The transition from homogeneous to heterogeneous flow in a gassed, stirred vessel

Much 'old' work has been undertaken studying gas-liquid systems in stirred reactors (Nienow(1)). However, this 'old' work has generally been limited to specific ungassed energy dissipation rates, (epsilon(T))(0), up to similar to 2 W kg(-1) and gas flow rates of up to similar to 2 vvm (or superficial gas velocity, nu(s), of < similar to 0.01 ms(-1)). Recent developments have led to the need to operate modern reactors at much higher values of epsilon(T) and nu(s). This preliminary study reports work under such conditions and also builds on studies at very high gas velocities in bubble columns, Under such conditions, a transition from homogeneous to heterogeneous flow occurs. The results show that under well dispersed conditions, the transition occurs at lower gas velocities for the coalescence-inhibited solutions in comparison to water. Possible reasons for these findings and for the formation of large bubbles at this transition are discussed. A simple model on the basis of a gas volume balance is proposed which matches the trend. The impact of the intense operating conditions on a range of other mixing parameters is also reported.