Modeling refrigerant maldistribution in microchannel heat exchangers with vertical headers based on experimentally developed distribution results

R410A and R134a upward flow in the transparent vertical header and distribution into the horizontal parallel microchannel tubes were investigated. Refrigerant entered into the header by the five tubes in the bottom pass and exited through the five tubes in the top pass, representing the flow in the outdoor coil under the heat pump mode of reversible systems. Inputting the experimental quality results into a microchannel heat exchanger model, the capacity degradation compared to the uniform distribution case was calculated. The capacity degradation is related to the coefficient of variation of refrigerant maldistribution, which is affected by header geometry and inlet conditions. The capacity degradation of the whole two-pass microchannel heat exchanger was calculated by inputting the derived empirical distribution function in to the model. It was found that the capacity was reduced by up to 30% for R410A and 5% for R134a, respectively, for the conditions examined. •R134a and R410A distribution in microchannel HXs with vertical header was explored.•A model was built with experiment data or empirical distribution function as input.•Maldistribution is related to HX capacity reduction compared to uniform case.•For R410A, the capacity of two-pass HX is reduced up to 30%.•For R134a, the capacity of two-pass HX is reduced up to 5%.