Heat and Mass Transfer Efficiencies of Multi-Impeller Gas-Viscous Liquids Contactors

Abstract

Measurements of impeller power P_g heat transfer coefficients stirred solution-coil h _cg and oxygen transfer coefficients k_La are carried out on two gas-viscous liquid contactors stirred by axial and radial impeller couples.

The lower impeller imposes the hydrodynamic regime especially n_CD, minimum of P_g/P_o = f(Re) curves and beginning of the working zone. For. the most important combinations, in particular DT-PBT n_CD, h_cg and k_La correlations (n ≥n_CD) are proposed.

Two new efficiency criteria have been defined E_H = h_cg/P_g and E_M = k_La/P_g in order to quantify the multiple impellers heat and mass transfer performances.

For all the studied systems, the complete un-flooding point (close to the loading point) represents the working optimum for h_cg and k_La too.

A great care must be paid for the multi-impellers choice because their relative performances estimated by E_H and E_M can reverse when the comparisons are not carried on in n_CD optima but with imposed h_{c g} or k_La.