Capillary-pressure suction, lower

Since, in general, lower permeability media exhibit higher capillary-pressure suction, we argue that it is more difficult to stabilize foam when the permeability is low. Indeed the concept of a critical capillary pressure for foam longevity can be translated into a critical permeability through use of the universal Leverett capillary-pressure J-function (.13) and, by way of example, the constant-charge model in Equation 2 for II ... 

When suction is generated within the sampling system, water is sucked inwards through the pores of the sampler until a corresponding capillary pressure occurs in the pores. If the capillary pressure in the sampler is lower than that in the soil, water flows from the soil into the sampler until the capillary pressure in the sampler and in the soil are equal. The maximum capillary pressure in a pore can be calculated by the following equation (Schubert, 1982) ... 

Polyhedral gas cells produced on aging thin flat walls are produced with junction points of the interconnecting channels (plateau borders). Due to the interfacial curvature, the pressure is lower and the film is thicker in the plateau border. A capillary suction effect of the liquid occurs from the centre of the film to its periphery. 

The basic design is that of the Ostwald viscometer a U-tube with two reservoir bulbs separated by a capillary, as shown in Figure 24a. The Hquid is added to the viscometer, pulled into the upper reservoir by suction, and then allowed to drain by gravity back into the lower reservoir. The time that it takes for the Hquid to pass between two etched marks, one above and one below the upper reservoir, is a measure of the viscosity. In U-tube viscometers, the effective pressure head and therefore the flow time depend on the volume of Hquid in the instmment. Hence, the conditions must be the same for each measurement. 

Figure 4.4.17. Description of the principal construction of a Knauer membrane osmometer A 300 1 - head thermostat, 2 - channel for syringe, 3 - calibration device with suction tube, 4 - calibration glass, 5 - c illary position MEASUREMENT, 6 - capillary position CALIBRATION, 7 - tension screws, 8 - cell retaining disc, 9 - upper half of measuring cell, 10 - sample introduction system, 11 -semipermeable membrane, 12 - lower half of measuring cell, 13 -pressure measuring system, 14 - cell thermostat, 15 - suction of calibration bottle. [Reprinted from the operating manual with permission from Dr. H. Knauer GmbH (Germany)].

For a hydrophilic media, the hquid phase is nonwetting, a lower hquid-phase pressure exists and provides a suction force to draw the connected hquid into smaller pores, where it will remain until removed by convechon or evaporation. Capillary flow through a hydrophilic porous media will flow in the direction of... 

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