Prediction of the volumetric mass transfer coefficient in pneumatic contactors

Semi-theoretical expressions are developed for the prediction of the volumetric mass transfer coefficient, (K_La_D)_T, in pneumatic contactors, using the correlation of Calderbank and Moo-Young Chem. Engng Sci.16, 39 (1961) for the mass transfer coefficient and the local isotropic turbulence theory for predicting bubble diameter. A direct proportionality of (K_La_D)_T to the gas hold-up is predicted, with an exponent of 1.2 on ε_G, while, in terms of physical parameters, (K_La_D)_T is predicted to be proportional to the 0.8 power of the superficial gas velocity for both bubble column and airlift contactors, and proportional to (1 + A_d/A_r)⁻² for airlift contactors, where A_d/A_r is the downcomer-to-riser cross-sectional area ratio. Experimental results obtained in bubble column and airlift contactors (external-loop and concentric-tube) of pilot-plant scale (ca. 50L liquid capacity), with water and 0.15 kmol m⁻³ NaCl solution as liquid media, were used to test the proposed expressions.