Pool boiling inversion through bubble induced macroconvection

While numerous surface geometries have been explored to achieve enhancements in pool boiling critical heat flux and heat transfer coefficient (HTC), their mechanistic contributions towards the characteristics of the pool boiling curve are not clear. Recently reported pool boiling curves in literature have shown a trend where an increase in heat flux leads to a decrease in wall superheat. Consequently, a negative slope in the pool boiling curve accompanied by a sharp increase in HTC, termed here as boiling inversion, is observed. We demonstrate that this inversion is due to vapor stream induced reinforcement of an impinging liquid jet over the non-boiling regions. This behavior is characteristic of surfaces developed using separate liquid-vapor pathways and macroconvection enhancement mechanism resulting in a highly efficient self-sustained boiling configuration. The increased jet impingement velocities lead to higher HTCs with lower wall superheats. The analytical models available in literature are employed to quantitatively explain this trend. Furthermore, a self-adjusting boiling mechanism is seen at play wherein a reduction in nucleation activity due to lowering of wall superheat counters the increase in HTC induced by the macroconvective currents.