FLOW REGIMES, GAS HOLD-UP AND AXIAL GAS MIXING IN THE GAS-LIQUID MULTISTAGE AGITATED CONTACTOR

Experimental data are reported on Row regimes, gas hold-up and axial g as mixing of a gas-liquid Multi-stage Agitated Contactor (MAC), consis ting of nine compartments [height, H, over diameter, D = 1; D = 0.09 m ) separated by horizontal baffles with an opening of 0.04 m and with o ne centrally positioned impeller per compartment (12-bladed turbine di sk; impeller diameter. d(1) = 0.03 m). For air-water and the liquid in batch, a homogeneous gas-liquid dispersion is realized with a stirrin g speed, N, above 15 s(-1) and a superficial gas velocity, u(G), below 0.12 ms(-1). These boundaries are affected unfavourably by either a c ocurrent or a countercurrent liquid Row. For nine combinations of thre e gases (air, helium and dichloro-difluoro methane) and three liquids (water, n-octane and monoethylene glycol) the gas holds-up, epsilon(G) , and the axial gas mixing were determined with the liquid in batch. E xperimental conditions were varied as follows: u(G), 0.01-0.09 ms(-1); N, 10-36.7 s(-1); liquid viscosity, eta L, 0.00041-0.021 Pa s; surfac e tension, sigma, 0.02-0.073 Nm(-1); liquid density, rho(L), 684-1113 kgm(-3) and gas density, rho(G), 0.16-5.16 kgm(-3) For all experiments , the residence time distribution of the gas phase could be described excellently with a Cascade of ideally mixed Tanks in series with Alter nating Backflow model (CTAB model). All 85 data epsilon(G) could be co rrelated with an average relative deviation of 11.0% by an extension o f Van Dierendoncks' empirical gas hold-up relation. The relative gas b ackflow (ratio between gas backflow and net gas Row) data could be cor related by a novel relation with average relative deviations of 14.5, 17.7 and 19.5% For air-water(18 data points), helium-n-octane (19 data points) and air-monoethylene glycol (12 data points) systems, respect ively.