Heat Transfer Performance of an Air-Cooled Tube in a Fluidized-Bed Furnace

摘要

Heat transfer tests were conducted with an air-cooled tube in a coal-fueled fluidized-bed furnace. A 12-mm-OD (0.5-in.) tube was used, and the tests were run in a 0.5 x 0.5 m (18 x 18 in.) furnace operating at atmospheric pressure and 900 exp 0 C (1650 exp 0 F). Results were obtained for an air flow inside the tube of 10 kg/hr (23 lb/hr) and a mean bed particle size of 460 mu m at fluidizing velocities of 0.2 to 0.7 msec (0.8 to 2.2 fps). The heat transfer coefficient from the bed to the tube wall increases from approx. 227 W/m exp 2 - exp 0 C (40 Btu/hr-ft exp 2 - exp 0 F) at a fluidizing velocity of 0.23 m/sec (0.76 fps) to a value of approx. 483 W/m exp 2 - exp 0 C (85 Btu/hr-ft exp 2 - exp 0 F) at a velocity of 0.5 m/sec (1.6 fps). At higher velocities, the heat transfer coefficient is constant at the higher value. The following conclusions have been reached on the basis of these results: (1) the value of the heat transfer coefficient assumed for the design of the ORNL furnace was considerably lower than those found in the tests, and, therefore, the design is conservative; thus the bed can operate at a lower temperature than the original design temperature; (2) the correlation in the literature for predicting the heat transfer parameter, Nu/Ar exp 0 . exp 22 , yields a value approx. 25% lower than was observed in testing. (ERA citation 04:024315)