Numerical simulation of bubble dynamics and heat transfer with transient thermal response of solid wall during pool boiling of FC-72

Abstract

Using the Ghost Fluid Method for sharp interface representation, bubble dynamics and heat transfer during single bubble pool boiling of saturated FC-72 are simulated numerically with transient thermal response of the heated SiO2 solid wall. A constant and uniform temperature is fixed on to the bottom surface of the solid wall in the simulations, and thus, both the spatio-temporal averaged heat flux and superheat on the top surface, which contacts the working fluid directly, are dependent variables instead of controllable ones. Multi-cycle simulations are carried out to eliminate the influence of unreal initial conditions. Steady periodical processes of single bubble pool boiling can be reached on the wall with a thickness of 1mm, while only quasi-steady ones on the wall with a thickness of 5mm due to the limited simulation time, which results in a smaller thermal penetration depth inside the solid wall compared with its thickness. Comparing with the prediction of the correlation by Zuber for the discrete bubble region and experimental data of single bubble pool boiling, the numerical results of boiling curves in both steady and quasi-steady cases exhibit the same trend. Transient heat conduction inside the solid wall is analyzed in detail. A sharp drop of the wall temperature is evident in the vicinity of the contact line due to violent evaporation in this tiny region. The area of the temperature drop moves with the contact line, resulting in a pseudo-periodical process of heat storage and release inside the solid wall, which exhibits a coupling effect with bubble dynamics and heat transfer. The thermal penetration depth caused by the processes of bubble growth and departure in a single bubble cycle is about 0.5mm in both steady and quasi-steady cases, which is much small than the heater thickness.