Experimental Investigation And Numerical Analysis On Separate Heat Pipe With Parallel Flow Heat Exchangers

In recent years,communication base stations have increased rapidly,which require heat dissipation all year round and consume a lot of energy.The micro-channel separation heat pipe equipped with efficient and compact micro-channel heat exchanger for the evaporation and condensation section brings following advantages : good heat transfer performance,low refrigerant filling rate,high EER,low air side pressure drop and so on,which effectively cope with the problems of the communication base station with small heat dissipation space and large heat flux density.Meanwhile,the heat pipe drive the refrigerant cycle to achieve heat transfer by temperature difference and the gravity without the need for compressors and other power equipment,and has good energy saving and noise prevention effects.In this paper,first of all,R134 a is used as the heat transfer medium,the parallel flow heat exchangers are used for the evaporation and condensation sections,and a gravitational separation heat pipe test bench was built to conduct experimental research.Through experiments,the changes of the heat transfer rate and the other performance parameters of the system under different working conditions are obtained,and the results are analyzed.When the outdoor temperature is 25 °C and the indoor and outdoor temperature difference is 20 K,the optimal filling ratio of the system is 90.22%.Then,according to the mass and energy conservation principle,based on the flow and heat transfer theory of the micro-channel heat exchanger,establishing the steady-state heat transfer model for the entire system and its components,and numerically calculating each model by MATLAB.The simulated heat tansfer rate,temperature and pressure at the inlet and outlet of the evaporation section,and temperature and pressure at the inlet and outlet of the condensation section were compared with the experimental data under different working conditions,and the maximum relative error was 8.46%.Finally,the following problems are studied by the established steady-state model:(1)The change trend of the optimal filling ratio of the system under different working conditions was reserched,and the range of the optimal filling ratito of the system was determined to be 80% ~100%.(2)Calculating the heat transfer coefficient of the evaporator and the condenser along the tube length under different filling ratio,and specifically analyzing the reasons of their change.(3)Calculating the total resistance pressure drop,mass flow rate and liquid level difference of the system at steady state,and combining with the three forms formed by the liquid level difference to explore the relationship between the heat transfer performance and dynamic performance of the system under variable operating conditions.(4)Calculating the heat transfer rate,resistance pressure drop and mass flow rate of the system at a higher indoor ambient temperature,and finding out its changing laws and related connections.(5)The effect of evaporator flow path distribution,the number allocation of flat tubes and the change of fin structure parameters on the system performance were explored,and optimization suggestions were made.