Effectiveness factors for heat transfer in fluidized beds

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Abstract
Rates of heat transfer associated with the evaporation of water from the surface of porous particles into air were measured for both packed and fluidized beds. Direct measurements of the temperature on the surface of these particles permitted the calculation of the heat transfer coefficient, hg, for both packed and fluidized bed systems. An effectiveness factor, χ, has been introduced to account for the non‐plug flow characteristics of fluidized beds. This quantity has been used to define the rate of particle to gas heat transfer as follows where (δt)m represents the log‐mean temperature difference across the bed and hg b is the heat transfer coefficient at the initiation of two phase fluidization defined as the “bubble point”. An analysis of the experimental measurements indicates that where g represents the ratio of the heat transfer factor of the fluidized bed to that corresponding at the bubble point of this bed. This effectiveness factor has also been related to the void fraction ratio as follows where ϵt, and ϵp, are the void fractions of the fluidized bed and its corresponding packed bed arrangement. This equation applies for ϵt/ϵp > 1.22.

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