brazed plate heat exchangers, two-phase distribution, visulization
When used as direct expansion (DX) evaporators, brazed plate heat exchangers (BPHEs) suffer from the maldistribution of the two-phase refrigerant flow among parallel plate channels. One of the critical mechanisms of two-phase maldistribution is the phase separation in the inlet header. This paper presents an experimental investigation of the two-phase refrigerant (R134a) flow in the inlet header of a brazed plate evaporator and its effects on the distribution. Visualization of two-phase flow is accomplished through a 3D-printed transparent window at the inlet header of the heat exchanger. The observed flow regime is periodic and three stages are identified in a cycle. The influence of the operating conditions on the two-phase flow regime is also explored. The two-phase flow distribution in the BHPE is quantified by an IR thermography-based method. The quantification results demonstrate that the two-phase flow regime in the inlet header significantly affects the distribution.