Separating variables with pressure drop

Only a limited number of attempts have been made to correlate the liquid hold-up or the equivalent in the pipe. Again it seems clear that the liquid hold-up will be significally influenced by the flow pattern, and that either separate correlations will be required for each flow pattern, or a master correlation incorporating those variables which influence flow pattern will need to be developed. With one or two exceptions the few existing correlations suffer from the same kind of disadvantage as those for the prediction of pressure drop. ... 

Often, as above, the simplest optimization criteria (e. g., low pressure) for separations must be tempered by practical requirements (e.g., high pressure drop). A wider knowledge of the many variables affecting separations must then be brought to bear in selecting true optimizing conditions. We will discuss optimization more fully in later chapters when we deal with specific methods. 

Perhaps the most important variable in the description of foam flow through porous rock is the mobility of the foam, the flow achieved for a given pressure drop. This quantity is defined as the simple ratio of the combined superficial flow rate to the imposed pressure gradient. This ratio is indicated in the first part of equation 2, in which the mobility, A, is given in terms of the combined flow rate, Q, the cross-sectional area of the sample, A, the pressure drop, AP, across the sample, and its length, L. As is well known, in the flow of an ordinary fluid through porous media, the mobility can be separated into two factors one has to do primarily with the properties of the rock, and the other, with the properties of the fluid. By using Darcy s relation, the mobility for the ordinary fluid is computed to be the ratio of effective rock permeability, k, to the fluid viscosity, n. 

Flow Maldistribution in Heat Exchangers with Phase Change. Two-phase flow maldistribution may be caused and/or influenced by phase separation, oscillating flows, variable pressure drops (density-wave instability), flow reversals, and other flow instabilities. For a review of pertinent literature, refer to Ref. 131. 

As with other separation equipment, the main characteristics of filters are the flow rate-pressure drop relationships and other performance characteristics such as the separation efficiency. In filtration however, these relationships are more complex as there are many variables and factors (cake thickness, mass of cake per unit area, specific cake resistance etc.) which greatly influence the process. 

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