Boiling heat transfer on hydrophilic-hydrophobic mixed surfaces: A 3D lattice Boltzmann study

In this paper, the boiling heat transfer performance on a type of hydrophilic-hydrophobic mixed surfaces is numerically investigated using a three-dimensional (3D) thermal multiphase lattice Boltzmann model with liquid-vapor phase change. The mixed surface is square-pillar textured with the pillar being composed of hydrophilic side walls and a hydrophobic top surface. Numerical simulations are carried out to investigate the influences of the contact angle of the hydrophilic region of the mixed surface, the pillar width, and the pillar height. It is found that an appropriate increase of the contact angle of the hydrophilic region, θphi, can promote the bubble nucleation on the bottom substrate and hence enhances the nucleate boiling on the hydrophilic-hydrophobic mixed surface, but a larger θphi may make the boiling enter the transition or film boiling regime. Moreover, it is shown that the heat flux initially increases with the increase of the pillar width and shows a declining trend after reaching its peak value. The optimal θphi and the optimal pillar width are found to decrease with the increase of the wall superheat, revealing that the hydrophilic region of the mixed surface should play an increasingly important role when the wall superheat increases. The orthogonal array tests are performed and it is found that the contact angle of the hydrophilic region is the most important influential factor among the three investigated factors.