Experimental research on heat transfer and pressure drop characteristics of R410a within an asymmetric plate evaporator

Conventional plate heat exchangers (PHE) have identical channel geometries on both hot and cold sides. This kind of symmetrical PHE cannot perform well in situations of evaporative heat transfer because the fluid flow rates on both sides are unbalanced. Asymmetric PHE provides channels of different cross-sectional flow areas to achieve balanced flow, which makes the pressure drops on both sides closer and leads to the enhancement of heat transfer. In this paper, experiments were carried out to study the heat transfer and pressure drop characteristics of an asymmetric plate evaporator (APE) with R410a as refrigerant and ethylene glycol (EG) solution as secondary refrigerant. For comparison, a conventional plate evaporator (CPE) was also tested under the same conditions. The operating conditions of the experiments are as follows: evaporation temperature, -2-8°C; inlet temperature of EG solution, 8-24°C; volume flow rate of EG solution, 30-80 L·min⁻¹; R410a mass flux, 13-44 kg·m⁻²·s⁻¹; heat flux, 4-13 kW·m⁻². The results imply that the APE has better heat transfer performance, the energy density of which is about 20%-40% higher than that of CPE. It means that the APE can make the size of heat exchanger smaller and reduce the charge of the refrigerant when the same heat duty is achieved. Through in-depth analysis, the R410a heat transfer coefficient of APE is estimated to be around 27% higher than that of CPE under the same Reynolds number, which demonstrates that the unequal depth corrugated structure of APE is beneficial for heat transfer. Moreover, the fanning friction factor of R410a in APE is lower than that in CPE under the same equivalent Reynolds number, which is mainly due to the smaller corrugation pressing depths of APE.