Axial mixing in modern packings, gas, and liquid phases: II. Two-phase flow

Axial mixing measurements of air and water under two-phase flow conditions were made in a large-scale packed column (0.43 m diameter) using tracer experiments. Part I of this article dealt with single-phase mixing in the same column, with the same internals. Four packings were studied: 25.4-mm ceramic Raschig rings, 25.4-mm metal Pall rings, Sulzer BX structured packing, and Flexipac 2 structured packing. Air and water flowed countercurrently through the column at atmospheric pressure and at gas rates varying from 0.25 kg/m²·s up to the flooding point, and liquid rates from 3.25 to 8.5 kg/m²·s. A diffusion-type model served to reproduce the experimental response curves obtained for both phases. The results confirmed previous observations for first-generation packings: axial mixing in the gas increases with both gas and liquid rates, whereas liquid-phase axial mixing is a decreasing function of liquid rate and is insensitive to gas rate up to the flooding point. It was also found that the BX packing produces the least mixing in both phases. The largest mixing effects in the gas phase are found for the Raschig rings, and the largest mixing effects for the liquid phase are found for Flexipac 2. Correlations were developed to reproduce the results, yielding an average ± 22% difference between experimental and correlated data.