Abstract:
The gas hold-up is an important hydrodynamic parameter that affects the interfacial
area of gas-liquid dispersions. The ability of liquid phase to support or hinder bubble
coaJescence significantly influences the gas hold-up. Presence of surface-active solutes
in liquid phases decreases the bubble coalescence ability; thus increases the gas holdup
in comparison to the pure solvent. The electrolytes and aliphatic alcohols are two
important groups that behave as surface-active solutes in aqueous solutions. In this
paper a systematic study was made to investigate the effect of aqueous solutions
electrolytes on gas hold-up. A 50 mm diameter bubble column was used for the
experimental study. Comprehensive data of gas hold-up with respect to concentrations
in four electrolyte-water solutions were generated. The enhancement of gas hold-up in
these types of solutions was observed at low concentration. The coalescence hindering
nature of electrolytes was explained by the dynamic surface effect i.e. the surface
tension gradient that. exists between bubble surface and bulk of the liquid and
quantified by the dimensionless parameter (crk2/cr). A gas hold-up model was
proposed which included the parameter (crk2/cr) to incorporate the coalescencehindering
phenomenon of liquids with gas hold-ups. The model predicts the trend and
magnitude of gas hold-ups in four electrolyte solutions adequately. The corresponding
concentrations of the maximum gas hold-up values were predicted satisfactorily. The
predicted values of maximum gas hold-ups deviated from the measured values by less
than 6%.
