Date of Award
Master of Science (MS)
Experimental data were obtained for the average gas convective and overall heat transfer coefficients for a vertical tube immersed in a fluidized bed containing four narrowly distributed particle size mixtures. Silica sand of weight-mean diameters ranging from 0.237 to 1.350 mm was used as the bed material. The static bed height was maintained at about 21 cm. The gas convective heat transfer coefficient was determined by measuring the amount of naphthalene sublimated from a vertical naphthalene tube of 0.0262 m in diameter and using an analogy between heat and mass transfer. The data were obtained at a bed temperature of about 333 K and superficial gas velocities of 0.1 to 1.1 m/s. The overall heat transfer coefficient was measured by placing a vertical heater ( D = 0.0262 m, L = 0.1012 m ) t h in the fluidized bed of average temperature 333 K and having fluidizing velocity of 0.1 to 1.1 m/s. The experimental data were examined using existing correlations. The gas convective heat transfer coefficient calculated using the correlation proposed by Xavier and Davidson (13) predicted the data within 25 percent. The overall heat transfer coefficients were compared with many existing correlations and models. The Martin (Z2) and Xavier and Davidson (13 ) models, and Wender and Cooper (^8) correlation predicted the data within 35 percent. However, for maximum overall heat transfer coefficient all of the four correlations (25^, 3j3, £0, ^1) are found to be reliable within 35 percent.
The gas convective and overall heat transfer coefficients were also obtained for widely distributed particle size mixtures. Two base particle sizes were selected (d = 0.896 and 1.350 mm). Mixtures containing 5, P 10, and 23 percent by weight of fines (0.237 mm) were prepared using 0.896 mm particles, and 10 and 34 percent of 0.545 mm sand were mixed with 1.350 mm particles. The average bed temperature was maintained at 333 K and the fluidizing velocity was varied from 0.45 to 0.95 m/s. The value of gas convective and overall heat transfer coefficients from the data were compared with the existing correlations. The correlations proposed by Xavier and Davidson (JU3) and Baskakov and Suprun (21) were found to predict the data well within 27 percent for the gas convective heat transfer. For the overall heat transfer coefficient, the Xavier and Davidson (^3) and Martin (22 ) model and Wender and Cooper (J3J3) correlation were recommended to predict the data within 32 percent. However, for maximum heat transfer coefficient all of the four correlations (2 5 3_9, 40^, _41) were good within 30 percent.
Finally, using the experimental data for narrowly and widely distributed particle size mixtures, the contribution of the gas convective heat transfer coefficient to the overall heat transfer coefficient was determined. It was observed that this contribution becomes significant at high gas velocities and velocities close to minimum fluidization.
Gupta, Ajay, "Gas Convective and Overall Heat Transfer Coefficient for a Vertical Tube Immersed in a Gas - Solid Fluidized Bed" (1986). Theses and Dissertations. 2753.