Patent Application
20080047690
This application is based on Japanese Patent Applications No. 2006-228966 filed on Aug. 25, 2006, and No. 2007-193143 filed on Jul. 25, 2007, the contents of which are incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a heat exchanger with a heat pipe.
2. Description of the Related Art
JP-A-4-45393 describes a heat exchanger using a loop type heat pipe, which is used for a hot water supply system. In the heat exchanger using the loop type heat pipe, a working fluid is circulated in a closed loop circuit to be evaporated and to be condensed. The working fluid is evaporated in an evaporation portion by absorbing heat from a thermal storage material, and is condensed in a condensation portion by radiating heat to water. In this heat exchanger, lower end portions of plural heat pipes communicate with each other by a lower communication portion (lower header), such that the working fluid condensed in the condensation portion flows into the plural heat pipes via the lower communication portion.
Furthermore, in a heat-pipe type heat exchanger, inner fins are located within heat pipes in order to increase a heat transmission area between the heat pipes and a working fluid and to improve pressure-resisting strength. Alternatively, in a case where inner fins are not provided in a heat-pipe type heat exchanger in which plural heat pipes are stacked and brazed, ribs are formed to improve brazing performance and pressure-resisting strength. Specifically, the heat pipe is provided with an inner fluid passage by oppositely arranging a first flat plate and a second flat plate, and the ribs protruding to the inner fluid passage are formed in the first flat plate and the second flat plate to contact at its tip ends.
The heat-pipe type heat exchanger is generally used for recovering heat of exhaust gas of an internal combustion engine of a vehicle so as to improve an engine-heating performance by using the exhaust heat. The temperature of exhaust gas may be increased to 900° C. in maximum. In contrast, water is normally used as the working fluid, and water is solidified (freeze) so that the volume expansion of about 9% is caused as compared with that in a liquid state. However, when water is used as the working fluid, the following problems may be caused.
For example, in a case where water is used as the working fluid in a heat exchanger having heat pipes provided with inner fins, when the working fluid is solidified at a low temperature condition such as the freeze point, the solidification of the working fluid starts firstly at portions contacting the heat pipes, the lower communication portion and the inner fins.
In view of the foregoing problems, it is an object of the present invention to provide a heat exchanger having an inner fin or ribs in a heat pipe, which can reduce inner pressure due to solidification of a working fluid thereby improving durability of the heat exchanger.
It is another object of the present invention to provide a heat exchanger having a heat-transmission area increasing member located in heat pipes, in which a bottom end of the heat-transmission area increasing member is positioned above a top surface of working fluid at least in a liquid state.
According to an aspect of the present invention, a heat exchanger includes an evaporation side heat pipe in which a working fluid flowing therein is heat exchanged with an exterior high-temperature fluid passing therethrough to be evaporated, a condensation side heat pipe in which the working fluid flowing therein is heat exchanged with an exterior low-temperature fluid passing therethrough to be condensed, and an evaporation side inner fin located in the evaporation side heat pipe to increase a heat transmission area of the evaporation side heat pipe with the working fluid. In the heat exchanger, the evaporation side heat pipe and the condensation side heat pipe are connected to form a closed cycle in which the working fluid circulates between the evaporation side heat pipe and the condensation side heat pipe, the evaporation side heat pipe is arranged such that the working fluid flows in the evaporation side heat pipe in a direction different from a horizontal direction, and the evaporation side inner fin located in the evaporation side heat pipe has a bottom end that is positioned above a top surface of the working fluid in a liquid state.
Thus, at a solidification start time of the working fluid, because the top surface of the working fluid does not contact the inner fin in the evaporation side heat pipes, heat transmission is slowly performed at the top surface of the working fluid, and the solidification of the working fluid at its top surface becomes later. Therefore, at the time where the top surface of the working fluid is solidified and closed, an amount of the liquid working fluid closed and sealed by the solid working fluid becomes smaller, thereby reducing an inner pressure due to the solidification of the liquid working fluid. Accordingly, the durability of the heat exchanger can be improved.
For example, the evaporation side heat pipe and the condensation side heat pipe may be arranged in an arrangement direction that is approximately parallel to the horizontal direction, and the condensation side heat pipe may be arranged such that the working fluid flows in the condensation side heat pipe in a direction different from the horizontal direction. Furthermore, a condensation side inner fin may be located in the condensation side heat pipe to increase a heat transmission area of the condensation side heat pipe with the working fluid. In this case, the condensation side inner fin located in the condensation side heat pipe has a bottom end that is positioned above a top surface of the working fluid in the liquid state within the condensation side heat pipe. Accordingly, at a solidification start time of the working fluid, the top surface of the working fluid does not contact the condensation side inner fin in the condensation side heat pipes, heat transmission is slowly performed at the top surface of the working fluid, and the solidification of the working fluid at its top surface can be made later. Therefore, at the time where the top surface of the working fluid is solidified and closed, an amount of the liquid working fluid closed and sealed by the solid working fluid becomes smaller, thereby reducing an inner pressure due to the solidification of the liquid working fluid. Thus, the durability of the heat exchanger can be improved.
The bottom end of the evaporation side inner fin or the condensation side inner fin may be positioned above a top surface of the working fluid in a solid state. In this case, the inner pressure generated due to the solidification of the working fluid can be further reduced in the heat exchanger.
According to another aspect of the present invention, a heat exchanger includes a heat pipe elongated in a longitudinal direction and closed at its longitudinal ends to have a working fluid sealed therein, and an inner fin located in the heat pipe to increase a heat transmission area of the heat pipe with the working fluid. Furthermore, the heat pipe has a first portion on one side of the longitudinal direction and a second portion on the other side of the longitudinal direction, the first portion of the heat pipe is located to evaporate the working fluid by heat-exchanging between the working fluid and an exterior high-temperature fluid, the second portion of the heat pipe is located to condense the evaporated working fluid, the heat pipe is arranged such that the working fluid flows in the heat pipe in a direction different from a horizontal direction, and the inner fin located in the heat pipe has a bottom end that is positioned above a top surface of the working fluid in a liquid state. Accordingly, at a solidification start time of the working fluid, the top surface of the working fluid does not contact the inner fin in the heat pipe, heat transmission is slowly performed at the top surface of the working fluid, and the solidification of the working fluid at its top surface becomes later. Therefore, at the time where the top surface of the working fluid is solidified and closed, an amount of the liquid working fluid closed and sealed by solid working fluid becomes smaller, thereby reducing an inner pressure due to the solidification of the liquid working fluid. For example, the heat pipe may be a straight pipe.
According to another aspect of the present invention, a heat exchanger includes an evaporation side heat pipe in which a working fluid flowing therein is heat exchanged with an exterior high-temperature fluid passing therethrough to be evaporated, and a condensation side heat pipe in which the working fluid flowing therein is heat exchanged with an exterior low-temperature fluid passing therethrough to be condensed. Furthermore, the evaporation side heat pipe and the condensation side heat pipe are connected to form a closed cycle in which the working fluid circulates between the evaporation side heat pipe and the condensation side heat pipe, and the evaporation side heat pipe is arranged such that the working fluid flows in the evaporation side heat pipe in a direction different from a horizontal direction. In addition, the evaporation side heat pipe includes a first flat plate, a second flat plate opposite to the first flat plate to form an inner fluid passage between the first flat plate and the second flat plate, in which the working fluid flows, and ribs provided in the first flat plate and the second flat plate to protrude into the inner fluid passage. In the heat exchanger, the ribs of the first flat plate and the second flat plate, opposite to each other, are joined to each other at its top ends, and the ribs are positioned above a top surface of the working fluid in a liquid state. Accordingly, at a solidification start time of the working fluid, the top surface of the working fluid does not contact the ribs, thereby the solidification of the working fluid at its top surface can be made later.
According to another aspect of the present invention, a heat exchanger includes a heat pipe elongated in a longitudinal direction and closed at its longitudinal ends to have a working fluid sealed therein. The heat pipe has a first portion on one side of the longitudinal direction, and a second portion on the other side of the longitudinal direction. The first portion of the heat pipe is located to evaporate the working fluid by heat-exchanging between the working fluid and an exterior high-temperature fluid, the second portion of the heat pipe is located to condense the evaporated working fluid, and the heat pipe is arranged such that the working fluid flows in the heat pipe in a direction different from a horizontal direction. In addition, the heat pipe includes a first flat plate, a second flat plate opposite to the first flat plate to form an inner fluid passage between the first flat plate and the second flat plate, in which the working fluid flows, and ribs provided in the first flat plate and the second flat plate to protrude into the inner fluid passage. In this heat exchanger, the ribs of the first flat plate and the second flat plate, opposite to each other, are joined to each other at its top ends, and the ribs are positioned above a top surface of the working fluid in a liquid state. Accordingly, at a solidification start time of the working fluid, the top surface of the working fluid does not contact the ribs, thereby the solidification of the working fluid at its top surface can be made later.
According to another aspect of the present invention, a heat exchanger includes an evaporation portion located to heat and evaporate a working fluid, and a condensation portion located to cool and condense the evaporated working fluid. In the heat exchanger, at least one of the evaporation portion and the condensation portion includes a plurality of heat pipes in which the working fluid flows, the evaporation portion and the condensation portion are connected to form a closed cycle in which the working fluid circulates between the evaporation portion and the condensation portion, the heat pipes are arranged such that the working fluid flows in the heat pipes in a direction different from a horizontal direction, the evaporation portion further includes a heat-transmission area increasing member located in each of the heat pipes to increase a heat transmission area of the heat pipe with the working fluid, and the heat-transmission area increasing member is located at a position separated from a top surface of the working fluid in a liquid state in a vertical direction. Accordingly, at a solidification start time of the working fluid, the top surface of the working fluid does not contact the heat-transmission area increasing member in the heat pipes, thereby heat transmission is slowly performed at the top surface of the working fluid, and the solidification of the working fluid at its top surface becomes later. Therefore, at a time where the top surface of the working fluid is solidified and closed, an amount of the liquid working fluid closed and sealed by solid working fluid becomes smaller, thereby reducing an inner pressure due to the solidification of the liquid working fluid. Accordingly, the durability of the heat exchanger can be improved.
For example, the heat-transmission area increasing member may be located in the heat pipe at a position upper than a top surface of the working fluid in a solid state, or lower than the top surface of the working fluid in the liquid state. Furthermore, the heat-transmission area increasing member may be an inner fin located inside the heat pipe, or may be ribs protruding from an inner wall surface of the heat pipe inside of the heat pipe.
Additional objects and advantages of the present invention will be more readily apparent from the following detailed description of preferred embodiments when taken together with the accompanying drawings. In which:
A first embodiment of the present invention will be now described with reference to
As shown in
The evaporation portion 1 is located within a cylindrical first box 100 in which exhaust gas having a high temperature from an engine flows. The cylindrical first box 100 is, for example, disposed in an exhaust cylinder of the engine. The evaporation portion 1 is constituted such that the exhaust gas is heat exchanged with a working fluid so as to heat and evaporate the working fluid.
The evaporation portion 1 includes a plurality of evaporation side heat pipes 3a. Each of the evaporation side heat pipes 3a is formed into a flat shape in a cross-section having a major dimension in a direction (face-back direction in the paper of
The condensation portion 2 is located in a second box 200 in which engine-cooling water having a relative low temperature flows. The second box 200 can be located in a water circuit in which engine-cooling water (coolant) circulates to cool the engine. In the condensation portion 2, the working fluid evaporated in the evaporation portion 1 and the engine-cooling water is heat exchanged so that the evaporated working fluid is condensed and the engine-cooling water is heated.
The condensation portion 2 includes a plurality of condensation side heat pipes 3b. Each of the condensation side heat pipes 3b is formed into a flat shape in a cross-section having a major dimension in a direction (face-back direction in the paper of
A pair of communication portions 5a, 5b are provided at longitudinal end sides of the heat pipes 3a, 3b to communicate with the heat pipes 3a, 3b at both end sides of the heat pipes 3a, 3b. The pair of the communication portions 5a, 5b are disposed to form a part of the evaporation portion 1 and a part of the condensation portion 2. In the communication portions 5a, 5b at both end sides of the heat pipes 3a, 3b, the one positioned at the upper side of the heat pipes 3a, 3b in the vertical direction is an upper communication portion 5a, and the other one positioned at the lower side of the heat pipes 3a, 3b in the vertical direction is a lower communication portion 5b.
The heat pipes 3a, 3b and the pair of the communication portions 5a, 5b are constituted to form a closed loop-type cycle. In the closed loop-type cycle, working fluid (e.g., refrigerant, water) is sealed therein to be evaporated and condensed. In this embodiment, water is used as the working fluid, as an example. The amount of the working fluid sealed in the closed loop-type cycle is set such that the liquid surface of the working fluid is positioned above the lower communication portion 5b. In
Side plates 7 for reinforcing the evaporation portion 1 are provided at two sides of the evaporation portion 1, to extend approximately in parallel with the longitudinal direction of the evaporation side heat pipe 3a.
As shown in
For example, the bottom end 8c of the inner fin 8 is positioned upper than the top surface position L of the working fluid in the liquid state. Furthermore, the bottom end 8c of the inner fin 8 is positioned upper than the top surface position S of the working fluid in the solid state, in this embodiment, as shown in
The inner fin 8 is formed by bending a plate member to have tip portions 8a and flat plate portions 8b which are alternately formed. The inner fin 8 is formed such that the tip portions 8a of the inner fin 8 contact inner walls of the evaporation side heat pipe 3a, and the flat plate portions 8b extend to opposite inner walls of the evaporation side heat pipe 3a.
Inner fins (not shown) may be provided at an upper portion within the condensation side heat pipe 3b in the vertical direction, similarly to the structure of the inner fins 8 of the evaporation side heat pipes 3a. In this case, the bottom ends of the inner fins of the condensation side heat pipes 3b can be positioned upper than the top surface position L of the working fluid in the liquid state, similarly to the evaporation side heat pipe 3a. Furthermore, the bottom end of the inner fins of the condensation side heat pipes 3b can be positioned upper than the top surface position S of the working fluid in the solid state, similarly to the structure of the evaporation side heat pipes 3a.
Next, operation of the heat exchanger 300 of the first embodiment with the above structure will be now described. In the heat exchanger 300 of the first embodiment, while exhaust gas passes through the evaporation portion 1 in the first box 100, the liquid working fluid within the evaporation side heat pipes 3a is evaporated by absorbing heat from the exhaust gas, such that the evaporated vapor-phase working fluid flows into the condensation portion 2 via the upper communication portion 5a. The evaporated vapor working fluid flowing into the condensation side heat pipe 3b is cooled and condensed by the engine-cooling water flowing in the second box 200, and the condensed working fluid flows into the evaporation portion 1 via the lower communication portion 5b. Accordingly, the working fluid is circulated in the heat pipes 3a, 3b and the communication portions 5a, 5b connected in a closed loop, thereby the exhaust heat from the exhaust gas of the engine is recovered to heat the engine-cooling water.
In a case where the exhaust gas does not pass through the evaporation portion 1 in the first box 100, if the outside air temperature becomes lower than the freeze temperature, the working fluid staying at the lower portion in the heat pipes 3a, 3b and the lower communication portion 5b is solidified.
At a solidification start time of the working fluid, because the top surface of the working fluid does not contact the inner fins 8, the heat transmission is slowly performed at the top surface of the working fluid, and the solidification of the working fluid at the top surface can be made later. In contrast, at the portions contacting the heat pipes 3a, 3b and the lower communication portion 5b, the working fluid solidifies relatively early as compared with the top surface of the working fluid. Therefore, the timing, at which the top surface of the working fluid is solidified, becomes later. As a result, as shown in
According to the first embodiment, the bottom ends 8c of the inner fins 8 are positioned above the top surface position S of the working fluid at the solid state. Thus, even when the top surface of the working fluid increases in accordance with the progress of the solidification of the working fluid, the top surface of the working fluid does not contact the inner fins 8. Because the top surface of the working fluid does not contact the inner fins 8, the solidification of the working fluid at the top surface can be made relatively slowly as compared with a case where the top surface of the working fluid contacts the inner fins 8.
The second embodiment of the present invention will be now described with reference to
In the above-described heat exchanger 300 of the first embodiment, the evaporation portion 1 and the condensation portion 2 are arranged in the arrangement direction approximately parallel to the horizontal direction. That is, the heat pipes 3a are arranged in parallel with the heat pipes 3b, and the upper and lower communication portions 5a, 5b are arranged to extend approximately perpendicular to the extending direction of the heat pipes 3a, 3b, in the above-described first embodiment.
In contrast, in a heat exchanger 300 of the second embodiment, a condensation portion 2 is arranged at an upper side of an evaporation portion 1, as shown in
Plate-type fins 4c formed from a thin plate material are joined to outer wall surfaces of the evaporation side heat pipes 3a. Upper and lower plates 51a, 51b have plural through holes at positions corresponding to the evaporation side heat pipes 3a, and are located at upper and lower end sides of the evaporation side heat pipes 3a.
The lower plate 51b is located at the lower end side of the evaporation side heat pipes 3a so that the through holes of the lower plate 51b correspond to the ends of the evaporation side heat pipes 3a. A lower tank plate 52b is joined to the lower plate 51b to be opposite to the bottom ends of the evaporation side heat pipes 3a. Therefore, a lower communication portion 5b is constructed by joining the lower tank plate 52b and the lower tank 51b.
Similarly, the upper plate 51a is located at the upper end side of the evaporation side heat pipes 3a so that the through holes of the upper plate 51a correspond to the ends of the evaporation side heat pipes 3a. An upper tank plate 52a is joined to the upper plate 51a to be opposite to the upper ends of the evaporation side heat pipes 3a. Therefore, an upper communication portion 5a is constructed by joining the upper tank plate 52a and the upper plate 51a.
A second box 200 for accommodating the condensation side heat pipes 3c can be formed by a flat water tank plate 201 and a water tank portion 202 having approximately a U-shaped cross section. The second box 200 is arranged at a top side of the evaporation portion 1 to be lie on the evaporation portion 1. The condensation portion 2 is located within the second box 200 such that the condensation portion 2 is arranged at the top side of the evaporation portion 1 and the condensation side heat pipes 3c extend in a direction approximately perpendicular to the extending direction of the evaporation side heat pipes 3a.
The condensation side heat pipes 3c constitute a drawn-cup type heat exchanger. For example, the condensation side heat pipe 3c is constructed by joining two plates 31c, 32c so as to form a tube shape. Plural tube-shaped heat pipes 3c are stacked so as to form a fluid flow portion 33c and tank portions 34c, 35c at two end sides of the heat pipes 3c in the longitudinal direction of the heat pipes 3c. The tank portions 34c, 35c form communication passages extending in the stacking direction of the condensation side heat pipes 3c, and communicate with the fluid flow portions 33c through communication holes.
A vapor gas introduction pipe 11 is located in the tank portion 34c to extend in the stacking direction, such that one end (lower end) of the vapor gas introduction pipe 11 is open in the upper communication portion 5a and the other end (upper end) is open at an area close to the top wall of the tank portion 34c. Therefore, via the vapor gas introduction pipe 11, the upper communication portion 5a communicates with the upper side area of the tank portion 34c, the inside of the tank portion 34c, the fluid flow portions 33c of the condensation side heat pipes 3c, and the tank portion 35c.
The return pipe 10 is located to penetrate the upper communication portion 5a of the evaporation portion 1, such that one end (upper end) of the return pipe 10 communicates with the tank portion 35c of the condensation portion 2, and the other end (lower end) of the return pipe 10 communicates with the lower communication portion 5b of the evaporation portion 1.
Similarly to the above-described first embodiment, the inner fins 8 are located at the upper portions in the evaporation side heat pipes 3a in the vertical direction, such that the bottom ends 8c of the inner fins 8 are positioned above the top surface position L of the working fluid in the liquid state, and above the top surface position S of the working fluid in the solid state. In contrast, the condensation side heat pipes 3c do not have therein an inner fin.
According to the heat exchanger 300 of the second embodiment, while the exhaust gas passes through the evaporation portion 1, the liquid working fluid within the evaporation side heat pipes 3a is evaporated by absorbing heat from the exhaust gas, and the evaporated vapor working fluid flows into the condensation portion 2 via the upper communication portion 5a. The vapor working fluid flowing into the condensation side heat pipes 3c is cooled and condensed by engine-cooling water, and the condensed liquid working fluid flows into the lower communication portion 5b via the return pipe 10, and then flows into the evaporation portion 1 via the lower communication portion 5b.
In a case where the exhaust gas does not pass through the evaporation portion 1, if the outside air temperature becomes lower than the freeze temperature of the working fluid, the working fluid staying at the lower portion in the heat pipes 3a, and the lower communication portion 5b is solidified.
At a solidification start time of the working fluid, because the top surface of the working fluid does not contact the inner fins 8, the heat transmission is slowly performed, and the solidification of the working fluid at its top surface becomes later. In contrast, at the portions contacting the heat pipes 3a and the lower communication portion 5b, the working fluid solidifies relatively early as compared with the top surface of the working fluid. Therefore, the timing, at which the top surface of the working fluid is solidified to be closed, becomes later. As a result, at the time where the top surface of the working fluid is closed by the solid working fluid, an amount of the liquid working fluid closed and sealed by the solid working fluid becomes smaller, thereby reducing an inner pressure due to the solidification of the liquid working fluid. Thus, the durability of the heat exchanger 300 can be improved, similarly to the above-described first embodiment.
According to the second embodiment, the bottom ends 8c of the inner fins 8 are positioned upper than the top surface position S of the working fluid at the solid state. Thus, even when the top surface of the working fluid increases in accordance with the solidification of the working fluid, the top surface of the working fluid does not contact the inner fins 8. Because the top surface of the working fluid does not contact the inner fins 8, the solidification of the working fluid at the top surface can be made relatively slowly as compared with a case where the top surface of the working fluid contacts the inner fins 8.
A third embodiment of the present invention will be now described with reference to
In the third embodiment, the heat exchanger 300 is a siphon-type heat exchanger in which a working fluid is circulated in heat pipes closed at two ends. As shown in
In this embodiment, plural heat pipes 3d are arranged in parallel to extend in a vertical direction. A first box 100 for passing through exhaust gas discharged from an engine is located at a lower area of the heat pipes 3d in the vertical direction. That is, a part of the heat pipes 3d, positioned on a lower side, is located inside the first box 100, and a part of the heat pipes 3d, positioned on an upper side, is located inside a second box 200. Plural plate fins 4c are joined to the outer surfaces of the heat pipes 3d, as shown in
Inner fins 8 are located inside the heat pipes 3d at a position above a predetermined position. Similarly to the above-described first embodiment, the inner fins 8 are located in the heat pipes 3a, such that the bottom ends of the inner fins 8 are positioned upper than the top surface position L of the working fluid in the liquid state, and upper than the top surface position S of the working fluid in the solid state.
Heat transmission fins 12 (heat transmission member) are located between the first box 100 and the second box 200 to partially contact both the first and second boxes 100, 200. The heat transmission fin 12 includes flat plate portion 12a, and a tip portion 12b located between adjacent two flat plate portions 12a to separate the adjacent two flat plate portions 12a by a predetermined distance. The tip portion 12b is bent from the flat plate portion 12a approximately by a right angle, for example. The tip portions 12b of the heat transmission fins 12 are joined to the first box 100 and the second box 200 to partially contact the first box 100 and the second box 200. Therefore, heat can be transmitted between the first box 100 and the second box 200 via the heat transmission fins 12.
According to the heat exchanger 300 of the third embodiment, while the exhaust gas passes through the evaporation portion 1, the liquid working fluid staying in the lower portion of the heat pipes 3d is evaporated by absorbing heat from the exhaust gas, and the evaporated vapor working fluid moves upwardly to the upper portion of the heat pipes 3d. The vapor working fluid flowing into the upper portion of the heat pipes 3d within the second box 200 is cooled and condensed by engine-cooling water, and the condensed liquid working fluid flows downwardly to return into the lower portion of the heat pipes 3d.
In a case where the exhaust gas does not pass through the evaporation portion 1, if the outside air temperature becomes lower than the freeze temperature of the working fluid, the working fluid staying at the lower portion in the heat pipes 3d is solidified.
At a solidification start time of the working fluid, because the top surface of the working fluid does not contact the inner fins 8, the heat transmission is slowly performed, and the solidification of the working fluid at its top surface becomes later. In contrast, at the portions contacting the heat pipes 3d, the working fluid solidifies relatively early as compared with the top surface of the working fluid. Therefore, the timing, at which the top surface of the working fluid is solidified to be closed, becomes later. As a result, at the time where the top surface of the working fluid is closed, an amount of the liquid working fluid closed and sealed by solid working fluid becomes smaller, thereby reducing an inner pressure due to the solidification of the liquid working fluid. Thus, the durability of the heat exchanger 300 can be improved, similarly to the above-described first embodiment.
According to the third embodiment, the bottom ends 8c of the inner fins 8 are positioned upper than the top surface position S of the working fluid at the solid state. Thus, even when the top surface of the working fluid increases in accordance with the solidification of the working fluid, the top surface of the working fluid does not contact the inner fins 8. Because the top surface of the working fluid does not contact the inner fins 8, the solidification of the working fluid at the top surface can be made relatively slowly as compared with a case where the top surface of the working fluid contacts the inner fins 8.
A fourth embodiment of the present invention will be now described with reference to FIGS. 7 to 9. In the fourth embodiment, the parts having the same functions as those of the first embodiment are indicated by the same reference numbers.
In the above-described first embodiment, the evaporation side heat pipe 3a is provided with the inner fin 8 at a position higher than a predetermined position above the top surface position S of the working fluid. In the fourth embodiment, instead of the inner fins, ribs are provided in the evaporation side heat pipes 3a.
As shown in FIGS. 7 to 9, the evaporation side heat pipe 3a is constructed with a flat first plate 31a and a flat second plate 32a which are arranged opposite to each other. The outer periphery of the first and second plates 31a, 32a are bonded by brazing to form an inner fluid passage 33a so that a working fluid flows in the inner fluid passage 33a.
A plurality of ribs 34a are formed in the first and second plates 31a, 32a to protrude into the inner fluid passage 33a. The ribs 34a can be formed such that top ends of the ribs 34a provided on the first plate 31a are joined to top ends of the ribs 34a provided on the second plate 31a, as shown in
Because the ribs 34a are formed to partially contact the first and second plates 31a, 32a, the brazing performance of a stacked member formed by stacking the evaporation side heat pipes 3a and the corrugated fins 4a (see
Plural ribs 34a are arranged to be separated from each other in a flow direction of exhaust gas (right-left direction of
According to the fourth embodiment, in a case where the exhaust gas does not pass through the evaporation portion 1, if the outside air temperature becomes lower than the freeze temperature of the working fluid, the working fluid staying at the lower portion in the heat pipes 3a and the lower communication portion 5b is solidified.
At a solidification start time of the working fluid, because the top surface of the working fluid does not contact any the ribs 34a, the heat transmission is slowly performed, and the solidification of the working fluid at its top surface becomes later. In contrast, at the portions contacting the heat pipes 3a and the lower communication portion 5b, the working fluid solidifies relatively early as compared with the top surface of the working fluid. Therefore, the timing, at which the top surface of the working fluid is solidified to be closed, becomes later. As a result, at the time where the top surface of the working fluid is closed by the solid working fluid, an amount of the liquid working fluid closed and sealed by solid working fluid becomes smaller, thereby reducing an inner pressure due to the solidification of the liquid working fluid. Thus, the durability of the heat exchanger 300 can be improved, similarly to the above-described first embodiment.
According to the fourth embodiment, the ribs 34a are positioned above the top surface position L of the working fluid at the liquid state, and above the top surface position S of the working fluid at the solid state. Thus, even when the top surface of the working fluid rises in accordance with the solidification of the working fluid, the top surface of the working fluid does not contact the ribs 34a. Because the top surface of the working fluid does not contact the ribs 34a, the solidification of the working fluid at the top surface can be made relatively slowly as compared with a case where the top surface of the working fluid contacts the ribs 34a.
The shapes and the positions of the ribs 34a formed in the evaporation side heat pipe 3a may be suitably changed without being limited to the ribs 34a shown in
Furthermore, when the evaporation side heat pipes 3a and the condensation side heat pipes 3b are arranged in parallel to each other as in the first embodiment, the condensation side heat pipes 3b may have the same structure as that of the evaporation side heat pipes 3a.
For example, similarly to the evaporation side heat pipe 3a, the condensation side heat pipe 3b is constructed with a flat first plate and a flat second plate which are arranged opposite to each other. The outer periphery of the first and second plates for the condensation side heat pipe 3b are bonded by brazing to form a condensation-side inner fluid passage so that the working fluid flows in the condensation-side inner fluid passage.
A plurality of ribs are formed in the first and second plates in the condensation side heat pipe 3b to protrude into the condensation-side inner fluid passage. The ribs can be formed in the condensation side heat pipe 3b such that top ends of the ribs provided on the first plate are joined to top ends of the ribs provided on the second plate. In addition, the ribs are arranged above the top surface of the working fluid in the vertical direction (longitudinal direction of the condensation side heat pipe 3b). Specifically, the ribs are located in upper portions of the condensation side heat pipes 3b in the vertical direction, such that the ribs are positioned upper than the top surface position L of the working fluid in the liquid state, and upper than the top surface position S of the working fluid in the solid state. Furthermore, the ribs may be also located in lower portions of the condensation side heat pipes 3b in the vertical direction such that the ribs are positioned lower than the top surface L of the working fluid in the liquid state.
Thus, at a solidification start time of the working fluid, because the top surface of the working fluid does not contact the ribs in the heat pipes 3b, 3b, the heat transmission can be slowly performed, and the solidification of the working fluid at its top surface becomes later. Therefore, at the time where the top surface of the working fluid is closed, an amount of the liquid working fluid closed and sealed by solid working fluid becomes smaller, thereby reducing an inner pressure due to the solidification of the liquid working fluid. Thus, the durability of the heat exchanger 300 can be improved.
Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art.
For example, the rib structure of the heat pipe 3a described in the fourth embodiment or the rib structure of the heat pipe 3a described in the modifications (
In the above-described embodiments, the longitudinal direction of the heat pipes 3a, 3b, 3d is positioned in the vertical direction. However, the longitudinal direction of the heat pipes 3a, 3b, 3d can be inclined relative to the vertical direction. Only when the condensed working fluid can be made to stay in a lower portion of the heat pipes 3a, 3b, 3d without being horizontally extended, the longitudinal direction of the heat pipes 3a, 3b, 3d may be suitably inclined relative to the vertical direction. That is, when the longitudinal direction of the heat pipes 3a, 3b, 3d is inclined relative to the horizontal direction or is perpendicular to the horizontal direction, it is possible for the condensed working fluid to stay in the lower portion of the heat pipes 3a, 3b, 3d. Only when the working fluid flows through the heat pipes 3a, 3b, 3d in a direction different from the horizontal direction, the arrangement of the heat pipes 3a, 3b, 3d can be suitably changed.
In the above-described embodiment, the working fluid may be suitably changed to any fluid normally used for evaporating and condensing. Furthermore, as a heating source for heating the working fluid in the evaporation portion 1, other high-temperature fluid can be suitably used instead of the exhaust gas of the engine. In addition, as the low-temperature fluid for radiating heat from the working fluid in the condensation portion 2, a fluid other than the engine-cooling water may be used. For example, as the low-temperature fluid, an engine oil, an inverter cooling water, etc. may be used.
In the above-described embodiment, as a heat-transmission area increasing member for increasing a heat transmission area of the heat pipe 3a, 3b, 3c, the inner fins 8 or the ribs 34a are used. However, the structure of the heat-transmission area increasing member is not limited to that, and can be suitably changed in accordance with the shape of the heat pipe 3a, 3b, 3d only when the heat-transmission area increasing member is located at a position separated from a top surface position L of the working fluid in the liquid state. More preferably, the heat-transmission area increasing member is positioned in the heat pipe 3a, 3b, 3c above the top surface position S of the working fluid in the solid state, or under the top surface position L of the working fluid in the liquid state.
Such changes and modifications are to be understood as being within the scope of the present invention as defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-228966 | Aug 2006 | JP | national |
| 2007-193143 | Jul 2007 | JP | national |
