Condensation of R1234yf in a plate heat exchanger with an offset strip fin flow structure for electric vehicle heat pumps

The energy-efficient plate heat exchanger (PHE) and refrigerant R1234yf, which has a low global warming potential (GWP), can be used to realize an energy efficient heat pump (HP) system for electric vehicles (EV), extending their driving range. Therefore, the characteristics of R1234yf in an offset-fin strip (OSF) flow-structured PHE are critical for heat-exchanger design. This study investigates the condensation heat transfer coefficient (C-HTC) and two-phase frictional pressure drop (2P-FPD) of R1234yf during condensation in an OSF flow-structured PHE under various operating conditions. First, a modified Wilson plot method was used to determine the multiplier (C) and Reynolds number exponential (n) for the coolant side as −0.426 and 0.494, respectively. When the heat flux (q), average vapor quality (x_a), and mass flux (G) increased, the C-HTC increased, whereas it decreased with saturation temperature (T_sat). Despite the force-convective condensation flow regime, the C-HTC increment was minimal with G at lower x_a owing to the lesser significance of the shear effect. Additionally, the 2P-FPD was unaffected by q but increased considerably with an increase in x_a and G and a decrease in T_sat. Based on the current experimental database, empirical correlations for forecasting friction factor and Nusselt number were developed with a 91% predictability.