Mass transfer principles

Kirwan, Mass Transfer Principles in Rousseau, Handbook of Separation Process Technology, Wiley, 1987. 

Mass-Transfer Principles Dilute Systems When material is transferred from one phase to another across an interface that separates the two, the resistance to mass transfer in each phase causes a concentration gradient in each, as shown in Fig. 5-26 for a gas-hquid interface. The concentrations of the diffusing material in the two phases immediately adjacent to the interface generally are unequal, even if expressed in the same units, but usually are assumed to be related to each other by the laws of thermodynamic equihbrium. Thus, it is assumed that the thermodynamic equilibrium is reached at the gas-liquid interface almost immediately when a gas and a hquid are brought into contact. 

Mass-Transfer Principles Concentrated Systems When sohrte concentrations in the gas and/or liqrrid phases are large, the eqrrations derived above for dihrte systems no longer are applicable. The correct eqrrations to rrse for concentrated systems are as Follows ... 

This chapter has presented an overview of mass transfer principles of relevance to the pharmaceutical scientist. Mass transfer is defined as the movement of mass... 

An overview of this kind is, of necessity, limited in detail. Readers interested in a more thorough development of mass transfer principles are encouraged to consult the references listed at the end of the chapter. In particular, Cussler s excellent textbook on diffusion is an accessible introduction to the subject geared toward the physical scientist [11], Those with a more biological orientation may prefer Friedman s text on biological mass transfer [12], which is also exceptional. A classic reference in the field is Crank s Mathematics of Diffusion [13], which contains solutions to many important diffusion problems. 

For the control volume, the heat flux at the boundary is given as if = hc(T — T. ). The diffusion mass flux supplying the reaction is given as m" = hm(yFj00 — yF ), where from heat and mass transfer principles hm — hc/cv. Let Vand S be the volume and surface area of the control volume. The reaction rate per unit volume is given as m " — AYf E ilRT] for the fuel in this problem. 

The mass-transfer principles presented above are derived for equimolecular counter-... 

Successful approaches to designing an extraction process begin with an appreciation of the fundamentals (basic phase equilibrium and mass-transfer principles) and generally rely on both experimental studies and mathematical models or simulations to define the commercial technology. Small-scale e3q)eriments using representative feed usually are needed to accurately quantify physical properties and phase equilibrium. Additionally, it is common practice in industry to perform... 

It should be noted that the term extraction is used throughout this chapter to signify solid-liquid extraction. Although supercritical extraction is governed by the same mass transfer principles as those describing extraction with liquid solvents, it is not discussed in this chapter. 

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