US20130312734A1

US20130312734A1 - Solar heat collecting pipe

Info

Publication number: US20130312734A1
Application number: US13/990,994
Authority: US
Inventors: Shinichirou KAWANE; Kenji Nakamura; Masayoshi Sakuma
Original assignee: Hitachi Ltd; Hitachi Plant Mechanics Co Ltd
Current assignee: Hitachi Ltd; Hitachi Plant Mechanics Co Ltd
Priority date: 2010-12-01
Filing date: 2011-11-09
Publication date: 2013-11-28
Also published as: WO2012073664A1

Abstract

[Problem] To present a solar heat collecting pipe capable of enhancing the heat collecting efficiency by suppressing the dissipation of energy transmitted to the heat medium passing through the inside of an inner pipe.

[Solving Means] In the solar heat collecting pipe 1 including the inner pipe 11 for receiving sunlight collected by the light collecting mechanism 2, and transmitting energy to the heat medium 14 passing through the inside, and the outer pipe 12 covering the outer circumference of the inner pipe 11, a solar heat absorbing film 11 a is applied in a portion exposed to sunlight of the inner pipe 11 of the solar heat collecting pipe 1 (the portion exposed to the reflected light of the sunlight at least on the surface of the inner pipe 11, and a heat reflecting film 11b is applied in a portion not exposed to sunlight from the light collecting mechanism 2.

Description

TECHNICAL FIELD

The present invention relates to a solar heat collecting pipe, more particularly to a solar heat collecting pipe having an inner pipe for receiving sunlight collected by a light collecting mechanism, and transmitting energy to a heat medium passing through the inside, and an outer pipe covering the outer circumference of the inner pipe for forming a heat insulating space.

BACKGROUND ART

Conventionally, a solar heat collecting pipe is proposed, which has an inner pipe for receiving sunlight collected by a trough type reflector, and transmitting energy to a heat medium passing through the inside, and an outer pipe covering the outer circumference of the inner pipe for forming a heat insulating space (see, for example, patent document 1).
Such conventional solar heat collecting pipe includes various measures for raising the light collecting efficiency of sunlight, and for example, the solar heat collecting pipe of patent document 1 proposes to be provided with a structural element for converging sunlight in the inner tube, in the outer pipe covering the outer circumference of the inner pipe transmitting energy to the heat medium passing through the inside, for forming a heat insulating space.

PRIOR ART LITERATURE

Patent Document

Patent document 1: Japanese Patent Application Laid-Open No. 2004-239603

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

In this manner, the conventional solar heat collecting pipe is mostly developed with the attention paid to the light collecting side of sunlight of the light collecting mechanism for enhancing the heat collecting efficiency, and the inner pipe in which heat medium passes inside has been proposed only with ideas for enhancing the heat converging efficiency by forming fine rough surfaces, or forming a surface reflection preventive layer or infrared ray reflection layer by coating with extremely special multiple layers.
The present invention is devised in the light of the conventional solar heat collecting pipe, and it is hence a primary object thereof to present a solar heat collecting pipe enhanced in heat collecting efficiency by suppressing dissipation of energy transmitted to the heat medium passing the inside of the inner pipe.
It is other object of the present invention to present a solar heat collecting pipe capable of supporting the solar heat collecting pipe while absorbing the thermal expansion (linear expansion) of the inner pipe when connecting adjacent solar heat collecting pipes.
It is another object of the present invention to present a solar heat collecting pipe capable of reducing heat transfer to the glass-made outer pipe.

Means for Solving the Problems

To achieve the objects, the solar heat collecting pipe of the present invention includes an inner pipe for receiving sunlight collected by a light collecting mechanism, and transmitting energy to a heat medium passing through the inside, and an outer pipe covering the outer circumference of the inner pipe for forming a heat insulating space, in which a solar heat absorbing film is applied in a portion exposed to sunlight from the light collecting mechanism at least on the surface of the inner pipe, and a heat reflecting film is applied in a portion not exposed to sunlight from the light collecting mechanism.
In this case, a solar heat absorbing film may be applied to the entire circumference of the surface of the inner pipe, and a heat reflecting film may be applied to a portion not exposed to sunlight from the light collecting mechanism, or a solar heat absorbing film may be applied to a portion exposed to sunlight from the light collecting mechanism of the inner pipe, and a heat reflecting film may be applied to a portion not exposed to sunlight from the light collecting mechanism.
The solar heat absorbing film may be composed of a chrome oxide layer.
The heat reflecting film may be composed of an aluminum foil or thin plate.
Further, mutually adjacent solar heat collecting pipes may be coupled together by forming threads in connection parts of the inner pipes of the solar heat collecting pips, and connecting in non-expanding state by connection members having threads formed at both ends, and a support shaft protruding in the horizontal direction from the surface of the inner pipe near the coupled position may be slidably inserted into a slit in a horizontal direction formed in a solar heat collecting pipe support member.
The solar heat collecting pipe support member may be formed in a groove structure having a ventilation space, for shutting out the sunlight emitted from the light collecting mechanism at an end part of the outre pipe fixed and inserted into the inner pipe.
The light collecting mechanism may be a trough type reflector having a parabolic section, and the solar heat collecting pipe support member may be affixed to the reflector, and the reflector and the solar heat collecting pipe may be oscillatably mounted on a platform by way of a common oscillating shaft.

Effects of the Invention

According to the solar heat collecting pipe of the invention, a solar heat absorbing film is applied in a portion exposed to sunlight from the light collecting mechanism at least on the surface of the inner pipe, and a heat reflecting film is applied in a portion not exposed to sunlight from the light collecting mechanism, and therefore dissipation of energy transmitted to the heat medium may be suppressed, so that the heat collecting efficiency may be enhanced.
Still more, the solar heat absorbing film may be composed of a chrome oxide film, and by a relatively inexpensive structure, it is effective to strength absorption of energy in the heat medium passing through the inside of the inner pipe.
In addition, the heat reflecting film may be composed of an aluminum foil or thin plate, and by a relatively inexpensive material, it is effective to suppress dissipation of energy transmitted to the heat medium passing through the inside of the inner pipe.
Further, mutually adjacent solar heat collecting pipes are coupled together by forming threads in connection parts of the inner pipes of the solar heat collecting pips, and connecting in non-expanding state by connection members having threads formed at both ends, and a support shaft protruding in the horizontal direction from the surface of the inner pipe near the coupled position is slidably inserted into a slit in a horizontal direction formed in a solar heat collecting pipe support member, and therefore the mutually adjacent solar heat collecting pipes are coupled easily and firmly by connecting mutually the inner pipes of the solar heat collecting pipes by screwing in non-expanding state by the connection members, and the vicinity of the coupled position can be supported while absorbing the thermal expansion (linear expansion) of the inner pipe by the solar heat collecting pipe support member.
Besides, the solar heat collecting pipe support member may be built in a groove structure having a ventilation space, capable of shutting out sunlight emitted from the light collecting mechanism, at the end part of the outer pipe affixed to the inner pipe, and therefore heat transfer to the glass-made outer pipe may be suppressed.
The light collecting mechanism is a trough type reflector having a parabolic section, and the solar heat collecting pipe support member is affixed to the reflector, and the reflector and the solar heat collecting pipe are oscillatably mounted on a platform by way of a common oscillating shaft, and therefore the reflector and the solar heat collecting pipe are composed as an oscillating body of an integral structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of a solar heat collecting device making use of a solar heat collecting pipe of the present invention, in which (a) is a front view, and (b) is a side sectional view.

FIG. 2 shows a different embodiment of a solar heat collecting device making use of a solar heat collecting pipe of the present invention, in which (a) is a front view, (b) is a plan view, and (c) is a side sectional view.

FIG. 3 shows an embodiment of a solar heat collecting pipe of the present invention, in which (a) is a schematic diagram of outline, (b1) and (b2) are schematic diagrams of a section, and (c) is an explanatory diagram of state of use.

FIG. 4 is an explanatory diagram showing a coupling and supporting structure of a solar heat collecting pipe.

FIG. 5 is an explanatory diagram of a solar heat collecting pipe, in which (a) is a front sectional view, (b) is an X-X end view of (a), and (c) is a Y-Y and Z-Z end view of (a).

PREFERRED EMBODIMENT

A preferred embodiment of a solar heat collecting pipe of the present invention I described below while referring to the accompanying drawings.
FIG. 1 shows an embodiment of a solar heat collecting device making use of a solar heat collecting pipe of the present invention.
This solar heat collecting device includes a solar heat collecting pipe 1 having an inner pipe 11 for receiving sunlight collected by a trough type reflector 2 having a parabolic section as a light collecting mechanism, and transmitting energy to a heat medium 14 passing through the inside, and an outer pipe 12 covering the outer circumference of the inner pipe 11 for forming a heat insulating space 13.
In this case, the solar heat collecting pipe 1 and the reflector 2 are mounted on a platform 3 so as to be capable of moving the central axis L1 of the solar heat collecting pipe 1 and the reflector 2 along the north-south axis, and oscillating the solar heat collecting pipe 1 and the reflector 2 by way of a common oscillating axis 4.
In addition, a sun tracing mechanism 5 is provided for rotating the oscillating axis 4 along with the motion of the sun, so that an extension direction of a side including a bisector L2 of the solar heat collecting pipe 1 and the reflector 2 may be always directed to the direction of the sun.
As a result, sunlight Sb always enters the reflector 2 in parallel to the plane including the bisector L2 of the reflector 2, and the reflected light is collected on the central axis L1 of the solar heat collecting pipe 1 mounted on the position of the focus of the reflector 2.
In this preferred embodiment, the reflector 2 is composed by joining an aluminum plate material as a support member and an aluminum plate member of high reflectivity as a mirror, and fitting them into a frame member of aluminum extrusion formed material, but, instead, a glass mirror of a flexible thin material that can be curved may be used.
Also in this preferred embodiment, the light collecting mechanism is the trough type reflector 2 having a parabolic section, but it may be also realized by a Fresnel mirror type reflector composed of a plurality of long planar division mirrors, or a known light focusing mechanism such as linear Fresnel lens 6 as shown in FIG. 2.
In the meantime, the solar heat collecting pipe 1 of the preferred embodiment includes, as shown in FIG. 3, the inner pipe 11 for receiving sunlight collected by the reflector 2 as light collecting mechanism, and transmitting energy to the heat medium 14 passing through the inside, and the outer pipe 12 covering the outer circumference of the inner pipe 11 for forming a heat insulating space, in which a solar heat absorbing film 11 a is applied in a portion exposed to sunlight from the reflector 2 at least on the surface of the inner pipe 11 of the solar heat collecting pipe 1 (the portion exposed to the reflected light of the sunlight Sb at the side of the reflector 2), and a heat reflecting film 11 b is applied in a portion not exposed to sunlight from the reflector 2 (the portion not exposed to the reflected light of the sunlight Sb at the opposite side of the reflector 2).
More specifically, in the portion exposed to sunlight from the reflector 2 at least on the surface of the inner pipe 11 (in the embodiment, the whole circumference ((b1) in FIG. 1) on the surface of the inner pipe 11 or the range of 180 degrees at the lower side ((b2) in FIG. 3), a chrome oxide plating layer is applied as the solar heat absorbing film 11 a.
Or the solar heat absorbing film 11 a may be formed in a limited area exposed to the sunlight from the reflector 2.
The chrome oxide plating layer as the solar heat absorbing film 11 a may be formed at a relatively low cost by forming chrome oxide plating on the surface of the inner pipe 11 made of a pickled steel pipe.
The material and the forming method of the solar heat absorbing film 11 a are not particularly limited, and the material includes nickel aside from chrome oxide, and the forming method is not limited to plating process, but includes spraying process, physical vapor deposition (PVD), or painting, or a black color may be applied on the surface in order to enhance absorption of solar heat, or a proper selective absorbing film may be applied, or other conventional method may be combined.
Further, in the portion not exposed to sunlight from the reflector 2 (in the embodiment, the range ((b1) in FIG. 3) of 180 degrees at the upper side of the surface of the solar heat absorbing film 11 a formed on the entire circumference of the surface of the inner pipe 11 or the range ((b2) in FIG. 3) of 180 degrees at the upper side of the surface of the inner pipe 11, an aluminum foil or thin plate is applied as the heat reflecting film 11 b.
Or the heat reflecting film 11 b may be formed in an entire area not exposed to sunlight from the reflector 2.
The aluminum foil or thin plate as the heat reflecting film 11 b may be formed at a relatively low cost, by adhering by way of a silicone resin or other adhesive agent.
In this case, by adhering the aluminum foil or thin plate by way of a silicone resin or other adhesive agent, in addition to the heat reflecting function, an adiabatic function of the adhesive agent may be applied (by foaming the adhesive agent, the adiabatic function may be further enhanced), and the energy transmitted to the heat medium 14 may be entrapped within the inner pipe 11, and energy dissipation may be suppressed.
The material and the forming method of the heat reflecting film 11 b are not particularly limited, and a white or silver heat-resistant adiabatic paint having a heat reflecting function (a function capable of entrapping the energy transmitted to the heat medium 14 within the inner pipe 11), for example, ceramic adhesive or silicone resin may be used as a binder, and micro-size hollow ceramics may be contained, or heat-resistant sheet materials made of glass wool or the like, and other conventional materials may be also used. Or an aluminum thin plate may be bonded physically by using any band.
The inner pipe 11 may be made of steel pipe, stainless steel pipe, and other metal pipe, and the outer pipe 12 is preferably made of Kovar glass pipe, borosilicate glass pipe, or the like.
The heat insulating space 13 usually insulates heat by forming a vacuum space between the inner pipe 11 and the outer pipe 12.
The heat medium 14 passing inside of the inner pipe 11 is water, heat medium oil, molten salt, or other heat medium functioning as a heat medium when heated to a temperature of hundreds of degrees centigrade, for example, about 400° C.
The solar heat collecting pipe 1 has the solar heat absorbing film 11 a applied in the portion exposed to sunlight from the reflector 2 as light collecting mechanism at least on the surface of the inner pipe 11, and the heat reflecting film 11 b applied in the portion not exposed to sunlight from the reflector 2, and therefore by the solar heat absorbing film 11 a, absorption of energy in the heat medium 14 passing the inside of the inner pipe 11 is enhanced, and by the heat reflecting film 11 b, energy transmitted to the heat medium 14 can be entrapped within the inner pipe 11, and dissipation of energy can be suppressed, so that the heat collecting efficiency may be enhanced.
Hereinafter, the performance of the solar heat collecting pipe is verified specifically.
[Case 1]

Heating temperature of heat medium: 400° C.
Size of reflector: width 2 m, length 5 m.
When entire surface of inner pipe is coated with solar heat absorbing film (chrome oxide plating layer):
- sx (273+400)⁴=11632 W/m²
- s (Stefan-Boltzmann constant)=5.67×10⁻⁸W/(m²·K⁴)
- Emissivity: e=0.6, supposing inner pipe surface area: 0.534 m²,
- Heat radiation amount: 0.6×11632×0.534=3.73 kW (1)
When entire surface of inner pipe is coated with solar heat absorbing film (chrome oxide plating layer), of which half circumference is coated with heat reflecting film (aluminum foil):
- Supposing aluminum foil emissivity: e=0.1,
- Heat radiation amount from portion of solar heat absorbing film (chrome oxide plating layer): 1.86 kW.
- Heat radiation amount from portion of heat reflecting film (aluminum foil): 0.31 kW.
- Overall heat radiation amount: 2.27 kW (2)
Heat amount absorbed by solar heat collecting pipe when direct insolation from the sun is 1 kW/m²:
When entire surface of inner pipe is coated with solar heat absorbing film (chrome oxide plating layer):
- Opposite side of reflector: 10×25/1000×0.9×0.95=0.11
- Reflector side: 10×1975/2000×0.9×0.9×0.95=7.60
- Overall heat radiation amount: 7.71 kW (3)
When entire surface of inner pipe is coated with solar heat absorbing film (chrome oxide plating layer), of which half circumference is coated with heat reflecting film (aluminum foil):
- Opposite side of reflector: 10×25/1000×0.9×0=0
- Reflector side: 10×1975/2000×0.9×0.9×0.95=7.60
- Overall heat radiation amount: 7.60 kW (4)
Heat efficiency
When entire surface of inner pipe is coated with solar heat absorbing film (chrome oxide plating layer):
- (3)-(1)=3.98 kW→heat efficiency: 3.98 kW/10 kW=39.8%.
When entire surface of inner pipe is coated with solar heat absorbing film (chrome oxide plating layer), of which half circumference is coated with heat reflecting film (aluminum foil):
- (4)-(2)=5.43 kW→heat efficiency: 5.43 kW/10 kW=54.3%.

[Case 2]

Heating temperature of heat medium: 200° C.
Size of reflector: width 2 m, length 5 m.
When entire surface of inner pipe is coated with solar heat absorbing film (chrome oxide plating layer):
- sx (273+200)⁴=2838 W/m²
- s (Stefan-Boltzmann constant)=5.67×10⁻⁸W/(m²·K⁴)
- Emissivity: e=0.6, supposing inner pipe surface area: 0.534 m²,
- Heat radiation amount: 0.6×2838×0.534=0.91 kW (5)
When entire surface of inner pipe is coated with solar heat absorbing film (chrome oxide plating layer), of which half circumference is coated with heat reflecting film (aluminum foil):
- Supposing aluminum foil emissivity: e=0.1,
- Heat radiation amount from portion of solar heat absorbing film (chrome oxide plating layer): 0.46 kW.
- Heat radiation amount from portion of heat reflecting film (aluminum foil): 0.08 kW.
- Overall heat radiation amount: 0.54 kW (6)
Heat amount absorbed by solar heat collecting pipe when direct insolation from the sun is 1 kW/m²:
When entire surface of inner pipe is coated with solar heat absorbing film (chrome oxide plating layer):
- Opposite side of reflector: 10×25/1000×0.9×0.95=0.11
- Reflector side: 10×1975/2000×0.9×0.9×0.95=7.60
- Overall heat radiation amount: 7.71 kW (7)
When entire surface of inner pipe is coated with solar heat absorbing film (chrome oxide plating layer), of which half circumference is coated with heat reflecting film (aluminum foil):
- Opposite side of reflector: 10×25/1000×0.9×0=0
- Reflector side: 10×1975/2000×0.9×0.9×0.95=7.60
- Overall heat radiation amount: 7.60 kW (8)
Heat efficiency
When entire surface of inner pipe is coated with solar heat absorbing film (chrome oxide plating layer):
- (7)-(5)=6.80 kW→heat efficiency: 6.80 kW/10 kW=68.0%.
When entire surface of inner pipe is coated with solar heat absorbing film (chrome oxide plating layer), of which half circumference is coated with heat reflecting film (aluminum foil):
- (8)-(6)=7.06 kW→heat efficiency: 7.06 kW/10 kW=70.6%.

Thus, as a result of verification of performance of the solar heat collecting pipe, by applying the heat reflecting film 11 b in the portion not exposed to sunlight from the reflector 2, the energy transmitted to the heat medium 14 could be entrapped within the inner pipe 11, and dissipation of energy could be suppressed, and hence the heat collecting efficiency could be enhanced, and in particular when the heating temperature of the heat medium is higher, it has been confirmed that the heat collecting efficiency is higher.
Further, as shown in FIG. 4 and FIG. 5, the both ends of the inner pipe 11 are affixed by way of an expansion difference absorbing mechanism 25 for absorbing the difference in thermal expansion (linear expansion) of the inner pipe 11 and the outer pipe 12, consisting of metal ring 25 a and bellows 25 b bonded to the end parts of the outer ring 12.
The adjacent solar heat collecting pipes 1 thus composed are coupled together by forming threads in connection parts 11 c of the inner pipes 11 of the solar heat collecting pipes 1, and connecting in non-expanding state by connection members 23 having threads formed at both ends, and a support shaft 24 protruding in the horizontal direction from the surface of the inner pipe 11 near the coupled position is slidably inserted into a slit 31 in a horizontal direction formed in solar heat collecting pipe support members 3 a 1 to 3 a 4, 3 b 1 to 3 b 3.
In this case, at one end side or near the one end side of the slit 31, a notch 32 opening upward may be formed continuously, so that the support shaft 24 may be inserted into the slit 31 more smoothly by way of the notch 32.
Consequently, the adjacent solar heat collecting pipes 1 are mutually coupled easily and firmly, by screwing and connecting the inner pipes 11 of the solar heat collecting pipes in non-expanding state by the connection members 23, and the vicinity of the coupled position can be supported while absorbing the thermal expansion (linear expansion) of the inner pipes 11 by means of the solar heat collecting pipe support members 3 a 1 to 3 a 4, 3 b 1 to 3 b 3.
Incidentally, the end part not coupled to the solar heat collecting pipe 1 of thus coupled solar heat collecting pipes 1 is formed as a free end, and, for example, by connecting a flexible pipe 26 to the inner pipe 11 of the solar heat collecting pipe 1, the thermal expansion (linear expansion) of the inner pipes 11 can be absorbed.
In the preferred embodiment, the solar heat collecting pipe support members 3 a 1 to 3 a 4, 3 b 1 to 3 b 3 are affixed to the trough type reflector 2 having a parabolic section as the light collecting mechanism, and the reflector 2 and the solar heat collecting pipe 1 are oscillatably mounted on the platform 3 by way of a common oscillating shaft 4, so that the reflector 2 and the solar heat collecting pipe 1 may be formed as an oscillating body of an integral structure.
Moreover, the solar heat collecting pipe support members 3 a 1 to 3 a 4, 3 b 1 to 3 b 3 are provided with a function of supporting while absorbing the thermal expansion (linear expansion) of the solar heat collecting pipe 1, more specifically, the inner pipes 11, and the expansion difference absorbing mechanism 25 consisting of metal ring 25 a and bellows 25 b bonded to the end part of the outer pipe 12 affixed to the inner pipe 11, specifically bonded to the end parts of the outer ring 12 is formed in a groove structure opened upward to the ventilation space for shutting off the sunlight exposed from the reflector 2 as the light collecting mechanism, and releasing heat by atmospheric convection.
As a result, through the expansion difference absorbing mechanism 25 consisting of metal ring 25 a and bellows 25 b bonded to the end part of the outer pipe 12, heat conduction to the outer pipe may be reduced.
The solar heat collecting pipe of the invention is described herein by referring to the preferred embodiment, but it must be noted that the present invention is not limited to this preferred embodiment alone, but may be changed and modified in various structures in a scope not departing from the true spirit thereof.

INDUSTRIAL APPLICABILITY

The solar heat collecting pipe of the invention is characterized by enhancing the heat collecting efficiency by suppressing dissipation of energy transmitted to the heat medium passing in the inside of the inner pipe, and hence it may be preferably used in an application of a solar heat collecting apparatus utilizing the solar heat collecting pipe.

DESCRIPTION OF THE REFERENCE NUMERALS

1 Solar heat collecting pipe
11 Inner pipe
11 a Solar heat absorbing film
11 b Heat reflecting film
11 c Connection part
12 Outer pipe
13 Heat insulating space
14 Heat medium
2 Reflector (light focusing mechanism)
6 Linear Fresnel lens (light focusing mechanism)
24 Support shaft
25 Expansion difference absorbing mechanism
25 a Metal ring
26 b Bellows
3 a 1 to 3 a 4, 3 b 1 to 3 b 3 Solar heat collecting pipe support member
31 Slit
32 Notch
Sb Sunlight

Claims

1. A solar heat collecting pipe comprising an inner pipe for receiving sunlight collected by a light collecting mechanism, and transmitting energy to a heat medium passing through the inside, and an outer pipe covering the outer circumference of the inner pipe for forming a heat insulating space, wherein a solar heat absorbing film is applied in a portion exposed to sunlight from the light collecting mechanism at least on the surface of the inner pipe, and a heat reflecting film is applied in a portion not exposed to sunlight from the light collecting mechanism.

2. The solar heat collecting pipe according to claim 1, wherein a solar heat absorbing film is applied to the entire circumference of the surface of the inner pipe, and a heat reflecting film is applied to a portion not exposed to sunlight from the light collecting mechanism.

3. The solar heat collecting pipe according to claim 1, wherein a solar heat absorbing film is applied to a portion exposed to sunlight from the light collecting mechanism of the inner pipe, and a heat reflecting film is applied to a portion not exposed to sunlight from the light collecting mechanism.

4. The solar heat collecting pipe according to claim 1, wherein the solar heat absorbing film is composed of a chrome oxide layer.

5. The solar heat collecting pipe according to claim 1, wherein the heat reflecting film is composed of an aluminum foil or thin plate.

6. The solar heat collecting pipe according to claim 1, wherein mutually adjacent solar heat collecting pipes are coupled together by forming threads in connection parts of the inner pipes of the solar heat collecting pips, and connecting in non-expanding state by connection members having threads formed at both ends, and a support shaft protruding in the horizontal direction from the surface of the inner pipe near the coupled position is slidably inserted into a slit in a horizontal direction formed in a solar heat collecting pipe support member.

7. The solar heat collecting pipe according to claim 6, wherein the solar heat collecting pipe support member is formed in a groove structure having a ventilation space, for shutting out the sunlight emitted from the light collecting mechanism at an end part of the outre pipe fixed and inserted into the inner pipe.

8. The solar heat collecting pipe according to claim 7, wherein the light collecting mechanism is a trough type reflector having a parabolic section, and the solar heat collecting pipe support member is affixed to the reflector, and the reflector and the solar heat collecting pipe are oscillatably mounted on a platform by way of a common oscillating shaft.

9. The solar heat collecting pipe according to claim 6, wherein the light collecting mechanism is a trough type reflector having a parabolic section, and the solar heat collecting pipe support member is affixed to the reflector, and the reflector and the solar heat collecting pipe are oscillatably mounted on a platform by way of a common oscillating shaft.

10. The solar heat collecting pipe according to claim 4, wherein the heat reflecting film is composed of an aluminum foil or thin plate.

11. The solar heat collecting pipe according to claim 2, wherein the solar heat absorbing film is composed of a chrome oxide layer.

12. The solar heat collecting pipe according to claim 11, wherein the heat reflecting film is composed of an aluminum foil or thin plate.

13. The solar heat collecting pipe according to claim 3, wherein the solar heat absorbing film is composed of a chrome oxide layer.

14. The solar heat collecting pipe according to claim 13, wherein the heat reflecting film is composed of an aluminum foil or thin plate.

15. The solar heat collecting pipe according to claim 2, wherein mutually adjacent solar heat collecting pipes are coupled together by forming threads in connection parts of the inner pipes of the solar heat collecting pips, and connecting in non-expanding state by connection members having threads formed at both ends, and a support shaft protruding in the horizontal direction from the surface of the inner pipe near the coupled position is slidably inserted into a slit in a horizontal direction formed in a solar heat collecting pipe support member.

16. The solar heat collecting pipe according to claim 15, wherein the solar heat collecting pipe support member is formed in a groove structure having a ventilation space, for shutting out the sunlight emitted from the light collecting mechanism at an end part of the outre pipe fixed and inserted into the inner pipe.

17. The solar heat collecting pipe according to claim 15, wherein the light collecting mechanism is a trough type reflector having a parabolic section, and the solar heat collecting pipe support member is affixed to the reflector, and the reflector and the solar heat collecting pipe are oscillatably mounted on a platform by way of a common oscillating shaft.

18. The solar heat collecting pipe according to claim 3, wherein mutually adjacent solar heat collecting pipes are coupled together by forming threads in connection parts of the inner pipes of the solar heat collecting pips, and connecting in non-expanding state by connection members having threads formed at both ends, and a support shaft protruding in the horizontal direction from the surface of the inner pipe near the coupled position is slidably inserted into a slit in a horizontal direction formed in a solar heat collecting pipe support member.

19. The solar heat collecting pipe according to claim 4, wherein mutually adjacent solar heat collecting pipes are coupled together by forming threads in connection parts of the inner pipes of the solar heat collecting pips, and connecting in non-expanding state by connection members having threads formed at both ends, and a support shaft protruding in the horizontal direction from the surface of the inner pipe near the coupled position is slidably inserted into a slit in a horizontal direction formed in a solar heat collecting pipe support member.

20. The solar heat collecting pipe according to claim 5, wherein mutually adjacent solar heat collecting pipes are coupled together by forming threads in connection parts of the inner pipes of the solar heat collecting pips, and connecting in non-expanding state by connection members having threads formed at both ends, and a support shaft protruding in the horizontal direction from the surface of the inner pipe near the coupled position is slidably inserted into a slit in a horizontal direction formed in a solar heat collecting pipe support member.