INT. OCRM. HF2%TMASS TRANSFER 0735-1933/86 $3.00 + .00 Vol. 13, pp. 305-314, 1986 ~_rg=~[onPress Ltd. Printed intheUnitedStates BED-TO-TUBE HEAT EXCHANGE COEFFICIENTS IN A SMALL, FINE-PARTICLED, COLD FLUIDIZED BED Enrico Sciubba Dipartimento di Meccanica e Aeronautica Universit~ dl Roma "La Saplenza" Via Eudossiana, 18 - 00187 Roma, Italy (Ccmmunicated byJ.P. HartnettandW'J. Minkowycz) ABSTRACT The paper describes an experimental study of the bed-to-tube heat tran£ fer coefficient in a laboratory-slze fluidized bed with uniform, homo- geneous, fine, almost spherical particles. The bed size is 0.2 x 0.2 meters, the dense phase is composed of glass "microspheres" wltha mini mum sphericity ~ ffi 0.85 and diameter of 0.5 millimeters; the fluidizing medium is air at about room temperature. The "cold" fluid (a water solution) flows inside of small tubes ar- ranged in several parallel arrays, and the local surface temperatures of the pipes as well as the overall heat exchanged are concurrently mea measured. The results cover a range of bed heights from very shallow (height to bed diameter ratio equal to 0.I) to deep (height to diameter ratio equal to 3), with the ratio superficial veloclty/minlmum fluldlzation velocity ranging from 1 to about 4. The results are compared with soma of the existing correlations, and both the qualitative and the quantitative agreement of predicted and experimental values are discussed in detail. Introduction Fluidized bed combustion is a technology which is entering its "mature" stadium: it is practical and quite successful for burning coal with high sul- phur content, and its use is being considered in refuse-incineration facili- ties: there are several small- and medlum-slze demonstration plants already operative, and executive plans already exist for large plants for coEmercial 305