Abstract
A novel experimental procedure to characterize the stability of foams is established. The procedure involves the unsteady state drainage of liquid from a stationary foam due to an applied pressure difference (forced drainage)- Unlike other bulk foam stability studies, this procedure uses a combination of the drainage rate and critical collapse pressure of the foam to describe foam stability. The drainage process is monitored by the change in electrical conductivity of the foam with time. Lemlich's correlation (1978a) is used to convert foam conductivities into liquid volumetric fractions. Experimental verification of this correlation in this work makes application of this technique possible. The critical collapse pressure of the foam is given by the pressure difference required to completely collapse a stationary foam column. This experimental procedure provides an easy, fast, and economical technique to characterize foam stability. This procedure is specifically applied to foams generated from AOS, CD 1045, and SDS. These foams are stable under our experimental conditions (applied pressure difference = 3-7 psi). The critical concentrations for these surfactants are found to be 0.014, 0.04, and 0.06 wt % respectively. A theoretical model based on Kraynik's work (1983) is developed. This model considers the effects of the applied pressure difference, finite film thickness, disjoining pressure, and film drainage on the entire drainage process. The experimental drainage profiles yield reasonably fair agreement with the predicted drainage profiles. Volumetric fraction of the liquid in the borders and the films can be individually calculated. The entire drainage process can be viewed as taking place through the Plateau borders with a significant contribution from the films only in the initial period of the drainage process. A parametric study is conducted to examine the effect of the various parameters on foam stability. The results indicate that foam stability is most sensitive to the initial bubble size distribution, nature and concentration of the surfactant, and the applied pressure difference.
Sheth, Vikas Rameshchandra (1993). Experimental characterization of foam drainage and stability. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1993 -THESIS -S554.