Hollow columnar structure of heat absorption fins, 4...Solar heat absorption film, 5 ... 7-pipe body heat radiation part, 6 ... heat radiation fin, 1 ...
...Vent hole, A...Heat absorption part, B...
...Heat transfer section, C... Heat dissipation section.

Claims (1)

[Claims] 1 A heat pipe for absorbing and transferring solar heat used in a solar heat collector, in which a plurality of continuous heat absorption fins made of thin metal plates are provided on the outer periphery of the container over the entire length of the heat absorption part, and each of these heat absorption fins The tip of the hollow columnar structure is bent, and each of the bent ends is welded or glued to a predetermined part to form a hollow columnar structure as a whole, and the openings at both ends are sealed. The structure is provided with a means for providing slight air permeability between the inside and outside of the structure, and is further characterized in that a solar heat absorbing film is formed on the entire outer peripheral surface by a method such as painting or chemical treatment. Heat pipe for solar heat collector.