The term cluster or streamer is commonly applied to a collection of particles held together by hydrodynamic forces. Inside a circulating fluidized bed a single cluster has a significant effect on the gas that flows around it. Recent experiments have suggested that large scale gas fluctuations occur as the air flows around the cluster body. This paper examines the effect a single cluster has on the surrounding gas flow. Experimental work focuses on a small riser with the ability to release a single cluster. A specially designed probe measures the gas velocity as the cluster travels by. Numerical work simulates the effect of airflow around a porous body. The fluctuation levels observed are comparable to the experiments. Both results show that large scale velocity fluctuations occur in the gas in the vicinity of a cluster. This has a large impact on gas and particle modeling and mixing inside a circulating fluidized bed.
In this study, the mass transfer of three-dimensional nonreactive gas-solid fluidized bed was investigated computationally. The influence of the inlet gas velocity and temperature on mass transfer of air to wet particles was analyzed. The simulation results indicated that the mass transfer coefficients of air to spherical sand particles was decreased from 2.12 to 1.66 m/s with increment of temperature from 300 to 360 K. Sherwood numbers of gas to cluster increased with the increase of inlet air velocity. CFD model of the gas-particle heat transfer have been implemented, the result showed that the heat flux of gas to particles increased with the increase of Reynolds number. Distributions of water vapor concentration and velocity in this bed were numerically predicted and the computed Sherwood and Nusselt numbers were compared with the estimated values from empirical equations.
We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero.