Effect of Noncondensibles on Condensation and Evaporation of Bubbles

The fraction of noncondensibles in a bubble controls the temperature driving force in the process of condensation and evaporation. It affects the vapor partial pressure, and consequently the apparent temperature of saturation. The present work deals with a bubble condensing in immiscible and miscible liquids, and with the evaporation of a bubble in an immiscible liquid. The complete, exact expression of the dimensionless apparent saturation temperature is formulated, and all its terms are examined, including the variation of physical properties. The analysis is extended over systems of R-113, pentane, and hexane. The exact relation is compared with previous approximate solutions and the limits of application are illustrated. At small temperature differences the approximate models are adequate. The discrepancy increases at high temperature differences. The rate of collapse is examined in a system of R-113 in water. Experimental rates of videotaped collapsing bubbles were obtained up to a temperature difference of 20°C. The effect of noncondensibles is most pronounced at the higher temperature difference. Comparison of theoretical curves at a temperature difference of 30°C shows the exact termination of the process to be faster than the approximate prediction. The deviation increases with the concentration of the noncondensibles. Relations formulated for evaporation of liquid in presence of noncondensibles were tested experimentally. Vapor of R-113 was experimentally obtained in a bubble of air down to 20°C below the satuaration temperature. The measurements showed good agreement with the predictions.