Lattice Boltzmann simulations of the pool boiling curves above horizontal heaters with homogenous and heterogeneous wettability

Abstract

A hybrid thermal lattice Boltzmann phase-change model was performed to simulate the pool boiling above a smooth horizontal heater. The effects of homogenous and heterogeneous wettability on entire boiling curves from the onset of nucleate boiling (ONB) to fully developed film boiling were investigated comprehensively. Results show that concerning the homogeneous and hydrophilic heater, increasing the wall wettability results in a high critical heat flux (CHF) and yields a rightward and upward shift of the boiling curve. It is also found that decreasing the wettability promotes the occurrence of ONB at a lower overheat, but it also makes the boiling process move into a film boiling regime with a lower degree of wall superheat. Regarding the homogeneous and hydrophobic heater, there are quite lower CHF and shorter transition boiling regime, whereas the CHF point and film boiling occur at a lower wall superheat. For the heterogeneous and hydrophilic heater, increasing the difference of wettability yields a leftward shift of the boiling curve. Furthermore, the effects of surface wettability and the width between two hydrophilic-hydrophobic mixed surface on boiling curves were studied, which indicated that decreasing the wettability of the hydrophobic surface produces an upward shift of boiling curve and decreasing the width generates a leftward and upward shift of the nucleate boiling pattern. Moreover, the enhancement of boiling heat transfer in terms of hydrophilic-hydrophobic mixed surfaces was also quantitively verified.