Mass transfer may be presented as a product of mass transfer rate and interfacial area. In a solid-liquid system, the interfacial area is maximized when all the solid particles are in contact with the fluid. However, how solid particles are actually being entrained at the base of a stirred vessel reactor is not yet fully understood.

The equipment manufacturers typically based their design on empirical correlations with a relatively large safety margin. This does not only increase the capital and energy costs but may cause many operating issues downstream such as particle breakdown. It is believe that the particles are likely to be picked up by a combination of mechanisms pending on the operation conditions. For examples, a particle is likely to be picked up by turbulence at a low viscosity environment whilst particles with a less demanding duty can easily be entrained by flow, which is less energy intensive than turbulence dominated environment.