Numerical study on heat and mass transfer characteristics in a randomly packed air cooling tower for large-scale air separation systems

摘要

To investigate the heat and mass transfer characteristics of the moist air-water counter-current flow in a randomly packed air cooling tower (RPACT) for large-scale air separation units, a 3-D Eulerian porous media computational fluid dynamics (CFD) model coupled with mass transfer equations was developed. A plastic Super ring (model 50-RLF1), with the highest porous resistance of the candidate materials, was selected as the optimal packing material for the RPACT. The effects of operating conditions and packing characteristics on the flow and coupled heat-mass transfer performance were analyzed, including pressure drop, liquid holdup, fluid temperature, wall film flow rate, humidity ratio, and the total heat transfer rate of the RPACT. Through model validation, it was found that the 3-D Eulerian porous media model built in this study can accurately predict the RPACT performance and is suitable for the configuration design and optimization. The investigation results show that both the F-factor and liquid load sensitively influence the performance, and there is an optimum range of operating conditions. The total heat transfer rate of the RPACT is 0.84% greater than the rated value designed by an industrial gas equipment producer, even with a packing depth reduced to 6 m from the designed value (8 m).