Gas-liquid interfacial area, bubble size and liquid-phase mass transfer coefficient in a three-phase external loop airlift bubble column

The interfacial area a was measured by the sulfite oxidation method in a three-phase external loop airlift bubble column suspending completely the different concentrations of ion exchange resin particles in aqueous carboxymethyl cellulose (CMC) solutions with a wide range of viscosity. The column had been previously studied for the circulating liquid velocity U-L, gas holdup epsilon(G) and volumetric gas-liquid oxygen transfer coefficient k(L)a in the two- and three-phase systems. The average bubble size d(B) and oxygen transfer coefficient k(L) were obtained as d(B) = 6 epsilon(G)/a and k(L) = (the previous k(L)a)/a, respectively. The similar studies were carried out in the internal loop airlift and normal bubble columns for comparison. The a values in the external loop airlift were found to be little affected by the column height and particles concentrations, and to decrease with increasing viscosity. All the three columns showed a linear dependence of a on epsilon(G). A simple correlation of a, d(B) or k(L) was proposed as a function of epsilon(G) and viscosity for the external loop airlift as well as both internal loop airlift and normal columns. A well-known relationship between k(L) and d(B) was confirmed to hold independent of column types and operating conditions for a given two or three phase system.