Local and average heat transfer coefficients in a fluidized bad heat exchanger Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/37720g76t

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  • Local and average heat transfer coefficients for heat transfer from internal tubes to a fluidized bed were investigated. A fluidized bed heat exchanger was compared to a baffled and an unbaffled exchanger in terms of power and heat transfer surface area requirements. The fluidized bed heat exchanger consisted of a 44 inch long, 5.75 inch inside diameter shell with 19, 3/4 inch diameter tubes arranged in a 1-1/16 inch triangular pitch. Fluidized solids were two narrow sized groups of Scotchlite glass beads having .0057 inch and .0188 inch average diameters. The fluidizing medium was air and there was no tube side fluid. Variables studied included particle size and concentration, superficial gas velocity, and different locations of the heat transfer surface. The local heat transfer coefficients were measured by means of a movable temperature probe in contact with the inner wall of a thin-walled tube through which a constant heat flux was maintained. Values of local coefficients ranging from 2 to 101 Btu/hr. ft².°F and average coefficients ranging from 6 to 35 Btu/hr.ft².°F were obtained. This represents a maximum increase of 50-fold for the local coefficients and 25-fold for the average coefficients over those for air alone. The fluidized bed consisted of areas of dense and sparse solids concentration. In the dense section of the bed, the local coefficients were essentially constant and higher values of the coefficients were obtained at lower flow rates. The opposite was true in the sparse section of the bed and variation of heat transfer coefficient with flow rate was similar to that for single phase fluids. Heat transfer surface location did not affect the average coefficients appreciably, however the local coefficients were affected slightly, the center tube having somewhat lower coefficients. The average heat transfer coefficients were found to increase as a power function of the solids concentration. The ratio of the heat transfer capacity of the fluidized bed exchanger to that of the unbaffled and baffled exchangers was considerably greater than unity, indicating its advantage as far as space requirements are concerned. An overall advantage of reduced heat requirement for the fluidized bed exchanger was found in the region of static bed heights transfer area and power over the baffled exchanger below five inches.
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  • description.provenance : Approved for entry into archive by Katy Davis(kdscannerosu@gmail.com) on 2014-05-30T15:51:33Z (GMT) No. of bitstreams: 1 NoeAlphonse1964.pdf: 3390154 bytes, checksum: 8d55d71170b9ab0768eb2f49d2233b74 (MD5)
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