Wettability effect on pool boiling: a review

This chapter aims at reviewing and discussing the effects of wettability on pool boiling heat transfer. Despite the studies carried out in the last half of the 20th century, enhancement of pool boiling heat transfer by surface wettability changes is still a very complex task to achieve and even to understand. Numerous studies have been proposed in the literature to improve heat transfer coefficients (HTCs) and/or to delay the occurrence of the critical heat flux (CHF) in pool boiling by increasing the number of nucleation sites, the nucleation rate and/or the rate of bubble detachment from the surface. However, many of them modify simultaneously both the chemical structure of either the liquid or the solid surface and the surface topography, making it difficult to separate the effects of each, and also failing to determine whether there are cross-effects due to interactions between them. The present review covers the wettability effect on pool boiling, from the fundamentals of nucleation and onset of boiling to bubble dynamics, and finally to their subsequent effects on the HTC and CHF. This exercise is then used to understand a variety of strategies developed to enhance pool boiling heat transfer. Theoretical approaches predicting heat fluxes and heat transfer coefficients are also addressed. Main conclusions on the role of wettability on pool boiling heat transfer are finally summarized and further research topics are suggested.