Liquid-flow arrangement

Un actual velocity (based on net area) Uf (from equation 11.81) 

The effect of entrainment on plate efficiency can be estimated using equation 11.78. 

As a rough guide the upper limit of xfr can he taken as 0.1 below this figure the effect on efficiency will be small. The optimum design value may be above this figure, see Fair (1963). 

The lower limit of the operating range occurs when liquid leakage through the plate holes becomes excessive. This is known as the weep point. The vapour velocity at the weep point is the minimum value for stable operation. The hole area must be chosen so that at the lowest operating rate the vapour flow velocity is still well above the weep point. 

Several correlations have been proposed for predicting the vapour velocity at the weep point see Chase (1967). That given by Eduljee (1959) is one of the simplest to use, and has been shown to be reliable. 

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FIGURE 12.44 Multipass liquid flow arrangements for crossflow tray columns. 

In the cross-flow arrangement, the argon gas flows at high linear velocity across the face of an orthogonal capillary tube containing sample solution. The partial vacuum causes liquid to lift above the end of the capillary. Here, it meets the argon and is nebulized. 

In this cross-flow arrangement, a thin film of sample solution is obtained as it flows around the edge of a small opening, through which there is a fast linear flow of argon. The liquid film is rapidly nebulized along the rim of the orifice. 

To accommodate smaller liquid flows of about 10 pl/min, micro-ultrasonic nebulizers have been designed. Although basically similar in operation to standard ultrasonic nebulizers, in these micro varieties, the end of a very-small-diameter capillary, through which is pumped the sample solution, is in contact with the surface of the transducer. This arrangement produces a thin stream of solution that runs down and across the center of the face of the transducer. The stream of sample... 

The simplest tray arrangement considering fluid flow and mechanical details is the cross-flow shown in Figure 8-84 (page 137). It fits the majority of designs. WTien liquid flows become small with respect to vapor flows the... 

Caps should be arranged on the plate in 60° equilateral layout, with the liquid flowing into Ae apex of the triangle rather than parallel to the base. The liquid flows normal to each row of caps. 

Figure 8-153. Simple side-to-side baffle arrangement, with liquid flow cascades, for baffle tray column. Used by permission. Fair, J. R., Hydrocarbon Processing, V. 72, No. 5 (1993) p. 75, Gulf Pub. Co., all rights reserved.

Figure 10-9A. Spiral flow heat exchanger, cross-flow arrangement for liquids, gases, or liquid/gaseous (condensable) fluids. (Used by permission Alfa Laval Thermal Inc., Bui. 1205 1993.)...

Liquid flows through a system of two tanks arranged in series, as shown below. The level control of tank 2 is based on the regulation of the inlet flow to the tank 1. This tank represents a considerable lag in the system. The aim of the controller is to maintain a constant level in tank 2, despite disturbances which occur in the flow F3. 

Pressure surge can be controlled by the use of surge vessels connected to the pipeline with a gas space above the liquid. If a pressure surge passes along the pipeline, liquid flows into the vessel through a check valve and the gas is compressed. Another valve then lets out the liquid at a controlled rate. This type of arrangement is used in large hydraulic lines. 

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