Particle phase boundary layer theory in vertical two-phase gas–solid flow

To gain understanding of the two-phase vertical gas–solid flow behaviour, the equations of gas–solid suspension flow are used to develop a model to predict the radial profiles of the volumetric fraction and the velocity of the solid particles. We derived two coupled differential equations for the volume fraction of the particles and the fluctuations of the particle velocity. These could be solved approximately, assuming the existence of a lean phase in the centre (the core) and a dense particle phase near the wall (the annulus). In this boundary layer theory, the method of matched asymptotic expansions could be employed. As a result, the obtained expressions have a generic character and the observed qualitative trends are insensitive with respect to the detailed modelling of the particle–turbulence and particle–particle interactions.