Weir dimensions

The height of the weir determines the volume of liquid on the plate and is an important factor in determining the plate efficiency (see Section 11.10.4). A high weir will increase the plate efficiency but at the expense of a higher plate pressure drop. For columns operating above atmospheric pressure the weir heights will normally be between 40 mm to 90 mm (1.5 to 3.5 in.) 40 to 50 mm is recommended. For vacuum operation lower weir heights are used to reduce the pressure drop 6 to 12 mm ( to in.) is recommended. 

Inlet weirs, or recessed pans, are sometimes used to improve the distribution of liquid across the plate but are seldom needed with segmental downcomers. 

With segmental downcomers the length of the weir fixes the area of the downcomer. The chord length will normally be between 0.6 to 0.85 of the column diameter. A good initial value to use is 0.77, equivalent to a downcomer area of 12 per cent. 

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Specify the diameter, height and weir dimensions and sketch the method of interface level control which is proposed. 

Most trays have outlet weirs devoted to maintaining the downcomer seal. But some trays have inlet weirs too, or inlet weirs, but no outlet weirs. A sketch of an inlet weir is shown in Fig. 9.2. Note the horizontal distance between the downcomer and the inlet weir (dimension x). This distance ought to be equal to or greater than the downcomer clearance—that is, the vertical space between the tray floor and the bottom edge of the downcomer. Unfortunately, a small deformation of the downcomer may push the downcomer quite close to the inlet weir. The resulting reduction in the horizontal clearance between the inlet weir and the downcomer will restrict the liquid flow. This will cause downcomer backup and tray flooding of the trays above. 

Enlarge the clearance between the downcomer face and the inlet weir (or equivalent), (see Figure 8-92 or 63) to 1.5 to 2 times the dimensions used for the other trays. 

Feedwater take-off. This will be from the bottom of the tank and preferably from the base with a weir pipe extending 50-100 mm up into the tank. If the take-off is from the side of the tank the bottom of the pipe bore must be a similar dimension up from the base. This allows sludge to remain in the tank, which should be inspected and cleaned as required. 

It is important to set close tolerances on the weir height, downcomer clearance, and plate flatness, to ensure an even flow of liquid across the plate. The tolerances specified will depend on the dimensions of the plate but will typically be about 3 mm. 

Prepare a sieve-plate column design for the chlorobenzene distillation and make dimensioned sketches showing details of the plate layout including the weir and the downcomer. 

C DIMENSIONS ARE IN METERS, FLOW IS IN KG MOLE/MIN C HOLDUP IS IN KG-MOLE C FRANCIS WEIR FORMULA USED REAL M,L,M1,M2... 

When the system which was to be linked to the autosampler system was purchased, it was found that the conductivity cell was excessively large and primarily designed to be fitted to a A" pipehne for analytical purposes this was clearly too large. However, the pH cell provided an Ingold standard electrode system with dimensions which allowed it to be placed within the conductivity sensor, as shown in Fig. 7.21. It is therefore possible to configure a flow cell in which the conductivity sensor houses the pH electrode. The latter also serves to take up most of the cell volume so that the wash-out requirements are not too excessive. The cell is filled by taking a sample from the autosampler with pump 1 hquid fills the cell and overflows via the weir arrangement and the top of the cell. 

To guarantee a proper downcomer seal, the bottom edge of a downcomer should be about V2 inch below the top edge of the outlet weir. This dimension should be carefully checked by process personnel when a tower is opened for inspection. It is quite easy for sloppy tray installation to distort this critical factor. 

Figure 3.17 Layout and dimensions of the integrated SPE-NCE with (b) photograph of the multilayer device (c) and (d) micrograph and diagram of the packed micro-SPE column between two shallow weirs [121].

PTCH = dimension center-to-center between bubble caps, in SLTSL = bubble cap slot measure from slot to weir top, in... 

Recalculate weir and downcomer dimensions by the same procedure as in Sec. 6.5.4. The results are summarized in Table 6.11. 

In order to further investigate and understand the unfavorable results regarding sample elution time of the weir-SMEC as compared to the grid-SMEC, microfluidic modeling of the flow profile immediately after the weir was performed. When the size of fluidic channels is in the dimensions of a few hundred micrometers or smaller and aqueous-based solutions are used, it is well known that pressure-driven fluid transport is usually heavily dominated by laminar flow. Therefore microfluidic modeling can be employed to investigate and study fluid flow characteristics in microchip designs prior to fabrication. 

The standard dimensions of the Parshall flume are shown in Table 3.1. If the steps nsed in deriving the eqnation for rectangnlar weirs are applied to the... 

Processed shale is removed at the top of the retort. A circumferential weir is provided to maintain a constant bed height in the upper stage. Entrained shale particles are removed from the product vapor by high-efficiency cylones located in the vapor disengagement section. The dimensions of this top section area, in fact, determined by the cyclone configuration. Superheated steam (1200°f, 650°C) is... 

Consider the absorber of Example 3.7. Assume that the wash oil is n-tetradecane (C14H30). The absorber will be a cross-flow sieve-tray tower with dg = 4.5 mm on an equilateral-triangular pitch 12 mm between hole centers, punched in stainless steel sheet metal 2 mm thick, with a weir height of 50 mm. Estimate the number of real trays required, the dimensions of the absorber, and the power required to pump the gas and the liquid through the tower. Design for a 65% approach to the flooding velocity. 

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