Two-phase flow distribution in multi-channel evaporators

Abstract

This study experimentally investigates the two-phase flow distribution of the low global warming potential refrigerant R1234ze(E) within a full-scale evaporator. The evaporator has two passes, each comprising eighteen parallel channels. The combined and individual effect of several parameters, including four different header and channel orientations, six inlet and outlet pipes positions, and the presence of an inlet flow device in the header, on the flow distribution are evaluated. To compare the two-phase flow distribution performance across different configurations, a uniformity coefficient is defined and calculated from infrared (IR) thermography images of the first pass of the evaporator. A test matrix of 24 experiments is designed using a design of experiments (DOE) technique. Six mass flow rates ranging from 0.02 to 0.065 kg/s are tested at vapor qualities of 0.18 or 0.3 and saturation temperatures of 5 °C or 25 °C. The results reveals that the header and channel orientation have the most significant impact. Optimal inlet and outlet pipe locations have been identified for each orientation. The uniformity coefficient results are compared with the evaporator thermal efficiency, showing four distinct linear trends depending on the header and channel orientation. These findings provide insights into the key-factors impacting two-phase flow distribution within evaporators, contributing to the understanding of optimal evaporator design and operation.