Crossflow counter

Water quality is important, not only from an environmental point of view but also in relation to the type of packing to be specified. Analysis of the circulating water is simple to obtain, but it is very seldom offered to the cooling tower designer. The quality, or lack of it, will determine the type of pack to be used, the selection of structural materials and whether the tower should be induced or forced draft, counterflow or crossflow. Water treatment, in the shape of chemicals to control pH and to act as counter-corrosion agents or as biocides, all has a bearing on tower selection. 

In the crossflow configuration widely used in the membrane separation industry today, the direction of the feed flow is perpendicular to that of the permeate flow. To increase the driving force for the permeate, a carrier stream to "sweep away the permeate is often used. In most of the membrane configurations such as tubes and multichannel monoliths described in Chapter 5, the carrier stream and the feed stream are generally co urrent or counter-current in direction. 

Fig. 1.59 Counter crossflow heat exchanger with two rows of tubes and two passageways...

For pure crossflow to a bank of tubes, or for a mixture of crossflow and counter-current flow, the factor is less than unity ... 

The gas flows horizontally, contacting by downflowing liquid. The effective driving force for mass transfer is between that for counter- and cocurrent contactors. Crossflow scrubbers have low pressure drop and usually require a lower liquid/gas ratio than either counter- or cocurrent scrubbers. The time of contact between gas and liquid is relatively low, and crossflow units are not reconunended for most chemical absorptions. Design procedures follow a finite-element approach the scrubber volume is divided into cubes, each of which is assumed to reach equilibrium. 

Flow arrangements for hollow-fiber membranes (a) countercurrent flow (ft) parallel and counter-current flow (c) radial crossflow. 

Botros and Brzustowski [77] studied the velocity field of propane TDFCF experimentally and numerically. Their study revealed a pair of counter-rotating vortices in the flame. Gollahalli and coworkers [78-80] measured the flow field and turbulent characteristics of gas jet flames in crossflow. At very low values of R, the effects of crossflow stream are more dominant and the jet fluid burns in the wake of a model stack. A recirculation vortex is created and the flame stabilizes on the wall of the recirculation bubble. Figure 29.17a presents the velocity vector field and streamlines obtained by Huang and Wang [45] for down-wash... 

FIGURE 6.19 Spiral wound module configurations (a) widiout sweep gas (reprinted with permission from MTR, Inc. ), (b) counter current flow with sweep and (c) crossflow with sweep. Both (b) and (c) reprinted from D. Reddy, T. Y. Moon, C.E. Reineke Counter current Dual flow spiral wound dual pipe membrane separation U.S. Patent 5,034,126, July 23,1991. (TakenfromFigure 1 of the T. 

Chapter 8 deals with the configuration of bulk flows of two phases/regions (one of which may be solid) perpendicular to the direction of force(s). The directions of motion of the two phases may be parallel to each other in either countercurrent or cocurrent fashion, or they may be in crossflow. Figures 8.1.1-8.1.4 illustrate the counter-current flow vs. force configuration for all three classes of separation systems. Conventional countercurrent devices/ processes of gas absorption/stripping, column distillation... 

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