We experimentally investigated the radiation heat exchange occurring in a gas-solid fluidized bed (kept at 25°C) between the fluidizing particles and a remotely-heated heat transfer surface (30°C). To evaluate this heat exchange, radiation emitted from the fluidizing particles towards the heated surface was measured through a transparent heat transfer surface using an infrared imager. Our experimental results revealed that the fluidizing particles are mainly heated by conduction during the contact period with the surface and/or by gas convection in the thermal boundary layer, and that these heated particles frequently emit a significant amount of radiation energy toward the surface. Based on these results, a method for evaluating the radiation heat exchange between the heat transfer surface and the fluidizing particles is proposed. The proposed method shows that particle diameter is one of the most significant parameters in the radiation heat exchange, and predicts that the radiation heat exchange increases with increasing particle diameter.
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