Three-phase CSTR model, with solid catalyst sites. (from Wu, McCready and Varma, 1995).
The application of their research is to cocurrent gas-liquid, packed bed ("trickle bed") reactors. These reactors exhibit a range of different flow regimes. A flow regime is the term for the static location and dynamic behavior of the individual phases. An important regime for these reactors is the "pulse" flow regime where strong disturbances travel through the bed. These have a well-defined frequency and they cause strong increases in the mass transfer as they flow past a certain point. Thus incorporation of a fluctuating mass transfer coefficient in the reaction model should help to describe the behavior seen in these reactors.