Mixing Characteristics of Gas and Liquid Flowing through Gas-Liquid Packed Beds

Abstract

The axial mixing characteristics of gas and liquid flowing through gas-liquid packed beds (in which bubbles rise up through a descending continuous liquid phase among packings), and liquid packed beds (through which liquid flows through packings without gas flow) are determined, by employing the methods of the transient response and the frequency response.The transient response curves of gas or liquid, obtained experimentally were plotted against (√τ-1/√τ) on normal probability papers, after having eliminated the end effects. Then, the straight lines were obtained, as suggested by Eq.(9). From the slope of the line, M=uL/2E or Pe=dpU/E were determined for each run. On the other hand, from the frequency response curves, the ratio of inlet to outlet amplitude and the phase lag of the sinusoidally-varying acid concentration were determined, and M and Pe were calculated, according to Eqs.(12) and (13).Dimensions of the experimental apparatus used and a range of variables studied are as follows:Tower; 10.0cm I. D., 110cm heightPackings; 1.0, 1.5, 2.0cm ceramic Raschig ringsGas (air) flow rate;0-10l/minLiquid (water) flow rate;0.45-11l/minPeriod of concentration wave; 63, 127, 253 secTracer; He, HCl Under these conditions, the experimental results indicate thati) The velocity of rising up and the mixing coefficients of bubbles in liquid packed beds are kept constant and independent of the gas flow rate.ii) In liquid packed beds, the Peclet number for liquid, (Pe)L, increases slightly from 0.65 to 1.3, as the Reynolds number for liquid, (Re)L is increased from 100 to 2000, as illustrated in Fig. 5.iii) In gas-liquid packed beds, the Peclet number for liquid varies over a wide range, as a function of the liquid flow rate and independent of gas flow rate. The generalized correlation for it is given by Eq.(20)