Packing equivalent diameter

The vapor Schmidt number, ScG and the effective gas velocity, ueff, are calculated by Eqs. (9.206) and (8.18), respectively. Values of the channel angle 0 and of the packing equivalent diameter, dare in Table 8.1. The liquid flow rate F is given by... 

Because this scrubber will operate at the new rates below the loading region of the packing, the pressure drop can be calculated using the method of Bravo etal. [10]. For this calculation, the packing equivalent diameter is 0.0602 ft, from the dimensions given in Table 2-3, and the void fraction is 0.97. The value of constant C3 is 3.08, the same as for other structured packings of similar surface areas (see Table 2-1). The superficial gas velocity is ... 

Particle diameter is a primary variable important to many chemical engineering calculations, including settling, slurry flow, fluidized beds, packed reactors, and packed distillation towers. Unfortunately, this dimension is usually difficult or impossible to measure, because the particles are small or irregular. Consequently, chemical engineers have become familiar with the notion of equivalent diameter of a partiele, which is the diameter of a sphere that has a volume equal to that of the particle. 

Figure 9-50. HETP and pressure drop data for a typical distillation system. Packing equivalent to X-200 (8 strands), stainless steel. System methylcyclohexane and toluene. Reflux Ratio 100%. Column Diameter 18 inches. Packed Height 5 feet. Used by permission ACS Industries, Inc., Separation Technology Division, Bull. B-129 (1992).

Tab. 3.3.1 Physical properties of the packed porous particles. The relaxation times were determined at a Larmor frequency of 300 MHz for protons of water adsorbed into saturated catalyst pellets (average error 2%). The equivalent diameter is defined by 6 Vp/Ap where Vp and Ap are volume and external surface of the particles, respectively.

An equivalent diameter de for flow through the bed can be defined as four times the cross-sectional flow area divided by the appropriate flow perimeter. For a random packing, this is equal to four times the volume occupied by the fluid divided by the surface area of particles in contact with the fluid. 

For a packed bed, substituting the equivalent diameter de from equation 9.20 into equation 1.65 gives... 

Re < 324 medium-dosely packed fibers with Re, Reynolds number Sc, Schmidt number (p, fiber packing dc, equivalent diameter. 

Equivalent diameter of structured-packing flow channel, in, values given in Tahle 8.1... 

With this definition, for spheres, the use of Equation 8.39 gives just the diameter of sphere. Expressions of equivalent diameters for different particle shapes as used in packed bed reactors are presented in Table 8.1. ... 

Stiegel and Shah34 reported the liquid holdup characteristics of a packed (with 0.318-cm polyethylene or 0.44-cm equivalent diameter packing) rectangular (16.8 cm x 2.06 cm) column. The column was approximately 122 cm high. The measurements were carried out with an air (in the flow range of 0 through 0.203 kg s 1 m 2) water system. The total liquid holdup was correlated by the relation... 

We will use these data to obtain a general relationship between the pressure drop per unit height of packed bed and the other variables. To search for an actual solution to this problem, we begin by performing a dimensional analysis, which can be realized without any experiment. We wdll assume that the pressure drop per unit height of packed bed, Ap/H, is a function of the equivalent packed body diameter, d, the fluid density, p, the fluid viscosity, q, and the mean packed bed fluid velocity, w. 

The equivalent packed body diameter, d, is related to the bed holdup, e, and specific packed surface, s, as well as via the relationship d = 4e/a. For the packed bed from spherical bodies (e = 0.44 and ct = 6/dp), the equivalent packed body diameter depends only on the sphere diameter. The mean internal packed bed fluid velocity represents the ratio between the fictive velocity and the packed bed porosity (e). According to these data, we can write ... 

The effective gas and liquid rates, Ug eff and U eff, take into account the flow angles, void fractions, and film thicknesses that derive from gross flow rates and packing geometry. The equivalent diameter is taken as the width of a corrugation. 

Inert packing equivalent to a length of six particle diameters shall be present in front of the catalyst bed This allows transition to steady flow conditions characteristic of the packed bed. 

For packed beds of spheres of different diameters or of non-spherical particles, and equivalent diameter has to be formed... 

The method presented above has been revised by Bravo et al. (1992). In the revised correlations the equivalent diameter is taken to be equal to the channel side S. The velocities are adjusted to allow for liquid holdup and the assumption that the packing is completely wetted has been dispensed with. 

Packing Angle (degrees) Equivalent Diameter (mm) Constant Cj... 

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