Homogeneous nucleation of gas bubbles in liquids

Abstract

Abstract The inadequacies of present knowledge of homogeneous bubble nucleation phenomena are discussed, and a new mathematical approach to modeling such processes is described. In brief, this approach utilizes two different criteria. First, it employs the conventional criterion for the minimum-size bubble which will not spontaneously collapse: D c = 4γ/(P 0 −P) , where Dc,γ, P0, and P, respectively, refer to the minimum bubble diameter, surface tension, and the original and final pressures. Second, a new criterion for spontaneous nucleation following decompression is proposed: α = β, where α = (4γ/P 0 D) (1+PD/4γ)e (3/2) / (1+PD/4γ) and for aqueous solutions at 37°C, β = 2 x 10 5 /H j ° where Hj0 is the empirical Henry's law constant (in atmospheres/mole fraction) for the solute gas in water at 37°C. The conventional criterion applies to bubbles after they are formed and is insensitive to the identity of the solvent and solute, except for the magnitude of the surface tension. However, the proposed new criterion governs the spontaneous formation of bubble nuclei and is influenced by the nature of the solvent-solute combination as well as by the imposed conditions. Hence, these two criteria collectively define the imposed conditions and resulting bubble sizes where stable nucleation may occur. An example case for aqueous solutions of He, N2, H2, O2, and CO2 at 37°C indicates that only He, H2, and N2 satisfy both criteria at levels of decompression where dysbarism symptoms have been observed. The results indicate that homogeneous nucleation of CO2 or H2O bubbles should be negligible at 37°C at nonnegative pressures and that practically complete decompression is required for nucleation of oxygen bubbles.