Effects of contact angle hysteresis on bubble dynamics and heat transfer characteristics in saturated pool boiling

Abstract

As an inherent physical phenomenon of the contact-line motion, the contact angle hysteresis (CAH) has an important effect on dynamic behaviors of bubble/bubbles from a solid surface. In this study, boiling heat transfer considering the CAH is investigated by employing a phase change lattice Boltzmann (LB) model. Effects of the CAH on the bubble/bubbles dynamics during the boiling process and the boiling curves for both the hydrophilic and hydrophobic hysteresis windows are studied in detail. It is found that the bubble base, bubble height and phase change rate increase as the increase of the width of hysteresis window. On the other hand, the pinning of three-phase contact line is observed during the bubble growth processes. And the pinning times increase with the contact angle hysteresis. For the hydrophilic hysteresis window, the bubble completely departs from the heater if a small range of the hysteresis window is considered, while a residual bubble is left when the bubble departs from the heater in the cases of the hysteresis window larger than an approximate critical value of 45°. For the hydrophobic hysteresis window, a residual bubble can be observed regardless of the level of the contact angle hysteresis. The numerical results also indicate that the CAH affects the position of bubbles coalescence. The bubbles merge above the heater for the hydrophilic hysteresis window with a small level of hysteresis. While the bubbles merge on the heater for the hydrophilic hysteresis window with a large level of hysteresis as well as for the hydrophobic hysteresis window. Moreover, as the increase of the width of the hysteresis window, the critical heat flux (CHF) as well as the Leidenfrost temperature (the minimum temperature for film boiling) decrease, and the transition boiling regimes become shorter. Finally, we present the fitting equations between the width of the hysteresis window and the CHF/Leidenfrost temperature. The results show that the CHF and the Leidenfrost temperature decrease linearly as the width of the hysteresis window increases.