Experimental Test And Numerical Simulation On Heat Transfer Characteristics Of Microchannel Heat Exchangers For Air Conditioning

Due to the advantages of high heat transfer efficiency,low refrigerant filling rate,safe and reliable operation,etc.,the microchannel heat exchanger has been investigated extensively in the air-conditioning field.Based on the characteristics of convective heat transfer and flow distribution of microchannel heat exchanger,experiments and numerical simulation are carried out in this paper,the research results have important engineering significance for improving the flow distribution and heat transfer characteristics of microchannel heat exchanger,and can provide theoretical basis and data support for practical application.Firstly,the experimental test platform of microchannel heat exchanger is set up,under different filling rates and environmental heat loads,the heat transfer characteristics of two microchannel heat exchangers are experimentally studied.Secondly,the numerical simulation study of the microchannel heat exchanger is carried out based on Fluent,the influence of different inlet and outlet position,inlet pipe diameter,splitter plate shape and splitter plate position on the refrigerant flow distribution is analyzed.Then,in the case of no splitter plate and middle splitter plate,the flow and heat transfer characteristics of gas-liquid two-phase flow are compared and analyzed by user-defined function（UDF）.In order to investigate the flow distribution characteristics of microchannel heat exchanger,three dimensionless parameters are introduced:non-uniformityη,relative standard deviation S₀ and ratio of maximum mass flow rate to minimum mass flow rateη₀.Finally,the research results show that:（1）For different filling rates,with the increase of filling rates,the cooling capacity of the two microchannel heat exchangers increases first and then decreases,the cooling capacity of microchannel heat exchanger A is greater than that of microchannel heat exchanger B.At the same time,the input power increases with the increase of filling rate,the input power of microchannel heat exchanger A is greater than that of microchannel heat exchanger B.（2）With the increase of filling rate,the EER of refrigeration system increases first and then decreases,when the filling rate of microchannel heat exchanger A is less than 1300 g,the EER increases by 9.75%for every 100 g filling rate increase;when the filling rate of microchannel heat exchanger B is less than 1200 g,the EER increases by 10.33%for every 100 g filling rate increase.Through fitting prediction,the optimum filling rate of microchannel heat exchangers A and B are 1330 g and1277 g,respectively.（3）Under different environmental heat loads,the cooling capacity increases with the increase of environmental heat load,and the input power rise rate is also increased.In addition,the refrigeration system EER also increases with the increasing of environmental heat load,but the rising rate gradually slows down,The EER of microchannel heat exchanger B is 7.58%higher than that of microchannel heat exchanger A.（4）The numerical simulation results show that:the inlet and outlet positions of microchannel heat exchanger are changed,the inlet and outlet are located at 1/2 of the header,and the refrigerant flow distribution is good.When changing the inlet pipe diameter,with the increase of the inlet pipe diameter,the inlet velocity decreases gradually,and the non-uniformity of flow distribution in the microchannel heat exchanger is improved.（5）The study on the splitter plate found that:compared with circular splitter plate and no splitter plate,η₀ and S₀ in rectangular splitter plate are the minimum,the non-uniformity of flow distribution is improved;compared with the structure of no splitter plate,upper splitter plate and lower splitter plate,the middle splitter plateη₀and S₀ are smaller than other splitter plates,that is,the middle splitter plate is better than other structures.（6）In the initial phase change and steady state of the gas-liquid two-phase flow,when comparing the middle splitter plate with no splitter plate,more uniform distribution of the volume fraction of the liquid phase in the flat tube,η₀ and S₀are small.In summary,the middle splitter is better than no splitter plate.