JP2014183107A - Cooling device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cooling device with a simplified structure.SOLUTION: A cooling device 100 includes: an evaporator 22 which draws heat from (cools) a CPU 10 by evaporative latent heat of water; an aspirator 26 which utilizes water flow and thereby suctions water vapor generated in the evaporator 22; a liquid circulation passage 28 and a pump 38 which supply water to the aspirator 26; and a condenser 30 which condenses the water vapor suctioned by the aspirator 26 to return the water vapor to water. Parts of the water condensed by the condenser 30 and the water to be supplied to the aspirator are supplied from a branch passage 40 branched from the liquid circulation passage 28 to the evaporator 22. The water which is not supplied to the evaporator 22 is supplied to the aspirator 26 as a refrigerant.

Description

  The present case relates to a cooling device.

  2. Description of the Related Art Conventionally, as a cooling device, a decompressed liquid refrigerant is supplied to a cooling unit provided in a heated member to be cooled, and the member to be cooled is caused by heat of vaporization when the liquid refrigerant is vaporized by heat of the member to be cooled in the supply unit. There is known an apparatus for cooling the water (see, for example, Patent Document 1).

JP-A-8-200195

  However, the cooling device as described above requires a large amount of device such as a pressure reducing device for reducing the pressure of the liquid refrigerant.

  In one aspect, an object of the present invention is to provide a cooling device with a simplified configuration.

  The cooling device described in the present specification includes an evaporation section that draws heat from a heat source by the latent heat of liquid evaporation, an aspirator that draws vapor generated in the evaporation section using the flow of the liquid, and a liquid that is supplied to the aspirator. A liquid supply mechanism for supplying, and a condenser for condensing the vapor sucked by the aspirator and returning the liquid to the liquid, wherein the liquid supply mechanism includes a liquid condensed by the condenser and a liquid supplied to the aspirator. Is a cooling device that supplies a part of the mixed liquid to the evaporation unit and supplies the remaining liquid to the aspirator.

  The cooling device described in the present embodiment has an effect that the configuration can be simplified.

It is a figure which shows typically the structure of the cooling device which concerns on one Embodiment. It is a table | surface which shows the relationship between the temperature of water, and a vapor pressure. It is a figure which expands and shows an aspirator. It is a flowchart (the 1) which shows the process of a control apparatus. It is a flowchart (the 2) which shows the process of a control apparatus. It is a figure which shows a comparative example.

  Hereinafter, one embodiment of a cooling device will be described in detail with reference to FIGS. The cooling device 100 according to the present embodiment is a device that cools an electronic device (heat source) such as a CPU mounted on a server.

  FIG. 1 schematically shows a configuration of a cooling device 100 that cools the CPU 10. As shown in FIG. 1, the cooling device 100 includes an evaporator 22 as an evaporation unit, an aspirator 26, a condenser 30, a gas-liquid separator 32, a pump 38, and a control device 50 as a control unit. Is provided.

  The evaporator 22 is in contact with the CPU 10 directly or via a heat conductor (not shown), and a cooling medium (water in this embodiment) is accommodated in the internal space. In the present embodiment, water is used as a cooling medium from the viewpoint of performance, safety, and low environmental load. The water in the evaporator 22 is heated by the CPU 10 that has generated heat to nucleate boil and become water vapor, and the CPU 10 is cooled by latent heat due to the water phase change (liquid to gas). One end of a steam pipe 24 is connected to the evaporator 22. Since cooling by latent heat is more efficient than air cooling or liquid cooling, it is possible to cope with a large amount of heat generation.

  FIG. 2 shows the relationship between water temperature and vapor pressure. According to FIG. 2, for example, when the inside of the evaporator 22 is maintained at 42 hPa, the water vapor and the water (liquid) are in equilibrium when the temperature of the water in the evaporator 22 is 30 ° C. That is, when the temperature in the evaporator 22 is changed from 30 ° C. to 40 ° C., for example, the vapor pressure is equilibrated at 74 hPa. Therefore, under the condition of keeping the inside of the evaporator 22 at 42 hPa, a difference of 32 hPa compared with the case of 30 ° C. Occurs. For this reason, in the evaporator 22, water (liquid) turns into water vapor. In the present embodiment, as described later, the degree of vacuum in the cooling device 100 (in the evaporator 22) is, for example, less than 50 hPa, thereby lowering the boiling point of water in the evaporator 22 and keeping the CPU 10 within the operating range (90 Cooling to about ℃ or less).

  As shown in an enlarged view in FIG. 3, the aspirator 26 has a T-shaped tube 52 therein. The T-shaped tube 52 includes a first tube 52a extending in the up-down direction in FIG. 3 and a second tube 52b extending in the left-right direction. The first pipe 52a has a narrowed shape in the vicinity of the middle portion thereof, and the second pipe 52b is connected to the narrowed portion 54. The aspirator 26 is in a state of being incorporated in the liquid circulation path 28, and water circulating in the liquid circulation path 28 flows through the first pipe 52a.

  In the aspirator 26, when water is supplied from the upper end side to the lower end side of the first pipe 52a, the water flow rate increases in the vicinity of the throttled portion 54, so the water pressure decreases due to the venturi effect. And by the fall of the pressure of this water, the gas in the 2nd pipe | tube 52b flows into a water flow, As a result, the inside of the 2nd pipe | tube 52b and the steam pipe 24 will be pressure-reduced. As a result, water vapor generated in the evaporator 22 flows into the aspirator 26 via the steam pipe 24.

  The aspirator 26 is made of a heat insulating material such as glass or resin. Accordingly, it is possible to suppress the occurrence of a phenomenon in which water vapor is cooled by the wall surface of the second pipe 52b and the like while passing through the second pipe 52b, condensed, and returned to water (water droplets). In this case, it is possible to suppress the water flow in the second pipe 52b from being hindered by condensed water (water droplets).

  Returning to FIG. 1, the condenser 30 is provided in a part of the liquid circulation path 28, and has a large number of radiating fins as an example. The condenser 30 is a condenser that can exchange heat between water flowing in the liquid circulation path 28 and the atmosphere, and has a function of condensing water vapor and returning it to water.

  The gas-liquid separator 32 is a device used when decompressing the inside of the cooling device 100 at the beginning of the operation (see FIGS. 4 and 5 and its description), and is mixed into the water flowing in the liquid circulation path 28. The gas is separated and released to the outside (atmosphere). The gas-liquid separator 32 is provided with an exhaust pipe 34 for releasing gas to the outside, and the exhaust pipe 34 is provided with an exhaust valve 36. Opening / closing control of the exhaust valve 36 is performed by the control device 50.

  The pump 38 is a device for creating a flow of water in the liquid circulation path 28. The operation of the pump 38 is controlled by the control device 50.

  A branch path 40 is branched from a part of the liquid circulation path 28 (downstream of the pump 38). The branch path 40 is connected to the evaporator 22. For this reason, a part of the water flowing through the liquid circulation path 28, that is, a part of the water evaporated and condensed in the evaporator 22 and a part of the water supplied to the aspirator 26 are transferred to the evaporator 22 via the branch path 40. It comes to be supplied. A part of the branch path 40 is provided with a water supply valve 42 as an adjusting mechanism, and an amount of water corresponding to the opening of the water supply valve 42 is supplied to the evaporator 22. The opening degree (5% to 100%) of the water supply valve 42 is controlled by the control device 50 in increments of 1%.

  The control device 50 comprehensively controls each part of the cooling device 100. A temperature sensor 46 for detecting the temperature of the CPU 10 is provided in the vicinity of the CPU 10. The evaporator 22 is provided with a vacuum degree sensor 44 for detecting the degree of vacuum inside the evaporator 22. The control device 50 controls the driving of the pump 38, the operation of the CPU 10 or the opening / closing of the exhaust valve 36 based on the detection results of the temperature sensor 46 and the vacuum degree sensor 44, and adjusts the opening of the water supply valve 42.

  In the present embodiment, since the water vapor sucked by the aspirator 26 is condensed in the water supplied to the aspirator 26 to become liquid (water), the inside of the cooling device 100 is a closed path of water. It can be said that.

  Next, the processing of the control device 50 will be described in detail based on FIGS. 4 and 5 with reference to other drawings as appropriate.

  4 and 5 show a series of processes of the control device 50 in a flowchart. 4 and 5 by the control device 50 is started from a state in which the power supply of the server provided with the cooling device 100 is turned on.

  In the process of FIG. 4, first, in step S <b> 10, the control device 50 starts driving the pump 38. When the pump 38 is driven, water flows through the liquid circulation path 28 and the first pipe 52 a of the aspirator 26. In this case, when the temperature of water is the same as room temperature (for example, 30 ° C.), the ultimate vacuum is 42 hPa from FIG.

  Next, in step S <b> 12, the control device 50 measures the degree of vacuum (P) in the evaporator 22 using the degree of vacuum sensor 44. Next, in step S14, the control device 50 determines whether or not the degree of vacuum (P) is smaller than 50 (hPa). Here, 50 hPa is the degree of vacuum in the cooling device 100 necessary for maintaining the cooling performance of the cooling device 100, and is a value slightly larger than the ultimate vacuum degree of the aspirator determined from the water temperature. If the determination in step S14 is negative, that is, if the degree of vacuum (P) is 50 hPa or more, the process proceeds to step S16, and the control device 50 opens the exhaust valve 36. By opening the exhaust valve 36, the gas mixed in the water flowing in the liquid circulation path 28 is separated in the gas-liquid separator 32 and is discharged from the exhaust pipe 34, so that the inside of the cooling device 100 (evaporator) 22)) begins to gradually decrease. Thereafter, the control device 50 returns to step S12.

  Then, the control device 50 repeats the measurement of the degree of vacuum while maintaining the exhaust valve 36 until the determination in step S14 is affirmed (until the degree of vacuum (P) becomes less than 50 hPa) (S12).

  On the other hand, if the determination in step S14 is affirmative, that is, if the required degree of vacuum (less than 50 hPa) is achieved in the cooling device 100, the control device 50 proceeds to step S18. In step S18, the control device 50 closes the exhaust valve 36. Thereby, the vacuum degree in the cooling device 100 (evaporator 22) can be maintained at less than 50 hPa.

  Next, in step S20, the control device 50 starts driving the CPU 10 (OFF → ON). If the control device 50 cannot directly control the start of driving of the CPU 10, an instruction to start driving may be issued to the control device that controls the drive of the CPU 10. When the CPU 10 generates heat after the CPU 10 is driven, water vapor is generated in the evaporator 22, and the generated water vapor is sucked into the aspirator 26 by the action of the aspirator 26. The sucked water vapor is mixed with water (refrigerant) flowing through the aspirator 26 in the first pipe 52a to form a two-phase flow, but the water vapor is condensed in the condenser 30 and returned to water. A part of the water sent to the downstream side by the pump 38 is supplied from the branch path 40 to the evaporator 22, and the rest is supplied to the aspirator 26.

  Next, in step S <b> 22, the control device 50 measures the temperature (T) of the CPU 10 using the temperature sensor 46. Next, in step S24, the control device 50 determines whether or not the temperature (T) of the CPU 10 is less than 90 ° C. When determination here is denied, ie, when the temperature of CPU10 is 90 degreeC or more, the control apparatus 50 transfers to step S26.

  If transfering it to step S26, the control apparatus 50 will judge whether the opening degree of the water supply valve 42 is larger than 99%. When judgment here is denied, it transfers to step S28 and the control apparatus 50 increases the opening degree of the water supply valve 42 1%. Thereby, the cooling effect by the evaporator 22 of CPU10 whose temperature is 90 degreeC or more can be heightened. On the other hand, if the determination in step S26 is affirmative, that is, if the opening of the water supply valve 42 is 100%, the amount of water supplied to the evaporator 22 cannot be increased any more. Accordingly, the control device 50 proceeds to step S30 and drives the CPU 10 in the power saving mode. When the control device 50 cannot directly control the drive of the CPU 10, an instruction may be issued to the control device that controls the drive of the CPU 10.

  After step S28 or S30, the control device 50 proceeds to step S36 and determines whether or not a server power-off command input from a user or the like has been received. When judgment here is denied, it returns to step S22.

  By the way, when judgment of step S24 is affirmed, ie, when the temperature of CPU10 is less than 90 degreeC, it transfers to step S32 and the control apparatus 50 has the opening degree of the water supply valve 42 less than 5%. Judge whether there is. When judgment here is denied, it transfers to step S34 and the control apparatus 50 reduces the opening degree of the water supply valve 42 1%. Thereby, it is possible to prevent the CPU 10 from being cooled more than necessary. After step S34, the control device 50 proceeds to step S36, and determines whether or not a power OFF command input from a user or the like has been received. When judgment here is denied, it returns to step S22.

  On the other hand, if the determination in step S32 is affirmative, that is, if the opening of the water supply valve 42 is less than 5%, the control device 50 proceeds to step S36 and the determination in step S36 is denied. In the case, the process returns to step S22. In the present embodiment, the minimum opening of the water supply valve 42 is set to about 5% assuming cooling when the CPU 10 is in an idle state (in the case of minimum heat generation).

  If the determination in step S36 is affirmative, that is, if a server power-off command is input from the user or the like, the processing proceeds to FIG.

  When the process proceeds to the process in FIG. 5, the control device 50 stops driving the CPU 10 in step S <b> 40. When the control device 50 cannot directly control the stop of driving of the CPU 10, an instruction may be issued to the control device that controls the driving of the CPU 10.

  Next, in step S <b> 42, the control device 50 measures the temperature (T) of the CPU 10 using the temperature sensor 46. Next, in step S44, the control device 50 determines whether or not the temperature (T) is less than 90 ° C. If the determination is negative, that is, if the temperature (T) is 90 ° C. or higher, the process proceeds to step S46.

  If transfering it to step S46, the control apparatus 50 will judge whether the opening degree of the water supply valve 42 is larger than 99%. If the determination here is affirmed, the opening degree of the water supply valve 42 cannot be increased any further, and the process directly returns to step S42. On the other hand, if the determination in step S46 is negative, that is, if the opening degree of the water supply valve 42 can be increased, the process proceeds to step S48, and the control device 50 increases the opening degree of the water supply valve 42 by 1%. Thereafter, the process returns to step S42, and the opening degree of the water supply valve 42 is increased by 1% until the temperature of the CPU 10 becomes less than 90 ° C. or the opening degree of the water supply valve 42 becomes 100%.

  On the other hand, if the determination in step S44 is affirmative, that is, if the temperature of the CPU 10 is less than 90 ° C., the process proceeds to step S50, and the controller 50 determines that the opening of the water supply valve 42 is less than 5%. Judge whether there is. When judgment here is denied, the control apparatus 50 transfers to step S52, reduces the opening degree of the water supply valve 42 1%, and returns to step S42. On the other hand, if the determination in step S50 is affirmative, the process proceeds to step S54, where the control device 50 stops driving the pump 38 and ends all the processes in FIGS.

  As can be seen from the above description, in the present embodiment, as an example, a function as a liquid supply mechanism that includes the liquid circulation path 28 and the pump 38 and supplies water to the aspirator is realized.

  As described above in detail, according to the present embodiment, the evaporator 22 that removes (cools) heat from the CPU 10 by the latent heat of evaporation of water and the water vapor generated in the evaporator 22 using the flow of water. An aspirator 26 for sucking, a liquid circulation path 28 for supplying water to the aspirator 26 and a pump 38, and a condenser 30 for condensing water vapor sucked by the aspirator 26 and returning it to water are provided. Therefore, in this embodiment, since the water vapor generated in the evaporator 22 is sucked using a simple mechanism such as the aspirator 26, the CPU 10 is effectively cooled with a simple configuration without using a large-scale decompression device. can do. In the present embodiment, after the water condensed in the condenser 30 and the water supplied to the aspirator 26 are mixed, a part of the water is supplied from the branch path 40 to the evaporator 22. In this case, a part of the system that supplies (circulates) water to the aspirator 26 and the system that condenses water vapor and returns to the evaporator 22 can be shared, so that each system is provided independently. Therefore, the apparatus can be simplified.

  Here, based on FIG. 6, a comparative example (a thermosiphon cooling device 200 used for cooling the CPU in the server) will be described. A cooling device 200 shown in FIG. 6 includes an evaporator 122 provided in contact with the CPU 10, a steam pipe 124, a condenser 130, and a water supply pipe 140.

  In the cooling device 200 of FIG. 6, as in the present embodiment, the water heated by the evaporator 122 boils to become water vapor, and the CPU 110 is cooled by the latent heat due to the phase change of the water (liquid → gas) at this time. It is like that. The water vapor generated in the evaporator 122 enters the condenser 130 through the vapor pipe 124, and is condensed in the condenser 130 and returned to water, and then supplied to the evaporator 122 through the water supply pipe 140. Further, in order to cool the CPU 110 within the operation limit temperature (about 90 ° C. or less), considering heat conduction between the heat receiving surface of the CPU 110 and the evaporator 122 and overheating at the time of phase change of the refrigerant, about 60 to 70 ° C. The water must boil at the following temperatures and take away latent heat. For this reason, the cooling device 200 of the comparative example is operated by containing water in a state where the inside of the device is reduced to 100 hPa or less and lowering the boiling point to about 50 ° C. or less (see FIG. 2).

  Here, when the cooling device 200 of FIG. 6 is used for server cooling, it is necessary to guarantee operation for several years (guarantee of reduced pressure state). Thus, in order to maintain and guarantee the reduced pressure state inside the apparatus, the cooling apparatus 200 needs to use hard parts and the like. For example, in the cooling device 200, all parts such as pipes are made of metal parts that do not leak, and it is necessary to use advanced welding or brazing techniques with sufficient vacuum resistance for assembling them. .

  On the other hand, in the cooling device 100 of the present embodiment, the inside of the evaporator 22 is positively evacuated using the aspirator 26 to actively maintain a low vacuum. Therefore, in the cooling device 100 of the present embodiment, some leakage can be allowed. Further, since the use of a resin pipe or the like is possible, the availability is improved and an advanced welding / brazing technique is not required, so that simple assembly is possible and the manufacturing cost can be reduced.

  In this embodiment, a heat insulating material such as glass or resin is used as the material of the aspirator 26. Thereby, the water vapor passing through the second pipe 52b is cooled by the water flowing through the first pipe 52a, condensed in the second pipe 52b to become a liquid, and the flow of water vapor in the second pipe 52b is hindered. The occurrence of the situation can be suppressed. The material of the entire aspirator 26 may not be a heat insulating material, and a heat insulating material may be employed as a material of at least a portion through which water vapor passes, that is, a material of at least the second pipe 52b portion.

  Moreover, in this embodiment, the refrigerant | coolant supplied to the aspirator 26 and the liquid supplied in the evaporator 22 are made into the same substance (water). Thereby, the structure which the vapor | steam generated in the evaporator 22 mixes with the refrigerant | coolant which flows through the aspirator 26 as shown in FIG. 1 is employable.

  In this embodiment, the temperature sensor 46 that detects the temperature of the CPU 10 and a water supply valve 42 that adjusts the amount of water supplied to the evaporator 22 are provided. Based on this, the opening degree of the water supply valve 42 is adjusted. As a result, an appropriate amount of water can be supplied according to the amount of heat generated by the CPU 10, so that appropriate cooling according to the temperature of the CPU 10 is possible.

  Further, in the present embodiment, a vacuum degree sensor 44 that detects the degree of vacuum in the evaporator 22 and a gas-liquid separator 32 that separates and extracts gas from water passing through the liquid circulation path 28 are provided. Based on the detection result by the vacuum degree sensor 44, the operation of the gas-liquid separator 32 is controlled. Thereby, the inside of the evaporator 22 can be set to an appropriate vacuum degree by using the aspirator 26 and the gas-liquid separator 32 without using a large-scale decompression device.

  In the above embodiment, when the temperature (T) of the CPU 10 is higher than 90 ° C., the case where the water supply valve 42 is increased in increments of 1% while monitoring the temperature (T) has been described. It is not a thing. For example, the amount of water to be supplied may be determined based on the amount of heat generated by the CPU 10 and the water supply valve 42 may be adjusted. In this case, the flow rate of water can be obtained from the calorific value / the latent heat of vaporization of water. For example, when cooling the exothermic heat of 220 W, assuming that the latent heat of vaporization of water is 2253 W / s, the flow rate is approximately 6 cc / min. You just have to decide. In addition, what is necessary is just to provide a flowmeter between the water supply valve 42 and the evaporator 22 of the branch path 40 when performing such a process.

  In the above embodiment, the case where water is used as the refrigerant used in the cooling device 100 has been described. However, the present invention is not limited to this, and for example, a medium such as ethyl alcohol, chlorofluorocarbon, or chlorofluorocarbon alternative can be used. It is.

  In addition, when mounting the cooling device 100 of the said embodiment in the server which has multiple CPU10, the number according to the number of CPU10, for example, the evaporator 22, the steam pipe 24, the aspirator 26, the branch path 40, and the water supply valve 42, for example. It is also possible to prepare only the other components (condenser 30, gas-liquid separator 32, pump 38, etc.).

  In the above embodiment, the case where the gas-liquid separator 32 is provided in the cooling device 100 has been described. However, the present invention is not limited to this, and in the case where the intrusion of air into the cooling device 100 is prevented, The liquid separator 32 may not be provided.

  In the above embodiment, the case where the water temperature is set to 30 ° C. at room temperature, the degree of vacuum in the cooling device 100 before driving the CPU 10 is set to 50 hPa, and the upper limit temperature of the CPU 10 is set to about 90 ° C. has been described. However, the present invention is not limited to this, and the value of the degree of vacuum and the upper limit temperature of the CPU 10 can be appropriately changed. In addition, a chiller can be inserted into the liquid circulation path 28 to actively lower the water temperature and operate at room temperature or lower.

  In the above embodiment, the case where the cooling device 100 is used for cooling the CPU of the server has been described. However, the present invention is not limited to this, and the cooling device 100 may be used for cooling electronic components other than the CPU in the server and devices (and component parts) other than the server.

  The above-described embodiment is an example of a preferred embodiment of the present invention. However, the present invention is not limited to this, and various modifications can be made without departing from the scope of the present invention.

In addition, the following additional remarks are disclosed regarding description of the above embodiment.
(Supplementary note 1) An evaporation section that takes heat from a heat source by the latent heat of vaporization of liquid,
An aspirator for sucking the vapor generated in the evaporating section using a liquid flow;
A liquid supply mechanism for supplying liquid to the aspirator;
A condenser for condensing the vapor sucked by the aspirator and returning it to a liquid,
The liquid supply mechanism supplies a part of the liquid obtained by mixing the liquid condensed in the condenser and the liquid supplied to the aspirator to the evaporation unit, and supplies the remaining liquid to the aspirator. A cooling device characterized by.
(Supplementary note 2) The cooling device according to supplementary note 1, wherein a heat insulating material is used as a material of at least a portion of the aspirator through which the steam passes.
(Additional remark 3) The said liquid is water, The cooling device of Additional remark 1 or 2 characterized by the above-mentioned.
(Appendix 4) A temperature sensor for detecting the temperature of the heat source;
An adjustment mechanism for adjusting the amount of liquid supplied to the evaporation section;
The cooling device according to any one of appendices 1 to 3, further comprising: a control unit that controls the adjustment mechanism based on a detection result of the temperature sensor.
(Additional remark 5) The vacuum degree sensor which detects the vacuum degree in the said evaporation part,
A gas-liquid separator that separates and removes gas from the liquid supplied to the aspirator;
The cooling device according to any one of supplementary notes 1 to 4, further comprising: a control unit that controls an operation of the gas-liquid separator based on a detection result of the vacuum degree sensor.

10 Heat source 22 Evaporator (evaporation part)
26 Aspirator 28 Liquid circulation path (part of liquid supply mechanism)
30 Condenser 32 Gas-liquid separator 38 Pump (part of liquid supply mechanism)
42 Water supply valve (adjustment mechanism)
44 Vacuum sensor 46 Temperature sensor 50 Control device (control unit)
100 Cooling device

Claims (3)

An evaporation section that takes heat away from the heat source by the latent heat of vaporization of the liquid;
An aspirator for sucking the vapor generated in the evaporating section using a liquid flow;
A liquid supply mechanism for supplying liquid to the aspirator;
A condenser for condensing the vapor sucked by the aspirator and returning it to a liquid,
The liquid supply mechanism supplies a part of the liquid obtained by mixing the liquid condensed in the condenser and the liquid supplied to the aspirator to the evaporation unit, and supplies the remaining liquid to the aspirator. A cooling device characterized by.   The cooling device according to claim 1, wherein a heat insulating material is used as a material of at least the portion of the aspirator through which the vapor passes. A temperature sensor for detecting the temperature of the heat source;
An adjustment mechanism for adjusting the amount of liquid supplied to the evaporation section;
The cooling device according to claim 1, further comprising: a control unit that controls the adjustment mechanism based on a detection result of the temperature sensor.

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