Pressure influence on saturated boiling of R141b over Cu and Si-coated surfaces

Abstract

Pool boiling has been a research topic of great interest over the decades due to its inherent capabilities of large heat transfer rates with narrow temperature gaps and it advocates its suitability in a large number of industrial applications. The present paper describes the effect of operating pressure on pool boiling of R141b over a plain Cu surface as well as Si-coated surface prepared by a direct current (DC) sputtering technique. The working fluid R141b undergoes saturated pool boiling under pressure ranging from −20 kPa(g) to + 30 kPa(g) with the acquired experimental data and trends compared with the existing correlations and theories. Within the pressure range considered, the surface superheat variation was insignificant at lower heat fluxes; however, at higher heat fluxes, the maximum reduction was found to be by 9.5°C and 14.8°C for the plain Cu surface and Si-coated surface, respectively, regarding the corresponding values of −20 kPa(g) pressure. With respect to the results under atmospheric conditions, at the pressure of + 30 kPa(g), a corresponding increase in heat transfer coefficient of 12.1% for the plain Cu surface and of 17.8% for a Si-coated surface was observed at a heat flux of 225 kW/m2 and 272 kW/m2, respectively. In comparison to the results under atmospheric pressure conditions, the accompanying augmentation in the critical heat flux was observed as 13.3% for the plain Cu and 21.2% for the Si-coated surfaces at a pressure of + 30 kPa(g). Based on the experimental data, a correlation is developed for predicting heat transfer coefficients within the given pressure range.