Adiabatic Two-Phase Pressure Drop of Refrigerants in Small Channels

The adiabatic pressure drop of two-phase refrigerant flow in small channels has been investigated. A rectangular channel with d _h = 148.0 μm has been tested with four refrigerants: R134a, R410A, propane (R290), and ammonia (R717). These data have been combined with data taken from five different channels, with d _h varying from 70 μm to 305 μm, of R134a. The measured pressure drops have been compared to many published separated-flow and homogeneous pressure drop models. A new correlation for C, the Chisholm parameter, has been developed based on the Reynolds number of the vapor phase (which contains the majority of the kinetic energy) and the dimensionless grouping ψ—a ratio of viscous to surface tension effects taken from the analysis of capillary flow performed by Sou and Griffith (1964). This allows the new correlation to account for the varying fluid properties (including surface tension) that are found in the different refrigerants. The new correlation takes flow regime into account by means of a Weber number based flow transition criteria, following the flow map of Akbar et al. (2003).