US20120312506A1 - Loop heat pipe - Google Patents
Loop heat pipe Download PDFInfo
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- US20120312506A1 US20120312506A1 US13/591,397 US201213591397A US2012312506A1 US 20120312506 A1 US20120312506 A1 US 20120312506A1 US 201213591397 A US201213591397 A US 201213591397A US 2012312506 A1 US2012312506 A1 US 2012312506A1
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- Prior art keywords
- evaporator
- space
- working fluid
- heat pipe
- loop heat
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- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
- F28D15/00—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies
- F28D15/02—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes
- F28D15/0266—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes with separate evaporating and condensing chambers connected by at least one conduit; Loop-type heat pipes; with multiple or common evaporating or condensing chambers
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
- F28D15/00—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies
- F28D15/02—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes
- F28D15/04—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes with tubes having a capillary structure
- F28D15/046—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes with tubes having a capillary structure characterised by the material or the construction of the capillary structure
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L23/00—Details of semiconductor or other solid state devices
- H01L23/34—Arrangements for cooling, heating, ventilating or temperature compensation ; Temperature sensing arrangements
- H01L23/42—Fillings or auxiliary members in containers or encapsulations selected or arranged to facilitate heating or cooling
- H01L23/427—Cooling by change of state, e.g. use of heat pipes
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
- F28D21/00—Heat-exchange apparatus not covered by any of the groups F28D1/00 - F28D20/00
- F28D2021/0019—Other heat exchangers for particular applications; Heat exchange systems not otherwise provided for
- F28D2021/0028—Other heat exchangers for particular applications; Heat exchange systems not otherwise provided for for cooling heat generating elements, e.g. for cooling electronic components or electric devices
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
- F28F2265/00—Safety or protection arrangements; Arrangements for preventing malfunction
- F28F2265/12—Safety or protection arrangements; Arrangements for preventing malfunction for preventing overpressure
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
- H01L2924/0001—Technical content checked by a classifier
- H01L2924/0002—Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
Definitions
- the embodiments discussed herein relate to a loop heat pipe used to cool heat generating components such as electronic devices.
- a loop heat pipe is known as a device for cooling various types of heat generating components, in which an evaporator and a condenser are connected in a loop via a vapor transport line and a liquid transport line.
- Liquid-phase working fluid evaporates in the evaporator due to heat supplied from an external heat source, and the vaporized working fluid is transported via the vapor transport line to the condenser, in which the vapor condenses back to a liquid by releasing heat. See, for example, Japanese Laid-open Patent Publication No. 2004-218887.
- FIG. 1A through FIG. 1C illustrate a conventional evaporator 1000 , where FIG. 1A is a cross-sectional view of the evaporator along the direction of flow of the working fluid, and FIG. 1B and FIG. 1C are cross-sectional views taken along the A-A′ line of FIG. 1A .
- a heat generating component 1010 such as an electronic device 1010 is generally shaped flat, and accordingly, the heat-receiving face 1002 of the evaporator 1000 of a loop heat pipe is made flat so as to be kept in stable contact with the heat generating component 1010 .
- To improve the cooling ability of the loop heat pipe it is desired to increase the internal volume of the evaporator 1000 as much as possible.
- a wick 1007 is provided in an evaporator case 1001 so as to be in close contact with the inner wall of the evaporator case 1001 .
- Heat is transferred promptly from the evaporator case 1001 to the wick 1007 and it allows the working fluid 1006 penetrating the wick 1007 to vaporize quickly.
- the vaporized working fluid is guided through grooves 1005 toward the vapor transport line 1004 .
- the temperature of the internal working fluid rises and the adhesion between the evaporator case 1001 and the wick 1007 is degraded. This state is illustrated in FIG. 1C .
- the internal pressure is applied toward the top face with a large area size, which causes the top wall to swell as illustrated in FIG. 1C .
- the evaporator body is made as thin as possible. In this circumstance, it is difficult to guarantee a thickness of the evaporator case 1001 enough to provide rigidity to resist the internal pressure.
- adhesion between the evaporator case 1001 and the inner wick 1007 is degraded.
- loop heat pipe It is desired for the loop heat pipe to maintain thermal contact between the evaporator case 1001 and the wick 1007 during operation to ensure the thermal performance even if the temperature and the pressure of the working fluid are increasing in the evaporator.
- a loop heat pipe includes:
- the evaporator includes
- a first space having a set of walls including a contact wall that comes into contact with the external heat source
- a through-hole formed in a dividing wall separating the first space and the second space to allow the first space and the second space to communicate with each other.
- FIG. 1A is a cross-sectional view of a conventional flat plate evaporator used in a loop heat pipe along a direction of flow of working fluid;
- FIG. 1B is a cross-sectional view of the evaporator taken along the A-A′ line of FIG. 1A , illustrating the non-operating state;
- FIG. 1C is a cross-sectional view of the evaporator taken along the A-A′ line of FIG. 1A , illustrating an issue arising in the conventional flat plate evaporator under application of heat;
- FIG. 2 is a general view of a loop heat pipe to which the present invention is applied;
- FIG. 3A is a cross-sectional view of an evaporator according to the first embodiment of the invention, along a direction of flow of working fluid;
- FIG. 3B is a cross-sectional view of the evaporator taken along the A-A′ line of FIG. 3A ;
- FIG. 4 is a diagram illustrating saturated vapor pressure curves of several working fluids as a function of temperature
- FIG. 5A is a schematic cross-sectional diagram of the evaporator in the non-operating state, for explaining the advantage of the first embodiment
- FIG. 5B is a schematic cross-sectional diagram of the evaporator under application of heat, for explaining the advantage of the first embodiment
- FIG. 6A illustrates an example of mounting the evaporator according to the first embodiment
- FIG. 6B is a perspective view of the mounted evaporator of FIG. 6A ;
- FIG. 7 is a graph illustrating an advantage of the loop heat pipe using the evaporator according to the first embodiment
- FIG. 8A illustrates a first modification of the evaporator of the first embodiment, which evaporator is in the non-operating state
- FIG. 8B illustrates the evaporator of the first modification illustrated in FIG. 8A , which is in the operating (heat absorbing) state;
- FIG. 9A illustrates a second modification of the evaporator of the first embodiment, which evaporator is in the non-operating state
- FIG. 9B illustrates the evaporator of the second modification illustrated in FIG. 9A , which is in the operating (heat absorbing state);
- FIG. 10A is a cross-sectional view of an evaporator according to the second embodiment along the direction of flow of the working fluid
- FIG. 10B is a cross-sectional view taken along the A-A′ line of FIG. 10A ;
- FIG. 11A is a schematic diagram for explaining an advantage of the evaporator of the second embodiment, which evaporator is in the non-operating state;
- FIG. 11B is a schematic diagram for explaining the advantage of the evaporator of the second embodiment, which is in the operating (heat absorbing) state;
- FIG. 12A illustrates a modification of the evaporator of the second embodiment, which evaporator is in the non-operating state
- FIG. 12B illustrates the evaporator of the modification, which is in the operating (heat absorbing) state
- FIG. 13A illustrates an example of mounting the evaporator according to the second embodiment
- FIG. 13B is a perspective view of the mounted evaporator of FIG. 13A ;
- FIG. 14 is a graph illustrating an advantage of the loop heat pipe using the evaporator of the second embodiment.
- FIG. 2 illustrates an overall structure of a loop heat pipe 1 to which the present invention is applied.
- the loop heat pipe 1 includes an evaporator 10 which vaporizes a liquid-phase working fluid due to heat supplied from a heat generating component (e.g., an electronic component), and a condenser 11 that causes a vapor-state working fluid to condense by removing the heat.
- the evaporator 10 and the condenser 11 are connected in a loop by a vapor line 14 for transporting the vaporized working fluid from the evaporator 10 to the condenser 11 and a liquid line 13 for transporting the liquid-state working fluid from the condenser 11 to the evaporator 10 .
- the liquid line 13 and the vapor line 14 form the connecting lines.
- a blast fan 12 is provided near the condenser 11 to enhance removal of heat.
- the working fluid in the vapor line 14 or the liquid line 13 is not necessarily 100% vapor or 100% liquid, and it is in a vapor phase and a liquid phase mixed with each other.
- the connecting lines are named the “vapor line” and the “liquid line” for the sake of convenience.
- FIG. 3A and FIG. 3B illustrate an evaporator 10 according to the first embodiment of the invention, where FIG. 3A is a cross-sectional view of the evaporator 10 along a direction of flow of the working fluid and FIG. 3B is a cross-sectional view taken along the A-A′ line in FIG. 3A .
- the evaporator 10 has a vaporization chamber (a first space) 40 A having a liquid supply path 46 , and a pressure adjusting chamber (a second space) 40 B for adjusting the pressure in the vaporization chamber 40 A.
- a pressure adjusting hole 55 is formed in a dividing wall 51 that separates between the vaporization chamber 40 A and the pressure adjusting chamber 40 B to allow the vaporization chamber 40 A and the pressure adjusting chamber 40 B to communicate with each other.
- the bottom face of an evaporator case 40 is a heat-receiving surface 42 .
- the evaporator 10 is mounted on a heat generating component such that the heat receiving surface 42 comes into contact with the heat generating component such as an electronic component (see FIG. 6A ) to receive heat from the electronic component.
- a wick (porous material) 47 is provided in the vaporization chamber 40 A so as to be kept in mechanical and thermal contact with the inner wall of the vaporization chamber 40 A.
- the (liquid-state) working fluid is supplied through the liquid line 13 into the vaporization chamber 40 A and penetrates into the wick 47 .
- the liquid absorbed in the wick 47 is heated by heat transferred from the evaporator case 40 to the wick 47 .
- the inner space of the evaporator 10 is maintained at a saturated vapor pressure of the working fluid.
- the working fluid is vaporized.
- the working fluid takes in latent heat.
- the vapor that has taken in the latent heat passes through grooves (vapor discharge grooves) 45 and flows into the vapor line 14 .
- a portion of the vapor passes through the pressure adjusting hole 55 and flows into the pressure adjusting chamber 40 B. Consequently, the pressures in the vaporization chamber 40 A and the pressure adjusting chamber 40 B become almost the same.
- the saturated vapor pressure within the utilized temperature range of the working fluid 49 is at or above the atmospheric pressure in the environment in which the loop heat pipe 1 is used.
- the evaporator case 40 is a flat plate case with an entire height of 18 mm, a width of 60 mm and a length of 70 mm.
- a double chamber structure is employed in which the pressure adjusting chamber 40 B is provided on the top of the vaporization chamber 40 A.
- the pressure adjusting chamber 40 B has a space with the dimensions 66 mm length ⁇ 56 mm width ⁇ 1 mm height.
- the pressure adjusting chamber 40 B and the vaporization chamber 40 A are separated from each other by a dividing wall 51 with a thickness of 2 mm.
- a pressure adjusting hole 55 with a diameter of 1 mm is formed in the dividing wall 55 so as to allow the pressure adjusting chamber 40 B to communicate with the vapor side of the vaporization chamber 40 A.
- the inner dimensions of the vaporization chamber 40 A are 66 mm length ⁇ 56 mm width ⁇ 11 mm height.
- the thickness of the walls defining the vaporization chamber 40 A is 2 mm on the whole.
- the material of the vaporization case 40 and the dividing wall 51 is oxygen-free copper in the first embodiment.
- Conventional flat evaporators are often made of a rigid material such as stainless so as to be tolerant of high internal pressure.
- the evaporator of the first embodiment does not necessarily use a rigid material, as will be described below. Rather, a material with a higher thermal conductivity than stainless is used such that the temperature distribution of the evaporator case 40 becomes uniform. For example, aluminum alloy can be used for reducing weight.
- the wick 47 arranged inside the vaporization chamber 40 A is made of sintered nickel.
- the porous diameter is about 10 ⁇ m, and the porosity is about 50%.
- the outer dimensions of the wick 47 are 50 mm length ⁇ 56 mm width ⁇ 11 mm height. Especially, the height of the wick 47 is set precisely such that the wick 47 is held in the vaporization chamber 40 A in close contact with the inner wall thereof. Fifteen grooves (vapor passages) 45 with a width of 1 mm and a depth of 2 mm are formed at a pitch of 3 mm in the top face and the bottom face (which come into contact with the ceiling and the bottom of the vaporization chamber 40 A, respectively). In the center of the wick 47 is formed a liquid supply path 46 with a height of 3 mm, a width of 40 mm and a length of 40 mm to take the working fluid 49 supplied from the liquid line 13 into the wick 47 .
- the vapor line 14 and the liquid line 13 connecting the evaporator 10 and the condenser 11 are copper pipes with an outer diameter of 6 mm, an inner diameter of 5 mm, and a length of 300 mm.
- the condenser 11 is also a copper pipe, like the vapor line 14 and the liquid line 13 , with an outer diameter of 6 mm, an inner diameter of 5 mm and a length of 400 mm. Radiation fins are thermally connected to the circumference of the pipe, and are cooled by the blast fan 12 (see FIG. 2 ).
- n-pentane is used as the working fluid 49
- other fluids with high saturation pressures including butane and ammonia can be used.
- FIG. 4 is a graph of saturation pressure curves of various fluids.
- n-pentane is used as the working fluid 49
- the boiling point at atmospheric pressure is about 36° C.
- the temperature of the working fluid 49 becomes near 50-70° C.
- butane or pentane is used as the working fluid 49
- the saturation pressure of the working fluid exceeds the atmospheric pressure in the temperature range of 50-70° C.
- the conventional evaporator illustrated in FIG. 1A the top wall of the case 1001 swells due to the internal pressure of the working fluid as illustrated in FIG. 10 .
- the contact between the evaporation case 1000 and the wick 1007 is degraded and the cooling performance lowers.
- a pressure adjusting chamber 40 B is provided on the top of the vaporization chamber 40 A, and a pressure adjusting hole 55 is formed in the dividing wall 51 to allow the vapor coming from the surface of the wick 47 to flow into the pressure adjusting chamber 40 B.
- the internal pressures in the vaporization chamber 40 A and the pressure adjusting chamber 40 B become equal.
- FIG. 5A and FIG. 5B are diagrams to explain an advantage of the first embodiment.
- the vapor pressure inside the vaporization chamber 40 A increases as the working fluid absorbed in the wick 47 is heated by heat transferred from the electronic component 20 .
- the vaporized working fluid flows into the pressure adjusting chamber 40 B through the pressure adjusting hole 55 , the vapor pressure applied to the dividing wall 51 from the vaporization chamber 40 A becomes equal to the vapor pressure applied to the dividing wall 51 from the pressure adjusting chamber 40 B. Accordingly, the dividing wall 51 with a surface which is in contact with the wick 47 is prevented from deforming due to the internal pressure.
- the top wall 53 of the evaporator case 40 (which is also the top wall of the pressure adjusting chamber 40 B in the first embodiment) expands and bends outward because the saturated vapor pressure of butane is higher than the atmospheric pressure. Even if the internal pressure in the vaporization chamber 40 A becomes high due to the increasing vapor pressure of the working fluid 49 , the thermal contact between the vaporization chamber 40 A and the wick 47 can be maintained satisfactorily because of no deformation in the dividing wall 51 .
- FIG. 6A and FIG. 6B illustrate a structure in which the evaporator 10 of the first embodiment is mounted over a heat generating component.
- the evaporator 10 of the loop heat pipe 1 is placed, via thermal grease 21 , over the electronic component 20 on a printed circuit board 30 and secured to the printed circuit board 30 using attachment screws 31 .
- the amount (rate) of heat absorption of the evaporator 10 is about 60 W in the first embodiment.
- the condenser 11 (not shown in FIG. 6A and FIG. 6B ) is cooled at the room temperature (25° C.) using a blast fan 12 (90 mm diameter, 12-volt driving voltage).
- FIG. 7 is a diagram illustrating the cooling ability of the loop heat pipe of the first embodiment, with a comparison example a loop heat pipe using a conventional evaporator illustrated in FIG. 1 .
- the horizontal axis of the graph represents amount of heat generated by a heater (i.e., the electronic component), and the vertical axis represents thermal resistance [° C./W] between the evaporator 10 and the condenser 11 .
- the thermal resistance indicates a difference between the temperature of the heat-receiving surface 42 of the evaporator 10 and the average temperature of the condense 11 per watt (divided by the quantity of heat generated by the electronic component 20 ).
- the loop heat pipe 1 of the first embodiment can maintain the cooling ability at the satisfactory level (by keeping the thermal resistance low). This is because the thermal contact between the dividing wall 51 of the evaporator case 40 and the wick 47 is maintained in the satisfactory state even if the temperature of the evaporator rises along with the increase in the quantity of heat generated from the electronic component.
- FIG. 8A and FIG. 8B illustrate a first modification of the evaporator of the first embodiment.
- an outer wall 63 e.g., the top wall 63
- the thickness of the dividing wall 61 is 2 mm
- the thickness of the top wall 63 of the evaporator case 40 is 1 mm.
- the outer wall (top wall) 63 is made thinner than the internal dividing wall 61 , the outer wall 63 swells outward (toward the atmosphere) due to the increased pressure of the vapor flowing into the pressure adjusting chamber 60 B through the pressure adjusting hole 65 , while little deformation occurs in the internal dividing wall 61 .
- This arrangement is advantageous to maintain the adhesion between the internal dividing wall 61 and the wick 47 constant.
- the thickness of the outer wall 63 is set half the thickness of the dividing wall 61 , the invention is not limited to this example.
- the outer wall 63 is designed with an appropriate thickness as long as the outer wall 63 is deformable without affecting the shape of the dividing wall 61 .
- the thickness of the outer wall 63 can be set to one fifth to two third of the thickness of the dividing wall 61 , depending on the type of the working fluid used in the loop heat pipe 1 .
- FIG. 9A and FIG. 9B illustrate a second modification of the evaporator of the first embodiment.
- the thicknesses of the top wall 73 and the internal dividing wall 71 of the evaporator 70 are similar to each other, but the dividing wall 71 is slightly curved toward the vaporization chamber 70 A in which the wick 47 is provided.
- the pressure adjusting chamber 70 B In the non-operating state, there is no deformation in the pressure adjusting chamber 70 B as illustrated in FIG. 9A .
- the pressure adjusting chamber 70 B expands as illustrated in FIG. 9B .
- the outer wall (top wall) 73 of the evaporator case 70 swells outward due to the vapor flowing into the pressure adjusting chamber 70 B through the pressure adjusting hole 75 .
- the internal dividing wall 71 also deforms toward the wick 47 so as to increase the curvature.
- a compressive force acts on the dividing wall 71 so as to press it against the wick 47 . Consequently, adhesion between the dividing wall 71 and the wick 47 is enhanced and the cooling ability of the loop heat pipe 1 is improved.
- the cooling ability of the loop heat pipe 1 is improved and settled with a simple structure, and stable operation of electronic equipment is realized.
- FIG. 10A and FIG. 10B illustrate an evaporator 80 according to the second embodiment of the invention, where FIG. 10A is a cross-sectional view along a direction of flow of the working fluid and FIG. 10B is a cross-sectional view taken along the A-A′ line of FIG. 10B .
- the evaporator 80 has a vaporization chamber (first space) 90 A with a liquid supply path 86 and a second fluid chamber (second space) 90 B with an airtight structure.
- the second fluid chamber 90 B is filled with a second fluid 100 that has a saturated vapor pressure higher than that of the working fluid supplied to the vaporization chamber 90 A at the same temperature. At least a portion of the second fluid 100 is in a liquid phase 100 b .
- the second fluid when ethanol is used as the working fluid, can be selected from the group of ethanol, pentane, butane, ammonia and so on.
- the selected fluid is introduced in the second fluid chamber 90 B with a portion thereof in a liquid phase. If the working fluid is pentane, then the second fluid is selected from the group of pentane, butane, ammonia and so on, and introduced in the second fluid chamber 90 B with a portion thereof in a liquid phase.
- the bottom face of the evaporator case 90 is the heat receiving face 82 .
- the evaporator 80 is mounted over a heat generating component 20 such that the heat receiving face 82 comes into contact with the heat generating component 20 (such as an electronic component 20 ) to receive heat from the electronic component 20 (see FIG. 11A and FIG. 11B ).
- a wick (a porous material) 47 is provided in the vaporization chamber 90 A so as to be mechanically and thermally in contact with the inner surface of the vaporization chamber 90 A.
- the evaporator case 90 is a flat plate case with an entire height of 18 mm, a width of 60 mm and a length of 70 mm.
- a double chamber structure is employed in which the second fluid chamber 90 B is provided on the top of the vaporization chamber 90 A.
- the second fluid chamber 90 B is an airtight space with the dimensions 66 mm length ⁇ 56 mm width ⁇ 1 mm height.
- the second fluid chamber 90 B and the vaporization chamber 90 A are separated from each other by a dividing wall 91 with a thickness of 2 mm.
- the inner dimensions of the vaporization chamber 90 A are 66 mm length ⁇ 56 mm width ⁇ 11 mm height.
- the thickness of the walls of the vaporization chamber 90 A is 2 mm on the whole.
- the material of the vaporization case 90 and the dividing wall 91 is oxygen-free copper in the second embodiment.
- Conventional flat evaporators are often made of a rigid material such as stainless so as to be tolerant of the high internal pressure.
- the evaporator of the second embodiment does not necessarily use a rigid material, as will be described below. Rather, a material with a higher thermal conductivity than stainless is used such that the temperature distribution of the evaporator case 90 becomes uniform. For example, aluminum alloy can be used for reducing weight.
- the wick 47 arranged inside the vaporization chamber 90 A is made of sintered nickel.
- the porous diameter is about 10 ⁇ m, and the porosity is about 50%.
- the outer dimensions of the wick 47 are 50 mm length ⁇ 56 mm width ⁇ 11 mm height.
- the height of the wick 47 is set precisely such that the wick 47 is held in the vaporization chamber 90 A in close contact with the inner wall thereof.
- Fifteen grooves (vapor passages) 45 with a width of 1 mm and a depth of 2 mm are formed at a pitch of 3 mm in the top face and the bottom face (which come into contact with the ceiling and the bottom of the vaporization chamber 90 A, respectively).
- a liquid supply path 86 with a height of 3 mm, a width of 40 mm and a length of 40 mm to take the working fluid 89 supplied from the liquid line 13 into the wick 47 .
- the vapor line 84 and the liquid line 83 connecting the evaporator 80 and the condenser 11 are copper pipes with an outer diameter of 6 mm, an inner diameter of 5 mm, and a length of 300 mm.
- the condenser 11 is also a copper pipe, like the vapor line 84 and the liquid line 83 , with an outer diameter of 6 mm, an inner diameter of 5 mm and a length of 400 mm. Radiation fins are thermally connected to the circumference of the pipe, and are cooled by the blast fan 12 .
- n-pentane is used as the working fluid 89 .
- the boiling point of pentane under the atmospheric pressure is 36° C.
- the temperature of the working fluid 89 reaches around 50-70° C. during the operation of the loop heat pipe 1 , and accordingly, the vapor pressure of pentane becomes at or above the atmospheric pressure.
- the second fluid chamber 90 B contains 1 cc of butane serving as the second fluid in advance.
- Butane is introduced in the second fluid chamber 90 B by evacuating the air from the second fluid chamber 90 B and inletting only butane, using the same method as introducing the working fluid in the loop heat pipe 1 .
- the vapor phase become dominant in the second fluid during operation of the heat generating component (i.e., the electronic component) 20 , and at least a portion of the second fluid is in a liquid phase throughout the operating state and non-operating state.
- FIG. 11A and FIG. 11B are schematic diagrams for explaining an advantage of the second embodiment.
- the saturated vapor pressure of butane is higher than that of n-pentane used as the working fluid 89 at the same temperature.
- the dividing wall 91 is pressed toward the lower pressure side, that is, toward the vaporization chamber 90 A in which the wick 47 is provided.
- the pressure difference between the working fluid 90 and the second fluid 100 becomes large.
- the dividing wall 91 is brought into closer contact with the wick 47 .
- the top wall 93 of the second fluid chamber 90 B swells outward because the pressure difference between the second fluid chamber 90 B and the atmospheric pressure is greater than the pressure difference between the vaporization chamber 90 A and the second fluid chamber 90 B.
- the dividing wall 91 also tends to swell toward the vaporization chamber 90 A, and the adhesion between the dividing wall 91 and the wick 47 is enhanced.
- FIG. 12A and FIG. 12B illustrate a modification of the evaporator 80 of the second embodiment.
- the thickness of the dividing wall 91 is 2 mm, which is the same as the thickness of the evaporator case 90 .
- the thickness of the dividing wall 91 a separating the vaporization chamber 90 A and the second fluid chamber 90 B of an evaporator 80 a is made less than the wall thickness of the evaporator case 90 , and it is, for example, 1 mm.
- FIG. 13A and FIG. 13B are schematic diagram illustrating a structure in which the evaporator 80 of the second embodiment is mounted over a heat generating component.
- the evaporator 80 of the loop heat pipe 1 is placed, via thermal grease 21 , over the electronic component 20 on a printed circuit board 30 and secured to the printed circuit board 30 using attachment screws 31 .
- the amount (rate) of heat absorption of the evaporator 80 is about 60 W in the second embodiment.
- the condenser 11 (not shown in FIG. 13A and FIG. 13B ) is cooled at room temperature (25° C.) using a blast fan 12 (90 mm diameter, 12-volt driving voltage).
- Heat transferred from the electronic component 20 to the evaporator case 90 vaporizes the working fluid 89 penetrating in the wick 47 .
- the second fluid with a saturated vapor pressure higher than that of the working fluid 89 and encapsulated in the second fluid chamber 90 B also vaporizes.
- the dividing wall 91 is pressed against the wick 47 in the vaporization chamber 90 A.
- FIG. 14 is a diagram illustrating the cooling ability of the loop heat pipe 1 of the second embodiment, with a comparison example a loop heat pipe in which a conventional wick structure illustrated in FIG. 1A through FIG. 1C is incorporated.
- the horizontal axis of the graph represents the amount (rate) of heat generated by a heater (i.e., the electronic component), and the vertical axis represents thermal resistance [° C./W] which is determined by dividing the difference between the average temperatures of the evaporator 10 and the condenser 11 by the quantity of heat generated by the electronic component 20 .
- the loop heat pipe 1 of the second embodiment can maintain the cooling ability in the satisfactory state (by maintaining the thermal resistance low). This is because the thermal contact between the dividing wall 91 (or 91 a ) of the evaporator case 90 and the wick 47 is maintained in the satisfactory state even if the temperature of the evaporator rises along with the increase in the quantity of heat transferred from the electronic component.
- the deformation of a copper (Cu) evaporator case 90 of 56 mm width is calculated when using pentane as the working fluid.
- the difference between the atmospheric pressure and the internal pressure of the evaporator case is 0.2 MPa at the LHP operating temperature (near 70° C.) as illustrated in FIG. 4 .
- the evaporator case expands and deforms outward by 95 ⁇ m. This state impairs thermal contact between the evaporator case and the wick and the thermal resistance increases.
- butane is introduced in the second fluid chamber 90 B illustrated in FIG.
- the internal pressure in the vaporization chamber 90 A is lower than the internal pressure in the second fluid chamber 90 B by 0.5 MPa. If the wick 47 is not arranged in the vaporization chamber 90 A, the dividing wall 91 of the evaporator case 90 will swells toward the vaporization chamber 90 A by 140 ⁇ m. However, because the wick 47 is provided in the vaporization chamber 90 A, the dividing wall 91 is pressed against the wick 47 and tight contact is produced between the dividing wall 91 and the wick 47 .
- the evaporator configuration of the second embodiment can further improve the cooling efficiency, compared to the first embodiment.
- the second space is provided only on the top of the evaporator case, opposite to the heat-receiving face, to define a double chamber structure because the top face has a large area size of a thermally conductive surface.
- the second space may be provided so as to cover at least one of the side walls of the vaporization chamber (first space). If the second space is provided so as to cover the top face and a pair of side faces of the vaporization chamber (first space), the double chamber structure is applied to three sides of the evaporator, except for the heat receiving surface. In this case, thermal adhesion between the wick and the vaporization chamber is further enhanced.
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Abstract
A loop heat pipe includes an evaporator to vaporize a working fluid due to heat supplied from an external heat source; a condenser to cause the vaporized working fluid to condense; and connecting lines to connect the evaporator and the condenser in a loop, wherein the evaporator includes a first space defined by a set of walls including a contact wall that comes into contact with the external heat source, a second space provided adjacent to at least one of the walls other than the contact wall, and a through-hole formed in a dividing wall separating the first space and the second space to allow the first space and the second space to communicate with each other.
Description
- This application is a continuation application of International Application PCT/JP2010/066329 filed on Sep. 21, 2010 designating the United States, which International application further claims the benefit of the earlier filing date of Japanese Patent Application No. 2010-075443 filed in Japan on Mar. 29, 2010, the entire contents of the International Application and the priority Japanese Application being incorporated herein by reference.
- The embodiments discussed herein relate to a loop heat pipe used to cool heat generating components such as electronic devices.
- A loop heat pipe is known as a device for cooling various types of heat generating components, in which an evaporator and a condenser are connected in a loop via a vapor transport line and a liquid transport line. Liquid-phase working fluid evaporates in the evaporator due to heat supplied from an external heat source, and the vaporized working fluid is transported via the vapor transport line to the condenser, in which the vapor condenses back to a liquid by releasing heat. See, for example, Japanese Laid-open Patent Publication No. 2004-218887.
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FIG. 1A throughFIG. 1C illustrate aconventional evaporator 1000, whereFIG. 1A is a cross-sectional view of the evaporator along the direction of flow of the working fluid, andFIG. 1B andFIG. 1C are cross-sectional views taken along the A-A′ line ofFIG. 1A . Aheat generating component 1010 such as anelectronic device 1010 is generally shaped flat, and accordingly, the heat-receivingface 1002 of theevaporator 1000 of a loop heat pipe is made flat so as to be kept in stable contact with theheat generating component 1010. To improve the cooling ability of the loop heat pipe, it is desired to increase the internal volume of theevaporator 1000 as much as possible. On the other hand, there is another demand for shaping the evaporator to be as compact as possible. To satisfy both demands, a flat plate loop heat pipe is used. - In order to efficiently remove heat from the
heat generating component 1010 during operation, it is desired to cause the workingfluid 1006 supplied through theliquid transport line 1003 to theevaporator 1000 to vaporize in an efficient manner. In this regard, awick 1007 is provided in anevaporator case 1001 so as to be in close contact with the inner wall of theevaporator case 1001. Heat is transferred promptly from theevaporator case 1001 to thewick 1007 and it allows the workingfluid 1006 penetrating thewick 1007 to vaporize quickly. The vaporized working fluid is guided throughgrooves 1005 toward thevapor transport line 1004. However, as the heat is transferred to theevaporator 1000, the temperature of the internal working fluid rises and the adhesion between theevaporator case 1001 and thewick 1007 is degraded. This state is illustrated inFIG. 1C . - In
FIG. 1C , when the saturated vapor pressure of the working fluid exceeds the atmospheric pressure at the operating temperature of the loop heat pipe, the internal surface of theevaporator case 1001 is pressed outward by the internal pressure of the working fluid. If the loop heat pipe is placed at ordinary temperature and pressure, and if the boiling point of the working fluid (such as pentane, R141B, butane, or ammonia) used in the loop heat pipe is above room temperature under standard atmospheric pressure, then theflat evaporator case 1001 deforms outward. If the evaporator has a cylindrical shape, the internal pressure is equally distributed in the circumferential direction and expansion of the evaporation case is less. In contrast, with the flat plate loop heat pipe, the internal pressure is applied toward the top face with a large area size, which causes the top wall to swell as illustrated inFIG. 1C . Especially when a flat plate evaporator is employed for the purpose of reducing the size and the weight of electric equipment, the evaporator body is made as thin as possible. In this circumstance, it is difficult to guarantee a thickness of theevaporator case 1001 enough to provide rigidity to resist the internal pressure. When theevaporator case 1001 swells due to the increasing internal pressure, adhesion between theevaporator case 1001 and theinner wick 1007 is degraded. This issue becomes more conspicuous at the top face of theevaporator case 1001 than the bottom face secured to the heat generating component 1010 (such as a CPU). Besides, agap 1020 is produced between theevaporator case 1001 and thewick 1007 at a higher temperature. In this state, sufficient heat cannot be transferred from theevaporator case 1001 to thewick 1007, and the working fluid is prevented from vaporizing from the surface of thewick 1007. Consequently, the cooling capacity is lowered. - It is desired for the loop heat pipe to maintain thermal contact between the
evaporator case 1001 and thewick 1007 during operation to ensure the thermal performance even if the temperature and the pressure of the working fluid are increasing in the evaporator. - According to an aspect of the embodiments, a loop heat pipe includes:
- an evaporator to vaporize a working fluid due to heat supplied from an external heat source;
- a condenser to cause the vaporized working fluid to condense; and
- connecting lines to connect the evaporator and the condenser in a loop,
- wherein the evaporator includes
- a first space having a set of walls including a contact wall that comes into contact with the external heat source,
- a second space provided adjacent to at least one of the walls other than the contact wall, and
- a through-hole formed in a dividing wall separating the first space and the second space to allow the first space and the second space to communicate with each other.
- The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims.
- It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive to the invention as claimed.
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FIG. 1A is a cross-sectional view of a conventional flat plate evaporator used in a loop heat pipe along a direction of flow of working fluid; -
FIG. 1B is a cross-sectional view of the evaporator taken along the A-A′ line ofFIG. 1A , illustrating the non-operating state; -
FIG. 1C is a cross-sectional view of the evaporator taken along the A-A′ line ofFIG. 1A , illustrating an issue arising in the conventional flat plate evaporator under application of heat; -
FIG. 2 is a general view of a loop heat pipe to which the present invention is applied; -
FIG. 3A is a cross-sectional view of an evaporator according to the first embodiment of the invention, along a direction of flow of working fluid; -
FIG. 3B is a cross-sectional view of the evaporator taken along the A-A′ line ofFIG. 3A ; -
FIG. 4 is a diagram illustrating saturated vapor pressure curves of several working fluids as a function of temperature; -
FIG. 5A is a schematic cross-sectional diagram of the evaporator in the non-operating state, for explaining the advantage of the first embodiment; -
FIG. 5B is a schematic cross-sectional diagram of the evaporator under application of heat, for explaining the advantage of the first embodiment; -
FIG. 6A illustrates an example of mounting the evaporator according to the first embodiment; -
FIG. 6B is a perspective view of the mounted evaporator ofFIG. 6A ; -
FIG. 7 is a graph illustrating an advantage of the loop heat pipe using the evaporator according to the first embodiment; -
FIG. 8A illustrates a first modification of the evaporator of the first embodiment, which evaporator is in the non-operating state; -
FIG. 8B illustrates the evaporator of the first modification illustrated inFIG. 8A , which is in the operating (heat absorbing) state; -
FIG. 9A illustrates a second modification of the evaporator of the first embodiment, which evaporator is in the non-operating state; -
FIG. 9B illustrates the evaporator of the second modification illustrated inFIG. 9A , which is in the operating (heat absorbing state); -
FIG. 10A is a cross-sectional view of an evaporator according to the second embodiment along the direction of flow of the working fluid; -
FIG. 10B is a cross-sectional view taken along the A-A′ line ofFIG. 10A ; -
FIG. 11A is a schematic diagram for explaining an advantage of the evaporator of the second embodiment, which evaporator is in the non-operating state; -
FIG. 11B is a schematic diagram for explaining the advantage of the evaporator of the second embodiment, which is in the operating (heat absorbing) state; -
FIG. 12A illustrates a modification of the evaporator of the second embodiment, which evaporator is in the non-operating state; -
FIG. 12B illustrates the evaporator of the modification, which is in the operating (heat absorbing) state; -
FIG. 13A illustrates an example of mounting the evaporator according to the second embodiment; -
FIG. 13B is a perspective view of the mounted evaporator ofFIG. 13A ; and -
FIG. 14 is a graph illustrating an advantage of the loop heat pipe using the evaporator of the second embodiment. -
FIG. 2 illustrates an overall structure of aloop heat pipe 1 to which the present invention is applied. Theloop heat pipe 1 includes anevaporator 10 which vaporizes a liquid-phase working fluid due to heat supplied from a heat generating component (e.g., an electronic component), and acondenser 11 that causes a vapor-state working fluid to condense by removing the heat. Theevaporator 10 and thecondenser 11 are connected in a loop by avapor line 14 for transporting the vaporized working fluid from theevaporator 10 to thecondenser 11 and aliquid line 13 for transporting the liquid-state working fluid from thecondenser 11 to theevaporator 10. Theliquid line 13 and thevapor line 14 form the connecting lines. In the example ofFIG. 2 , ablast fan 12 is provided near thecondenser 11 to enhance removal of heat. - The working fluid in the
vapor line 14 or theliquid line 13 is not necessarily 100% vapor or 100% liquid, and it is in a vapor phase and a liquid phase mixed with each other. During operation of theloop heat pipe 1, for the most part the working fluid inside thevapor line 14 is in the vapor phase, while for the most the working fluid inside theliquid line 13 is in the liquid phase. In this regard, the connecting lines are named the “vapor line” and the “liquid line” for the sake of convenience. -
FIG. 3A andFIG. 3B illustrate anevaporator 10 according to the first embodiment of the invention, whereFIG. 3A is a cross-sectional view of theevaporator 10 along a direction of flow of the working fluid andFIG. 3B is a cross-sectional view taken along the A-A′ line inFIG. 3A . In the first embodiment, theevaporator 10 has a vaporization chamber (a first space) 40A having aliquid supply path 46, and a pressure adjusting chamber (a second space) 40B for adjusting the pressure in thevaporization chamber 40A. Apressure adjusting hole 55 is formed in a dividingwall 51 that separates between thevaporization chamber 40A and thepressure adjusting chamber 40B to allow thevaporization chamber 40A and thepressure adjusting chamber 40B to communicate with each other. - In the example illustrated in
FIG. 3A andFIG. 3B , the bottom face of anevaporator case 40 is a heat-receivingsurface 42. Theevaporator 10 is mounted on a heat generating component such that theheat receiving surface 42 comes into contact with the heat generating component such as an electronic component (seeFIG. 6A ) to receive heat from the electronic component. A wick (porous material) 47 is provided in thevaporization chamber 40A so as to be kept in mechanical and thermal contact with the inner wall of thevaporization chamber 40A. The (liquid-state) working fluid is supplied through theliquid line 13 into thevaporization chamber 40A and penetrates into thewick 47. The liquid absorbed in thewick 47 is heated by heat transferred from theevaporator case 40 to thewick 47. The inner space of theevaporator 10 is maintained at a saturated vapor pressure of the working fluid. When the temperature of the working fluid has reached the boiling point under the saturated vapor pressure, the working fluid is vaporized. During vaporization, the working fluid takes in latent heat. The vapor that has taken in the latent heat passes through grooves (vapor discharge grooves) 45 and flows into thevapor line 14. Simultaneously, a portion of the vapor passes through thepressure adjusting hole 55 and flows into thepressure adjusting chamber 40B. Consequently, the pressures in thevaporization chamber 40A and thepressure adjusting chamber 40B become almost the same. The saturated vapor pressure within the utilized temperature range of the workingfluid 49 is at or above the atmospheric pressure in the environment in which theloop heat pipe 1 is used. - Explanation is made of the exemplified structure of the
evaporator 10 illustrated inFIG. 3A andFIG. 3B . Theevaporator case 40 is a flat plate case with an entire height of 18 mm, a width of 60 mm and a length of 70 mm. A double chamber structure is employed in which thepressure adjusting chamber 40B is provided on the top of thevaporization chamber 40A. Thepressure adjusting chamber 40B has a space with the dimensions 66 mm length×56 mm width×1 mm height. Thepressure adjusting chamber 40B and thevaporization chamber 40A are separated from each other by a dividingwall 51 with a thickness of 2 mm. Apressure adjusting hole 55 with a diameter of 1 mm is formed in the dividingwall 55 so as to allow thepressure adjusting chamber 40B to communicate with the vapor side of thevaporization chamber 40A. The inner dimensions of thevaporization chamber 40A are 66 mm length×56 mm width×11 mm height. The thickness of the walls defining thevaporization chamber 40A is 2 mm on the whole. - The material of the
vaporization case 40 and the dividingwall 51 is oxygen-free copper in the first embodiment. Conventional flat evaporators are often made of a rigid material such as stainless so as to be tolerant of high internal pressure. In contrast, the evaporator of the first embodiment does not necessarily use a rigid material, as will be described below. Rather, a material with a higher thermal conductivity than stainless is used such that the temperature distribution of theevaporator case 40 becomes uniform. For example, aluminum alloy can be used for reducing weight. - The
wick 47 arranged inside thevaporization chamber 40A is made of sintered nickel. - The porous diameter is about 10 μm, and the porosity is about 50%. The outer dimensions of the
wick 47 are 50 mm length×56 mm width×11 mm height. Especially, the height of thewick 47 is set precisely such that thewick 47 is held in thevaporization chamber 40A in close contact with the inner wall thereof. Fifteen grooves (vapor passages) 45 with a width of 1 mm and a depth of 2 mm are formed at a pitch of 3 mm in the top face and the bottom face (which come into contact with the ceiling and the bottom of thevaporization chamber 40A, respectively). In the center of thewick 47 is formed aliquid supply path 46 with a height of 3 mm, a width of 40 mm and a length of 40 mm to take the workingfluid 49 supplied from theliquid line 13 into thewick 47. - The
vapor line 14 and theliquid line 13 connecting theevaporator 10 and thecondenser 11 are copper pipes with an outer diameter of 6 mm, an inner diameter of 5 mm, and a length of 300 mm. Thecondenser 11 is also a copper pipe, like thevapor line 14 and theliquid line 13, with an outer diameter of 6 mm, an inner diameter of 5 mm and a length of 400 mm. Radiation fins are thermally connected to the circumference of the pipe, and are cooled by the blast fan 12 (seeFIG. 2 ). - Although in the first embodiment n-pentane is used as the working
fluid 49, other fluids with high saturation pressures including butane and ammonia can be used. -
FIG. 4 is a graph of saturation pressure curves of various fluids. When n-pentane is used as the workingfluid 49, the boiling point at atmospheric pressure is about 36° C. During operation of theloop heat pipe 1, the temperature of the workingfluid 49 becomes near 50-70° C. If butane or pentane is used as the workingfluid 49, the saturation pressure of the working fluid exceeds the atmospheric pressure in the temperature range of 50-70° C. With the conventional evaporator illustrated inFIG. 1A , the top wall of thecase 1001 swells due to the internal pressure of the working fluid as illustrated inFIG. 10 . The contact between theevaporation case 1000 and thewick 1007 is degraded and the cooling performance lowers. In contrast, with theevaporator 10 of the first embodiment with the double chamber structure, apressure adjusting chamber 40B is provided on the top of thevaporization chamber 40A, and apressure adjusting hole 55 is formed in the dividingwall 51 to allow the vapor coming from the surface of thewick 47 to flow into thepressure adjusting chamber 40B. The internal pressures in thevaporization chamber 40A and thepressure adjusting chamber 40B become equal. -
FIG. 5A andFIG. 5B are diagrams to explain an advantage of the first embodiment. When butane is used as the workingfluid 49, the vapor pressure inside thevaporization chamber 40A increases as the working fluid absorbed in thewick 47 is heated by heat transferred from theelectronic component 20. Because the vaporized working fluid flows into thepressure adjusting chamber 40B through thepressure adjusting hole 55, the vapor pressure applied to the dividingwall 51 from thevaporization chamber 40A becomes equal to the vapor pressure applied to the dividingwall 51 from thepressure adjusting chamber 40B. Accordingly, the dividingwall 51 with a surface which is in contact with thewick 47 is prevented from deforming due to the internal pressure. On the other hand, thetop wall 53 of the evaporator case 40 (which is also the top wall of thepressure adjusting chamber 40B in the first embodiment) expands and bends outward because the saturated vapor pressure of butane is higher than the atmospheric pressure. Even if the internal pressure in thevaporization chamber 40A becomes high due to the increasing vapor pressure of the workingfluid 49, the thermal contact between thevaporization chamber 40A and thewick 47 can be maintained satisfactorily because of no deformation in the dividingwall 51. -
FIG. 6A andFIG. 6B illustrate a structure in which theevaporator 10 of the first embodiment is mounted over a heat generating component. Theevaporator 10 of theloop heat pipe 1 is placed, viathermal grease 21, over theelectronic component 20 on a printedcircuit board 30 and secured to the printedcircuit board 30 using attachment screws 31. - The amount (rate) of heat absorption of the
evaporator 10 is about 60 W in the first embodiment. At this time, the condenser 11 (not shown inFIG. 6A andFIG. 6B ) is cooled at the room temperature (25° C.) using a blast fan 12 (90 mm diameter, 12-volt driving voltage). -
FIG. 7 is a diagram illustrating the cooling ability of the loop heat pipe of the first embodiment, with a comparison example a loop heat pipe using a conventional evaporator illustrated inFIG. 1 . The horizontal axis of the graph represents amount of heat generated by a heater (i.e., the electronic component), and the vertical axis represents thermal resistance [° C./W] between the evaporator 10 and thecondenser 11. The thermal resistance indicates a difference between the temperature of the heat-receivingsurface 42 of theevaporator 10 and the average temperature of the condense 11 per watt (divided by the quantity of heat generated by the electronic component 20). The smaller the thermal resistance, that is, the smaller the temperature difference between the heat-receivingsurface 42 and thecondenser 11, the greater is the heat transfer rate from theevaporator 10 to thecondenser 11. Consequently, the cooling ability is improved. - With the conventional loop heat pipe, the internal pressure in the evaporator increases as the quantity of heat increases, and the gap between the
evaporator case 1001 and thewick 1007 spreads as illustrated inFIG. 1C . In this situation, the thermal resistance increases, and the cooling ability is impaired. In contrast, theloop heat pipe 1 of the first embodiment can maintain the cooling ability at the satisfactory level (by keeping the thermal resistance low). This is because the thermal contact between the dividingwall 51 of theevaporator case 40 and thewick 47 is maintained in the satisfactory state even if the temperature of the evaporator rises along with the increase in the quantity of heat generated from the electronic component. -
FIG. 8A andFIG. 8B illustrate a first modification of the evaporator of the first embodiment. In this modification, an outer wall 63 (e.g., the top wall 63) of the evaporator that defines thepressure adjusting chamber 60B is made thinner than the dividingwall 61 separating thevaporization chamber 60A and thepressure adjusting chamber 60B. For example, the thickness of the dividingwall 61 is 2 mm, and the thickness of thetop wall 63 of theevaporator case 40 is 1 mm. In the non-operating state, there is no deformation of thepressure adjusting chamber 60B occurring as illustrated inFIG. 8A . In operation (during heat absorption), thepressure adjusting chamber 60B expands as illustrated inFIG. 8B . Because the outer wall (top wall) 63 is made thinner than theinternal dividing wall 61, theouter wall 63 swells outward (toward the atmosphere) due to the increased pressure of the vapor flowing into thepressure adjusting chamber 60B through thepressure adjusting hole 65, while little deformation occurs in theinternal dividing wall 61. This arrangement is advantageous to maintain the adhesion between theinternal dividing wall 61 and thewick 47 constant. Although inFIG. 8A andFIG. 8B , the thickness of theouter wall 63 is set half the thickness of the dividingwall 61, the invention is not limited to this example. Theouter wall 63 is designed with an appropriate thickness as long as theouter wall 63 is deformable without affecting the shape of the dividingwall 61. The thickness of theouter wall 63 can be set to one fifth to two third of the thickness of the dividingwall 61, depending on the type of the working fluid used in theloop heat pipe 1. -
FIG. 9A andFIG. 9B illustrate a second modification of the evaporator of the first embodiment. In the second modification, the thicknesses of thetop wall 73 and theinternal dividing wall 71 of theevaporator 70 are similar to each other, but the dividingwall 71 is slightly curved toward thevaporization chamber 70A in which thewick 47 is provided. In the non-operating state, there is no deformation in thepressure adjusting chamber 70B as illustrated inFIG. 9A . In operation (during heat absorption), thepressure adjusting chamber 70B expands as illustrated inFIG. 9B . The outer wall (top wall) 73 of theevaporator case 70 swells outward due to the vapor flowing into thepressure adjusting chamber 70B through thepressure adjusting hole 75. Simultaneously, theinternal dividing wall 71 also deforms toward thewick 47 so as to increase the curvature. A compressive force acts on the dividingwall 71 so as to press it against thewick 47. Consequently, adhesion between the dividingwall 71 and thewick 47 is enhanced and the cooling ability of theloop heat pipe 1 is improved. - According to the arrangements of the first embodiment, the cooling ability of the
loop heat pipe 1 is improved and settled with a simple structure, and stable operation of electronic equipment is realized. -
FIG. 10A andFIG. 10B illustrate anevaporator 80 according to the second embodiment of the invention, whereFIG. 10A is a cross-sectional view along a direction of flow of the working fluid andFIG. 10B is a cross-sectional view taken along the A-A′ line ofFIG. 10B . In the second embodiment, theevaporator 80 has a vaporization chamber (first space) 90A with aliquid supply path 86 and a second fluid chamber (second space) 90B with an airtight structure. The secondfluid chamber 90B is filled with asecond fluid 100 that has a saturated vapor pressure higher than that of the working fluid supplied to thevaporization chamber 90A at the same temperature. At least a portion of thesecond fluid 100 is in aliquid phase 100 b. Referring to the graph inFIG. 4 , when ethanol is used as the working fluid, the second fluid can be selected from the group of ethanol, pentane, butane, ammonia and so on. The selected fluid is introduced in the secondfluid chamber 90B with a portion thereof in a liquid phase. If the working fluid is pentane, then the second fluid is selected from the group of pentane, butane, ammonia and so on, and introduced in the secondfluid chamber 90B with a portion thereof in a liquid phase. - In the example illustrated in
FIG. 10A andFIG. 10B , the bottom face of theevaporator case 90 is theheat receiving face 82. Theevaporator 80 is mounted over aheat generating component 20 such that theheat receiving face 82 comes into contact with the heat generating component 20 (such as an electronic component 20) to receive heat from the electronic component 20 (seeFIG. 11A andFIG. 11B ). A wick (a porous material) 47 is provided in thevaporization chamber 90A so as to be mechanically and thermally in contact with the inner surface of thevaporization chamber 90A. The workingfluid 89 supplied via theliquid line 83 to thevaporization chamber 90A penetrates in thewick 47 and is vaporized by heat transferred from theevaporation case 40 to thewick 47. The vaporized fluid flows through thegrooves 45 formed in thewick 47 into thevapor line 84. A portion of the second fluid encapsulated in the secondfluid chamber 90B is also vaporized by heat in theevaporation case 90 during operation of the electronic component. In this state, avapor phase 100 a and aliquid phase 100 b coexist. - Explanation is made of the exemplified structure of the
evaporator 80 illustrated inFIG. 10A andFIG. 10B . Theevaporator case 90 is a flat plate case with an entire height of 18 mm, a width of 60 mm and a length of 70 mm. A double chamber structure is employed in which the secondfluid chamber 90B is provided on the top of thevaporization chamber 90A. The secondfluid chamber 90B is an airtight space with the dimensions 66 mm length×56 mm width×1 mm height. The secondfluid chamber 90B and thevaporization chamber 90A are separated from each other by a dividingwall 91 with a thickness of 2 mm. The inner dimensions of thevaporization chamber 90A are 66 mm length×56 mm width×11 mm height. The thickness of the walls of thevaporization chamber 90A is 2 mm on the whole. - The material of the
vaporization case 90 and the dividingwall 91 is oxygen-free copper in the second embodiment. Conventional flat evaporators are often made of a rigid material such as stainless so as to be tolerant of the high internal pressure. In contrast, the evaporator of the second embodiment does not necessarily use a rigid material, as will be described below. Rather, a material with a higher thermal conductivity than stainless is used such that the temperature distribution of theevaporator case 90 becomes uniform. For example, aluminum alloy can be used for reducing weight. - The
wick 47 arranged inside thevaporization chamber 90A is made of sintered nickel. The porous diameter is about 10 μm, and the porosity is about 50%. The outer dimensions of thewick 47 are 50 mm length×56 mm width×11 mm height. Especially, the height of thewick 47 is set precisely such that thewick 47 is held in thevaporization chamber 90A in close contact with the inner wall thereof. Fifteen grooves (vapor passages) 45 with a width of 1 mm and a depth of 2 mm are formed at a pitch of 3 mm in the top face and the bottom face (which come into contact with the ceiling and the bottom of thevaporization chamber 90A, respectively). In the center of thewick 47 is formed aliquid supply path 86 with a height of 3 mm, a width of 40 mm and a length of 40 mm to take the workingfluid 89 supplied from theliquid line 13 into thewick 47. - The
vapor line 84 and theliquid line 83 connecting theevaporator 80 and the condenser 11 (seeFIG. 2 ) are copper pipes with an outer diameter of 6 mm, an inner diameter of 5 mm, and a length of 300 mm. Thecondenser 11 is also a copper pipe, like thevapor line 84 and theliquid line 83, with an outer diameter of 6 mm, an inner diameter of 5 mm and a length of 400 mm. Radiation fins are thermally connected to the circumference of the pipe, and are cooled by theblast fan 12. - In the second embodiment, n-pentane is used as the working
fluid 89. The boiling point of pentane under the atmospheric pressure is 36° C. The temperature of the workingfluid 89 reaches around 50-70° C. during the operation of theloop heat pipe 1, and accordingly, the vapor pressure of pentane becomes at or above the atmospheric pressure. The secondfluid chamber 90B contains 1 cc of butane serving as the second fluid in advance. Butane is introduced in the secondfluid chamber 90B by evacuating the air from the secondfluid chamber 90B and inletting only butane, using the same method as introducing the working fluid in theloop heat pipe 1. The vapor phase become dominant in the second fluid during operation of the heat generating component (i.e., the electronic component) 20, and at least a portion of the second fluid is in a liquid phase throughout the operating state and non-operating state. -
FIG. 11A andFIG. 11B are schematic diagrams for explaining an advantage of the second embodiment. When butane is used as thesecond fluid 100, the saturated vapor pressure of butane is higher than that of n-pentane used as the workingfluid 89 at the same temperature. There is no deformation in the secondfluid chamber 90B in the non-operating state. Assuming that the temperatures on the working fluid side (in thevaporization chamber 90A) and the second fluid side (in the secondfluid chamber 90B) of theevaporator case 90 are substantially the same during operation, then the dividingwall 91 is pressed toward the lower pressure side, that is, toward thevaporization chamber 90A in which thewick 47 is provided. As the temperature rises, the pressure difference between the workingfluid 90 and thesecond fluid 100 becomes large. As the temperature of theevaporator case 90 rises due to heat transferred from theheat generating component 20, the dividingwall 91 is brought into closer contact with thewick 47. In this state, thetop wall 93 of the secondfluid chamber 90B swells outward because the pressure difference between the secondfluid chamber 90B and the atmospheric pressure is greater than the pressure difference between thevaporization chamber 90A and the secondfluid chamber 90B. At this time, the dividingwall 91 also tends to swell toward thevaporization chamber 90A, and the adhesion between the dividingwall 91 and thewick 47 is enhanced. -
FIG. 12A andFIG. 12B illustrate a modification of theevaporator 80 of the second embodiment. In the above-described example, the thickness of the dividingwall 91 is 2 mm, which is the same as the thickness of theevaporator case 90. In the modification, the thickness of the dividingwall 91 a separating thevaporization chamber 90A and the secondfluid chamber 90B of an evaporator 80 a is made less than the wall thickness of theevaporator case 90, and it is, for example, 1 mm. With this arrangement, there is no deformation in the secondfluid chamber 90B in the non-operating state (FIG. 12A ), and the dividingwall 91 a is more deformable during operation or heat absorption. Consequently, the dividingwall 91 a and thewick 47 come into tight contact with each other under higher compressive force (FIG. 12B ). -
FIG. 13A andFIG. 13B are schematic diagram illustrating a structure in which theevaporator 80 of the second embodiment is mounted over a heat generating component. Theevaporator 80 of theloop heat pipe 1 is placed, viathermal grease 21, over theelectronic component 20 on a printedcircuit board 30 and secured to the printedcircuit board 30 using attachment screws 31. The amount (rate) of heat absorption of theevaporator 80 is about 60 W in the second embodiment. At this time, the condenser 11 (not shown inFIG. 13A andFIG. 13B ) is cooled at room temperature (25° C.) using a blast fan 12 (90 mm diameter, 12-volt driving voltage). Heat transferred from theelectronic component 20 to theevaporator case 90 vaporizes the workingfluid 89 penetrating in thewick 47. Simultaneously, the second fluid with a saturated vapor pressure higher than that of the workingfluid 89 and encapsulated in the secondfluid chamber 90B also vaporizes. The dividingwall 91 is pressed against thewick 47 in thevaporization chamber 90A. -
FIG. 14 is a diagram illustrating the cooling ability of theloop heat pipe 1 of the second embodiment, with a comparison example a loop heat pipe in which a conventional wick structure illustrated inFIG. 1A throughFIG. 1C is incorporated. The horizontal axis of the graph represents the amount (rate) of heat generated by a heater (i.e., the electronic component), and the vertical axis represents thermal resistance [° C./W] which is determined by dividing the difference between the average temperatures of theevaporator 10 and thecondenser 11 by the quantity of heat generated by theelectronic component 20. The smaller the thermal resistance, that is, the smaller the temperature difference between the heat-receivingsurface 82 and thecondenser 11, the greater is the heat transfer rate from theevaporator 80 to thecondenser 11. Consequently, the cooling ability is improved. - With the conventional loop heat pipe, the temperature of the evaporator rises as the quantity of heat increases, and the gap between the
evaporator case 1001 and thewick 1007 spreads as illustrated inFIG. 1C . In this situation, the thermal resistance increases, and the cooling ability is impaired. In contrast, theloop heat pipe 1 of the second embodiment can maintain the cooling ability in the satisfactory state (by maintaining the thermal resistance low). This is because the thermal contact between the dividing wall 91 (or 91 a) of theevaporator case 90 and thewick 47 is maintained in the satisfactory state even if the temperature of the evaporator rises along with the increase in the quantity of heat transferred from the electronic component. - To support the above-described advantage, the deformation of a copper (Cu)
evaporator case 90 of 56 mm width is calculated when using pentane as the working fluid. With the conventional structure illustrated inFIGS. 1A-1C , the difference between the atmospheric pressure and the internal pressure of the evaporator case is 0.2 MPa at the LHP operating temperature (near 70° C.) as illustrated inFIG. 4 . Under this condition, the evaporator case expands and deforms outward by 95 μm. This state impairs thermal contact between the evaporator case and the wick and the thermal resistance increases. In contrast, when butane is introduced in the secondfluid chamber 90B illustrated inFIG. 11 , the internal pressure in thevaporization chamber 90A is lower than the internal pressure in the secondfluid chamber 90B by 0.5 MPa. If thewick 47 is not arranged in thevaporization chamber 90A, the dividingwall 91 of theevaporator case 90 will swells toward thevaporization chamber 90A by 140 μm. However, because thewick 47 is provided in thevaporization chamber 90A, the dividingwall 91 is pressed against thewick 47 and tight contact is produced between the dividingwall 91 and thewick 47. - According to the comparison between the graphs of
FIG. 14 andFIG. 7 , it is understood that the evaporator configuration of the second embodiment can further improve the cooling efficiency, compared to the first embodiment. - In the first and second embodiments, the second space is provided only on the top of the evaporator case, opposite to the heat-receiving face, to define a double chamber structure because the top face has a large area size of a thermally conductive surface. However, the second space may be provided so as to cover at least one of the side walls of the vaporization chamber (first space). If the second space is provided so as to cover the top face and a pair of side faces of the vaporization chamber (first space), the double chamber structure is applied to three sides of the evaporator, except for the heat receiving surface. In this case, thermal adhesion between the wick and the vaporization chamber is further enhanced.
- All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of superiority or inferiority of the invention. Although the embodiments of the present inventions have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.
Claims (13)
1. A loop heat pipe comprising:
an evaporator to vaporize a working fluid due to heat supplied from an external heat source;
a condenser to cause the vaporized working fluid to condense; and
connecting lines to connect the evaporator and the condenser in a loop,
wherein the evaporator includes
a first space having set of walls including a contact wall that comes into contact with the external heat source,
a second space provided adjacent to at least one of the walls other than the contact wall, and
a through-hole formed in a dividing wall separating the first space and the second space to allow the first space and the second space to communicate with each other.
2. The loop heat pipe according to claim 1 , wherein the second space is provided adjacent to a wall opposite to the contact wall.
3. The loop heat pipe according to claim 2 , wherein a vapor pressure of the working fluid is higher than an atmospheric pressure, and wherein a thickness of an outer wall separating the second space and the atmosphere is less than a thickness of the dividing wall between the first space and the second space.
4. The loop heat pipe according to claim 2 , wherein a vapor pressure of the working fluid is higher than an atmospheric pressure, and wherein the dividing wall between the first space and the second space is swelled toward the first space.
5. The loop heat pipe according to claim 3 , wherein the working fluid is selected from a group of pentane, butane and ammonia.
6. The loop heat pipe according to claim 4 , wherein the working fluid is selected from a group of pentane, butane and ammonia.
7. The loop heat pipe according to claim 1 , wherein a porous material is provided along an inner wall of the first space, and a flow path is formed in the porous material through which the working fluid supplied from one of the connecting lines passes.
8. The loop heat pipe according to claim 1 , wherein the evaporator is made of a material with a thermal conductivity higher than that of stainless.
9. A loop heat pipe comprising:
an evaporator to vaporize a working fluid due to heat supplied from an external heat source;
a condenser to cause the vaporized working fluid to condense; and
connecting lines to connect the evaporator and the condenser in a loop,
wherein the evaporator includes
a first space having a first set of walls including a contact wall that comes into contact with the external heat source, and
a second space provided adjacent to at least one of said walls other than the contact wall and defined by a second set of walls, the second space being filled with a second fluid that has a saturated vapor pressure higher than that of the working fluid at a same temperature.
10. The loop heat pipe according to claim 9 , wherein at least a part of the second fluid is in a liquid phase when the loop heat pipe is not activated.
11. The loop heat pipe according to claim 9 , wherein a thickness of a dividing wall separating the first space and the second space is less than a thickness of an outer wall separating the second space from an atmosphere.
12. The loop heat pipe according to claim 9 , wherein a porous material is provided along an inner wall of the first space, and a flow path is formed in the porous material through which the working fluid supplied from one of the connecting lines passes.
13. The loop heat pipe according to claim 9 , wherein the evaporator is made of a material with a thermal conductivity higher than that of stainless.
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2010075443 | 2010-03-29 | ||
JP2010-075443 | 2010-03-29 | ||
PCT/JP2010/066329 WO2011121819A1 (en) | 2010-03-29 | 2010-09-21 | Loop heat pipe |
Related Parent Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/JP2010/066329 Continuation WO2011121819A1 (en) | 2010-03-29 | 2010-09-21 | Loop heat pipe |
Publications (1)
Publication Number | Publication Date |
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US20120312506A1 true US20120312506A1 (en) | 2012-12-13 |
Family
ID=44711595
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US13/591,397 Abandoned US20120312506A1 (en) | 2010-03-29 | 2012-08-22 | Loop heat pipe |
Country Status (4)
Country | Link |
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US (1) | US20120312506A1 (en) |
JP (2) | JPWO2011121819A1 (en) |
CN (1) | CN102792119A (en) |
WO (1) | WO2011121819A1 (en) |
Cited By (7)
Publication number | Priority date | Publication date | Assignee | Title |
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US20160330868A1 (en) * | 2015-05-05 | 2016-11-10 | Cooler Master Co., Ltd. | Cooling module, water-cooled cooling module and cooling system |
US20190035713A1 (en) * | 2017-07-28 | 2019-01-31 | Qualcomm Incorporated | Systems and methods for cooling an electronic device |
US20190360759A1 (en) * | 2018-05-25 | 2019-11-28 | Purdue Research Foundation | Permeable membrane microchannel heat sinks and methods of making |
US10985085B2 (en) * | 2019-05-15 | 2021-04-20 | Advanced Semiconductor Engineering, Inc. | Semiconductor device package and method for manufacturing the same |
CN113776370A (en) * | 2020-11-03 | 2021-12-10 | 山东交通学院 | Curved arc wall drainage loop heat pipe |
CN113776371A (en) * | 2020-11-03 | 2021-12-10 | 山东交通学院 | Linear wall guide loop heat pipe |
EP3907456A4 (en) * | 2019-01-29 | 2022-02-23 | Smarth Technology Ltd. | Phase change heat radiating device |
Families Citing this family (3)
Publication number | Priority date | Publication date | Assignee | Title |
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SK822013A3 (en) | 2013-09-11 | 2015-04-01 | Žilinská Univerzita V Žiline | Compact evaporator with closed circuit |
WO2016201080A1 (en) * | 2015-06-09 | 2016-12-15 | Hamilton Sunstrand Corporation | Modular heat exchanger design |
CN109612315A (en) * | 2019-01-29 | 2019-04-12 | 株洲智热技术有限公司 | Phase-change heat radiating device |
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US4816814A (en) * | 1987-02-12 | 1989-03-28 | International Business Machines Corporation | Vector generator with direction independent drawing speed for all-point-addressable raster displays |
JPS63201493A (en) * | 1987-02-16 | 1988-08-19 | Furukawa Electric Co Ltd:The | Heat pipe |
JP2005079483A (en) * | 2003-09-03 | 2005-03-24 | Hitachi Ltd | Electronic apparatus |
JP2005259747A (en) * | 2004-03-09 | 2005-09-22 | Sony Corp | Heat transport apparatus and electronic device |
US20060162903A1 (en) * | 2005-01-21 | 2006-07-27 | Bhatti Mohinder S | Liquid cooled thermosiphon with flexible partition |
CN101307996B (en) * | 2007-05-17 | 2010-06-02 | 私立淡江大学 | Flat-plate evaporators structure and loop type hot pipe possessing flat-plate evaporators structure |
-
2010
- 2010-09-21 JP JP2012508014A patent/JPWO2011121819A1/en active Pending
- 2010-09-21 CN CN2010800652950A patent/CN102792119A/en active Pending
- 2010-09-21 WO PCT/JP2010/066329 patent/WO2011121819A1/en active Application Filing
-
2012
- 2012-08-22 US US13/591,397 patent/US20120312506A1/en not_active Abandoned
-
2013
- 2013-08-23 JP JP2013173479A patent/JP2013231597A/en not_active Withdrawn
Cited By (9)
Publication number | Priority date | Publication date | Assignee | Title |
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US20160330868A1 (en) * | 2015-05-05 | 2016-11-10 | Cooler Master Co., Ltd. | Cooling module, water-cooled cooling module and cooling system |
US10410954B2 (en) * | 2015-05-05 | 2019-09-10 | Cooler Master Co., Ltd. | Cooling module, water-cooled cooling module and cooling system |
US20190035713A1 (en) * | 2017-07-28 | 2019-01-31 | Qualcomm Incorporated | Systems and methods for cooling an electronic device |
US10622282B2 (en) * | 2017-07-28 | 2020-04-14 | Qualcomm Incorporated | Systems and methods for cooling an electronic device |
US20190360759A1 (en) * | 2018-05-25 | 2019-11-28 | Purdue Research Foundation | Permeable membrane microchannel heat sinks and methods of making |
EP3907456A4 (en) * | 2019-01-29 | 2022-02-23 | Smarth Technology Ltd. | Phase change heat radiating device |
US10985085B2 (en) * | 2019-05-15 | 2021-04-20 | Advanced Semiconductor Engineering, Inc. | Semiconductor device package and method for manufacturing the same |
CN113776370A (en) * | 2020-11-03 | 2021-12-10 | 山东交通学院 | Curved arc wall drainage loop heat pipe |
CN113776371A (en) * | 2020-11-03 | 2021-12-10 | 山东交通学院 | Linear wall guide loop heat pipe |
Also Published As
Publication number | Publication date |
---|---|
CN102792119A (en) | 2012-11-21 |
WO2011121819A1 (en) | 2011-10-06 |
JP2013231597A (en) | 2013-11-14 |
JPWO2011121819A1 (en) | 2013-07-04 |
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