OSCILLATING BUBBLES ON A HOT SURFACE

This presentation describes a nonlinear dynamics of bubbles forming on a hot surface. In particular, we compare the behavior of bubbles in three regimes evaporative, nucleate boiling, and film boiling regimes. A bubble appears on a hot surface when the heat flux from the surface is high enough to overcome the Laplace pressure across the surface of the bubble. Once a bubble nucleates on a surface, one might expect that the subsequent evaporation of the liquid phase would make the bubble expand monotonically until it leaves the surface. In real, nucleating bubbles expand monotonically only in evaporative regime. In the other two regimes, the size of the bubbles oscillates with varying frequency and amplitude depending on the heat flux and the convection patterns in the bulk liquid. We suspect that such a behavior suggests that the bubbling dynamics in these three regimes are fundamentally different: while the growth of a bubble in evaporative regime is determined essentially by the evaporation rate on the hot surface, the much more dynamic behavior of a bubble in nucleate and film boiling regime is the result of the interplay between two driving forces evaporation near the solid surface and condensation near the top of a bubble. Such a competition becomes unsteady when the heat flux is high; therefore, boiling pattern switches from a quasi-static evaporative one to periodic nucleate boiling, and eventually to chaotic film boiling.