Thermal Control Method Study And Characteristics Optimization Of Heat Pipe Radiator Systems On GEO Orbit

High requirements for temperature control of optical remote sensing instruments for earth observation on three-axis stabilized geostationary orbit satellites lead to difficulties of thermal control system.The main factor determined by the geostationary orbit is the sunlight.The variable midnight sunlight on the optical system every day,the variable dramatic change of the external heat flux of west and east heat dissipation surfaces every day,and the variable dramatic change of the external heat flux of north and south heat dissipation surfaces every year are the major technical challenges caused by sunlight.Under the variable internal heat source and external heat flux due to the geostationary orbit,how to minimize the temperature fluctuations of the satellite optical payloads and simultaneously meet the demand of minimizing the thermal control compensation power consumption are the background and original study of this article.Considering the technological maturity and risks,the cooling system with grooved heat pipe radiant panels of the stabilized geostationary orbit optical loading refrigerator was designed and simulated,and ground start tests of radiant panels coupled with heat pipe and ground vacuum tests of the thermal control system were carried out.It had been demonstrated in orbit that the engineering demands could be satisfied by using the traditional temperature control radiator with grooved heat pipe panels,but it required more heating power for temperature control system and the heating power increased sharply as the controlling temperature increased.The scheme of temperature controlled by loop heat pipe was proposed and temperature control radiator with loop heat pipe was developed to reduce the temperature control power demanded by the radiation thermal control system.By changing the heat transfer resistance of the loop heat pipe,the responses of the target temperature and external heat flux change could be matched with lower temperature control power.The fluctuations of target temperature were decreased efficiently with optimal temperature control method.Under different working conditions,the flexibility of the thermal control system was improved as the dependence of temperature control power on the target temperature point declined.In the thesis,a one-dimensional thermal model the numerical simulation program of radiant panel coupled with the heat pipe were established and developed;by means of switch type temperature control,the temperature response state and stable state of the loop heat pipe was obtained;and the response status of the radiant panel and heat pipe interior was calculated when the external heat flux was varied with square and sine functions.Results showed that the temperature control power of the radiant cooling system with loop heat pipe was much lower than the radiator with grooved heat pipe.Using the switch type temperature control method,the controlling temperature in stable state fluctuated in a certain range and deviated from the target temperature.With the increment of target controlling temperature of the compensator,the average temperature control power of the compensator?and the deviation temperature of the evaporator were increased.External heat flux varied with square and sine functions was satisfied by radiant panel with loop heat pipe,and the temperature change stayed stable without concussion.When external heat flux varied with square-wave,the temperature changes of the evaporator,gas pipeline and compensator were increased with the temperature increment of the radiant panel.Components temperature fluctuations of the radiant panel were not affected by the change of frequency in the same temperature range.When external heat flux varied with sine functions,the temperature fluctuations frequency of the evaporator and compensator were increased with the decrement of the temperature fluctuations frequency of the radiant panel.The temperature fluctuations of the evaporator and compensator were increased with the temperature increment of the radiant panel at the same frequency.The prototypes of temperature control radiant cooling system with LHP using ammonia and propylene as working fluid were designed and developed.Experimental results showed that the desired temperature control effects could be achieved by controlling the compensator temperature when using propylene as the working fluid in the loop heat pipe.In switch mode,the difference between transient temperature and target temperature became larger as the compensator temperature was increased.The temperature fluctuation was 2.63K in stable state when the compensator temperature was-60?;the temperature fluctuation was 5.2K in stable state when the compensator temperature was 30?.The time delay reduced while the temperature control power of compensator was increased.The temperature control power fluctuation was increased above 10?and then decreased as the controlling temperature became more larger.The computational model was verified to be reasonable and accurate through the comparison of experimental and numerical simulation results.The temperature control method with PID parameters optimized by genetic algorithms was used to reduce the large temperature fluctuation and deviation in switch temperature control mode.Numerical simulation results using the loop heat pipe mode showed that the temperature fluctuation of compensator and evaporator could be reduced significantly when PID temperature control method was adopted and the temperature fluctuation of evaporator was 0.1K.The temperature control power and the temperature difference between the compensator and evaporator were increased and the temperature control time was decreased as the target temperature of compensator was increased.The last part of this article provided the summary and conclusions,and pointed out the direction of further research to solve the existing problems.