Mass transfer considerations

To minimise the energy consumption of the compressor the loading pf solute (F in equation 10.3) should approach its equilibrium value. To design an extraction unit in which this aim is achieved, the mass transfer behaviour of the system should be known. If, for example, a packed bed is to be extracted, the bed length should be sufficient for saturation at the outlet to be approached. 

This and other factors influencing the sizing of the extraction towers are examined in the worked example in section 10.6. In this example a mass transfer model developed from the experimental work of Barr [10], Chami [11] and Bemardo-Gil [12] on the extraction of oil from ground rape-seed is used. 

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Thermodynamic and Mass-Transfer Considerations Multi-component vapor mixture includes several different cases all the components may be hquids at the lowest temperature reached in the condensing side, or there may be components which dissolve substantially in the condensate even though their boiling points are below the exit temperature, or one or more components may be both noncondensable and nearly insoluble. 

Mass transfer considerations are critical in any bioprocess. In typical, aerobic, suspended cell fermentations, the major concern is the oxygen transfer rate, determined by the overall mass transfer coefficient, kft, and the driving force. In three-phase biofluidization, in which the cells are immobilized as a biofilm or within carrier particles, the situation is further complicated by possible intraparticle diffusion limitations. Numerous recent studies have addressed these issues. 

The change in concentration of the phase would depend on the flow-rate, even if the transfer coefficients and rate of transfer did not. This equation is not truly one for the additivity of resistances, for each resistance has a scale factor, LM or GM. The ratio of GM to Lm is usually dictated by the plant production the individual values GM and LM are normally controlled by the physical capacity of the equipment rather than by mass transfer considerations, which control the contacting length rather than the flow-area of the equipment. 

MASS TRANSFER CONSIDERATIONS FOR THE ENANTIOSELECTIVE HYDROGENATION OF a-KETO ESTERS CATALYZED BY CINCHONA MODIFIED Pt/Al203... 

Mass Transfer Considerations in Entrapped Culture Systems. 32... 

Solichien MS, O Brien D, Hammond EG, and Glatz CE. Membrane-based extractive fermentation to produce propionic and acetic acids Toxicity and mass transfer considerations. Enzyme Microbial Technol, 1995 17(1) 23-31. 

Connor M. A. (1983) Heat and mass transfer considerations in fuel production from wood wastes by pyrolysis. Regional Journal of Energy, Heal and Mass Transfer, 5, 179-94. 

Connor M.A. (1983). Heat and Mass Transfer Considerations in Fuel Production from Wood Wastes by Pyrolysis. Reg. J. Energy Heat Mass Transfer, S (3), 179-194. 

Before going any further, it is important to emphasize the fact that drying is largely a mass transfer problem mass transfer considerations are usually more important than... 

The absorption of ozone by cyanide solutions in stirred reactors is complicated by mass transfer considerations. The presence of ozone gas in the exhaust from such a reactor does not indicate that equilibrium has been obtained between ozone gas bubbles and ozone in solution, but rather that the mass transfer through the individual bubbles is not complete, because of the resistance on the gas side. In other words, mass transfer controls the reaction, as the ozone will react almost instantaneously with the cyanide ion in solution. The presence of some metals, particularly copper, appears to speed up the absorption by acting as oxygen carriers. A solution of ozone in dilute acid decomposes somewhat more quickly when a trace of cupric ion is added. The presence of these metal catalysts, if this be their function, does not appear to be a necessary condition to ozone oxidation. What is important is that adequate mass transfer time and surface be available, as would be found in a countercurrent packed tower. 

Let us consider mass and heat transfer of under a transverse flow of packets of cylinders with unstaggered chess arrangement. At sufficiently high Reynolds numbers, the tubes in the first row of a packet are in conditions close to the conditions of mass transfer for an isolated cylinder (if the gap between tubes is of the order of the cylinder radius), while the mass transfer considerably increases in the subsequent rows. This effect is produced by the fact that the first rows serve as flow turbulizers. The stabilization of mass and heat transfer is about 10% after the fourth row, and is complete after the 14th row. In what follows, we take a tube of radius a as the characteristic length, and the velocity U = Ui/ip as the characteristic flow velocity, where U[ is the flow velocity remote from the cylinder and t/> is the maximum narrowing coefficient for the packet cross-section downstream. 

Hayhurst, A. N., and Kittelson, D. B. "Heat and Mass Transfer Considerations in the Use of Electrically Heated Thermocouples of Iridium versus an Iridium/Rhodium Alloy in Atmospheric Pressure Flames." Combustion and Flame 28 (1977) 301-17. 

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