Effect of surface wettability on nucleate boiling – A DNS study

Complexity in nucleate boiling arises due to non-equilibrium thermodynamics intertwined with heat, mass and momentum transport and surface processes. Wettability of surfaces plays an important role in the nucleate boiling heat transfer coefficient. We develop a direct numerical simulation model framework using our in-house TPLS Solver. The so-called Diffuse Interface Method is implemented via Cahn-Hilliard Equation to determine the vapour-liquid interface position. This method also removes stress singularity at the contact line and enables the use of contact-angle boundary conditions to prescribe surface wettability. We present simulations to analyse the effect of the superheat and bubble size for different wettabilities, especially on growth-rates and departure stages of the bubble. Our analysis shows the importance of surface tension on the departure conditions. Our simulations show that inertia-controlled growth is extremely rapid and more likely to be observed in small embryo bubble with high wettability. Conversely, the limited growth rate in the heat transfer-controlled growth is the dominant effect for low wettability cases. We compare our simulations against our nucleate boiling experiments using FC-72 on silicon surfaces.
*ThermaSMART, EMBOSS project