A study of heat transfer to tubes in the freeboard region of a fluidized bed was conducted in a column of cross section 0.254 m x 0.432 m and height 3.00 m. The operating variables covered included superficial gas velocity (up to 1.7 m/s), average particle diameter (102, 470, and 890 (mu)m), height of the instrumented tube above the expanded bed surface (up to 0.6 m), horizontal tube spacing, position of tube within the tube bundle, and number of tubes. Silica sand particles were fluidized by air in all experimental runs. An instrumented oil-cooled tube of outer diameter 25.4 mm was used to collect heat transfer data. / Heat transfer coefficients to tubes in the freeboard were found to be significantly influenced by the superficial gas velocity, average particle diameter, and height of the tube above the expanded bed surface. The heat transfer coefficient increased with increasing superficial gas velocity and decreasing distance between the tube and the bed surface due to increased impingement of particles on the tube. The heat transfer coefficient for a tube in the freeboard was found to increase with decreasing particle size as for immersed tubes. The effects of horizontal tube spacing and single tube versus bundle were found to be small, less than 20%, over the range of experimental conditions investigated. / Values of heat transfer coefficients for a tube in the splash zone, in the immediate vicinity of the expanded bed, are nearly as favourable as for immersed tubes. The high rates of heat transfer are associated with impingement of particles on the heat transfer tube. / The experimental results are in qualitative agreement with the few data available in the literature. The present experimental data were correlated in a form suitable for design purposes. The correlation approaches limits at low and high heights above the expanded bed surface. At the bed surface, heat transfer coefficients correspond to in-bed values. Heat transfer coefficients for tubes far removed from the bed surface correspond to dilute phase suspension or to air alone in cross flow, depending on particle size. The correlation fits the data obtained in this work to within (+OR-) 12%. / Entrainment rates for the finest silica sand particles were measured with and without tubes in the freeboard. Under conditions of the present experimental work, entrainment rates were affected very little by the presence of tubes in the freeboard. The entrainment rates were compared with entrainment correlations available in the literature. There were substantial differences between data and almost all of the correlations. Fair agreement was obtained with the Zenz and Weil correlation for saturation carrying capacity. / Hydrodynamics of bed and particles motion around tubes were also investigated visually, photographically and by means of pressure profiles. The information obtained was helpful in explaining the heat transfer results.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.68496 |
| Date | January 1980 |
| Creators | George, Safa Edward |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Chemical Engineering) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 000090105, proquestno: AAINK50446, Theses scanned by UMI/ProQuest. |
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