Study on the Heat Transfer Characteristics of Particle Cluster in Circulating Fluidized Bed

As a kind of newly high efficiency and low pollution combustion technology, the circulating-fluidized-bed combustion technology takes great advantages to others in fields of environmental protection and burning inferior fuels. In some local place with high concentration of particles in circulating fluidized bed, particle’s clusters are formed. The heat transfer characteristics of clusters are different from isolated single particles. To do research with the heat transfer characteristics of particle clusters is important.The convection heat transfer characteristics of gas (air\smog) and isolated particles cluster were numerically studied in the stream. It is found that the total surface heat transfer coefficient of cluster has a linear growth with the increase of gas velocity and cluster’s temperature, and it has an accelerate growth with the increase of porosity; it decrease with the increase of particles number in one cluster. The heat transfer capacity of cluster-to-smog is better than cluster-to-air. In the same conditions, the single isolated particle’s heat transfer capacity is better than any single particle in cluster.The combined heat transfer (convection and radiation) characteristics of smog and particle cluster were numerically studied in the stream, it is found that the radiation parameters of the smog affects a lot, the calculation volume is important when simulating the radiation heat transfer between particle’s cluster and gas. The radiation heat transfer characteristics of particle cluster are affected by some factors as following: The total surface radiation heat transfer coefficient increase with the increase of velocity of the smog and the growth of cluster’s porosity, but the increase speed slow down. And the Total surface radiation heat transfer coefficient has an accelerate increase with the growth of smog temperature, and it decrease as the particle number increase in one cluster, it has an approximate linear growth with the increase of particle’s emission rate. The total surface radiation heat transfer coefficient increase as the smog’s absorption coefficient increases.