Comparative experiments on the flow morphology of liquid nitrogen and water in perforated structured packing

Abstract

Cryogenic distillation is the primary method for air separation, with corrugated plate packing as the main packing for heat and mass transfer between nitrogen and oxygen. The perforated structure on the corrugated plate packing can directly change the liquid distribution characteristics, thereby affecting the packing’s flow and mass transfer performance. Currently, the effect of perforated structure is mainly revealed by room temperature fluids such as water and air, while on the practical cryogenic fluids such as liquid nitrogen, it is seldom studied. In this study, the effects of perforation size ranging from 2 to 8 mm on the flow of water and liquid nitrogen on the perforated plates were investigated and compared by a high-speed camera. It was observed that water could hardly flow through the perforations, it completely covers the perforations, forming a continuous liquid film on the surface of the perforations. The expected role of perforations in redistributing water on the back side of the corrugated plate is relatively minor. While for liquid nitrogen, the presence of the perforated structure helps fluid redistribution on the back side of the plate, as it can easily flow through the perforations with diameters between 2 mm and 8 mm. It is found that when the perforation diameter exceeds 6 mm, liquid nitrogen will form suspended liquid droplets within the holes, which could be a risk of premature flooding. Under similar conditions, the wetting rate of liquid nitrogen reaches 86.90 % −99.48 %, higher than that of water which is about 10.26 % −78.82 %. The results show that perforations have quite different effects on the flow characters of water and liquid nitrogen due to their disparate physic properties.