Refrigerant distribution in the vertical header of the microchannel heat exchanger – Measurement and visualization of R410A flow

• Increasing quality, the distribution is worse. At low qualities, increasing the mass flux, the distribution is better.
• Due to increase in mass flux, greater number of the microchannel tubes improves the distribution.
• Churn flow in the header has better distribution than separated flow since the mixture is more homogenous.
• To achieve good distribution, the liquid and vapor mass flux in the header should be kept within certain value.
• An empirical liquid distribution correlation was obtained using the liquid take-off ratio.

This paper presents the R410A adiabatic upward flow in three vertical headers of microchannel heat exchangers. All microchannel tubes are inserted into the half depth. The objectives are to explore what affects R410A distribution and attempt to predict the distribution. R410A is circulated into the header through the (5 or 10) tubes in the bottom pass and exits through the (5 or 10) tubes in the top pass. It represents the flow in the outdoor heat exchanger (usually used as the condenser) when it is used as the evaporator in the heat pump mode of reversible systems. The quality was typically varied from 0.2 to 0.8 and the mass flow rate from 1.5 to 4.5 kg h−1 per tube. The best distribution was observed at high mass flux and low quality. The experiment and visualization reveals the flow pattern effects in terms of homogeneity and momentum. The churn flow had better distribution since the two-phase mixture was more homogenous and the distribution was better at high mass flux in the header because the higher momentum liquid was able to reach the top exit tube.