Sieve holes force

Figure 2.2 shows a simple sieve tray, with a single hole. Why is it that the liquid flows over the 3-in outlet weir, rather than simply draining down through the sieve hole It is the force of the vapor (or better, the velocity of the vapor), passing through the sieve hole, which prevents... 

With no clearance between the bottom of tray 3 s downcomer and tray deck 4, the resid could not flow through the downcomer. Hence, it had to drain through the sieve holes. At 4,000 Ib/hr of stripping steam, a large static head of liquid was needed to overcome the force of the up-flowing steam. This static head of resid filled the space between the tray decks and caused excessive re-entrainment of resid into the flash zone— which then flooded the wash oil trays. 

By repeating this process in successive stages, the deuterium oxide is increased to a concentration of 15%. The ten extraction towers of the plant contain sieve trays. Water flows downward across each tray in successirai. H2S gas is forced upward, bubbling through the sieve holes for contact with the water. This is shown in Fig. 7.9. 

The reciprocating motion of the sieve plate generates vortices in the biosuspension. Each vortex region represents the elementary volume of the bioreactor. When the gas dispersion element moves upwards, the biosuspension is forced to pass through the holes of the sieve plates From each hole, a jet of biosuspension flows downward into the space between two sieve plates. The jet reverses direction as the element reverses direction. Very effective dispersive action is due to the periodic generation of bubbles, which renews the larger interfacial area on each reversal of direction. The important design characteristics of this reactor are summarized in Table XXV. 

A sieve-tray tower has an ID of 5 ft, and the combined cross-sectional area of the holes on one tray is 10 percent of the total cross-sectional area of the tower. The height of the weir is 1.5 in. The head of liquid over the top of the weir is 1 in. Liquid gradient is negligible. The diameter of the perforations is in., and the superficial vapor velocity (based on the cross-sectional area of the empty tower) is 3.4 ft/s. The pressure drop due to passage of gas through the holes may be assumed to be equivalent to 1.4 kinetic heads (based on gas velocity through holes). (Tray thickness = hole diameter and active area = 90 percent of total area-see Fig. 16-12). If the liquid density is 50 lb/ft3 and the gas density is 0.10 lb/ft3, estimate the pressure drop per tray as pounds force per square inch. 

In nonagitated (static) extractors, drops are formed by flow through small holes in sieve plates or inlet distributor pipes. The maximum size of drops issuing from the holes is determined not by the hole size but primarily by the balance between buoyancy and interfacial tension forces acting on the stream or jet emerging from the hole. Neglecting any viscosity effects (i.e., assuming low dispersed-phase viscosity), the maximum drop size is proportional to the square root of interfacial tension a divided by density difference Ap ... 

In the AOCS Method Ac 2-4l (1987), the soybean sample is first cleaned on a 3.2 mm (8/64-in) round-hole sieve. Then 10 g ofwhole soybeans are placed in a tared moisture dish and placed in a forced-draft air oven at 130 3°C for 3 h. 

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