Pressure gradient force

Jnenial F orcei" Viscous Forces" Pressure gradient ri. 0 = f e 0... 

Mass flow is a bulk movement of hydrocarbons in monophase or dissolved in water. It requires an external force (pressure gradient or structural stress) and a well-defined conduit or plumbing system. The microseepage resulting from mass flow is therefore characteristically confined to a small area or belt, within which the anomalies are of high contrast and often contain some high molecular-weight hydrocarbons. 

Driving force Pressure gradient Pressure gradient Pressure gradient Ionic gradient... 

The mobilization of the residual oil saturation in a water-wet system requires that the discontinuous globules be connected to form a flow channel. In an oil-wet porous medium, the film of oil around the sand grains needs to be displaced to large pore channels and be connected in a continuous phase before it can be mobilized. The mobilization of oil is governed by the viscous forces (pressure gradients) and the interfacial tension forces that exist in the sand grain-oil-water system. 

Now the force per unit volume exerted on the porous medium by the pressure gradient in the gas is -grad p, where p, as distinct from is the physical pressure of the gaseous mixture. This is the force which must be balanced in our model by the external forces acting on the dust particles, so... 

Consistent with this model, foams exhibit plug flow when forced through a channel or pipe. In the center of the channel the foam flows as a soHd plug, with a constant velocity. AH the shear flow occurs near the waHs, where the yield stress has been exceeded and the foam behaves like a viscous Hquid. At the waH, foams can exhibit waH sHp such that bubbles adjacent to the waH have nonzero velocity. The amount of waH sHp present has a significant influence on the overaH flow rate obtained for a given pressure gradient. 

When pure water is forced through a porous ultrafiltration membrane, Darcy s law states that the flow rate is direcdy proportional to the pressure gradient ... 

Mass Transport. An expression for the diffusive transport of the light component of a binary gas mixture in the radial direction in the gas centrifuge can be obtained directly from the general diffusion equation and an expression for the radial pressure gradient in the centrifuge. For diffusion in a binary system in the absence of temperature gradients and external forces, the general diffusion equation retains only the pressure diffusion and ordinary diffusion effects and takes the form... 

When clay or similar material is dried, often a pressure gradient is developed by the forces of repulsion between particles as shrinkage brings the particles close together (25). This gradient forces Hquid toward the surface and the resulting moisture profile resembles that characteristic of Hquid diffusion. 

When the isobars are essentially straight, the balance between the pressure gradient force and the coriolis force results in a geostrophic wind parallel to the isobars. 

When the isobars are curved, an additional force, a centrifugal force outward from the center of curvature, enters into the balance of forces. In the case of curvature around low pressure, a balance of forces occurs when the pressure gradient force equals the sum of the coriolis and centrifugal forces (Fig. 17-12) and the wind continues parallel to the isobars. In the... 

Fig. 17-13. Balance of forces resulting in gradient wind around high pressure. Note that the wind speed is greater for a given pressure gradient force than that around low pressure.

In the friction layer where the isobars are curved, the effect of frictional drag is added to the forces discussed under gradient wind. The balance of the pressure gradient force, the coriolis deviating force, the centrifugal force, and the frictional drag in the vicinity of the curved isobars results in wind flow around low pressure and high pressure in the Northern Hemisphere, as shown in Fig. 17-16. 

Consider a cake of moulding resin between the compression platens as shown in Fig. 4.63. When a constant force, F, is applied to the upper platen the resin flows as a result of a pressure gradient. If the flow is assumed Newtonian then the pressure flow equation derived in Section 4.2.3 may be used... 

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