The effect of vessel diameter on time dependent gas hold-up variations in highly viscous impeller agitated liquids

Time dependent gas hold-up generated in the 0.3 and 0.6 m diameter vessels using high viscosity castor oil and carboxy methyl cellulose (CMC) solution was compared on the basis of impeller speed (N) and gas velocity (VG). Two types of hold-up were distinguished—the hold-up due to tiny bubbles ( ft) and total hold-up ( f), which included large and tiny bubbles. It was noted that vessel diameter (i.e. the scale of operation) significantly influences (i) the trends and the values of f and ft, and (ii) the values of τ (a constant reflecting the time dependency of hold-up). The results showed that a scale independent correlation for gas hold-up of the form f or ft=A(N or PG/V)a(VG)b, where “a” and “b” are positive constants is not appropriate for viscous liquids. This warrants further investigations into the effect of vessel diameter on gas hold-up in impeller agitated high viscosity liquids (μ or μa>0.4 Pa s).