Falling Film Evaporation of HFO-1233zd(E) in Vertical Rectangular Minichannels Consisting of Serrated-Fins

Abstract

In the present study, the characteristics of heat transfer are experimentally investigated on the falling film evaporation of alternative pure refrigerant HFO-1233zd(E) in a plate-fin heat exchanger having a vertical rectangular minichannels of 2.11 mm hydraulic diameter consisting of serrated-fins. The refrigerant liquid is supplied to the channel through 37 holes of a liquid distributor. The liquid flowing down vertically is heated electrically from the rear wall of the channel and evaporated. The experimental parameters are as follows: the mass velocities are varied 7.4∼55.1 [kg/(m2s)], the heat fluxes are varied 8.7∼50 [kW/m2] and the pressures are about 100 [kPa]. In the case of small mass velocity being smaller than 20 [kg/(m2s)], heat transfer coefficient decreases monotonously and gradually with increase of quality and take value of 5∼1[kW/m2K]. It is thought that the cause of lower value of heat transfer coefficient is occurring dry patch and aria enlargement of dry area in the downstream region. In the case of large mass velocity being larger than 41 [kg/(m2s)], the value of heat transfer coefficient becomes larger with increase of quality except for the case of mass velocity being 41 [kg/(m2s)] and heat flux being 50[kW/m2]. Improved heat transfer is to be thinkable that the liquid and vapor flow becomes dripping in the middle-stream region, and turns into mist flow with thin liquid film on the fin surface in the downstream region of quality being larger than 0.4.