Heat-transfer rate variations from the surface of a heater probe in a magnetofluidized bed

A cylindrical strip heater heat-transfer probe is designed and employed to measure heat-transfer coefficients in the horizontal configuration at three angular positions (0, 90 and 180 degrees) relative to gas flow while submerged in a magnetically stabilized fluidized bed of 1086 mu m iron shots. The superficial air velocity is varied up to about 3.8 m s(-1), and measurements have been conducted for five values of magnetic-field intensity up to 5662 A m(-1). In each case,pressure drops across the bed and a section of it are determined to obtain values of superficial minimum fluidization and minimum bubbling velocities, and gross bed voidage. The heat-transfer coefficient is found to be dependent on the angular position at the horizontal cylindrical probe immersed in the bed. The magnetic field destabilizes the gas pocket at the upstream side of the probe and this characteristically influences the h(w) values. The magnetic interparticle forces augment the gas flow in the equatorial lateral zones by the formation of a channel at the probe surface leading to gas bypassing. At the downstream side, the variation is somewhat similar to the variation observed for the total heat-transfer coefficient. Experimental minimum bubbling velocities are well corrected by a semitheoretical expression proposed by the authors. (C) 1997 Elsevier Science Ltd.