Two-phase flow patterns and pressure drop of a low GWP refrigerant R-1234ze(E) in a plate heat exchanger under adiabatic conditions

The flow characteristics and flow pattern maps of R-1234ze(E) in a plate heat exchanger (PHE) are investigated at various vapor qualities and mass fluxes through flow visualizations. In the two-phase flow of R-1234ze(E) in the PHE, five dominant flow regimes are observed according to the vapor quality: slug flow, wavy liquid film flow, pulsating annular flow, vapor-preferred path annular flow, and entire annular flow. The flow characteristics of each flow regime in the PHE are analyzed in detail. The flow patterns in the PHE differ considerably from those in the smooth circular tube (SCT) owing to the corrugation and channel geometry of the PHE. The asymmetric flow observed in the PHE is explained with liquid and vapor-preferred paths. The flow pattern maps in the PHE and SCT are developed and compared based on the visualization results. Additionally, the relationship between the frictional pressure drop and the flow regimes is determined to be trivial, whereas the fluctuation in the pressure drop has a strong dependence on the flow regimes owing to intermittent flooding. (C) 2019 Elsevier Ltd. All rights reserved.