Pressure drop, trays residual

As noted, the weir crest 4, is calculated on an equivalent clear-liquid basis. A more realistic approach is to recognize that in general a froth or spray flows over the outlet weir (settling can occur upstream of the weir if a large calming zone with no dispersers is used). Bennett et al. [AIChE J., 29, 434 (1983)] allowed for froth overflow in a comprehensive study of pressure drop across sieve trays their correlation for residual pressure drop h L in Eq. (14-100) is presented in detail in the previous (seventh) edition of this handbook, including a worked example. Although more difficult to use, the method of Bennett et al. was recommended when determination of pressure drop is of critical importance. 

The Bennett et al. correlation. This correlation was shown (31) to predict experimental sieve tray pressure drop data more accurately than Fair s correlation. The correlation is based on froth regime considerations and is not applicable to the spray regime. The Bennett et al. calculation of dry pressure drop is identical to Fair s, using Eqs. (6.42) and (6.43) and the Liebson et al- correlation (Fig. 6.21a). To calculate the h, term in Eq. (6.41), Bennett et al. depart from the concept of clear liquid flow corrected for aeration effects [Eq. (6.47a)]. Instead, they use Eq, (6.476) and a model of froth flow across the weir. Their residual pressure drop, hn, is a surface tension head loss term, which is important for trays with very small holes ([Pg.317]

Residual pressure drop, i.e., total tray pressure drop less diy pressure drop less dear liquid height, in of liquid. 

The feed to the column is 242.02 moles/hr of aqueous ethanol at a temperature of 110°F. The feed composition is 85.64 mole % ethanol. The distillation is carried out at 50 psia at the reboiler. The pressure drop is assumed to be 0.14 psi per tray. The vapor boil-up at the reboiler is set at 800 moles/hr. The reflux temperature is 154.45°F. The aqueous phase is stripped to remove dissolved entrainer and residual ethanol. The calculation control is set to reduce ethanol in the overhead vapors to 13.85 mole %. 

The decrease in pressure, as the vapor flows upward through a tray, is the sum of the pressure drop through the perforations and the residual drop through the froth or spray ... 

A —pressure drop resulting from depth of liquid on tray Aj, =residual pressure drop... 

It is also necessary to use a safe method for storing contaminated pipets until they can be washed. They should be placed horizontally in a pan containing enough suitable decontaminant solution to allow their complete immersion (209), rather than being dropped vertically into a cylinder. There are several reasons for avoiding the use of vertical cylinders. First, hydraulic pressure will force an aerosol of residual liquids and contaminants from the bore of the pipet out through its upper end as it is dropped into the cylinder. Second, flat trays can be placed directly in the autoclave, thus... 

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