Experimental Investigation of Heat Transfer and Pressure Drop for Two-Phase R134A Flow in a 1.65 mm Glass Tube

Heat transfer in small scale media is a phenomenon that has been increasingly scrutinized in the past few decades. Refrigerant flow in microscale tubes and channels is a promising solution to be used in future refrigeration technology. Experimental studies are significant for the rating of the heat transfer and pressure drop in a given channel, and are important tools for optimizing applicable designs. An overview of the previous studies in this area has shown that most of the research does not focus on the low mass flow rates encountered in household refrigeration systems. In the current study, heat transfer in a copper tube with 1.65 mm inner diameter with two-phase R134a flow is experimentally investigated under low mass flow rate conditions. In the set-up constructed, instead of constant wall heat flux, which is the boundary condition mainly used in the microscale heat transfer studies in literature, constant wall temperature approach is applied. The experimental procedure is designed to focus on the temperatures and the flow rates observed during evaporation in a typical household refrigeration cycle. Since the flow is in the two-phase region, experiments for different quality values of R134a are conducted by pre-heating the refrigerant at different saturation temperatures and pressures. In microscale flow, a major problem is the increase in pressure drop compared to conventionally-sized channels, and the two-phase flow regime contributes to this increase. Therefore, in addition to the heat transfer, the pressure drop of the refrigerant along the tube is also measured. Thus, for various quality values, the pressure drop and the heat transfer for the refrigerant flow are examined. The experimental data obtained will be useful information for the two-phase flow modeling and the model verification.