On the role of structural disjoining pressure to boiling heat transfer of thermal nanofluids

Research on nanofluids has progressed rapidly since their enhanced thermal conductivities were identified about a decade ago. For boiling heat transfer with nanofluids, however, many contradictory results have been reported, which cannot be explained by conventional theories developed for pure fluids. Recent progress in colloidal science shows that the presence of nanoparticles could enhance the spreading and wettability of base fluids through a long-range structural disjoining pressure. This article explores theoretically the influence of structural disjoining pressure to the nucleate boiling heat transfer through a four-zoned microlayer evaporation model. The influence of particle size, particle concentration, and heat flux on the structural disjoining pressure and the interfacial shape of the microlayer are investigated. The calculated equilibrium interfacial shape shows that the meniscus is displaced toward the vapor phase in the presence of nanoparticles, an implication of enhanced wettability. Such an improved wettability affects the number of active nucleate sites and bubble dynamics significantly, which could be one of the important parameters that is responsible for the controversy of boiling heat transfer with nanofluids reported in the literature.