Title:
Exhaust heat recovering device
Kind Code:
A1


Abstract:
A waste heat recovery system having a heat pipe provided with a heat switch function limiting an amount of heat transported to a condenser in accordance with the increase in the amount of heating of the evaporator, having the evaporator arranged at an exhaust pipe for carrying exhaust gas of the internal combustion engine, and having the condenser arranged in a cooling water passage for carrying cooling water of the internal combustion engine and using the heat pipe to transport waste heat of exhaust gas to cooling water, characterized in that an insulating part formed between the evaporator and condenser is provided with a wall part for preventing heat transmission from an external fluid.



Inventors:
Yamanaka, Yasutoshi (Kariya-city, JP)
Hamada, Shinichi (Anjo-city, JP)
Inoue, Seiji (Nukata-gun, JP)
Kohara, Kimio (Nagoya-city, JP)
Application Number:
11/396987
Publication Date:
05/22/2008
Filing Date:
04/03/2006
Assignee:
DENSO Corporation (Kariya-City, JP)
Primary Class:
Other Classes:
165/51
International Classes:
F28F27/00
View Patent Images:
Related US Applications:



Primary Examiner:
FORD, JOHN K
Attorney, Agent or Firm:
HARNESS DICKEY (TROY) (Troy, MI, US)
Claims:
1. A waste heat recovery system to transport waste heat of exhaust gas to cooling water, comprising: a heat pipe having an evaporator arranged at the exhaust gas pipe for carrying exhaust gas of the internal combustion engine, a condenser arranged in a cooling water passage for carrying cooling water of the internal combustion engine, and a heat switch limiting the amount of heat transported to the condenser in accordance with the increase in the amount of heating of the evaporator, and an insulating part formed between the evaporator and condenser is provided with a wall part for preventing heat transmission from an external fluid.

2. A waste heat recovery system as set forth in claim 1, wherein the wall part is provided at the upstream side of the flow of the external fluid of the insulating part.

3. A waste heat recovery system as set forth in claim 1, wherein wall parts are connected to the evaporator and condenser and are separated by a predetermined amount of clearance formed between the evaporator and the condenser, and the separated wall parts are connected by an elastic part having elasticity.

4. A waste heat recovery system as set forth in claim 1, wherein a plurality of heat pipes are provided, and first end sides of the plurality of heat pipes are provided with a connector connecting the plurality of heat pipes together.

5. A waste heat recovery system as set forth in claim 4, wherein the evaporator is arranged under the condenser, and the connector is provided at the evaporator end side and arranged at the outer surface or inside of the exhaust pipe.

6. A waste heat recovery system as set forth in claim 1, wherein the inside wall of each heat pipe is provided with a wick extending from the evaporator to the condenser, and the evaporator is arranged above the condenser.

7. A waste heat recovery system as set forth in claim 1, wherein an exhaust pipe part forming part of the exhaust pipe and a cooling water passage part forming part of the cooling water passage are provided, the exhaust pipe part is joined with the evaporator, and the cooling water passage part is joined with the condenser.

Description:

TECHNICAL FIELD

The present invention relates to a waste heat recovery system using heat pipes to recover waste heat of exhaust gas of an internal combustion engine and utilizing it for heating cooling water of the internal combustion engine, for example, is suitably used for a vehicle provided with an internal combustion engine.

BACKGROUND ART

As a conventional waste heat recovery system, for example, as shown in the reference (Wolf Dietrich Munzel, Daimler-Benz AG, “Heat Pipes for Recovery from Exhaust Gas of a Diesel Engine in a Passenger Car”, Proc. of International Heat Pipe Conference in Grenouble, France, 1987, pp. 740-743), one is known where the evaporator among the evaporator and condenser of the heat pump is placed in an engine exhaust pipe and the condenser is brought into heat contact with the engine cooling water. In this waste heat recovery system, waste heat of the exhaust gas is transported to the engine cooling water by the heat pipes, whereby the engine cooling water at the time of a low temperature is positively heated and the warmup performance of the engine and heating performance of a heater using the engine cooling water as a heat source are improved.

Here, it is described that by limiting (reducing) the amount of working medium sealed in the heat pipes, even if the engine speed rises (amount of exhaust heat increases), the evaporator will dry out and the transport of heat will be able to be suppressed.

However, in this waste heat recovery system, no consideration is particularly seen regarding the heat of the insulating part formed between the evaporator and condenser. For example, if the insulating part is struck by cooling air or another low temperature fluid, the working medium evaporated at the evaporator will end up being condensed at this insulating part and the waste heat of the exhaust gas will no longer be able to be transported to the condenser.

DISCLOSURE OF THE INVENTION

The object of the present invention, in consideration of the above problem, is to provide a waste heat recovery system utilizing heat pipes which prevents condensation of the working medium at the insulating part and enables reliable heat transport from the evaporator to the condenser.

The present invention employs the following technical means to achieve the above object.

In a first aspect of the present invention, there is provided a waste heat recovery system having a heat pipe (110) provided with a heat switch function limiting an amount of heat transported to a condenser (110B) in accordance with the increase in the amount of heating of the evaporator (110A), having the evaporator (110A) arranged at an exhaust pipe (11) for carrying exhaust gas of the internal combustion engine (10), and having the condenser (110B) arranged in a cooling water passage(30) for carrying cooling water of the internal combustion engine (10) and using the heat pipe (110) to transport waste heat of exhaust gas to cooling water, characterized in that an insulating part (110C) formed between the evaporator (110A) and condenser (110B) is provided with a wall part (160) for preventing heat transmission from an external fluid.

Due to this, even if the external fluid has a temperature lower than the cooling water temperature, the working medium inside the heat pipe (110) evaporated at the evaporator (110A) can be prevented from condensing at the insulating part (110C), so reliable heat transport from the evaporator (110A) to the condenser (110B) becomes possible.

In a second aspect of the present invention, the wall part (160) is provided at the upstream side of the flow of the external fluid of the insulating part (110C).

Due to this, the flow of the external fluid is blocked by the wall part (160) and is prevented from striking the insulating part (110C), so by setting the minimum extent of the wall part (160), the working medium can be prevented from condensing at the insulating part (110C).

In a third aspect of the present invention, wall parts (160) are connected to the evaporator (110A) and condenser (110B) and are separated by a predetermined amount of clearance (161) formed between the evaporator (110A) and the condenser (110B), and the separated wall parts (160) are connected by an elastic part (162) having elasticity.

Due to this, the heat strain at the wall parts (160) caused by the temperature difference between the evaporator (110A) and condenser (110B) can be absorbed by the clearance (161) and elastic part (162). Further, while the wall parts (160) are separated, since they are joined by the elastic part (162), the assembly efficiency will not fall.

Further, when the amount of heat transported to the condenser (110B) due to the heat switch function increases, the heat conduction from the evaporator (110A) is blocked by the clearance (161), so the restriction of the heat transport will not be impaired.

In a fourth aspect of the present invention, a plurality of heat pipes (110) are provided, and first end sides of the plurality of heat pipes (110) are provided with a connector (140) connecting the plurality of heat pipes (110) together.

Due to this, by providing just one location of the connector (140) with a seal (141), it becomes possible to evacuate the inside to a vacuum and seal in a working medium.

In a fifth aspect of the present invention, the evaporator (110A) is arranged under the condenser (110B), and the connector (140) is provided at the evaporator (110A) end side and arranged at the outer surface or inside of the exhaust pipe (11).

Due to this, the working medium in the connector (140) is also heated positively by the exhaust gas, so dry out for activation of the heat switch function (cessation of waste heat recovery) can be performed earlier.

In a sixth aspect of the present invention, the inside wall of each heat pipe (110) is provided with a wick extending from the evaporator (110A) to the condenser (110B), and the evaporator (110A) is arranged above the condenser (110B).

Due to this, even if the evaporator (110A) is arranged above the condenser (110B) in accordance with the set positions of the exhaust pipe (11) and cooling water passage (30), heat transport between the two (110A, 110B) becomes possible.

In a seventh aspect of the present invention, an exhaust pipe part (130A) forming part of the exhaust pipe (11) and a cooling water passage part (150A) forming part of the cooling water passage (30) are provided, the exhaust pipe part (130A) is joined with the evaporator (110A), and the cooling water passage part (150A) is joined with the condenser (110B).

Due to this, it is possible to provide a waste heat recovery system (100) enabling the exhaust pipe (11) and cooling water passage (30) to be easily joined as a single heat exchanger.

Further, the reference numerals in parentheses of the means show the correspondence with the specific means described in the later explained embodiments.

Below, the present invention will be more readily understood from the attached drawings and the description of the preferred embodiments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing the state of the waste heat recovery system mounted in a vehicle.

FIG. 2A is a front view of a waste heat recovery system in a first embodiment, and FIG. 2B is a right side view of the same.

FIG. 3 is a graph showing the amount of heat transferred to engine cooling water according to a waste heat recovery system.

FIG. 4A is a front view of a waste heat recovery system in a second embodiment, and FIG. 4B is a right side view of the same.

FIG. 5A is a front view of a waste heat recovery system in a third embodiment, and FIG. 5B is a right side view of the same.

FIG. 6A is a front view of a waste heat recovery system in a first mode of a fourth embodiment, and FIG. 6B is a right side view of the same.

FIG. 7A is a front view of a waste heat recovery system in a second mode of a fourth embodiment, and FIG. 7B is a right side view of the same.

FIG. 8A is a front view of a waste heat recovery system in a third mode of a fourth embodiment, and FIG. 7B is a right side view of the same.

BEST MODE FOR CARRYING OUT THE INVENTION

A first embodiment of the present invention is shown in FIG. 1 to FIG. 3. First, the specific configuration will be explained. A waste heat recovery system 100 of the present embodiment is applied to a vehicle (automobile) having an engine 10 as a drive source for running. In this connection, FIG. 1 is a schematic view showing the state of the waste heat recovery system 100 mounted in a vehicle, FIG. 2A is a front view showing the waste heat recovery system 100, FIG. 2B is a right side view of FIG. 2A, and FIG. 3 is a graph showing the amount of heat transferred to the engine cooling water by the waste heat recovery system 100.

As shown in FIG. 1, a vehicle engine 10 is a water-cooled internal combustion engine which has an exhaust pipe 11 from which exhaust gas is exhausted after fuel is burned. The exhaust pipe 11 is provided with a catalytic converter 12 for purifying the exhaust gas.

Further, the engine 10 has a radiator circuit 20 by which the engine 10 is cooled by circulation of engine cooling water (hereinafter, “cooling water”) and a heater circuit 30 for heating air-conditioning air using the cooling water (warm water) as a heat source.

The radiator circuit 20 is provided with a radiator 21. The radiator 21 is cooled by heat exchange of the cooling water circulated by a water pump 22 with the outside air. Further, the radiator circuit 20 is provided inside it with a bypass passage (not shown) through which cooling water circulates bypassing the radiator 21 and is designed so that a thermostat (not shown) adjusts the amount of cooling water circulated through the radiator 21 and the amount of cooling water circulating through the bypass passage. In particular, at the time of engine warmup, the amount of cooling water at the bypass passage side is increased and warmup is promoted (that is, overcooling of the cooling water by the radiator 21 is prevented).

The heater circuit (corresponding to the cooling water passage in the present invention) 30 is provided with a heater core 31 as a heating use heat exchanger and is designed so that cooling water (warm water) is circulated by the water pump 22. The heater core 31 is placed in an air-conditioning case of a not shown air-conditioning unit. The air-conditioning air sent in accordance with the blower is heated by heat exchange with warm water.

The waste heat recovery system 100 has a plurality of tubes 110. One end side of each tube 110 is arranged inside the exhaust pipe part 130A, while the other end side is arranged inside the cooling water passage part 150A (water tank 150). The constituent members (explained below) are made of a stainless steel material provided with a high corrosion resistance. After the constituent members are assembled, they are soldered together by solder material provided at the abutting parts and engaging parts. Further, the exhaust pipe part 130A is interposed in the exhaust pipe 11 at the part forming the downstream side of the catalytic converter 12. Cooling water in the heater circuit 30 is circulated in the cooling water passage part 150A.

Below, FIGS. 2A and 2B will be used to explain details of the waste heat recovery system 100. The tubes 110, as explained later, are evacuated to a vacuum, then a working medium is sealed in them in predetermined amounts so that the tubes act as heat pipes. They are used in a posture with their longitudinal directions in the vertical direction. The bottom side forms the evaporator 110A, the top side forms the condenser 110B, and the section between the two 110A and 110B forms the insulating part 110C (bottom heat type). Further, the inside walls of the tubes 110 corresponding to the condenser 110B are provided with wicks (porous substances) comprised of metal mesh, metal felt, sintered metal, etc. (not shown).

Here, the tubes 110 are formed into flat shapes by combining two tube plates 111, 112 facing each other. A plurality of (here, four) these are stacked along the left-right direction in FIG. 2A. These tubes 110 are blocked at their top ends and are opened at their bottom ends. Further, the tubes 110 are arranged so that a plurality of columns (for example, three columns) in the left-right direction in FIG. 2B (not shown).

In the evaporator 110A (region from the bottom ends of the tubes 110 toward the top sides to a position over the center), the sections between the stacked tubes 110 and the outsides of the outermost tubes 110 are provided with corrugated type fins 120 formed into clamp sectional shapes from a thin sheet material.

The bottom ends (openings) of the tubes 110 are formed into square outer shapes and are joined to a first plate 131 formed with tube holes at positions corresponding to the tubes 110. Further, the tubes 110 are passed through tube holes of a second plate 132 similar to the first plate 131, while the second plate 132 is arranged at a position forming the top ends of the fins 120 and is joined with the tubes 110. Further, like the second plate 132, a third plate 133 is arranged at a boundary position between the condenser 110B and the insulating part 110C and is joined to the tubes 110.

The two outermost fins 120 in the stacking direction of the tubes 110 (fins 120 at left and right sides in FIG. 2A) are provided with side plates 134 forming square outside shapes. The side plates 134 are joined to the fins 120. The bottom ends and the top ends of the side plates 134 are joined to the first plate 131 and second plate 132.

The first plate 131, second plate 132, and two side plates 134 form a duct having a square passage cross-section. This duct forms the exhaust pipe part 130A. Therefore, the evaporator 110A and fins 120 are arranged inside the exhaust pipe part 130A. Further, the two openings of the exhaust pipe part 130A have an inlet side attachment 135 and an outlet side attachment 136 joined with them. The two attachments 135, 136 form the same shapes. The attachment 135 is a square frame having an opening 135a the same as the opening of the exhaust pipe part 130A. The four corners are provided with attachment holes 135b for attachment to the exhaust pipe 11.

The bottom surface of the first plate 131 (bottom surface of exhaust pipe part 130A) is joined to a shallow-bottom tank (corresponding to the connector the present invention) 140 opening at the first plate 131 side. The tubes 110 are connected together by this tank 140. At the center of the tank 140, a sealing pipe 141 connected to the inside of the tank 140 is provided.

Further, the tubes 110 are evacuated to a vacuum from the sealing pipe 141, then a working medium is sealed in them, then the sealing pipe 141 is sealed. The working medium used here is water. Water has a boiling point of usually (at one atmosphere) 100° C., but since the tubes 110 are evacuated, the boiling point becomes 30 to 40° C. Further, the working medium used may also be, in addition to water, alcohol, a fluorocarbon, chlorofluorocarbon, etc.

The top surface of the third plate 133 is joined with a water tank 150 of a flat box shape opening to the third plate 133 side. The water tank 150 is provided with, at the left side face in FIG. 2A, an inlet pipe 151 and, further, is provided with, at the facing right side face, with an outlet pipe 152. The pipes 151, 152 are connected to the inside of the water tank 150. The third plate 133, water tank 150, and two pipes 151, 152 form the cooling water passage part 150A. The condenser 110B is arranged inside the cooling water passage 150A.

Outside of the insulating part 110C, insulating wall parts 160 are provided for preventing the cooling air flowing through the region in the vehicle where the waste heat recovery system 100 is arranged (corresponding to the external fluid in the present invention) from striking the insulating part 110C. Here, the cooling air flows from the left to right direction in FIG. 2A. The insulating wall parts 160 are provided at the left and right sides in FIG. 2A. The insulating wall parts 160 are plate-shaped members with bottom ends joined to the second plate 132 (evaporator 110A) and with top ends joined to the third plate (condenser 110B) 133. Further, the insulating wall parts 160 are separated by formation of a predetermined amount of a notch (corresponding to the clearance in the present invention) 161 between the evaporator 110A and condenser 110B. The separated wall parts 160 are connected by a curved part (corresponding to elastic part in the present invention) 162 formed curved and having elasticity as a plate spring.

In the thus configured waste heat recovery system 100, the exhaust pipe part 130A is interposed in the exhaust pipe 11 at the part forming the downstream side of the catalytic converter 12 and is fixed there by the two attachments 135, 136. Further, the inlet pipe 151 and outlet pipe 152 of the cooling water passage part 150A are connected to the heater circuit 30. The exhaust pipe part 130A forms part of the exhaust pipe 11, while the cooling water passage part 150A forms part of the heater circuit 30.

Next, the operation based on the above configuration will be explained. When the engine 10 is operated, the water pump 22 is operated and cooling water circulates through the radiator circuit 20 and heater circuit 30. The cooling water circulating through the heater circuit 30 flows through the cooling water passage part 150A of the waste heat recovery system 100. Further, the exhaust gas of the fuel burned in the engine 10 passes through the catalytic converter 12 and from the exhaust pipe 11 through the exhaust pipe part 130A of the waste heat recovery system 100 to be discharged into the air.

In the waste heat recovery system 100, the water (working medium) in the tubes 110 receives heat from the exhaust gas flowing through the exhaust pipe part 130A at the tank 140 and evaporator 110A and boils and vaporizes to form steam which rises inside the tubes 110 and flows into the condenser 110B. The steam flowing into the condenser 110B is cooled by the cooling water flowing through the cooling water passage part 150A and becomes condensed water at the wicks provided at their inside walls. This descends by gravity and returns to the evaporator 110A.

In this way, the heat of the exhaust gas is transmitted to the water and is transported from the evaporator 110A to the condenser 110B. When the steam condenses at this condenser 110B, the heat is discharged as the latent heat of condensation, whereby the cooling water flowing through the cooling water passage part is heated. Further, there is also part of the heat of the exhaust gas which is moved through the walls of the tubes 110 by heat conduction from the evaporator 110A to the condenser 110B.

Further, as shown in FIG. 3, along with the amount of exhaust heat, which increases in accordance with the load of the engine 10, the amount of heat transported from the evaporator 110A to the condenser 110B, that is, the amount of heat transfer to the cooling water, increases until a predetermined load (heat transfer amount switching point) (waste heat recovery by heat pipes ON).

In this way, when the engine 10 is started when the outside air temperature is relatively low, the waste heat recovery by the heat pipes is turned ON, the cooling water is positively heated, and the warmup of the engine 10 is promoted, so the friction loss of the engine 10 is reduced, the increase in fuel for improving the low temperature starting ability is suppressed, and the fuel economy performance is improved. Further, the heating performance of the heater core 31 using the cooling water as a heat source is improved.

On the other hand, when the engine 10 increases in load to a predetermined load and the amount of exhaust heat further increases, evaporation of the water in the evaporator 110A is promoted and the flow rate of the steam toward the condenser 110B side (toward the top) increases. Further, due to the flow rate of the steam at this time, the condensed water condensed at the condenser 110B is inhibited from descending and the condensed water remains held by the wicks. This being the case, the water of the evaporator 110A completely evaporates (dries out), the heat transport by the evaporation and condensation of water is stopped, and the amount of heat transmitted to the cooling water side becomes only the heat conduction through the tubes 110 (waste heat recovery by heat pipes OFF). Further, the switching ON and OFF of the waste heat recovery by the heat pipes corresponds to the heat switch function.

Therefore, if continuing the waste heat recovery while the amount of exhaust heat is increasing along with the increase in load of the engine 10, the cooling water temperature rises too much, the heat radiation ability of the radiator 21 (for example, 4 kW) is exceeded, and overheating results. By switching to waste heat recovery OFF at this time, this inconvenience is prevented.

Further, the inventors confirmed this in actual cars during which they obtained a 3 to 5% effect for the fuel economy performance in a 1.5 liter class gasoline car, 40 km/h, and an outside air temperature of 0 to 25° C. and, further, an effect of +5 to 8° C. for the inlet water temperature of the heater core 31.

Here, in this embodiment, the insulating part 110C of the tubes 110 is provided with insulating wall parts 160, so even when for example the temperature of the cooling air striking the insulating part 110C is lower than the cooling water temperature like in a cold region, the cooling air is prevented from striking the insulating part 110C, so the steam evaporated at the evaporator 110A can be prevented from condensing at the insulating part 110C and reliable heat transport from the evaporator 110A to the condenser 110B becomes possible.

Further, the insulating wall parts 160 are separated by the notch 161, and the separated wall parts 160 are connected by a curved part 162 having elasticity, so the heat strain occurring at the insulating wall parts 160 due to the temperature difference between the evaporator 110A and the condenser 110B can be absorbed by the notch 161 and the curved part 162. Further, while the insulating wall parts 160 are separated, since they are joined by the curved part 162, the assembly efficiency will not fall. Further, when the amount of heat transported to the condenser 110B due to the heat switch function increases, the heat conduction from the evaporator 110A is blocked by the notch 161, so the restriction of the heat transport will not be impaired.

Further, since a tank 140 connecting a plurality of tubes 110 is provided, by providing just one location of the connector 140 with a sealing pipe 141, it becomes possible to evacuate the inside to a vacuum and seal in a working medium.

Further, since the evaporator 110A is arranged under the condenser 110B and the tank 140 is provided at the evaporator 110A side end and arranged so as to contact the exhaust pipe part 130A (first plate 131), the working medium in the tank 140 is also positively heated by the exhaust gas and the dry out for activating the heat switch function (turning waste heat recovery OFF) is performed early.

Further, since the exhaust pipe part 130A forming part of the exhaust pipe 11 and the cooling water passage part 150A forming part of the heater circuit 30 are joined integrally with the evaporator 110A and condenser 110B to form the waste heat recovery system 100, it is possible to easily attach the exhaust pipe 11 and heater circuit 30 as a single heat exchanger.

A second embodiment of the present invention is shown in FIGS. 4A and 4B. The second embodiment comprises the first embodiment where the tubes 110 and fins 120 are changed to the tubes 110a and fins 120a.

The tubes 110a are flat type tubes 110 comprised of two tube plates 111, 112 combined to form round tube types. Further, the fins 120a are comprised of the corrugated type fins 120 provided with tube burring holes and are formed as plate types through which the tubes 110a are inserted. Further, in the condenser 110B, to improve the heat transmission with the cooling water side, plate type water side fins 120b are attached. Due to this, similar effects to the first embodiment can be obtained.

A third embodiment of the present invention is shown in FIGS. 5A and 5B. The third embodiment is comprised of the first embodiment eliminating the tubes 110, water tank 150, and insulating wall parts 160 and stacking plate type fins 120c to form tubes 110b, a water tank 150a, and insulating wall parts 160a.

The fins 120c are provided with pluralities of holes having burring parts 121. By stacking the fins 120c, the burring parts 121 are successively connected whereby tubes 110b corresponding to round tubes are formed.

The outer circumferences of the fins 120c corresponding to the condenser 110B are provided with raised edges 122. By stacking the fins 120c, the raised edges 122 are successively connected and a water tank 150a corresponding to a box shaped vessel is formed. Further, the pluralities of burring parts 121 of the fins 120c corresponding to the condenser 110B are provided with water holes so as to enable cooling water to circulate across the entire water tank 150a.

Further, the ends of the fins 120c corresponding to the insulating parts 110C are provided with bent parts 123. By stacking the fins 120c, the bent parts 123 are successively aligned, whereby insulating wall parts 160a corresponding to the plurality of separated plate-shaped members are formed.

Due to this, the tubes 110, water tank 150, and insulating wall parts 160 are eliminated and the price can be lowered.

Fourth embodiments of the present invention are shown in FIG. 6A to FIG. 8B. The fourth embodiments are comprised of the above first to third embodiments where the evaporators 110A of the tubes 110, 110a, and 110b are arranged above the condensers 110B to form top heat types. The waste heat recovery systems 100 shown in FIGS. 6A and 6B, FIGS. 7A and 7B, and FIGS. 8A and 8B, appearance wise, are comprised of the waste heat recovery systems 100 explained in FIGS. 2A and 2B, FIGS. 4A and 4B, and FIGS. 5A and 5B inverted vertically and with the inside walls of the tubes 110, 110a, and 110b provided with wicks extending from the condensers 110B to the evaporators 110A.

Due to this, even if the evaporator 110A is arranged above the condenser 110B in accordance with the positions of the exhaust pipe 11 and heater circuit 30 set in the vehicle, heat transport between the two 110A, 110B becomes possible.

Finally, another embodiment will be explained. In the above embodiments, the explanation was given providing insulating wall parts 160 at two locations at the upstream side and downstream side of the cooling air flow, but the invention is not limited to this. It is also possible to provide a wall part at only one location at the upstream side of the cooling air flow. Due to this, the flow of the cooling air is effectively blocked by the insulating wall part 160 and can be prevented from striking the insulating part 110C, so by setting the minimum extent of an insulating wall part 160, condensation of the working medium at the insulating part 110C can be prevented. Further, conversely, insulating wall parts 160 may also be provided at all of the circumference of the insulating part 110C (four locations).

Note that the present invention was explained in detail based on specific embodiments, but a person skilled in the art can make various changes, modifications, etc. without departing from the claims and concept of the present invention.