Packings voids

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... 

Characteristics of particulate solids (packing, void, density)... 

The linear superficial flow velocity in the packing voids v is calculated from volumetric flow rate Lin, voidage fraction of the adsorbant bed e and column diameter d as... 

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 )... 

When the diameter of the particles is very small in comparison with the diameter of the container, the wall effect may be appreciable. The method of accounting for the difference in packing voids with regard to flow of fluids is discussed in Chapter 13. 

Eq(10-16)is known to conform closely with experimental observations. The chief difficulties in applying Eq (10-16) are due to determination of the constants C and Kv. These are functions of many variables including temperature, packing voids, and particle size. 

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. 

Specific heats of metals and hydrides are easily determined and typically fall in the range of 0.1-0.2 cal/g°C. Thermal conductivity is a little more difficult to determine. The conductivity of the metal or hydride phase is not sufficient the effective conductivity of the bed must be determined. This depends on alloy, particle size, packing, void space, etc. Relatively little data of an engineering nature is now available and must be generated for container optimization. Techniques to improve thermal conductivity of hydride beds are needed. As pointed out earlier, good heat exchange is the most important factor in rapid cycling. 

Catalyst particle size 0.5-1 mm Packing void fraction 0.75... 

Packing void fraction and porosity Experiment + moment analysis + parameter estimation e and et Experiment + moment analysis et, set e et (from manufacturer), set e... 

Values of a and Ch are characteristic of the particular type and size of packing, as listed together with packing void fraction, e, and other packing constants in Table 4.1. Because the specific liquid holdup in the preloading region is constant, equation (4-3) does not involve gas-phase properties or gas velocity. 

Blockage of column frits or channeling in a column bed will cause a loss of resolution. Any packing void will be a source of dead volume and thus of band spreading this can be checked by carefully removing the front frit from the eolumn. A void is indicative of the imminent end of the column s usefulness, especially in SEC, which is inherently dependent on peak widths and column efficiency. 

The free volume concept has been successfully used for describing the glass transition phenomenon and the Pick s law of diffusion tor polymers. One of such successful examples is the Williams-Landel-Ferry(WLF) equation [72,73], which provides the relationship between the time-temperature superposition shift factor and temperature. The free volume is considered to be the holes resulting from the packing void or irregularity of polymeric molecules. This concept will be continuously used in this section for deriving the viscosity equation ol both polymer melts and polymer solutions. 

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

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