ANALYSIS OF BUBBLE TRANSLATION DURING TRANSIENT FLASH EVAPORATION

An analysis was performed of the rise characteristics of bubbles, which are also growing, in a pressure field which is decreasing exponentially with time. The bubble rise and growth occur due to flash evaporation caused by reducing the pressure in the vapor space above a pool of liquid. Basset's bubble momentum equation was modified to include the effects of the generated pressure wave, and to include bubble growth. The solution of the differential equation was obtained for three different expressions for the bubble drag, for pressure ratios of 0.1-0.9, Jakob numbers of 5-113, Weber numbers of 0-0.16, and time constants of the pressure transient down to 5 ms. Results indicate that different bubble drag expressions give bubble velocities which differ by as much as 100%. The pressure term introduced by the authors has a negligible effect in the range of parameters considered here but becomes significant for very rapid depressurization rates, and the initial velocity of the bubble has little effect on the bubble's subsequent rise velocity.