Re-entrainment Mechanisms and Governing Parameters

Below we give a short account of some work that has been done in one of the author s (Hoffmann) own research group (Austrheim, 2005) in the framework of the HiPGaS (High Pressure Gas Separation) project, which sheds some light on the nature of the phenomenon of re-entrainment, and points the way to the formulation of predictive models. 

Re-entrainment from cyclones may take place due to droplet entrainment from the film of separated liquid on the cyclone wall close to the exit from the cyclone, or from some edge at the outlet. We focus on the former, and assume that if re-entrainment takes place from an edge rather than a wall, the parameters governing the process will be the same or similar. 

Different mechanisms of entrainment from a liquid film on a wall dominate in different film flow regimes. In a classic paper, Ishii and Grolmes (1975) summarize four basic mechanisms for entrainment from a liquid film into a gas flowing co-currently above it. The two that are likely to be relevant in demisting cyclones are illustrated in Fig. 13.7.1. 

The flow regime in the film depends on the film Reynolds number  

We have to refer to their paper for the details of the derivation, but their criterion for the onset of entrainment is  

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