Dry hole pressure drop

CALCULATION OF h0, THE HEAD EQUIVALENT TO THE DRY HOLE PRESSURE DROP... 

The dry hole pressure drop for a sieve tray may be calculated by use of the following equation for thick plate orifices... 

Orifice coefficient. Figure 8-129, read at 0.41 tray/hole gives Cq orifice coefficient = 0.75 Hole velocity = 347/8.66 = 40.06 fps Dry Tray pressure drop... 

Low dry tray pressure drop. On sieve and fixed valve trays, this means high (>11 percent) fractional hole area. On moving valve trays, this means venturi valves (smooth orifices) or long-legged valves (>15 percent slot area). On all trays, the channeling tendency and severity escalate rapidly as the dry pressure drop diminishes (e.g., as fractional hole area increases). 

Application Systems where high capacity near-design rates to be maintained in continuous service. Handles suspended crystal and small solid materials, as well as polymer forming materials. Holes become plugged in salting-out systems where trays run hot and dry (as underside of bottom tray). Good in vacuum or low-pressure-drop design. 

Using these calculated ratios, AHAA and THDIA, a hole discharge coefficient factor CFCV is calculated from a curve-fitted equation in Fig. 18-14 in the Chemical Engineer s Handbook [14], CFCV is a factor in Eq. (3.112) for calculating the sieve tray dry pressure drop. 

The total pressure drop across a tray is the sum of the pressure drop across the disperser unit, hd (dry hole for sieve trays dry valve for valve trays), and the pressure drop through the aerated mass hh i.e.,... 

Between the closed and open balance points, the dry pressure drop is constant (Fig. 6.216), and equals the pressure drop at either the closed or open balance points. Therefore, Eq. (6.44a) can be used, with uh in Eq. (6.42) set equal to the velocity at the closed balance point, u-uk cBp- Alternatively, Eq, (6.446) can be used with uh in Eq. (6.42) set equal to the velocity at the open balance point, uvh Qbp-Note that between the open and closed balance points the hole velocity at the relevant balance point, and not the actual gas velocity of gas through the holes, is used as uh in Eq. (6.42). 

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]

Pressure drop. Pressure drop is calculated as per Secs. 6.3.1 to 6.3.3, using Fair s pressure drop correlation. Usually, it is good practice to design for a pressure drop of 3 to 5 in of liquid (approximately 0.08 to 0.12 psi) per tray. If outside this range it is best to adjust the fractional hole area (if dry pressure drop dominates) or the weir height (if wet pressure drop dominates). 

Pilot-scale particle collection efficiency has been found to be similar to the cold and dry experiments over 300 hours filtration time, Figure 12 presents a relatively constant pressure drop over time for the hot and dry experiments conducted on the pilot-scale filter under a gas flowrate of 20 Nm /h (80 Nm /hr/m ), with a particle load of 3000 mg/Nm and using Ottawa sand as the filtering media. Deep holes on Figure 12 are air pulses to back-flush the solids plugging the exits. 

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