Experimental And Simulative Study On Performance Of Micro-channel Separate Heat Pipe

The separate heat pipe is a novel and highly efficient heat transfer technology. The difference between separate heat pipe and traditional heat pipe lies in the separated arrangement of evaporator and condenser. The number and position of evaporator and condenser can be set up flexibly according to the actual demand and long distance transmission of heat can be achieved. So the separate heat pipe is widely used in air conditioning industry. Micro-channel heat exchanger is getting more and more attention of air conditioning industry and researchers for its characteristics of low refrigerant charge and pressure drop, high heat transfer performance and light quality. So micro-channel heat exchangers is been taken as the evaporator and condenser of the separate heat pipe in this paper, which can greatly improve the heat transfer efficiency and reduce the power consumption of air-conditioning by combining the advantages of both.Firstly, the effects of the filling ratio on the heat transfer rate,EER,refrigerant pressures and temperatures, and the variation of optimal filling ratio range and heat transfer rate under two air volumes and different outdoor temperatures are investigated by experimental test of separate micro-channel heat pipe(SMHP) carried out in enthalpy difference laboratory. The results show that: the optimal filling ratio of is 79.3%~105.8% and the maximum heat transfer rate and EER are 4.0k W and 11.8, respectively. The results of experimental test under different working conditions show that: the increase of temperature difference between indoor and outdoor can improve heat transfer performance of SMHP significantly. When the filling ratio is 99.1%, EER increases from 4.8 to 11.8 as the temperature difference increased from 5℃ to 10℃, and increases by 71.6% as the temperature difference increased from 10℃ to 20℃。Then, a steady-state mathematical model is built based on conservation laws of momentum, energy and mass. And the model is validated with experimental data in this paper, and the predictive range of optimum filling ratio agrees well with the results of experiment. As to the maximum cooling capacity and mass flow rate, the relative errors of the simulation and experiment are 3.9% and 9.7%, respectively.Finally, the performance parameters such as h eat transfer coefficients of evaporator and condenser, Reynolds number in evaporator, liquid film thickness of condenser in the direction of flow are analyzed and the heat transfer in the evaporator and condenser channel is described by simulate results. The effect of air volume, indoor and outdoor temperature on t he heat transfer performance and flow characteristics were calculated by the steady state model. Based on the simulation, the influence of structure parameters of micro-channel heat exchanger such as flat tube height, fin pitch, fin height, louver pitch, louver angle and height difference of heat exchanger on the heat transfer performance and flow resistance of the SMHP are analyzed,which can give a reference to the optimization design of the system.