Boiling is always known as a desirable high heat transfer rate in low temperature process. Boiling, due to the inherent complexities of phase change as well as the presence of two phases, is the subject of attention and review of new methods and improvements on previous methods are presented in simulations. In the past, the activities carried out in the field of boiling were experimental works and obtaining semi-experimental relationships. This study investigates film boiling on a horizontal periodic surface in three dimensions through direct numerical simulations. To solve the momentum and energy equations in both phases, a finite difference/front tracking method is used that accounts for inertia, viscosity and interface deformation. One of the challenging aspects of front tracking method is breakup and coalescence of bubbles. Previous works continued the simulations up to the breakup and release of the bubble. The purpose of this study is long time simulation of boiling. Here an innovative topology changing algorithm is used to overcome this challenge, So, simulations are carried out over sufficiently long times to capture several bubble release cycles and to eva‎luate the quasi steady-state Nusselt number (Nu) ̅. Effect of the Grashof and Jacob numbers on the interface dynamics, heat transfer, and fluid flow is studied. By increasing the Grashof number, buoyancy suppresses the viscous effect, so the average size of departing bubbles decreases and the average Nusselt number increases as well. Wall superheat has direct influence on Jacob number. At relatively low Jacob numbers, the bubbles are released periodically from the vapor film, but as the Jacob number increases, permanent vapor jets are formed and become thicker. However the bubble size and the average Nusselt number decrease. The effect of unit cell size is investigated. It is observed that (Nu) ̅ does not change much with unit cell size. To examine the effect of initial perturbation, single mode and multimode cases were simulated. The initial perturbation has no significant effect on the (Nu) ̅. Density ratio is studied and it is observed that the stationary steady state condition is reached at a shorter time.

سعيد مرتضوي

علي‌اكبر عالم‌رجبي

مهرداد تقي‌زاده منظري، ابراهيم شيراني، رامين كوهي‌ كمالي