DEPRESSURIZATION EFFECTS ON THE THERMAL FIELDS AND HEAT TRANSFER DURING HEMI-SPHERICAL BUBBLE GROWTH ON A HEATED SURFACE

摘要

A numerical simulation has been carried out which predicts the growth and wall heat-transfer characteristics of a bubble atop a heated flat surface in an otherwise quiescent pool of liquid. In accordance with the experimental conditions and observations of Merte et al. (1995), the simulations are carried out on a constant heat flux surface in microgravity, and the bubble maintains a hemispherical shape with no contribution of a microlayer. The model, computational technique, and interface tracking methodology provide very high spatial and temporal resolution. This is true for the micrometer-sized nucleus in metastable equilibrium with its surrounding liquid at the end of the measured waiting time, through the surface tension, transition, and heat transfer controlled growth domains where the bubble expands to macro-sized. The simulations indicate that the rapid depressurization of the vapor bubble as it expands occurs in conjunction with a like drop in the vapor temperature. This establishes a substantial temperature gradient and subsequent evaporative cooling effect of the heater surface near the moving triple interface. The influence of bulk liquid advection and transient conduction is discussed in relation to the bubble dynamics.