Mass transfer area, effective

Ae 2 total effective mass transfer area of packing for gas-hquid contact... 

Effective Interfacial Mass-Transfer Area a In a packed tower of constant cross-sectional area S the differential change in solute flow per unit time is given by... 

The high surface-to-volume ratio can also significantly improve both thermal and mass transfer conditions within micro-channels in two ways firstly, the convective heat and mass transfers, which take place at the multi-phase interface, are improved via a significant increase in heat and mass transfer area per unit volume. Secondly, heat and mass transfers within a small volume of fluid take a relatively short time to occur, enabling a thermally and diffusively homogeneous state to be reached quickly. The improvement in heat and mass transfer can certainly influence overall reaction rates and, in some cases, product selectivity. Perhaps one of the more profound effects of the efficient heat and mass transfer property of micro-reactors is the ability to carry potentially explosive or highly exothermic reactions in a safe way, due to the relatively small thermal mass and rapid dissipation of heat. 

In trickle beds, the gas-to-liquid, kigaGL, and liquid-to-particle, kfaLS, coefficients are used to represent the effect of the external mass transfer resistances. The interfacial areas aGl and <2ls refer to the effective mass transfer surface per unit volume of empty reactor. Due to the fact that the coefficients kig and klL cannot be easily estimated independently from the corresponding interfacial areas aGL and aLS respectively, by simple experimental techniques, correlations are normally reported for the products kigaGL and k,a]S (Smith, 1981). 

As noted earlier, the rate of mass transfer is proportional to the interfacial area. Effective mass transfer requires that a high specific interfacial area (interfacial area per unit volume) should be created. For a droplet dispersion such as exists in most extraction processes, the specific interfacial area is given by... 

Whereas the laboratory fluidized bed is generally operated with no internals, plant equipment often must contain bundles of heat-exchanger tubes. Screens, baffles, or similar internals are frequently used to redisperse the bubble gas in industrial reactors. The mass-transfer area is thus increased relative to the fluidized bed without internals the extra area can be utilized to partially offset the conversion-reducing effects of bed diameter and gas distributor [122]. 

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