Role of condensation on boiling heat transfer in a confined chamber

A theoretical model of the coupled boiling and condensation phase changer heat transfer in a confined chamber is developed and numerically analyzed based on the modified hybrid lattice Boltzmann method. The interaction of boiling and condensation behavior is investigated with particular attention focused on the influence of condensation surface wettability on the boiling heat transfer process. Besides, the temperature response and the detailed two-phase flow pattern inside the chamber with different condensation surface wettability are evaluated. The results indicated that an optimal contact angle of 85 degrees for the condensation surface wettability promoted the heat transfer on the evaporation surface. Subsequently, two modified condensation surfaces (biphilic surface with alternative hydrophilic and hydrophobic regions and gradient surface with a gradual wettability transition from hydrophilic to hydrophobic) are proposed for further heat transfer enhancement of the confined chamber. The results of the boiling curves, the two-phase flow pattern and the local/averaged heat transfer coefficient on the evaporation surface indicated that, compared with the single wettability with the optimal contact angle, both modified condensation surfaces can achieve a higher critical heat flux and a higher boiling heat transfer coefficient. Among these, the biphilic surface can achieve relatively better heat transfer performance.