Electric field inspired alternating surface wettability for enhancing pool boiling heat transfer performance: A lattice Boltzmann method study

Electric field and surfactants have been proven to potentially alter surface wettability on demand. In this work, alternating wettability inspired by an electric field has been used to enhance boiling heat transfer performance in terms of critical heat flux (CHF) over a rough surface by using two-dimensional lattice Boltzmann simulations. In alternating wettability, the surface wettability changes with time between hydrophobic and hydrophilic. The effects of the parameters, including alternating wettability time-period and wettability contrast on the boiling process have been revealed. The simulation results show that for the alternating wettability: when surface is hydrophobic bubble expansion is faster, and then wettability transition to hydrophilic quickly retracts three-phase contact line leading to faster bubble shrinking as compared to constantly hydrophobic and constantly hydrophilic surfaces. Furthermore, the rapid shrinking of the bubble tends to disintegrate vapor film on the surface at high wall superheats, resulting in a 53% enhancement in CHF compared to a constantly hydrophilic surface. The bubble departure takes much longer time for too small/large time-periods of alternating wettability. The CHF increases with time-period, becomes maximum at a certain value and then reduces. The CHF also increases with wettability contrast, becomes largest for hydrophilic and hydrophobic contact angles 55^o and 107^o, respectively, and decreases with further increase in wettability contrast due to high potential for vapor film formation.