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

Abstract

This paper explores the effects of fluid properties on two-phase flow in the vertical header and refrigerant distribution into horizontal branch tubes. R410A and R134a are used as the working fluid. Refrigerant enters into the header by five microchannel tubes in the bottom pass and exits through the five microchannel tubes in the top pass representing the flow in the outdoor microchannel heat exchanger of reversible systems under heat pump mode. The difference of fluid properties causes the flow pattern and refrigerant distribution results of R410A and R134a different between each other. Non-dimensional analysis shows that the inertia of R410A is higher than that of R134a. At low qualities, when the flow regime is churn, the higher inertia enables top tubes to receive more liquid so that the distribution of R410A is a little better than that of R134a. At high qualities, when it is likely semiannular, the higher inertia causes more bottom tubes are bypassed by the liquid film of semi-annular flow. It results in worse R410A distribution than R134a, though more liquid reaches the top tubes for R410A. The coefficient of variation of refrigerant distribution is applied in this study to generalize the results of both R410A and R134a at various header geometries and inlet flow conditions. A distribution function is derived for predicting R410A and R134a distribution in future.

Refrigerant Distribution Characteristics in Vertical Header of Flat-Tube Heat Exchanger without Internal Protrusion

“…Byun and Kim [2] tested and visualized the refrigerant distribution in the vertical header made for simulating an actual evaporator. Zou and Hrnjak [3][4][5][6] studied the distribution characteristics of the header with the internal protrusion of 10 flat tubes, where the refrigerant flows from the lower five flat tubes to the upper five flat tubes. However, Byun and Kim's and Zou and Hrnjak's flow channel geometries are too complicated for understanding the basic characteristics of the distribution of a vertical header.…”