Surface tension of cavitation bubbles

Abstract

We have studied homogeneous cavitation in liquid nitrogen and normal liquid helium. We monitor the fluid content in a large number of independent mesopores with an ink-bottle shape, either when the fluid in the pores is quenched to a constant pressure or submitted to a pressure decreasing at a controlled rate. For both fluids, we show that, close enough to their critical point, the cavitation pressure threshold is in good agreement with the Classical Nucleation Theory (CNT). In contrast, at lower temperatures, deviations are observed, consistent with a reduction of the surface tension for bubbles smaller than two nanometers in radius. For nitrogen, we could accurately measure the nucleation rate as a function of the liquid pressure down to the triple point, where the critical bubble radius is about one nanometer. We find that CNT still holds, provided that the curvature dependence of the surface tension is taken into account. Furthermore, we evaluate the first- and second-order corrections in curvature, which are in reasonable agreement with recent calculations for a Lennard-Jones fluid.

Solvent Cavitation during Ambient Pressure Drying of Silica Aerogels

“…The nucleation rate showed an extreme dependence on the radius of the smallest pores. The liquid temperature also has a strong influence on the nucleation rate, promoting cavitation at higher temperatures as already reported elsewhere. ,, …”

“…The liquid temperature also has a strong influence on the nucleation rate, promoting cavitation at higher temperatures as already reported elsewhere. 26,27,29 To evaluate what would be a reasonable nucleation rate for cavitation in silica gels, the numerical estimates of J were compared with the experimental growth rate of vapor/air from the μCT analysis. The growth rate per unit volume and per unit time was calculated as J exp (r) = Δf̅ air /(Δt • 4πr 3 /3), where Δf̅ air is the difference of the average volume fraction of vapor/ air in gel M4 taken between t cav and t MS , with t cav the time of cavitation onset and t MS the time of maximum shrinkage, and Δt = t cav −t MS = 4.1 h. Δf̅ air /Δt was a good approximation of the vapor/air growth rate (Figure S21).…”

“…The liquid temperature also has a strong influence on the nucleation rate, promoting cavitation at higher temperatures as already reported elsewhere. 26 , 27 , 29 …”

“…Cavitation occurs by the nucleation of vapor bubbles in larger pores ahead of the pore constriction, where the effects of confinement by the matrix are less strong. − The evaporation proceeds at the meniscus and is sustained by the liquid flow toward the pore constriction at the expense of the formation and growth of the bubbles. The onset of cavitation depends on the state of the liquid: its saturation vapor pressure, surface tension, and temperature; − and on the properties of the porous media: the pore size distribution, ,,, the stiffness of the solid matrix, , and the presence of defects …”