Capillary micromanometer

A device for foam dispersity determination by measuring the local foam expansion ratio and the pressure in Plateau borders is illustrated in Fig. 4.4. It consists of a glass container equipped with platinum electrodes and a micromanometer. The container bottom is a porous plate (a sintered glass filter). The pressure Ap is measured with a capillary micromanometer and the expansion ratio is determined by the electrical conductivity of the foam. The manometer and the electrodes are positioned so that to ensure a distance of 1.0-1.5 cm between them and the porous plate. When the distance is small the liquid in the porous... 

A mobile capillary micromanometer that can be set at various levels of the foam column, thus allowing pressure measurements at different points, can be used to evaluate the dependence of the radius of border curvature on the coordinates of either gravitational field or pressure gradient [51,68]. For a simultaneous determination of both the pressure and the radius of border curvature at non-steady state flow (for example, gravitational drainage) a system of a number of micromanometers can be used. 

The reduced pressure in foam Plateau borders can be measured with a capillary manometer, developed by Khristov et al. [31,32]. A number of modifications of such a micromanometer are available. 

The main element of any micromanometer is a capillary hermetically welded to a porous plate (usually a sintered glass filter) with a suitable size of pores. This filter ensures a contact between the liquid in the capillary and the foam Plateau borders. 

From the ratio between the air volume in the wider capillary part and the liquid in the capillary it is possible to calibrate the micromanometer for various ranges of pressure change. A disadvantage of these manometers is that a liquid flowing from the micromanometer can enter the foam. 

Fig. 4.3. Schematic presentation of the compensatory micromanometer 1 - capillary with a porous plate ...

The radius of border curvature in a polyhedral foam which conforms the condition r/a 1 is the easiest to determine. If a micromanometer is used to measure the capillary pressure pa, then the radius of border curvature r can be calculated by combining Eqs. (1.40) and (1.45)... 

As confirmed by the experimental studies, the border profile corresponds to the cylindrical model only at the final stage of the drainage process when the capillary pressure in borders is close to the equilibrium value. That is why Eq. (5.37) can be used to calculate Cexp reached at the final drainage stage. However, it must be kept in mind that the pressure should be measured with a micromanometer at the foam column top. 

The capillary pressure was measured by two independent methods by a compensatory and closed micromanometers and by an optical method for determination of the radius of border curvature [57,58], The data in Table 5.2 indicate that at Apo = 104 Pa the final capillary pressure is equal to the applied pressure drop in all cases studied. At Ap0 = 2104 Pa the capillary pressure reaches an equilibrium value only in foams from non-ionic surfactants. For... 

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