Kinetics of establishing pressure in the foam liquid

The kinetics of establishing equilibrium pressure provides information not only about foam drainage but also for other important parameters, such as the time for reaching equilibrium state in the borders and films and the radius of border curvature and border profile during liquid flow and drainage under pressure drop. 

Kinetics of establishing pressure in the foam uquid phase 

The influence of the pressure drop value on the rate of pressure (Ap) change is clearly seen in Fig. 5.7, curves 1 and 2, for a NP20 foam. For example, the time needed for establishing 50% relative pressure at Ap0 = 5 103 Pa is twice less than at Ap0 = 104 Pa. For a NaDoS foam such a time difference is less pronounced. For example, 50% relative pressure at the two values of Apo is established for 14 and 20 min, respectively. However, for relative pressures more than 70-80% this time difference becomes more distinct. 

It is worth noting that different radii of curvature correspond to the same equilibrium capillary pressure pa = Apo in foams from various surfactants because of the different surface 

The border profile was studied in order to analyse qualitatively the influence of various foam parameters (surfactant kind and foam film type, foam column height, pressure drop, etc.) on the drainage process as well to check the validity of drainage models [12], The foam was placed in a cylindrical vessel (diameter 2.5 to 4 cm), similar to vessel 6 in Fig. 1.4. It was covered with a lid to prevent evaporation. The pressure above the foam was equal to the atmospheric pressure. The border profile was determined by simultaneous measurement of the capillary pressure at various levels of the foam column, i.e. the r(H) dependence in the direction of liquid flow was evaluated. Thus it was found that the best approximation (among the discussed in Section 5.3.3) appears to be the parabolic model of border profile. 

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