Cross-flow heat transfer in the freeboard region of a fluidized bed

This paper describes an experimental investigation of heat transfer in two tube banks, one in-line and one staggered, located in the freeboard region of a gas fluidized bed. The objectives of this study are twofold. Firstly, examination of the local heat transfer results is used to identify the dominant heat transfer mechanisms. Secondly, the overall heat transfer performance of the two tube configurations is of relevance for the design, selection and siting of heat exchangers for fluidized bed combustors. The experimental results show that the dominant influence on heat transfer is the local concentration of particles, with the impact over the rear of tubes by particles disengaging from the flow having a significant effect on wake heat transfer. The latter mechanism is less important for tubes in the first and second rows of the in-line array, due to the shielding effect of the surrounding tubes. This difference in wake heat transfer contributes to higher mean Nusselt numbers, on average,for the tubes located in the staggered array.