A Mathematical Model Studies In The End Effect Zone In Rotating Packed Bed

The end effect zone of packing is the most significant section for mass transfer in rotating packed bed (RPB). The end effect zone which occurs in the part of the packing close to the liquid entry ranges from the inner edge of packing to a few millimeters depths in the radial direction. The liquid breaks up into chunks as it enters the packing due to rapid shear and collision with the packing. The liquid flow pattern is complex in the end effect zone. Part of the liquid is intensely torn and sheared into droplets in the radial direction. The other part of the liquid will adhere to the wire mesh packing under the influence of viscous force and the liquid film forms on the surface of the packing in the circumferential direction. In the way, the liquid droplet continuously turn into liquid film until the liquid is all captured by the packing at the end of the end effect zone. On a macro scale, the liquid is transferred to the circumferential direction from the radial direction. Base on the N-S equation and mass conservation equation, eq(2-18)can be used to describe the length of the end effect zone:The range of the end effect zone is correlated with the rotating speed o, the initial liquid velocity u0, the inner diameter r0and the equivalent diameter de. The end effect zone is in direct proportion to u0and de while it is inversely proportional to a and r0. The model calculation values agree well with the visualization experimental results. A gas-liquid chemisorption process with CO2in NaOH solution is employed to verify the calculation results of the model. According to the change rules of the packing layers’overall gas-phase mass transfer coefficient, we study the range of the end effect zones. Above all, our study shows the end effect zone is a significant section of packing for mass transfer. Reducing the thickness of the packing is able to narrow the volume of RPB to improve the dynamic balance. The model from this work can provide the theory support on the optimal design of the RPB.