Local heat transfer coefficients of R32 and R410a condensation inside a brazed plate heat exchanger (BPHE)

Abstract

This paper presents the local heat transfer coefficients of R32 and R410A complete condensation inside a Brazed Plate Heat Exchanger (BPHE). A new test section, with one channel on the refrigerant-side and two channels on the water-side, was specifically designed and manufactured for measuring the local heat transfer coefficient in refrigerant two-phase heat transfer in BPHE. The test section includes two thick corrugated plates instrumented with 36 copper-constantan thermocouples for measuring the plate surface temperature, the heat flux and the heat transfer coefficient in 9 different positions along the refrigerant channel. The experimental tests were carried out at a saturation temperature around 30°C, in the refrigerant mass velocity range 10 − 39 kg m−2s−1 with an inlet vapour quality around 1.00 and an outlet vapour quality ranging from 0.04 to 0.27. A transition point between gravity controlled and forced convection condensation was found for a refrigerant mass velocity around 20 kg m−2s−1. The experimental data was compared against theoretical models: Nusselt (1916) analysis for vertical surface predicts very well the data in gravity controlled condensation, while Longo et al. (2015) model shows a fair agreement with the forced convection condensation data.