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Concentration of solid particles of ash and inert material present in the combustion chamber of a circulating fluidised-bed boiler is very high, giving rise to some disadvantages. At the same time, the required temperature level in the combustion chamber is guaranteed by circulation of solid particles. In this work numerical simulation of gas-solid particle flow has been performed in the frame of a two-fluid model, namely the Eulerian approach for the dispersed phase, for conditions of the circulating fluidised bed, ranging from moderate to high mass ratios of the flow. An incorporated original model of closure of transport equations of the dispersed phase permitted to account the interparticle collisions which might be indispensable to proper numerical simulation of the process in the circulating fluidised bed under discussion. The results of this work would help to improve the processes occurring in the combustion chamber of the circulating fluidised-bed boiler.
The deposition of aluminium oxide 12 and 23 μm particles onto a horizontal flat plate within the laminar boundary layer in the free‐stream moderate turbulent flow was studied. The present numerical model considered the deposition onto the surface to be a probabilistic process determined both by hydrodynamics and the adhesive behaviour of particles and surface. Numerical simulation was realised for the flat‐plate laminar boundary layer. The two‐fluid approach was used for writing the Euler equations for a carrier gas and particulate phase. The effects of gravity and lift forces on the particles velocities and mass concentration, occurring within the boundary layer, and deposition were studied separately for various particle sizes. It was revealed that gravity and lift forces have decisive influence on the behaviour of solid particles taken place within the laminar boundary layer and on their deposition that is expressed via the distributions of the particles transverse velocity and mass concentration. These effects become more pronounced for the larger 23 μm particles. This fact, coupled with the higher probability of entrainment by the surface, results in their larger deposition velocity. The given study is the attempt to combine the hydrodynamic and adhesive aspects of the particles deposition for its more accurate estimate that is suitable for various practical devices.
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