Distribution characteristics of two-phase refrigerant in a return junction connecting parallel narrow channels

A flat tube heat exchanger has attracted attention as one of the solutions to improve energy efficiency and reduce the amount of refrigerant in the development of the air conditioning unit for global warming prevention. An experimental study is carried out to examine the heat exchanger header patterns capable of appropriately distributing gas-liquid two-phase refrigerant into several narrow channels in an inclined flat-tube heat exchanger return junction for the purpose of improving both condensation and evaporation heat transfer performance. First, distribution of the gas-liquid two-phase refrigerant are examined using a return junction model with lower four inlet tubes and upper four outlet tubes to obtain the slit pattern achieving a uniform distribution. Next, an improved slit pattern is examined to obtain a desired distribution rather than a uniform one. Furthermore, an S-shaped path which has two slits is proposed to improve both condensation and evaporation heat transfer performance, and its heat transfer performances is evaluated using the heat exchanger with the S-shaped path. As a result, the overall heat transmission coefficient of the flat-tube heat exchanger with the S-shaped path is improved by about 5% in evaporation and 10% in condensation compared to that of a heat exchanger without the slit.