Bubble Nucleation in Superheated Liquid-Liquid Emulsions

An investigation of the process by which bubbles form in superheated liquid-liquid emulsions is reported. A theoretical model for the rate of bubble nucleation is developed that is valid for any binary liquid system. Because of the interesting "microexplosion" phenomenon postulated to occur during combustion of fuel/water emulsions, special attention is focused on hydrocarbon/ water/surfactant mixtures. The model predicts that in these systems nucleation takes place at the interface between the two liquids but that the vapor bubbles rest entirely within the hydrocarbon phase. The maximum superheat limits of emulsions containing 83% by volume hydrocarbon (benzene, n-decane, n-dodecane, n-tetradecane, and n-hexadecane), 15% water and 2% surfactant were measured experimentally at 1 atm and found to be in good agreement with the predictions of the theoretical model. The superheat limits of these emulsions are lower than those of either pure liquid. However, for microexplosion of an emulsified fuel droplet, the superheat limit of the fuel/water emulsion must be less than the boiling point of the fuel. Only the n-hexadecane/water emulsion satisfies this criterion at atmospheric pressure.