Experimental Study On Nucleate Pool-Boiling Heat Transfer of R141b Over Plain and Micro-Finned Cylindrical Surfaces at Different Pressures

Abstract

Micro-finned cylindrical surfaces find wide applications as enhanced surfaces for heat transfer in heat exchangers used in refrigeration and chemical process industries. In the present study, the experimental investigation of pool-boiling heat transfer of refrigerant R141b has been carried out at different pressures (between 100 and 175 kPa) and heat flux that ranges from 20 to 100 kW/m2 over a plain and micro-finned cylindrical surface. It was observed that with the micro-finned cylindrical surface, boiling performance was improved for all tested pressures. The average increase in the boiling heat-transfer coefficient is 7-35% in comparison to the plain surface at respective pressure between 100 and 175 kPa. With the rise in pressure, the boiling heat-transfer coefficient for the micro-finned cylindrical surface increases at a higher rate as compared to the plain surface. This is due to the combined effect of the enhanced surface and decrease in surface tension of the liquid with pressure. The bubble departure diameter decreases with an increase in pressure, as with increased pressure the surface tension decreases, thereby causing an early detachment of the bubble from the surface. The experimental values of bubble departure diameter were compared with the well-known correlations and were found to be within ± 20%.