Experimental investigation on two-phase countercurrent flow and mass transfer of oxygen and nitrogen on corrugated packing surface

The air separation method based on cryogenic distillation is the primary technique for large-scale production of nitrogen, oxygen, and other industrial gases. Due to the high difficulty and cost associated with cryogenic distillation experiments, the real two-phase flow characteristics of cryogenic fluids on corrugated packings are rarely revealed. With the help of cryogenic visualization experimental technique, for the first time, this study analyzes the impact of countercurrent gas flow on the flow characteristics of liquid film in corrugated packing at low temperatures, examining the mass transfer rates. Result shows that the counterflow gas has almost no effect on the flow pattern of water, and the wettability shows no significant change when F factor increases from 0 to 2 Pa0.5. However, it has a noticeable impact on the flow of nitrogen. As the F factor increases from 0 to 1.32 Pa0.5, the flow boundary of liquid nitrogen gradually shrinks, the wettability decreases, and eventually, droplet splashing occurs. With further increase in the F factor to 1.65 Pa0.5, dry zones and reverse ripples appear at the bottom of the corrugated plate. Meanwhile, due to the influence of the flow characteristics, the mass transfer rate first increases and then decreases as the F factor increases. For spray densities of 10 m3, 20 m3/(, and 30 m3/(m2·h), the maximum mass transfer rates are achieved at F factors of 1.37, 1.70, and 1.71 Pa0.5, respectively. The above results indicate that considering both liquid nitrogen flow stability and mass transfer rate on corrugated packing surface, the optimum F factor can be extended to 1.3 Pa0.5 in the actual distillation process to get a high mass transfer performance, which is larger than the commonly used F factor with range of 0.8–1.0 Pa0.5.