Packings void pressure

Reynolds number for gas S = length of corrugation side Uge = effective velocity of gas Ug = superficial velocity of gas Ui = superficial velocity of liquid Ap = pressure drop per unit packed height e = packing void fraction 0 = angle of flow channel (from horizontal) fi = viscosity p = density... 

At higher gas rates, a portion of the energy of the gas stream is used to support an increasing quantity of liquid in the column. For all liquid rates, a zone is reached where pressure drop is proportional to a gas flow rate to a power distinctly higher than 2 this zone is called the loading zone. The increase in pressure drop is due to the liquid accumulation in the packing voids (region BC or B C )... 

As liquid rates are raised, the liquid occupies some of the cross-section area, making the openings for gas flow smaller. The pressure drop curve will parallel A-B but will be somewhat above it. At high liquid flow rates, the packing voids fill up with frothy liquid. A portion of the energy of the gas is used to support the liquid in the column and pressure drop becomes proportional to the gas rate raised to a power different (usually lower) than 2 (region A -B ). The point where the packing voids fill up, i.e., when tower operation switches from vapor-continuous (normal) to liquid continuous is termed phase inversion. 

The catalyst particle size and shape should be optimized to achieve maximum activity and maximum heat transfer while minimizing the pressure drop. The high mass velocities in steam reforming plants (Gm = 40.000 - 70.000 kg m % 0 necessitate a relatively large catalyst particle size to obtain a low pressure drop across the catalyst bed but the particle size is limited by the requirement for effective packing. The pressure drop depends strongly on the void fraction of the packed bed and decreases with particle size (Figure 7). 

Packing Void Fraction Bulk Weight Ib/te Single Phase Pressure Drop (in. H20/ft) Gt = 900 Gt = 1600 ... 

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 ... 

Although most cakes consist of polydisperse, nonspherical particle systems theoretically capable of producing more closely packed deposits, the practical cakes usually have large voids and are more loosely packed due to the lack of sufficient particle relaxation time available at the time of cake deposition hence the above-derived value of 17.6 pm becomes nearer the 10 pm limit when air pressure dewatering becomes necessary. 

Isotherm measurements of methane at 298 K can be made either by a gravimetric method using a high pressure microbalance [31], or by using a volumetric method [32]. Both of these methods require correction for the nonideality of methane, but both methods result in the same isotherm for any specific adsorbent [20]. The volumetric method can also be used for measurement of total storage. Here it is not necessary to differentiate between the adsorbed phase and that remaining in the gas phase in void space and macropore volume, but simply to evaluate the total amount of methane in the adsorbent filled vessel. To obtain the maximum storage capacity for the adsorbent, it would be necessary to optimally pack the vessel. 

FIGURE 2.12 Pressure drop as a function of liquid fiow through a packed bed of Superose 6 prep grade packed in a HR 10/30 column. At high velocities of the mobile phase the beads are compressed and the void channels reduced, which leads to a high pressure drop. If this happens, the material can be resuspended and packed at a lower flow rate. [Reproduced from Hagel and Andersson (1984), with permission.]... 

Dixon and coworkers [25] have performed several CFD simulations of fixed beds with catalyst particles of different geometries (Figure 15.9). The vast number of surfaces and the problems with meshing the void fraction in a packed bed have made it necessary to limit the number of particles and use periodic boundary conditions to obtain a representative flow pattern. Hollow cylinders have a much higher contact area between the fluid and particles at the same pressure drop. However, with a random packing of the particles, there wiU be a large variation... 

The Waters system uses a plastic cartridge which is inserted into a device (the Z-module) that subjects the column to radial compression, ie pressure is applied along the radial axis of the column tube. The flexible wall of the column then moulds itself into the voids that are present in the wall regions of the column. This method is claimed to produce an improvement in the packed bed structure, better column performance and longer useful column life. 

---