Mass transfer coefficient regime similarity

The valnes of the mass-transfer coefficient are measured at various impeller speeds using a model gas-liquid system such as CO2-H2O. Using these results of vs. N, a similar relationship is obtained for the given gas-liqnid system using the square root diffusivity relationship. Thus, at any impeller speed, the specific rate of absorption under mass transfer-controlled conditions (regime 2) can be obtained and is eqnal to ki[A]. ... 

The mass transfer coefficient increases only slightly with temperature, so above a certain temperature the reaction becomes mass transfer controlled. Further increases in temperature give almost no change in conversion. The transition to mass transfer control occurs at a lower temperature for very reactive species, such as H2 and CO, than for hydrocarbons, but the kinetics of oxidation are often not known. The design temperature and flow rate are based on lab tests or experience with similar materials. The reactor is usually operated in the mass transfer control regime, where the conversion depends on the rate of mass transfer and the gas flow rate. 

---