A CHF model for saturated pool boiling on a heated surface with micro/nano-scale structures

A theoretical model is developed to predict the critical heat flux in pool boiling on a heated surface with micro/nano structures based on a force balance analysis, with effects of the capillary wicking force and modification of the critical instability wavelength taken into consideration. An analytical expression for CHF of a heated surface with micro/nano-size structures is obtained in terms of the surface roughness factor, the solid fraction as well as the contact angle explicitly. It is shown that geometric parameters of these micro/nano structures influence the ability of liquid spreading on a hydrophilic surface, effectively supplying liquid to the heated surface, and thus delaying the occurrence of the CHF. The micro/nano-sized cavities provide additional sites for vapor formation, altering the critical distance between vapor columns and thus reducing the critical instability wavelength. The critical wavelength for the occurrence of critical heat flux is obtained based on the change in surface free energy. The predicted values of CHF on heated surfaces with micro/nano-size structures in pool boiling obtained from the present model are found in agreement with existing experimental data.