Heat transfer and pressure drop in plate heat exchanger refrigerant evaporators

Plate heat exchangers (PHE’s) are being used to an increasing extent as refrigerant evaporators but published information on their performance in this mode is rather limited. In this paper, two-phase heat transfer and pressure drop characteristics are presented for PHE’s when used as refrigerant liquid over-feed evaporators. Laboratory experiments were carried out with three industrial PHE’s having different chevron angle combinations, using refrigerant R134a and R507A. Measurements were made over ranges of mass flux, heat flux and corresponding outlet vapour qualities, and the effects of these parameters on the thermal and hydraulic performance of the evaporators were evaluated. Additional field test data of thermal performance were collected from ammonia and R12 water chillers, operating as thermosiphon evaporators. Based on all these data, empirical correlations are proposed for predicting the refrigerant boiling heat transfer coefficient and two-phase frictional pressure drop in PHE’s.