High resolution local heat transfer and pressure drop infrared measurements of two-phase flow of R245fa within a compact plate heat exchanger

Abstract

An experimental study is presented to characterize two-phase thermal and hydraulic performance of a prototype corrugated plate heat exchanger with small pressing depth. In particular, upward flow boiling of low pressure refrigerant R245fa was investigated for a prototype fabricated with two plates of only 1mm pressing depth with a chevron angle of 65°. High spatial and temporal resolution infrared measurements were obtained by self-calibration of the IR camera to measure local (pixel-by-pixel) heat transfer coefficients during diabatic tests and local frictional pressure drops over the entire plate during adiabatic tests. Two-phase experiments were carried out for mass fluxes from 10 to 85kgm−2s−1, heat fluxes from 225 to 4100Wm−2, saturation temperatures from 19 to 35°C and vapor qualities from 0.05 to 0.90. The two-phase frictional pressure drops increased with mass flux and vapor quality while they decreased with increasing saturation temperature. A new correlation for predicting the local frictional pressure gradient through the test section was proposed. The present model captured the entire frictional pressure drop database within a bandwidth of ±30%, providing a mean absolute error of 10% and mean error of 0.2%. The local flow boiling heat transfer coefficients were found to increase with mass flux, heat flux and saturation temperature while rising, leveling off and then decreasing with increasing vapor quality.