HEAT TRANSFER CHARACTERISTICS OF A FINNED HORIZONTAL TUBE IN A FBC

This study is to investigate the chracteristics of heat transfer of a horizontal tube, equipped with radial fins of trianglar profile, immersed in a high-temperature fluidized bed. The heat transfer variations are compared with those of a smooth tube experimentally.
The finned tubes and smooth tube, with outside and inside diameters of 48.6mm and 30.6mm, are made of steel. The depth of the fin is 5mm and the angles of fin are 25 °, 30 °, 35 °, 40 °, 45 ° and 50 °. Experiments are conducted at three different bed temperatures of 720, 800 and 880°C. A granular refractory (silica sand) is used as bed material with mean particle diameters of 0.96mm and 1.37mm.
The maximum heat transfer coefficient is achieved by the rake angle of 25 ° for the particle size 0.96mm of bed material, and by the rake angle of 30 ° for the particle size 1.37mm. These coefficients are about 2 and 1.8 times higher than the case for the smooth tube, respectively. The heat transfer coefficient for the finned tube is greater than that for the smooth tube. Also the rake angle of the finned tube for the maximum heat transfer coefficient changes depending on the particle size of bed material, and the effect of the rake angle becomes more distinct as the bed temperature increases.