RU213247U1 - Thermoregulating heating device based on a loop heat pipe - Google Patents

Abstract

The utility model relates to the field of heat engineering and can be used to create adjustable heat transfer devices for heating automatic spacecraft equipment, in particular landing spacecraft operating in conditions of solar energy deficiency, as well as in autonomous heat engineering devices operating in harsh climatic conditions.

The temperature-controlled heating device based on a loop heat pipe contains an evaporator with a capillary-porous insert (CPV) in contact with a heat generator, a condenser in contact with thermostatically controlled equipment, a steam pipeline, a condensate pipeline and a valve with a bellows filled with an inert gas. The valve is made two-way and is installed in the condensate pipeline at the outlet of the condenser with the ability to regulate and stop the circulation of the coolant. The internal volume of the condenser exceeds the volume of the circulating heat carrier, excluding spontaneous flow of the heat carrier from the condenser to the evaporator when the condensate pipeline is closed. In this case, all elements of the evaporator (including CPV) are made of the same material.

The proposed heating device allows for controlled heating of equipment depending on its actual temperature under conditions of changing ambient temperature or changes in heat release from the equipment. In this case, the regulation is carried out by passive means, and the LHP is capable of operating under gravitational conditions and, if necessary, as a conventional unregulated LHP under weightless conditions. 4 w.p. f-ly, 6 ill.

Description

The utility model relates to the field of heat engineering and can be used to create adjustable heat transfer devices for heating automatic spacecraft equipment, in particular landing spacecraft operating in conditions of solar energy deficiency, as well as in autonomous heat engineering devices operating in harsh climatic conditions.

A known system for thermal control of the instrument compartment in the Soviet automatic self-propelled vehicles "Lunokhod-1" and "Lunokhod-2", where the gas circulating through the sealed instrument compartment, if necessary, was directed through the corresponding gas ducts, or to the installation site of a radioisotope heat source (RHS) when heating was required gas, or into a radiator when cooling of the gas was required. [A.P. Vinogradov Movement laboratory on the moon LUNOHOD-1, M.: "Nauka", 1971, p. 30-33, 128 pp.]. Thus, in the gas-filled sealed instrument compartment of the Lunokhod, it was possible to maintain the specified temperature regime with the equipment turned on and off, as well as at low night and high daytime temperatures, which increased as a result of the impact of solar thermal radiation on the Lunokhod. If the heating of the equipment was not needed, the gas circulation was carried out bypassing the RHS, and then the RHS itself, which could not be "turned off" during the operation of the Lunokhod, was heated to a temperature significantly higher (by tens of degrees) than the temperature of the heated object, which allowed the RHS (in " idle mode) to dump almost all the heat into the environment.

Due to the significant temperature difference between the RHE in idle mode and in the mode of heating the circulating gas, it becomes possible to use part of the generated heat of the RHS for heating the instrument compartment. For example, a RHS with an effective radiation surface of 0.1 m ² (this may be the part of the RHS case open to the outside) at a temperature of 250°C is capable of dissipating a thermal power of about ~420 W into the environment. When extracting (with the help of circulating gas) heat from the RHS and lowering its temperature, for example, to 50°C, the surface in question will remove only ~60 W, therefore, the difference between the two named powers can be used as a useful thermal power for heating a third-party object, in this case, the instrument compartment, the temperature of which is below 50°C.

The distribution of gas flows in the STR in the modes of cooling and heating of the instrument compartment of the Lunokhods was carried out using shutters, the position of which was automatically set by the control unit (CU) and, thus, the set temperature of the gas in the instrument compartment, as well as the equipment installed in it, was maintained.

As a rule, for spacecraft used on the lunar surface, equipment was heated from RHS on a lunar night, since solar batteries were not operating on board the spacecraft during this period for a long time. Consequently, in Lunokhods, even on a lunar night, it was necessary to ensure gas circulation, for which it was necessary to ensure the continuous operation of the fan and the control unit and, accordingly, to have the necessary supply of electricity in the onboard battery (approximately for two Earth weeks). This was a significant drawback of this technical solution, since it reduced the reliability of the spacecraft and reduced the time of its active existence.

These shortcomings are partially eliminated in a temperature-controlled heating device developed for the Chinese landing lunar spacecraft of the Chang'e series, where also with the help of RHS 1, Fig. 1 “night” heating of dashboards 2 is carried out [Jianyin Miao, Qi Zhong, Qiwei Zhao, Xin Zhao Spacecraft Thermal Control Technologies, 2020, Springer, 372 p.].

This heating device uses the same principle of using RHS as in Lunokhods, i.e. RHS operating temperature is maintained at two limit levels: low-temperature, when RHS heats instrument panels, and high-temperature, when heat does not enter instrument panels and is dissipated directly into the environment. However, not gas is used here as a heat carrier, but two-phase ammonia circulating in a closed evaporative-condensing circuit. The fundamental difference between this system and the Lunokhod thermal control system is that a mechanical supercharger (i.e., neither a pump nor a fan) is used to ensure the circulation of a two-phase coolant in the circuit of the instrument panel heating system. The circulation of the coolant occurs due to the difference in heights at the installation sites of the evaporator 3 and condenser 4 on the spacecraft, i.e. in conditions of lunar gravity, the pressure of a liquid column is used. The liquid evaporates in the RHS installation area (the evaporator is located here), then the vapor condenses in the condenser installed above the evaporator (on the instrument panels), then the condensate (i.e. liquid ammonia) flows into the flow tank 5, and from it it returns to evaporator. Thus, the circulation and transfer of heat are provided "in a passive mode", without the consumption of electricity from the spacecraft's onboard battery.

In order to stop the heating of the instrument panels on a lunar day, the outlet pipe from the flow tank is closed using solenoid valve 6, so all the liquid in the circuit is gradually collected in the flow tank, and the evaporator is completely dried. With a "drained" evaporator, the RHS can give off heat only through its radiation to the environment and therefore it heats up to temperatures of 200-300°C. On a lunar night, the valve is opened and the liquid begins to flow down by gravity into the evaporator, since the reservoir is located above it. As a result, the circuit resumes its operation, the circulation of two-phase ammonia is restored, and the RHS temperature drops to normal values, commensurate with the allowable temperature of the instrument panels.

The advantage of the technical solution developed in the Chang'e project is the energy independence of the two-phase circuit operation during the moonlit night and the relative simplicity of the solution. However, to send a command to turn the heating circuit on and off (using an electrovalve) in Chang'e, an operator or an automatic control unit is still required, which reduces the reliability of the device. In addition, during the flight stage and when the spacecraft is in orbits of celestial bodies under weightless conditions, the instrument panels of the landing spacecraft also need to be heated, which requires the presence of electric heaters and, accordingly, leads to an increase in the required power of the onboard power supply system and an increase in the mass of the spacecraft.

Thus, the main disadvantages of this technical solution are the continued dependence on the onboard control complex for turning on / off the heating mode, as well as the need for gravity to ensure the operation of the device.

The closest analogue to the claimed thermostatic heating device, selected as a prototype, is a thermostatic device that allows for passive control of the heating of the instrument compartment/panel using an autonomous heat transfer device made on the basis of RHS and a loop heat pipe (LHP) [RF No. 2474780, F28D February 15, 2013]. The device includes an evaporator 7 containing a capillary-porous insert (CPV) 8 and in contact with a constantly operating heat generator 9, two condensers 10, 11, in contact, respectively, with a thermostatically controlled equipment 12 and a radiator 13 and a three-way valve 14 with a bellows 15 filled with an inert gas. The evaporator is connected to the condensers via steam line 16 and condensate line 17. The technical solution according to RF patent No. 2474780 does not use the principle of maintaining two significantly different RHS temperature potentials (as in Lunokhods and Chang'e spacecraft). The RHS temperature is always within the operating temperatures of the LHP evaporator. At the same time, the device can simultaneously (at a given power ratio) heat the dashboard and dissipate heat into the environment, with the possibility of transferring up to 100% of thermal energy to both the dashboard and the environment. The distribution of the circulating flows of the two-phase coolant is carried out by a three-way valve, which is a completely passive device and is able to maintain the set temperature of the dashboard. The main disadvantage of this heating device is its relatively large weight and size characteristics. To ensure the dissipation of RHS heat into the environment at low temperatures, a special RHE is needed, which has significant dimensions, requires a “suitable place” in the spacecraft, and has a mass.

The technical problem solved by the proposed utility model is to reduce the weight and dimensions of a thermostatic heating device based on LHP and RHS, which provides controlled heating of equipment without the cost of electricity for the control and operation of the heating device.

These tasks are ensured by the fact that in a well-known temperature-controlled heating device based on a loop heat pipe, containing an evaporator with a capillary-porous insert (CPV) in contact with a heat generator, a condenser in contact with thermostatically controlled equipment, a steam pipeline, a condensate pipeline and a valve with a bellows filled with an inert gas, the novelty is that the valve is made two-way and is installed in the condensate pipeline at the outlet of the condenser with the possibility of regulating and stopping the circulation of the heat carrier, while the internal volume of the condenser exceeds the volume of the circulating heat carrier, excluding spontaneous flow of the heat carrier (by gravity) from the condenser to the evaporator, when the condensate line, and all elements of the evaporator, including CPV, are made of the same material.

In addition, the body of the evaporator and the capillary-porous insert are made of nickel.

In addition, two-phase ammonia is used as a heat carrier.

In addition, the inner cavity of the condenser on the outlet side has a recess, the capacity of which exceeds the volume of the circulating coolant.

In addition, the valve of the heating device, when the device is installed on board the landing spacecraft, is additionally equipped with a locking mechanism that ensures that the valve is fixed in the open position until the spacecraft is landed on the surface of a celestial body.

The introduction of a two-way valve into the structure of the device makes it possible to ensure the regulation of the circulating coolant and complete shutdown of the circulation, depending on the vapor pressure of the two-phase coolant in the condenser, without issuing control commands.

Installing a valve at the outlet of the condenser allows, when the valve is closed, to stop the circulation of the coolant in the circuit on a moonlit night and collect all the liquid coolant in the condenser.

Exceeding the internal volume of the condenser of the volume of the circulating coolant makes it possible to exclude spontaneous flow of the coolant from the condenser to the evaporator through the steam pipeline when the condensate pipeline is closed.

The use of the same material for the components of the evaporator makes it possible to avoid damage and depressurization of the LHP possible as a result of thermal deformation of the evaporator.

The execution of the evaporator body and capillary-porous insert of Nickel allows you to obtain the optimal combination of thermophysical and strength characteristics of the components of the evaporator.

The use of ammonia as a two-phase coolant ensures the possibility of long-term operation of the heating device under conditions of repeated periodic drying of the evaporator with its temperature rising above the allowable temperature of the liquid coolant.

The presence in the inner cavity of the condenser on the outlet side of a recess, the capacity of which exceeds the volume of the circulating coolant, makes it possible not to introduce a reservoir into the condenser structure in the form of a separate element for collecting liquid. At the same time, if only a part of the condenser functions as a reservoir, the tracing of the condenser on the dashboard with thermostatic equipment installed is simplified.

Additional supply of the heating device valve, when the device is installed on board the landing SC, with a locking mechanism that ensures the valve is fixed in the open position before the SC landing on the surface of a celestial body, makes it possible to ensure the constant operation of the LHP in weightlessness.

The essence of the invention is illustrated by drawings, where:

Fig. 1 - a schematic diagram of a two-phase circuit for heating the instrument panels of the Chang'e spacecraft in active mode (on a moonlit night);

Fig. 2 - a schematic diagram of a two-phase circuit for heating the instrument panels of the Chang'e spacecraft in the passive mode (on a lunar day);

Fig. 3 is a schematic diagram of a heating device prototype (RF patent 2474780);

Fig. 4 - thermostatic heating device in the mode of coolant circulation and equipment heating;

Fig.5 - thermostatic heating device in the mode of no circulation of the coolant and stop heating equipment;

Fig. 6 - valve of the thermostatic heating device with a locking mechanism.

The heating device based on the loop heat pipe and RHS contains an evaporator 18, which has thermal contact with a constantly operating heat generator (i.e., RHS) 19. The evaporator 18 is equipped with a capillary-porous insert 20, which in LHP performs the functions of a capillary pump, a hydraulic seal, a thermal shutter and steam generator. The outlet of the evaporator is connected by means of a steam line 21 to the inlet of the condenser 22 intended for heating the spacecraft equipment. The outlet of the condenser 23 through a two-way valve 24 with a bellows 25 is connected to the inlet to the evaporator using a condensate line 26. The two-way valve 24 either directs the coolant to the evaporator or stops circulation, and can also provide transitional, intermediate states. At the same time, the bellows 25 is an actuator that ensures the appropriate position of the valve stem 27. The internal cavity of the bellows 25 is filled with an inert gas and does not have direct contact with the LHP coolant. The gas pressure in the bellows determines the control temperature as it balances the saturated vapor pressure in the condenser. Under zero gravity conditions (at the stage of delivery of the spacecraft to a celestial body), the LHP can operate as a conventional unregulated LHP. To do this, either the valve setting temperature is chosen above the temperature of the equipment at the stage of delivery, or a locking mechanism 28 is installed, which ensures the open position of the valve.

The proposed heat transfer device operates as follows. In the active mode, the RHS heat from the evaporator 18 is transferred to the condenser 22 due to the condensation in it of the steam coming from the evaporator. The condensate freely returns to the evaporator through the condensate line 26, since the valve 24 installed in the condensate line is open. The open position of the valve is provided by its set temperature, which (in active mode) is higher than the temperature of the equipment. Thus, the coolant circulates and the (idle) equipment is heated. In the active mode, the device operates at night, when there is no sunlight in the spacecraft location area for a long time and there is a shortage of onboard electricity.

During the day, in the presence of sunlight, the equipment will start working and the temperature of the panel with the installed equipment will exceed the set value corresponding to the valve setting temperature, then the device will go into passive mode. Accordingly, the saturation pressure in the LHP condenser will also increase, the bellows 25 will change the position of the rod 27 and close the outlet 23 from the condenser 22. The liquid will begin to collect in the condenser and after a while the circulation will stop, because the evaporator will dry out and the heating of the equipment will stop. RHS 19 will heat up to the maximum temperature at which all its heat will be dissipated into the environment.

With a decrease in the ambient temperature or with a decrease in heat release from the equipment, its temperature will begin to fall, the saturation pressure in the condenser will decrease, the bellows will “unclench”, move the rod and, as a result, the exit from the condenser will open. Due to the liquid draining (from the condenser to the evaporator), the circulation of the coolant will resume, the evaporator will be replenished with the liquid coolant and the heating of the equipment will begin. In this way, controlled (cyclic) heating is achieved, and the valve operation is controlled by the actual condenser temperature, which is closest to the temperature of the equipment itself.

Under weightless conditions, at the stage of delivery to a celestial body, LHP works like a conventional unregulated LHP, if necessary. This mode can be provided by the locking mechanism 28.

The presented technical solution makes it possible to create a heat transfer device that provides controlled heating of equipment depending on its actual temperature under conditions of changing ambient temperature or changing heat release from the equipment. In this case, the regulation is carried out by passive means, and the LHP is capable of operating under gravitational conditions and, if necessary, as a conventional unregulated LHP under weightless conditions.

Claims (5)

1. A temperature-controlled heating device based on a loop heat pipe, containing an evaporator with a capillary-porous insert (CPV) in contact with a heat generator, a condenser in contact with thermostatically controlled equipment, a steam pipeline, a condensate pipeline and a valve with a bellows filled with an inert gas, characterized in that the valve is made two-way and is installed in the condensate line at the outlet of the condenser with the possibility of regulating and stopping the circulation of the heat carrier, while the internal volume of the condenser exceeds the volume of the circulating heat carrier, excluding spontaneous flow of the heat carrier from the condenser to the evaporator when the condensate line is closed, and all elements of the evaporator (including CPV) are made from one material. 2. The device according to claim 1, characterized in that the evaporator body and the capillary-porous insert are made of nickel. 3. The device according to claim 1, characterized in that two-phase ammonia is used as a coolant. 4. The device according to claim 1, characterized in that the internal cavity of the condenser on the outlet side has a recess, the capacity of which exceeds the volume of the circulating coolant. 5. The device according to claim 1, characterized in that the valve of the heating device, when the device is installed on board the landing spacecraft, is additionally equipped with a locking mechanism that secures the valve in the open position until the spacecraft lands on the surface of a celestial body.

Images