Two-phase refrigerant maldistribution and optimization design in novel alternatively-laminated-microchannel-tube (ALMT) heat exchangers with vertical headers

Abstract

The novel alternatively-laminated-microchannel-tube (ALMT) heat exchanger contains two pairs of vertical headers and alternatively laminated microchannel flat tubes, which realizes high-efficient heat transfer between water and refrigerant and shows energy-saving potential in large-scale air conditioners. However, the microchannel flat tubes are upright inserted into vertical headers and are susceptible to refrigeration maldistribution. In this article, two-phase refrigerant maldistribution and optimization design in ALMT heat exchangers with vertical headers are studied experimentally and numerically. Refrigerant maldistribution is experimentally measured and its flow behaviors are explored with CFD simulations. The R410A is used as the working fluid. Results show that more liquid refrigerant is supplied to middle tubes but less to both ends under phase separation and gravity. Therefore, the decentered orifice plate (DOP) and parallel multi-chamber (PMC) are designed to improve refrigerant distribution. Both DOP and PMC promote gas-liquid phase mixing by accelerating refrigerant flow. The DOP creates the nested loop flow and PMC forms separate chambers inside vertical header to distribute refrigerant to each flat tube uniformly. Moreover, the formation conditions for nested loop flow are established. The average standard deviation of refrigerant flow rate reduces from 0.21 to 0.07 with DOP, and to 0.03 with PMC, respectively.