Particles convective heat transfer

The scale models must be carefully designed. Failure to match the important dimensionless parameters will lead to erroneous simulation results. Modeling can be extended to particle convective heat transfer. Wear or erosion of in-bed surfaces can be qualitatively studied, although quantitative assessment requires the identification and simulation of additional wear-related parameters. 

In general, gas-to-particle or particle-to-gas heat transfer is not limiting in fluidized beds (Botterill, 1986). Therefore, bed-to-surface heat transfer coefficients are generally limiting, and are of most interest. The overall heat transfer coefficient (h) can be viewed as the sum of the particle convective heat transfer coefficient (h ), the gas convective heat transfer coefficient (h ), and the radiant heat transfer coefficient (hr). 

Overall bed-to-surface heat transfer coefficient = Gas convective heat transfer coefficient = Particle convective heat transfer coefficient = Radiant heat transfer coefficient = Jet penetration length = Width of cyclone inlet = Number of spirals in cyclone = Elasticity modulus for a fluidized bed = Elasticity modulus at minimum bubbling = Richardson-Zaki exponent... 

Han, G. Y., Experimental Study of Radiative and Particle Convective Heat Transfer in Fast Fluidized Beds, Ph.D. Dissertation, Lehigh University (1992)... 

C c Specific heat of particles Interparticle clearance hp Particle convective heat transfer coefficient... 

In circulating fluidized beds, the clusters move randomly. Some clusters are swept from the surface, while others stay on the surface. Thus, the heat transfer between the surface and clusters occurs via unsteady heat conduction with a variable contact time. This part of heat transfer due to cluster movement represents the main part of particle convective heat transfer. Heat transfer is also due to gas flow which covers the surface (or a part of surface). This part of heat transfer corresponds to the gas convective component. 

Derive the axial profile of the particle convective heat transfer coefficient in a circulating fluidized bed of fine particles using the information given in 10.4.1. It can be assumed in the derivation that particles in the bed are all in a cluster form. 

The particle convective heat transfer component is usually treated on the basis of the penetration or packet theory originally proposed by Mickley and Fairbanks (1955) assuming that the clusters are formed next to the immersed surface (e.g., Subbarao and Basu, 1986 Basu and Nag, 1987 Zhang et ai, 1987 Liu et ai, 1990). In that case, the clusters of solids and voids or dispersed phase are assumed to come into contact with the heat transfer surface alternatively, and the heat transfer coefficient can be given as follows ... 

Sastry, S.K., Shen, G.Q., and Blaisdell, J.L. 1989. Effect of ultrasonic vibration on fluid-to-particle convective heat transfer coefficients. Journal of Food Science 54(1) 229-230. 

In most dense gas-solid fluidization systems, particle circulation (e.g., induced by the bubbles) is the primary cause of particle convective heat transfer. The heat transfer rate is high when there is an extensive solids exchange between the in-bed region and the region near the heat transfer surface. In light of the relative importance of the particle convective component, more discussion is focused on particle convective heat transfer in the following sections in the context of the heat transfer models and corresponding correlations. 

Explain what is meant by particle convective heat transfer in a fluidized bed. In which Geldart group is particle convective heat transfer dominant ... 

The particle convective heat transfer coefficient may then be found from the physical properties of the... 

Han GY. Experimental study of radiative and particle convective heat transfer in fast fluidized beds. PhD dissertation, Dept, of Chem. Eng., Lehigh University, Bethlehem, PA, 1992. 

Gas-convective increases for small particles decreases for coarse particles No influence on particle-convective heat transfer Gas-convective heat transfer increases... 

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