HEAT-TRANSFER RATE VARIATIONS FROM THE SURFACE OF A HEATER PROBE IN AMAGNETOFLUIDIZED BED

A cylindrical strip heater heat-transfer probe is designed and employe d to measure heat-transfer coefficients in the horizontal configuratio n at three angular positions (0, 90 and 180 degrees) relative to gas f low 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 ma gnetic-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 depen dent on the angular position at the horizontal cylindrical probe immer sed in the bed. The magnetic held destabilizes the gas pocket at the u pstream 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 prob e surface leading to gas bypassing. At the downstream side, the variat ion is somewhat similar to the variation observed for the total heat-t ransfer coefficient. Experimental minimum bubbling velocities are well corrected by a semitheoretical expression proposed by the authors. (C ) 1997 Elsevier Science Ltd.