A Study of Bubble Departure in Forced-Convection Boiling

Visual observations in a boiling liquid flow indicate that, as the flow velocity is increased, the size of bubbles leaving the heating surface decreases. The purpose of this investigation is to arrive at a criterion for bubble departure in forced-convection nucleate boiling. Photographic studies indicate that a little before departure a “neck” is formed joining the almost spherical bubble to the heating surface. From a consideration of the hydrodynamic stability of the bubble-and-neck model, the departure-size-to-velocity relationship may be predicted. Measured departure radii in a forced-convection boiling water system taken by means of high-speed photography are satisfactorily correlated with the results derived analytically.