Evaluation of pressure, surface characteristics and fluid properties effect on pool boiling heat transfer over plain and external micro-finned cylindrical surfaces

Abstract

Pool boiling is extensively used in high and low-temperature heat exchangers as it results in a high heat transfer coefficient compared to natural and single-phase forced convection. Pool boiling experimental conducted over a plain cylindrical surface (PS) and four external micro-finned cylindrical surfaces (MFCSs), with R123 and R141b at different pressures in the heat flux range 20-100 kW/m2, have been presented in this paper. The objective of the present study is to explore the effect of pressure, surface characteristics and fluid properties on pool boiling heat transfer over plain and micro-finned cylindrical surfaces. The boiling heat transfer coefficient across micro-finned cylindrical surfaces was higher than it was for plain cylindrical surfaces due to lower surface wettability. In comparison to a plain cylindrical surface, the boiling heat transfer coefficient with pressure increases on average by 69% to 84% for the MFCS-1, MFCS-2, MFCS-3, and MFCS-4 with R123. At all tested pressures, pool boiling over a plain cylindrical surface with R123 yields a higher boiling heat transfer coefficient than previous experiments with R141b, whereas pool boiling over micro-finned cylindrical surfaces differs based on the combined effect of the micro-finned surface geometry, surface wettability, heat flux, pressure, and fluid properties.