A model to predict the effect of surface wettability on critical heat flux

Critical heat flux (CHF) in pool boiling experiments corresponds to the heat flux at which a vapor film is formed on the heated surface resulting from the replacement of liquid by vapor adjacent to this surface. Poor thermal conductivity of vapor can severely deteriorate heat transfer. It is important that systems operate below this limit which is a strong limitation to heat transfer due to the huge increase of the thermal resistance near the wall. The concept of macro- and micro-contact angles has been introduced in a previous paper (Phan et al., 2010 [28]) to describe the bubble growth processes. In this paper, an explicit relation between the bubble departure diameter and the contact angle has been presented. Based on these results, we propose a model of critical heat flux, taking into account the effects of the wettability of the fluid, whose property is known to strongly influence boiling heat transfer. A new correlation for CHF, dependent on the contact angle, is proposed. It is found in fair agreement with existing experimental results concerning subcooled boiling to describe the variation of CHF with wettability.