Axial mixing in modern packings, gas and liquid phases: I. Single-phase flow

An experimental study was conducted in a 0.43-m-ID packed column to determi ne the axial mixing properties of air and water under single-phase flow con ditions. The packings used were 25.4-m ceramic Raschig rings, one modern ra ndom packing, 25.4-mm metal Pall rings; two structured packings, Sulzer BX and Flexipac 2. The column was operated at ambient conditions with flow rat es varying from 0.4 to 4 kg/m(2) . s for the gas and from 3.25 to 8.5 kg/m( 2) . s for the liquid. Axial mixing was experimentally determined via dynam ic response studies based on the pulse injection technique. The diffusion-t ype model served to reproduce the experimental response curves satisfactori ly and proved to be a suitable means of describing axial mixing in both pha ses. The results confirm previous observations for first-generation packing s. Axial mixing is much greater in the liquid than in the gas; axial mixing in the gas increases with gas rate, whereas axial mixing in the liquid dec reases with liquid rate. It was also found that the two structured packings produce the lowest levels of axial mixing in the gas. Surprisingly, the gr eatest mixing effects in the liquid were obtained for Flexipac 2 structured packing. correlations were developed to represent the experimental mixing and liquid holdup data, yielding an average +/- 16% difference between expe rimental and correlated data. Mixing measurements in gas or liquid under tw o-phase flow conditions will be discussed in Part II.