18 May 2017
This paper presents an investigation of port level refrigerant flow maldistribution in microchannel heat exchanger (MCHX). The objective is to observe and quantify port level refrigerant flow maldistribution induced by the uneven heat transfer caused by air condition change in air flow direction. A microchannel heat exchanger model which is comprehensively validated by experimental data is employed to simulate a 4-pass 36-tube microchannel condenser with 18 rectangular ports in each tube. The effects of refrigerant mass flux, refrigerant inlet quality, refrigerant saturation delta T and air velocity are explored. The coefficient of variation (CoV) is introduced to quantify the port level flow maldistribution. For condensation tube, the mass flow rate increases first, then decreases along air flow direction. There is a peak in the concave maldistribution curve where the corresponding port holds the maximum mass flow rate. The parametric study shows that large refrigerant mass flux, large inlet vapor quality and small air inlet velocity tends to bring the peak of the maldistribution curve forward. The maximum CoV of maldistribution observed is 0.1424 and the maximum MCHX capacity percentage degradation for the sample inlet tube is 33% and the largest capacity degradation for the entire MCHX is 3.66%. This study indicates that port level maldistribution has significant impact on heat exchanger performance. The conclusions of this study serve as a contribution, which can enhance the design of MCHX geometry and its operation condition to make the refrigerant flow distribution more uniform in port level.