Comparison and generalization of R410A and R134a distribution in the microchannel heat exchanger with the vertical header

This article presents the experimental results of R410A and R134a distribution in the vertical header of a reversible outdoor microchannel heat exchanger. Two-phase refrigerant enters into the test header through multiple parallel microchannel tubes in the bottom pass and exits throughmultiple parallelmicrochannel tubes in the top pass, representing the flow in the outdoor microchannel heat exchanger of a reversible system under heat pump mode. The difference in fluid properties between R410A and R134a causes the difference in flow patterns and refrigerant distribution results. Non-dimensional analysis shows that the inertia of R410A is higher than that of R134a, with the following results: (1) at low qualities (churn flow), more liquid R410A reaches the top tubes, so R410A distribution is a little better than R134a; (2) at high qualities (semi-annular flow), more bottom tubes are bypassed by the liquid film of R410A, so R410A distribution is worse than R134a, even though more liquid reaches the top tubes for R410A. The distribution results of R410A and R134a are generalized with coefficient of variation, flow regime map, and a distribution function.