Critical Heat Flux on a Vertical Surface in Saturated Pool Boiling at High Pressures

Abstract

This paper investigates the CHF in saturated pool boiling of ethanol, R141b, and water on a 7 mm diameter vertical copper surface at high pressures. The pressures are from 0.1 to 3 MPa for ethanol, 0.1 to 1.5 MPa for R141b, and 0.1 to 0.8 MPa for water. The results show that the occurrence of CHF is accompanied by the formation of large vapor masses covering most of the heating surface with all three liquids over the whole range of pressures investigated here. The well-known Kutateladze-type CHF correlation explains the variations in the CHF with pressure well for ethanol and R141b, and underestimates the pressure dependence of the CHF for water. A correlation considering the effect of surface wettability on the CHF agrees fairly well with the CHF for water in the whole range of pressures here, when the temperature dependence of the contact angle determined from available data is incorporated into the correlation. This suggests that it is necessary to consider changes in surface wettability with pressure to be able to predict the CHF of water at high pressures.