FIG. 24 Effect of the electrolyte concentration on the steady-state height. The values of the parameters used are: ρ=1000 kg/m , µ=1 cP, ψ=19

doi:10.1201/9780203021262-22

Chapter

FIG. 24 Effect of the electrolyte concentration on the steady-state height. The values of the parameters used are: ρ=1000 kg/m , µ=1 cP, ψ=19

ABSTRACT

G=0.0001 m/s, cel=0.005 M, and T=298 K. Clearly, H0 increases with bubble size. This can be explained as follows: In general, in a foam column draining under gravity, the curvature of the Plateau border channels (rp) is the largest and the capillary pressure is the smallest at the foam/liquid interface where rp=R0. For a given Пmax, the smaller the bubble size is, the smaller is the decrease in rp required for the capillary pressure to rise to Пmax. This means that collapse starts at smaller heights, resulting in smaller values of H0. Fig. 29 shows a plot of z2−z1 versus time for two bubble sizes. It is clear that there is a qualitative difference because the foam with R0=0.3 mm collapses to reach an equilibrium height, whereas the foam with R0=0.125 mm collapses completely. This is because (σ/R0) is less than Пmax for the former and greater than Пmax for the latter.