Qualitative Analysis of Concentration Profiles and Mass Transfer

Illustration 1.6 Qualitative Analysis of Concentration Profiles and Mass Transfer 

Case 1 Here the concentrations in both the gas and liquid phase diminish in the positive direction, causing solute to transfer from the gas to the liquid phase. The fact that the interfacial liquid mole fraction is higher than the gas concentration is no impediment. It is merely an indication of high gas solubility, a perfectly normal and acceptable phenomenon. 

Hypothetical concentration profiles near a gas-Hquld interface. 

Case 2 The gas-phase concentration here increases in the positive direchon so that no transfer of solute from gas to liquid can take place. Neither can there be any transfer in the opposite sense, because the liquid concentrahon rises in the negative direction. Such profiles arise only in cases when solute is generated by chemical reaction at the gas-liquid interface. The product solute then diffuses from the interface into the bulk fluids. 

Case 3 This case involves decreasing concentrations in both phases, but the decrease is in the negative direction. Solute will therefore desorb from the liquid into the gas phase. Gas solubility is low because the interfacial concentrations are nearly idenhcal. 

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