Design and Two-Phase Distribution Characteristic of Two-Stage Distribution Vertical Header for Microchannel Heat Exchangers

The two-phase distribution uniformity of a refrigerant is an important factor affecting the heat exchanger performance. To address the poor uniformity of the liquid phase in the vertical header of the microchannel heat exchanger, a design scheme of a two-stage distribution header is proposed. The gas and liquid flow ratios of each branch under different dryness and total mass flow rates are compared by two-phase refrigerant distribution testing. The top branch of the empty header does not have a sufficient amount of liquid, while the bottom has excess liquid. The relative standard deviation (RSD) of the liquid phase for each branch is larger than 95%. The multiflow header uses the bottom inlet cavity to distribute the liquid, and then the liquid flows upward in the multiflow channel and enters the annular cavity through the side outlet hole. The liquid RSD of each branch is larger than 60%. When the core flow-regulated cavity and top distribution cavity are added into the multiflow header, the distribution performance is satisfactory, with RSDs of liquid and gas phases below 5% and 15%, respectively.