CN116067209A - Novel capillary core loop heat pipe and preparation method thereof - Google Patents

Novel capillary core loop heat pipe and preparation method thereof Download PDF

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CN116067209A
CN116067209A CN202111286847.7A CN202111286847A CN116067209A CN 116067209 A CN116067209 A CN 116067209A CN 202111286847 A CN202111286847 A CN 202111286847A CN 116067209 A CN116067209 A CN 116067209A
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capillary core
heat pipe
liquid
chamber
loop
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CN116067209B (en
Inventor
李晓坤
杨沛东
郭春生
杨珺博
于永升
周晓雨
姜鲲
薛丽红
李蒸
韩卓晟
逯晓康
刘百川
黑吉芳
李宝瑞
张元坤
李文涵
刘淼
候蕊蕊
李华杰
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Shandong University
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Shandong University
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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
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B21/00—Machines, plants or systems, using electric or magnetic effects
    • 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
    • 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
    • F28D15/06—Control arrangements therefor

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Sustainable Development (AREA)
  • Devices That Are Associated With Refrigeration Equipment (AREA)

Abstract

The invention provides a loop heat pipe with a novel evaporation end structure, which comprises an evaporation end, a condensation end, a gas pipeline and a liquid pipeline, wherein the liquid absorbs heat and evaporates at the evaporation end, enters the condensation end through the gas pipeline to conduct condensation and heat release, and enters the evaporation end through the liquid pipeline after heat release. Four chambers are arranged in the shell, and are a gas buffer chamber, a capillary core chamber, an auxiliary capillary core chamber and a liquid reservoir respectively, wherein the gas buffer chamber, the capillary core chamber and the auxiliary capillary core chamber form an evaporator; the auxiliary capillary core of the auxiliary capillary core chamber is wrapped around the liquid storage chamber, the aperture of the auxiliary capillary core is smaller than that of the capillary core, and the auxiliary capillary core is matched with the hole on one side of the main capillary core, so that the reflux liquid working medium can directly enter the front end of the capillary core for evaporation. The auxiliary capillary core is added into the liquid storage chamber of the heat pipe and is inserted into the capillary core, so that the axial capillary force of the loop is enhanced, large bubbles of a liquid pipeline in the capillary core can be effectively reduced, reverse heat leakage is reduced, the stable forward running of the heat pipe is ensured, and the capillary suction speed of the heat pipe is increased to 0.6g/s.

Description

Novel capillary core loop heat pipe and preparation method thereof
Technical Field
The invention belongs to the field of loop heat pipes, and particularly relates to an auxiliary control device for a heat pipe.
Background
The heat pipe technology is a heat transfer element called a "heat pipe" invented by George Grover (Los Alamos) national laboratory in the United states of Amersham (1963), which fully utilizes the heat conduction principle and the rapid heat transfer property of a phase change medium, and rapidly transfers the heat of a heating object to the outside of a heat source through the heat pipe, and the heat conduction capability of the heat pipe exceeds that of any known metal.
The heat pipe technology is widely applied to the industries of aerospace, military industry and the like before, since the heat pipe technology is introduced into the radiator manufacturing industry, the design thought of the traditional radiator is changed, a single radiating mode of obtaining a better radiating effect by simply relying on a high-air-volume motor is eliminated, the heat pipe technology is adopted to enable the radiator to obtain a satisfactory heat exchanging effect, and a new world of the radiating industry is opened up. At present, the heat pipe is widely applied to various heat exchange devices, including the field of space heat dissipation.
The loop heat pipe refers to a loop closed loop heat pipe. Typically consisting of an evaporator, a condenser, a liquid reservoir and vapor and liquid lines. The working principle is as follows: the heat load is applied to the evaporator, the working medium evaporates on the outer surface of the evaporator capillary core, the generated steam flows out of the steam channel and enters the steam pipeline, then enters the condenser to be condensed into liquid and supercooled, the reflux liquid enters the liquid trunk through the liquid pipeline to supply the evaporator capillary core, and the circulation is carried out, and the circulation of the working medium is driven by the capillary pressure generated by the evaporator capillary core without external power. Because the condensing section and the evaporating section are separated, the loop heat pipe is widely applied to comprehensive application of energy and recovery of waste heat.
The semiconductor refrigerator is also called a thermoelectric refrigerator (Thermo Electric Cooler, TEC), and the TEC utilizes the Peltier effect (Peltier effect) to directly convert the input electric energy into temperature difference so as to realize refrigeration, thereby being a refrigeration mode based on the thermoelectric phenomenon. The peltier effect is a phenomenon in which when a direct current passes through a conductor made of two different materials, electrons at different energy levels in the two conductors start to move and form a current, and when electrons move from a high energy level to a low energy level, excessive energy is released to the outside, otherwise, energy is absorbed from the outside, and the energy is absorbed or released in the form of heat at the boundary of the two materials, so that heat is absorbed at one end and released at the other end of the thermocouple. In addition, when the direct current direction is changed, the refrigerating end and the heat-releasing end of the thermocouple are also exchanged.
The thermoelectric refrigerator has the main advantages of small volume, small mass, no moving parts, high reliability, no pollution, rapid refrigeration and high temperature control precision. Thermoelectric coolers have been used in space vehicles for cooling star sensors and infrared sensors, such as the goddard space center of NASA, which is based on three-stage thermoelectric coolers to dissipate heat from infrared detectors and to cool two-loop heat pipe reservoirs of return cabins of the flying test vehicle No. five. The test result of the latter shows that the thermoelectric refrigerator effectively forms the temperature difference between the evaporator and the liquid storage device, and ensures the normal starting and stable operation of the loop heat pipe.
The working principle of the TEC is shown in figure 1. The TEC is formed by serially connecting tens of pairs of thermocouples formed by P, N type semiconductors, and the junction of the two materials is covered by a ceramic plate which is insulating and has good heat conduction performance. Because all the refrigerating ends are concentrated on one side and the heating ends are concentrated on the other side, the TEC can amplify the inconspicuous Peltier effect when a single thermocouple is electrified, so that a larger temperature difference is generated between the heating surface and the refrigerating surface. After the temperature of the heating surface is controlled by external heat dissipation measures, the lower refrigerating temperature can be achieved at the refrigerating surface.
Compared with the traditional evaporation compression refrigeration or absorption refrigeration, the TEC has the advantages of small volume, no vibration and noise, high working reliability, rapid refrigeration, simple operation, rapid switching of heating/refrigerating surfaces, easy cold adjustment and the like. However, the TEC also has some disadvantages such as low refrigeration efficiency, high dependence on materials, high processing cost, etc., so that it is mainly applied to occasions with small refrigeration space and small refrigeration capacity.
In experiments carried out by the applicant, the use of thermoelectric refrigerator temperature control as one of the means of LHP accurate temperature control has certain uniqueness, and can heat or refrigerate the liquid storage cavity. While most other LHP temperature control means simply heat the reservoir or liquid tube or direct vapor into the reservoir through a bypass and not through the condenser. Besides the function of precisely controlling the temperature, the refrigerating function of the thermoelectric refrigerator can improve the performance of the loop heat pipe to a certain extent. And part of the increased power consumption can be transmitted to the cold end together with the load through the loop heat pipe by connecting the hot end of the TEC with the evaporator, and no extra heat dissipation channel is needed.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a novel structure space loop heat pipe auxiliary control system based on a thermoelectric refrigerator. The system is mainly formed by compounding a TEC temperature regulating system and a temperature sensing automatic control system. The temperature regulating system is formed by connecting a TEC, a heat conducting copper sheet and a direct current power supply in series; the automatic control system is formed by connecting a singlechip, a temperature sensor, a double-circuit relay, an MOS tube and the like. In addition, the device uses an Arduino Uno singlechip to realize the control of the whole link. The close fit of the heat dissipation system and the heat preservation system ensures the normal operation of the heat dissipation component.
In order to achieve the above purpose, the invention adopts the following technical scheme:
the utility model provides a set up loop heat pipe of thermoelectric refrigerator, includes thermoelectric refrigerator (TEC), heat conduction copper sheet, evaporimeter and reservoir, the evaporimeter is connected to the reservoir, its characterized in that, thermoelectric refrigerator's refrigeration face is connected with the upper surface heat of reservoir, and heat conduction copper sheet lower surface's a part is connected with the upper surface heat of evaporimeter, and heat conduction copper sheet lower surface's another part is connected with at thermoelectric refrigerator's upper surface heat.
The utility model provides a novel loop heat pipe of evaporation end structure, loop heat pipe includes evaporation end, condensation end, gas pipeline and liquid pipeline, liquid absorbs heat at evaporation end evaporation, and it releases heat to get into the condensation end through gas pipeline and condenses, and the liquid after the release passes through liquid pipeline and gets into evaporation end, its characterized in that, evaporation end includes the shell. Four chambers are arranged in the shell, and are a gas buffer chamber, a capillary core chamber, an auxiliary capillary core chamber and a liquid reservoir respectively, wherein the gas buffer chamber, the capillary core chamber and the auxiliary capillary core chamber form an evaporator; the auxiliary capillary core of the auxiliary capillary core chamber is wrapped around the liquid storage chamber, the aperture of the auxiliary capillary core is smaller than that of the capillary core, and the auxiliary capillary core is matched with the hole on one side of the main capillary core, so that the reflux liquid working medium can directly enter the front end of the capillary core for evaporation.
Preferably, the length of the hole of the wick becomes gradually shorter from the central position to the peripheral position of the wick.
Preferably, the length of the capillary wick aperture 9 is progressively shorter in magnitude from the central position to the peripheral position of the wick.
Preferably, the liquid storage device is connected with the evaporator, the refrigeration surface of the thermoelectric refrigerator is thermally connected with the upper surface of the liquid storage device, one part of the lower surface of the heat conducting copper sheet is thermally connected with the upper surface of the evaporator, and the other part of the lower surface of the heat conducting copper sheet is thermally connected with the upper surface of the thermoelectric refrigerator.
Preferably, the thermoelectric refrigerator is further provided with a double-circuit relay, an MOS tube and a direct-current power supply, wherein the double-circuit relay is connected with the TEC, the MOS tube is connected with the double-circuit relay, a loop is formed by connecting the direct-current power supply, the MOS tube and the TEC arranged above the loop heat pipe liquid storage device through wires, the direct-current power supply is responsible for supplying power to the thermoelectric refrigerator, the double-circuit relay can change the power supply direction of the TEC by changing the states of a normally-on interface and a normally-off interface, and the MOS tube can control the on-off of the loop.
Compared with the prior art, the invention has the following advantages:
1) And optimizing the structure of the heat pipe. The auxiliary capillary core is added into the liquid storage chamber of the heat pipe and inserted into the capillary core, so that the axial capillary force of the loop is enhanced, the large bubbles of the liquid pipeline in the capillary core can be effectively reduced, the reverse heat leakage is reduced, the stable forward running of the heat pipe is ensured, and the capillary suction speed of the heat pipe is increased to 0.6g/s.
2) According to the invention, the TEC is controlled to be in a forward power supply state, so that the temperature difference between the evaporator and the liquid reservoir is increased, and the temperature difference can be intelligently controlled, thereby ensuring the quick start of the loop heat pipe.
3) The thermoelectric refrigerator is applied to the loop heat pipe, has small volume, small mass, no moving parts, high reliability, rapid pollution-free refrigeration and high temperature control precision, effectively forms the temperature difference between the evaporator and the liquid reservoir, ensures the normal starting and stable operation of the loop heat pipe, and can maintain the stable temperature when the thermal power fluctuates.
4) The thermoelectric refrigerator is innovatively combined with the automatic control system, the starting and stopping and the power of the thermoelectric refrigerator are automatically controlled through the real-time monitoring of the temperature of the evaporator, the control effect of assisting and accurately controlling the temperature of the heat pipe can be integrally achieved, and the purpose of saving energy can be achieved through controlling the running power and the running time of the TEC.
5) The capillary suction function of the traditional heat pipe capillary core is separated from the liquid reflux function. The heat transfer distance is obviously improved, and the furthest heat transfer distance can reach 10m. The anti-gravity capacity is also obviously enhanced, and the height of the anti-gravity can reach 5m. The outstanding performance solves the problems of the use azimuth and the length limitation of the traditional heat pipe, and has extremely high applicability in space.
6) The heat pipe has high heat transfer efficiency. The device adopts a nickel-based capillary ammonia working medium loop heat pipe, adopts small-particle-size T255 spherical nickel powder as a raw material, and g-C3N4 and NaCl particles as pore formers, wherein the porosity of the nickel-based capillary core is up to 75%, the capillary suction speed is up to 0.6g/s, the heat resistance of the heat pipe can be stabilized at 0.15+/-0.01 ℃/W under the 60% filling quantity, the heat pipe is lower than the current universal range of 0.18-0.32 ℃/W in the market, the overall heat transfer power can be up to 400W, the limit power is 100W higher than that of the common heat pipe, and the overall heat transfer performance is greatly improved.
Drawings
FIG. 1 is a schematic diagram of TEC operation;
fig. 2 is a basic structure and a working principle diagram of the loop heat pipe of the invention.
Fig. 3 is a TEC layout and energy cycle diagram.
Fig. 4 is a graph of evaporator temperature operation at a heating power.
Fig. 5 is a diagram of a TEC auxiliary control system.
FIG. 6 is a diagram showing the internal structure of a preferred evaporation end of the present invention.
Detailed Description
The following describes the embodiments of the present invention in detail with reference to the drawings.
A loop heat pipe, as shown in figure 2, comprises an evaporation end, a condensation end, a gas pipeline and a liquid pipeline, wherein the liquid absorbs heat and evaporates at the evaporation end, enters the condensation end through the gas pipeline to conduct condensation and heat release, and the liquid after heat release enters the evaporation end through the liquid pipeline. The working principle is as follows: and the evaporation end is subjected to heat load, the working medium evaporates on the outer surface of the evaporation end capillary core, generated steam flows out of the steam channel and enters the steam pipeline, then enters the condensing end to be condensed into liquid and supercooled, the reflux liquid enters the liquid trunk through the liquid pipeline to supply the evaporation end capillary core, and the circulation is carried out, and is driven by capillary pressure generated by the evaporation end capillary core without external power. Because the condensing end and the evaporating end are separated, the loop heat pipe is widely applied to comprehensive application of energy and recovery of waste heat.
As shown in fig. 3, the evaporation end comprises an evaporator, a liquid reservoir, a heat conducting copper sheet and a thermoelectric refrigerator (Thermo Electric Cooler, TEC), wherein the liquid reservoir is connected with the evaporator, the refrigeration surface of the thermoelectric refrigerator is thermally connected with the upper surface of the liquid reservoir, one part of the lower surface of the heat conducting copper sheet is thermally connected with the upper surface of the evaporator, and the other part of the lower surface of the heat conducting copper sheet is thermally connected with the upper surface of the thermoelectric refrigerator.
The thermoelectric refrigerator is applied to the loop heat pipe, has the advantages of small volume, small mass, no moving parts, high reliability, no pollution, rapid refrigeration and high temperature control precision, effectively forms the temperature difference between the evaporator and the liquid reservoir, ensures the normal starting and stable operation of the loop heat pipe, and can maintain the stable temperature when the thermal power fluctuates.
Preferably, the heat pipe is used in a heat dissipation system for an aerospace system, such as a satellite.
Preferably, the loop heat pipe further comprises a double-circuit relay, an MOS tube and a direct current power supply, the double-circuit relay is connected with the TEC, the MOS tube is connected with the double-circuit relay, a loop is formed by connecting the direct current power supply, the MOS tube, the double-circuit relay and the TEC arranged above the loop heat pipe reservoir through wires, the direct current power supply is responsible for supplying power to the thermoelectric refrigerator, the double-circuit relay can change the power supply direction of the TEC by changing the states of a normally-on interface and a normally-off interface, and the MOS tube can control the on-off of the loop.
According to the invention, the power supply direction of the TEC is changed by setting the two-way relay to change the states of the normally-on interface and the normally-off interface, and the MOS tube can control the on-off of the loop, so that the intelligent control of the TEC is realized.
Preferably, the singlechip is connected with the two-way relay, the MOS tube and a temperature sensor arranged at the lower side of the evaporator, and can receive temperature data at the evaporator as judgment factors to control the working states of the two-way relay and the MOS tube.
Preferably, as shown in fig. 5, in the TEC auxiliary system, a direct current power supply, a MOS tube, a two-way relay and a TEC installed above a loop heat pipe evaporator are connected by a rubber wire to form a loop. The direct current power supply with controllable power is responsible for supplying power to the TEC and is connected with the MOS tube in a one-way mode, so that the MOS tube can flexibly control the on-off of a loop, and the function of a switch valve is achieved. The two-way relay is connected with the MOS tube and the TEC, and the power supply direction of the TEC can be changed by changing the states of the normally-on interface and the normally-off interface. The singlechip is connected with the two-way relay, the MOS tube and the temperature sensor arranged on the other side of the evaporator, the DuPont wire, the bread board, the wiring terminal and other parts are used for completing the wiring and the fixation of the control system, the external control and the state display of each loop are realized by utilizing the electronic elements such as the touch/self-locking keys, the LED lamps and the like, and the temperature at the evaporator can be received as a judging element to control the working states of the two-way relay and the MOS tube.
Preferably, in the normal power supply mode, the singlechip receives the signal of the temperature sensor and transmits the temperature data of the evaporator to the computer end at regular intervals (for example, 1 second) through the serial port, meanwhile, the dual-path relay is controlled to keep the TEC in a forward power supply state (namely, the contact surface with the liquid storage device is a refrigerating surface, the contact surface with the heat conducting copper sheet is a heating surface), and the MOS tube is controlled by the singlechip to keep a conducting state. In the working mode, the TEC loop is always kept in a conducting state, and constant-power auxiliary refrigeration of the loop heat pipe can be realized by adjusting parameters of a direct-current power supply. The rapid start-up of the loop heat pipe can be promoted by the above operation. And fast cycling in operation.
Preferably, the temperature control feedback mode is provided when it is desired to increase the temperature difference between the evaporator and the reservoir, for example when the detected temperature of the evaporator is too low. In the temperature control feedback mode, the singlechip receives the temperature of the evaporator fed back by the temperature sensor, compares the temperature with the target temperature set by the system to obtain data, and controls the power of the direct current power supply provided to the TEC according to the obtained data.
Preferably, if the detected temperature of the evaporator is higher than the target temperature, the singlechip data control reduces the power of the direct-current power supply provided to the TEC, and if the detected temperature of the evaporator is lower than the target temperature, the singlechip data control increases the power of the direct-current power supply provided to the TEC.
Preferably, the singlechip calculates the TEC power required by realizing temperature control based on a PID algorithm, and outputs PWM signals with different duty ratios to the grid electrode of the MOS tube, so that the output power of the TEC is changed and closed-loop control is realized. Meanwhile, the singlechip also judges whether the temperature of the evaporator reaches a peak value or not and changes from rising to falling, so that the power input to the TEC is stopped, and the TEC is closed. If the detected evaporator temperature reaches a peak, the power input to the TEC is terminated. In the process, the singlechip controls the double-way relay to keep a forward power supply state, and simultaneously outputs the voltage currently provided by the grid electrode of the MOS tube and the real-time temperature of the evaporator to the computer through the serial port at regular intervals (for example, 1 second).
Preferably, the reverse power mode is provided when it is desired to reduce the temperature difference between the evaporator and the reservoir, for example, when the detected temperature of the evaporator reaches a peak value or is higher than a peak value. In the reverse power supply mode, the singlechip receives the signals of the temperature sensor and transmits the temperature data of the evaporator to the computer end at regular intervals (for example, 1 second) through the serial port, meanwhile, the MOS tube is kept in a conducting state, the working state of the double-way relay is switched, the direct-current power supply supplies power to the TEC in a reverse mode, the refrigerating surface of the TEC transfers heat to the evaporator through the heat-conducting copper sheet, and the heating surface is directly contacted with the liquid reservoir. In the working mode, the TEC loop is always kept on, the temperature difference between the loop heat pipe evaporator and the liquid storage device is rapidly reduced by switching the heating surface and the cooling surface, and the pressure difference required by the normal operation of the loop heat pipe is also reduced, so that the mode can realize the rapid stop operation of the loop heat pipe.
Table 1 shows the components and their functions in the device
Figure BDA0003333190520000061
As a preferred choice of specific devices, a semiconductor refrigeration sheet of model TES1-7103 is selected according to the design requirement of the control system, the size of the model refrigeration sheet is 23mm 3.8mm, which is similar to the diameter of the loop heat pipe accumulator, 71 pairs of P, N type semiconductors are arranged in the loop heat pipe accumulator, the maximum refrigeration power can reach 13W, and the maximum temperature difference between the refrigeration surface and the heating surface can reach 64 ℃.
Maintaining the temperature difference between the evaporator and the reservoir of the loop heat pipe is one of the keys of the normal operation of the loop heat pipe, and the capillary force generated by the capillary core in the evaporator can provide a passive liquid sealing effect, so that the pressure difference between the evaporator and the reservoir is maintained, and the temperature difference is a main driving factor for forming the pressure difference.
The temperature difference between the evaporator and the liquid reservoir is the result of energy transfer balance of each part of the loop heat pipe, and the temperature difference can be represented by the formula (1):
Q e,cc ＝R e,cc ΔT e,cc ＝cm(T sat -T sub ) (1)
wherein R is e,cc Represents the thermal leakage resistance, deltaT, of the shell e,cc Represents the temperature difference between the evaporator and the liquid storage device, c is the specific heat capacity of the liquid working medium, m represents the mass flow of the working medium, T sat The temperature of saturated working medium in the reservoir is represented by T sub Indicating the temperature of the working medium at the inlet of the reservoir.
The formula (2) can be obtained by properly changing the above formula:
ΔT e,cc ＝cm(T sat -T sub )/R e,cc (2)
as can be seen from (2), the temperature difference between the evaporator and the liquid reservoir is mainly determined by the supercooling degree T of the reflux working medium in the loop heat pipe liquid reservoir sat -T sub Thermal leakage resistance R of shell e,cc 。
In order to increase the temperature difference between the loop heat pipe evaporator and the liquid reservoir, the temperature control characteristic of the TEC is utilized, the refrigerating surface of the TEC is arranged above the liquid reservoir, and the heating surface is connected to the evaporator through a copper sheet, so that the temperature difference between the loop heat pipe liquid reservoir and the evaporator is increased. After TEC auxiliary refrigeration is installed, the temperature difference between the loop heat pipe evaporator and the liquid reservoir can be represented by the formula (3):
ΔT e,cc ＝(Q tec,l -cm(T sat -T sub ))/R e,cc (3)
in which Q tec,l Representing the cooling power of the TEC.
As can be seen from the formula (3), after TEC auxiliary refrigeration is started, the refrigeration power of the TEC also becomes a key factor for influencing the temperature difference between the evaporator and the liquid storage device in the normal working state of the loop heat pipe, and the TEC refrigeration power has the largest influence on the temperature difference between the evaporator and the liquid storage device under the conditions that the operation temperature of the loop heat pipe is low and the supercooling quantity of the reflux working medium is small. Therefore, under the condition that the heat leakage resistance of the loop heat pipe shell is unchanged, the TEC is used for assisting in refrigeration, so that the temperature difference between the loop heat pipe evaporator and the liquid reservoir can be effectively increased, and the operation performance of the loop heat pipe is effectively improved.
Fig. 4 shows the temperature operating curve of the loop heat pipe evaporator at a certain heating power. Throughout the curve, the evaporator temperature undergoes three stages of up-down-plateau, where point a is the highest point at which the curve temperature operates. In the operating curve before point a, the evaporator is continuously heated, the loop heat pipe is not fully started, and the refrigerating efficiency is lower than the heat release efficiency, so that the temperature of the evaporator is continuously increased. The point A represents that the refrigerating efficiency and the heat release efficiency of the loop heat pipe are equal, and the starting condition of the loop heat pipe is enough to cope with heat release, so that the temperature turning point of the point A is used as a mark for controlling the TEC to be automatically closed, and the optimal solution of assisting the starting of the heat pipe and saving the power consumption is achieved.
According to the temperature control characteristics of TEC, an Arduino singlechip is used as a control core, and electronic elements such as TEC, a double-circuit relay, a metal-oxide semiconductor field effect transistor (MOS tube), a temperature sensor and the like with proper parameters are selected in combination with control requirements, so that a TEC auxiliary system for assisting loop heat pipe operation is designed, and the overall design idea of the system is shown in figure 5.
In the TEC auxiliary system, a direct current power supply, an MOS tube, a double-circuit relay and a TEC arranged above a loop heat pipe evaporator are connected through a wire to form a loop, the direct current power supply with controllable power is responsible for supplying power to the TEC, the double-circuit relay can change the power supply direction of the TEC by changing the states of a normally-on interface and a normally-off interface, and the MOS tube can flexibly control the on-off of the loop. The singlechip is connected with the two-way relay, the MOS tube and the temperature sensor arranged on the other side of the evaporator, and can receive the temperature of the evaporator as a judgment factor to control the working states of the two-way relay and the MOS tube.
Through the control loop, the following three operation modes are designed for the system:
1. normal power mode
In a normal power supply mode, the singlechip receives a signal of the temperature sensor and transmits temperature data of the evaporator to the computer end every second through the serial port, meanwhile, the dual-way relay is controlled to keep the TEC in a forward power supply state (namely, the contact surface of the TEC and the liquid storage device is a refrigerating surface, the contact surface of the TEC and the heat conducting copper sheet is a heating surface), and the MOS tube is controlled by the singlechip to keep a conducting state. In the working mode, the TEC loop is always kept in a conducting state, and constant-power auxiliary refrigeration of the loop heat pipe can be realized by adjusting parameters of a direct-current power supply.
2. Temperature control feedback mode
In a temperature control feedback mode, the singlechip receives the temperature of the evaporator fed back by the temperature sensor, compares the temperature with a target temperature set by a system to obtain an error value, calculates the TEC power required to be provided for realizing temperature control based on a PID algorithm, and outputs PWM signals with different duty ratios to the grid electrode of the MOS tube, so that the output power of the TEC is changed and closed-loop control is realized. Meanwhile, the singlechip also judges whether the temperature of the evaporator reaches a peak value or not and changes from rising to falling, so that the power input to the TEC is stopped, and the TEC is closed. In the process, the singlechip controls the double-way relay to keep a forward power supply state, and simultaneously outputs the voltage currently provided for the grid electrode of the MOS tube and the real-time temperature of the evaporator to the computer through the serial port every second.
3. Reverse power mode
In a reverse power supply mode, the singlechip receives a signal of the temperature sensor and transmits temperature data of the evaporator to the computer end every second through the serial port, meanwhile, the MOS tube is kept in a conducting state, the working state of the double-circuit relay is switched, the direct-current power supply supplies power to the TEC in a reverse mode, the refrigerating surface of the TEC transfers heat to the evaporator through the heat conducting copper sheet, and the heating surface is directly contacted with the liquid reservoir. In the working mode, the TEC loop is always kept on, the temperature difference between the loop heat pipe evaporator and the liquid storage device is rapidly reduced by switching the heating surface and the cooling surface, and the pressure difference required by the normal operation of the loop heat pipe is also reduced, so that the mode can realize the rapid stop operation of the loop heat pipe.
The control core of the system is selected from an Arduino Uno singlechip, the Arduino is a flexible and convenient open-source electronic prototype platform, a C-like voice processing/writing development environment is used, and control program codes can be written at a computer end through an Arduino IDE and then uploaded to the singlechip through a data line to realize control. Because of the open source characteristic, arduino can conveniently combine the existing electronic components and interact with various software, so that an efficient control system is designed, and the requirement of the research can be well met.
The temperature sensor of the system needs to be attached to the side face of the loop heat pipe evaporator, and high sensor precision is needed for realizing accurate temperature control, so that the research selects a patch type DS18B20 temperature sensor for the TEC auxiliary system. The DS18B20 temperature sensor has higher measurement precision, the measurement precision is +/-0.5 ℃ within the range of-10 to +85 ℃, the highest resolution is 0.0625 ℃, the two-way communication can be realized with a singlechip through a single-wire interface mode, and the power can be directly supplied by 5V voltage of Arduino.
The normal work of TEC requires a direct current stabilized power supply to supply power, and the research selects a UTP3313TFL-II type adjustable direct current stabilized power supply, wherein the maximum output power of the power supply is 90W, the output voltage range is 0-30V, the output current range is 0-3A, the resolution ratio of voltage and current is 10mV and 1mA respectively, and the power supply has a constant voltage mode and a constant current mode, so that the experimental requirement can be met.
As shown in fig. 6, the evaporation end includes a housing. Four chambers are arranged in the shell, namely a gas buffer chamber 12, a capillary core chamber 10, a secondary capillary core chamber 8 (the gas buffer chamber 12, the capillary core chamber 10 and the secondary capillary core chamber 8 form an evaporator) and a liquid reservoir 13. The gas buffer chamber is connected with the capillary core chamber, the capillary core chamber is connected with the auxiliary capillary core chamber, the auxiliary capillary core chamber is connected with the liquid storage chamber, the capillary core chamber and the auxiliary capillary core chamber are respectively provided with a capillary core and an auxiliary capillary core, and the aperture of the auxiliary capillary core is smaller than that of the capillary core.
Preferably, the housing is made of stainless steel; the capillary core arranged in the capillary core chamber 10 is a nickel-based capillary core, and can absorb heat from the high-power device and transfer the heat to the working medium, and the working medium changes phase to take away the heat; a plurality of holes 9 (preferably 3 holes) are drilled on one side of the capillary core and used as drainage channels, so that radial capillary force can be increased; the upper surface of the capillary core is carved with a channel, so that the liquid ammonia can be conveniently dissipated after being vaporized into saturated gas. The auxiliary capillary core chamber 8 is formed by wrapping an auxiliary capillary core made of stainless steel wire mesh with the aperture of preferably 20 microns around the liquid storage chamber, and the aperture of the auxiliary capillary core is smaller than that of the capillary core. The axial capillary force can be further enhanced, large bubbles of a liquid pipeline in the capillary core can be effectively destroyed, reverse heat leakage is reduced, and stable forward running of the heat pipe is ensured. The auxiliary capillary core is matched with the hole on one side of the main capillary core, so that the reflux liquid working medium can directly enter the front end of the capillary core for evaporation. The liquid storage chamber can ensure that the capillary core is always soaked by the liquid working medium, no pretreatment is needed before the evaporator is started, the heat pipe can be started by directly applying a heat load to the evaporator, and the liquid storage and supply of the capillary core of the evaporator are ensured. The gas buffer chamber improves the escape rate of gas from the capillary core, balances the diffusion rate of the gas, reduces the resistance of the gas diffusion and ensures the gas to be diffused smoothly.
Preferably, the length of the capillary wick aperture 9 is progressively shorter from the central position to the peripheral position of the wick. Through a large number of numerical simulation and experimental researches, the length of the hole 9 provided with the capillary core is gradually shortened, so that the stable forward effect of the heat pipe is better, and the technical effect of 8-10% can be improved. The above empirical formula is also a result of a great deal of experimental study performed in the present application, and is an invention point of the present application, and is not common knowledge in the art.
It is further preferred that the width of the holes 9 of the wick gradually becomes shorter from the central position to the peripheral position of the wick is larger as it is older. Through a large number of numerical simulation and experimental researches, the stable forward effect of the heat pipe can be optimized through the arrangement. The above empirical formula is also a result of a great deal of experimental study performed in the present application, and is an invention point of the present application, and is not common knowledge in the art.
According to the method, an optimal capillary length distribution relation optimization formula is found through a large amount of researches.
The outer shell is of a circular structure, the inner diameter of the outer shell is 2R, the length of the hole 9 of the capillary core at the center of the outer shell is L, and the length L of the hole 9 of the capillary core at the position R from the center is as follows: l=b×l-c×l (R/R) a Wherein a, b, c are coefficients, satisfying the following requirements:
1.082<a<1.109,0.99<b<1.01，0.358<c<0.363。
further preferably, a=1.096, b=1, c=0.361.
The above empirical formula is also a result of extensive experimental studies conducted in the present application, is an optimized structure for the length distribution of the pores 9 of the capillary wick, is also an inventive point of the present application, and is not common knowledge in the art. Preferably, the through-hole area of the capillary wick's hole 9 becomes gradually smaller from the central position to the peripheral position of the wick.
It is further preferable that the width of the through hole area of the hole 9 of the wick becomes smaller gradually from the central position to the peripheral position of the wick, the longer the width. Technical effect reference is made to the previous relationship of the variation in the length of the capillary wick aperture 9.
The shell is of a circular structure, the inner diameter of the shell is 2R, the area of the hole 9 of the capillary core at the center of the shell is S, and the area S of the hole 9 of the capillary core at the distance R from the center is as follows:
s＝b*S-c*S*(s/S) a wherein a, b, c are coefficients, satisfying the following requirements:
1.085<a<1.113,0.99<b<1.01，0.347<c<0.359。
further preferably, a=1.099, b=1, c=0.353.
The above empirical formula is also a result of extensive experimental studies conducted in the present application, is an optimized structure for the area distribution of the holes 9 of the capillary wick, is also an inventive point of the present application, and is not common knowledge in the art.
The working flow of the evaporation end is as follows: the liquid working medium starts from the liquid storage chamber and enters the liquid trunk inside the capillary core through the auxiliary capillary core, so that the liquid is uniformly supplied to the capillary core, and the capillary core is always in a soaking state. The working medium absorbs heat and evaporates on the outer surface of the capillary core, and generated steam flows out of the steam channel, enters the steam pipeline and then enters the gas buffer chamber. In the process, the capillary core provides power for driving the working medium to circulate.
By arranging the auxiliary capillary core, the aperture of the auxiliary capillary core is smaller than that of the capillary core. Compared with the existing loop heat pipe, the axial capillary force can be enhanced, reverse heat leakage is reduced, and large bubbles in the liquid pipeline are destroyed. The principle is as follows: the high-mesh auxiliary capillary core has very small pore diameter, so that the capillary force can be increased to a certain extent, and the suction capability is enhanced; in the process of reverse running, the auxiliary capillary core with small aperture can also burst bubbles, so that certain bubbles are filtered out, and reverse heat leakage is reduced.
Fig. 6 shows a specific structure of the four chambers of the shell, namely a gas buffer chamber, a capillary core chamber, an auxiliary capillary core chamber and a liquid reservoir from right to left, wherein liquid enters from the right end and gas exits from the left end in normal operation, and the side holes are filling interfaces through which liquid working media can be filled into the loop heat pipe.
The innovation of the invention is as follows:
1) The thermoelectric refrigerator is applied to the loop heat pipe, has small volume, small mass, no moving parts, high reliability, rapid pollution-free refrigeration and high temperature control precision, effectively forms the temperature difference between the evaporator and the liquid reservoir, ensures the normal starting and stable operation of the loop heat pipe, and can maintain the stable temperature when the thermal power fluctuates.
2) The thermoelectric refrigerator is innovatively combined with the automatic control system, the starting and stopping and the power of the thermoelectric refrigerator are automatically controlled through the real-time monitoring of the temperature of the evaporator, the control effect of assisting and accurately controlling the temperature of the heat pipe can be integrally achieved, and the purpose of saving energy can be achieved through controlling the running power and the running time of the TEC.
3) And optimizing the structure of the heat pipe. The auxiliary capillary core is added into the liquid storage chamber of the heat pipe and inserted into the capillary core, so that liquid ammonia can quickly enter the capillary core, the contact area between the liquid ammonia and the capillary core is enlarged, the axial capillary force of a loop is enhanced, large bubbles of a liquid pipeline in the capillary core can be effectively reduced, reverse heat leakage is reduced, the stable forward running of the heat pipe is ensured, and the capillary suction speed of the heat pipe is increased to 0.6g/s.
4) The heat pipe has high heat transfer efficiency. The device adopts a nickel-based capillary ammonia working medium loop heat pipe, adopts small-particle-size T255 spherical nickel powder as a raw material, and g-C3N4 and NaCl particles as pore formers, wherein the porosity of the nickel-based capillary core is up to 75%, the capillary suction speed is up to 0.6g/s, the heat resistance of the heat pipe can be stabilized at 0.15+/-0.01 ℃/W under the 60% filling quantity, the heat pipe is lower than the current universal range of 0.18-0.32 ℃/W in the market, the overall heat transfer power can be up to 400W, the limit power is 100W higher than that of the common heat pipe, and the overall heat transfer performance is greatly improved.
While the invention has been described in terms of preferred embodiments, the invention is not so limited. Various changes and modifications may be made by one skilled in the art without departing from the spirit and scope of the invention, and the scope of the invention should be assessed accordingly to that of the appended claims.

Claims (5)

1. The utility model provides a novel loop heat pipe of evaporation end structure, loop heat pipe includes evaporation end, condensation end, gas pipeline and liquid pipeline, liquid absorbs heat at evaporation end evaporation, and it releases heat to get into the condensation end through gas pipeline and condenses, and the liquid after the release passes through liquid pipeline and gets into evaporation end, its characterized in that, evaporation end includes the shell. Four chambers are arranged in the shell, and are a gas buffer chamber, a capillary core chamber, an auxiliary capillary core chamber and a liquid reservoir respectively, wherein the gas buffer chamber, the capillary core chamber and the auxiliary capillary core chamber form an evaporator; the auxiliary capillary core of the auxiliary capillary core chamber is wrapped around the liquid storage chamber, the aperture of the auxiliary capillary core is smaller than that of the capillary core, and the auxiliary capillary core is matched with the hole on one side of the main capillary core, so that the reflux liquid working medium can directly enter the front end of the capillary core for evaporation.
2. The loop heat pipe of claim 1 wherein the length of the wick's aperture is progressively shorter from a central location to a peripheral location of the wick.
3. The loop heat pipe of claim 2 wherein the length of the wick's aperture 9 progressively shorter is greater in magnitude from the wick's central location to the peripheral location.
4. The loop heat pipe of claim 1 wherein the reservoir is connected to the evaporator, the cooling surface of the thermoelectric cooler is thermally connected to the upper surface of the reservoir, a portion of the lower surface of the thermally conductive copper sheet is thermally connected to the upper surface of the evaporator, and another portion of the lower surface of the thermally conductive copper sheet is thermally connected to the upper surface of the thermoelectric cooler.
5. The loop heat pipe of claim 4 further comprising a dual relay, a MOS tube and a dc power supply, the dual relay being connected to the TEC, the MOS tube being connected to the dual relay, the dc power supply, the MOS tube, the dual relay and the TEC mounted above the loop heat pipe reservoir being connected by wires to form a loop, the dc power supply being responsible for powering the thermoelectric cooler, the dual relay being capable of changing the power direction of the TEC by changing the states of the normally-on and normally-off interfaces, and the MOS tube being capable of controlling the on and off of the loop.
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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101344344A (en) * 2008-08-25 2009-01-14 南京大学 Heat pipe semiconductor refrigeration and cold accumulation system
CN103344143A (en) * 2013-06-08 2013-10-09 北京航空航天大学 Evaporator and liquid reservoir used for loop heat pipe and application thereof
CN111649609A (en) * 2020-06-23 2020-09-11 山东大学 Flat plate type loop heat pipe evaporator with comb-shaped structure carbon fiber capillary core
CN113566628A (en) * 2021-06-29 2021-10-29 苏州浪潮智能科技有限公司 Loop heat pipe adopting surrounding type liquid storage cavity
CN114993080A (en) * 2020-11-05 2022-09-02 山东大学 Loop heat pipe evaporator

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101344344A (en) * 2008-08-25 2009-01-14 南京大学 Heat pipe semiconductor refrigeration and cold accumulation system
CN103344143A (en) * 2013-06-08 2013-10-09 北京航空航天大学 Evaporator and liquid reservoir used for loop heat pipe and application thereof
CN111649609A (en) * 2020-06-23 2020-09-11 山东大学 Flat plate type loop heat pipe evaporator with comb-shaped structure carbon fiber capillary core
CN114993080A (en) * 2020-11-05 2022-09-02 山东大学 Loop heat pipe evaporator
CN113566628A (en) * 2021-06-29 2021-10-29 苏州浪潮智能科技有限公司 Loop heat pipe adopting surrounding type liquid storage cavity

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