Drive pressure

Templeton obtained data of the following type for the rate of displacement of water in a 30-/im capillary by oil (n-cetane) (the capillary having previously been wet by water). The capillary was 10 cm long, and the driving pressure was 45 cm of water. When the meniscus was 2 cm from the oil end of the capillary, the velocity of motion of the meniscus was 3.6 x 10 cm/sec, and when the meniscus was 8 cm from the oil end, its velocity was 1 x 10 cm/sec. Water wet the capillary, and the water-oil interfacial tension was 30 dyn/cm. Calculate the apparent viscosities of the oil and the water. Assuming that both come out to be 0.9 of the actual bulk viscosities, calculate the thickness of the stagnant annular film of liquid in the capillary. 

The factors to consider in the selection of cross-flow filtration include the cross-flow velocity, the driving pressure, the separation characteristics of the membrane (permeability and pore size), size of particulates relative to the membrane pore dimensions, and the hydrodynamic conditions within the flow module. Again, since particle-particle and particle-membrane interactions are key, broth conditioning (ionic strength, pH, etc.) may be necessary to optimize performance. 

Consider first penetration into a cylindrical pore. An estimate of the extent of penetration can be obtained by equating the back pressure of trapped air to the capillary driving pressure. Then the distance. r penetrated into a pore of length / and radius r is then ... 

If the driving pressure is taken to be the capillary pressure, 2yivCOS0/r, Eq. 23 may be integrated, assuming 9 and r] are constant to give the Washburn equation [43] which shows the penetration jCt is proportional to the square root of time t... 

P is the driving pressure and the second term in the brackets represents the back pressure of trapped air. The back pressure can be neglected when the driving pressure is appreciable. With this simplification, integration of Eq. 28 gives the limiting distance of penetration JCmax as... 

With typical values of = 6 x 10 N s/m and b = 0.01 s, penetration will be about ten diameters under a driving pressure of 1 N/mm- (ca. 10 atmospheres). With a higher initial viscosity of 6 x 10 N s/m — perhaps as a result of delay in applying the same adhesive — penetration would only be 3.2 diameters. 

The contiguous resei"voirs of gas or water that contribute the drive pressures for an oil well can cause a problem. Gas and, in some cases, water, are more mobile than oil in an oil reservoir. As a result, during production the oil-gas or oil-water surface can move toward the region of reduced pressure around the borehole. If the interface reaches the borehole, the driver fluid will enter the well and be produced along with the oil. Since gas is not as valu-... 

The reduction in driving pressure of a flow of water through a plant... 

Resistance in the arterioles of the working muscles is regulated locally. As discussed previously, active hyperemia results in production of several factors that cause metabolic vasodilation. Exercising muscles generate COz, H+ and K+ ions, heat, and adenosine. The vasodilator effect of these locally produced substances overrides the vasoconstrictor effect of the sympathetic system in the muscle. As a result, local vascular resistance is decreased. The combination of increased driving pressure and decreased local vascular resistance causes an increase in blood flow to the working muscles. 

Theoretical considerations of charges of limited diameter have taken one of two forms. The former assumes that the effects are best described as a result of the curvature of the wave front in the explosive (this can be demonstrated experimentally), or of reduction of the driving pressure by lateral expansion. Solutions of this type have been given by Eyring and co-workers and by Jones. Alternatively, the variation in velocity of... 

The normal coronary system consists of large epicardial or surface vessels (Rj) that offer little resistance to myocardial flow and intramyocardial arteries and arterioles (R2), which branch into a dense capillary network to supply basal blood flow (Fig. 11-1). Under normal circumstances, the resistance in R2 is much greater than that in Rj. Myocardial blood flow is inversely related to arteriolar resistance and directly related to the coronary driving pressure. 

Encouraged by the X-ray and contact angle results, we performed some preliminary gas-permeation measurements. Here, a self-supporting film is required and only the longer block copolymers were used. Fluoro-PSB-II and Fluoro-triblock were coated on porous Celgard 2400 membranes the measurements were taken at room temperature at a driving pressure of 5 bars. Since no absolute polymer layer thickness has been determined, only relative values of the permeability are given (Table 10.6). In the case of the separation of C02 from... 

Extrusion granulator subclasses primarily are distinguished by the orientation of extrusion surfaces and driving pressure production mechanism. 

The projected fragments in this case are preformed. Consequently the factor I is included to account for gas leakage between pre-formed fragments. This loss of driving pressure is claimed to be of the order of 10% (Ref 24)... 

The viscosity dictates the driving pressure. For high-speed analysis, the ratio of viscosity to diffusion coefficient should be as small as possible. Hydrogen would be the best choice, followed by helium. 

An interface has an effective driving pressure if its displacement decreases the total system s free energy. This effective pressure can derive from any mechanism by which a material stores energy, but for many cases it arises from only two sources the volumetric free-energy differences between the interface s adjacent phases, and mechanical pressure differences due to reduction of the interfacial energy. 

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