Mass transfer applications

Material Balances Whenever mass-transfer applications involve equipment of specific dimensions, flux equations alone are inadequate to assess results. A material balance or continuity equation must also be used. When the geometiy is simple, macroscopic balances suffice. The following equation is an overall mass balance for such a unit having bulk-flow ports and ports or interfaces through which diffusive flux can occur ... 

Used in mass-transfer applications. Condensation Number... 

The principle of the perfectly-mixed stirred tank has been discussed previously in Sec. 1.2.2, and this provides essential building block for modelling applications. In this section, the concept is applied to tank type reactor systems and stagewise mass transfer applications, such that the resulting model equations often appear in the form of linked sets of first-order difference differential equations. Solution by digital simulation works well for small problems, in which the number of equations are relatively small and where the problem is not compounded by stiffness or by the need for iterative procedures. For these reasons, the dynamic modelling of the continuous distillation columns in this section is intended only as a demonstration of method, rather than as a realistic attempt at solution. For the solution of complex distillation problems, the reader is referred to commercial dynamic simulation packages. 

This section concerns the modelling of countercurrent flow, differential mass transfer applications, for both steady-state and non-steady-state design or simulation purposes. For simplicity, the treatment is restricted to the case of a single solute, transferring between two inert phases, as in the standard treatments of liquid-liquid extraction or gas absorption column design. 

Chapter 3 concerns the dynamic characteristics of stagewise types of equipment, based on the concept of the well-stirred tank. In this, the various types of stirred-tank chemical reactor operation are considered, together with allowance for heat effects, non-ideal flow, control and safety. Also included is the modelling of stagewise mass transfer applications, based on liquid-liquid extraction, gas absorption and distillation. 

The systematic description of heat and mass transfer applications in freeze drying is considered in this section. Mechanistic interpretations are discussed in the fol-... 

Aeration injectors, like the one shown in Fig. 14-100 by Penberthy [a division of Houdialle Industries (penberthy-online.com/jetl.asp)], are used to provide mass transfer in gas-liquid applications, and simple impingement aerators (Fig. 14-101) are sometimes used for mass-transfer applications. 

The purpose of this chapter is to present a general framework for dealing with the effect of mass transfer on heat transfer and the effect of heat transfer on mass transfer. Applications to distillation operations are included in this chapter mass and energy transfer in multicomponent condensation is considered in Chapter 15. 

This result may now be interpreted in terms of a heat transfer application (Example 7.1) or a mass transfer application (Example 7.6). 

For gas-liquid mass transfer applications, Manbrane Corporation (Minneapolis, Minnesota) offers modules that are designed for this specific purpose. These modules fit within standard PVC pipes and contain multiple fiber bundles, each containing around 500 fibers. The fibers are potted into polyurethane at one end only and are individually sealed at the other end so that there is no exhaust stream. That is, all enter gas exits by diffusing across the membrane into the surrounding water, leading to 100% gas transfer efficiency. The packing density is only 10%, and fibers are eomposed of a 1 rm layer of polyurethane sandwiched between two layers of microporous polyethylene inside and out diameters are 220 and 270 pm, respectively [55]. 

Microemulsions formed with components of Systems I and II were used as desiccant fluids in water absorption operations. The amount of surfactant in the samples prepared was set at 50% to avoid turbidity that would be formed below that concentration level. In Figure 15.6, the amount of water that can be transferred from natural gas to the desiccant fluid (C, in ppm) is given as a function of time for System I, at three different gas flow rates 300, 700, and 1200mL mur. It was observed that 240 min was required to attain the maximal dehydration capacity of the system at the lower flow rate. The concentration of water in the desiccant fluid decreases with increasing gas flow rate, because of the relatively high viscosity of the fluid and the reduced contact time between phases at higher flow rates. Viscosity is therefore an important parameter to be considered in such mass transfer applications. On the other hand, higher gas flow rates are favorable... 

For free convection problems, Eqs. 5.130, 5.131, and 5.132 can easily be translated to mass transfer applications using Table 4.16. 

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