Packing size effects on the liquid circulation property in an external‐loop packed bubble column

Packing size effects on the fluid dynamics in an external‐loop packed bubble column with Raschig rings of three different effective diameters (4.9, 14.1, and 40.7 mm) in the riser were investigated. The overall gas holdup, liquid circulating velocity and gas–liquid mass transfer coefficient were respectively measured by volume expansion, tracer‐response, and dynamic oxygen‐absorption techniques. CFD simulation with the Euler–Euler two‐fluid method was used to predict the liquid circulating velocity by treating the packing as a porous medium. Compared to the empty column, the gas holdup was found to increase in the presence of packing, however, the liquid circulating velocity and gas–liquid mass transfer coefficient are rather complicated. Specifically, the gas holdup increases with the decrease of packing size, while the liquid circulating velocity is on the contrary, and the maximal gas–liquid mass transfer coefficient is achieved under packing diameter of 14.1 mm.