Experiment 6 - 6 FLUIDIZATION Pressure drop and heat...

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45 6. FLUIDIZATION: Pressure drop and heat transfer in a Fluidized-Bed System When a gas (or liquid) is passed upward through a bed of solid particles, and the fluid velocity is steadily increased, the particles eventually start to move and become suspended in the fluid. The term fluidization and fluidized-bed are used to describe the condition of fully suspended particles, since the suspension behaves as a dense fluid [1]. Due to the vigorous mixing and large contact area between gas and particles, a fully fluidized-bed has little temperature variation (bulk of the bed is practically at a uniform temperature), and gas usually has a temperature close to that of the bed. In addition, circulation of particles in the bed which is caused by rising bubbles results in large heat-transfer rates between the bed and immersed or containing heat transfer surfaces. Fluidized beds are used in a number of processes both catalytic (hydrocarbon cracking and re-forming) and non-catalytic (roasting of sulfide ores, coking of petroleum residues, incineration of sewage sludge and drying). Article by Botterill, available in the lab provides a brief review of gas-fluidized-bed systems and the relevant theory, please read the article before starting the experiment. The objectives of the present experiment are as follows: 1)- To investigate the relationship between bed pressure drop and air superficial velocity (upward air velocity) through a bed of granular material and to determine the minimum fluidization velocity. 2)- To investigate the effects of air superficial velocity, particle size of the solid material and depth of immersion on the surface heat transfer coefficient for a hot surface in an air fluidized- bed Apparatus Figure 3 shows a schematic diagram of fluidization and fluidized-bed heat transfer unit used in this experiment. A bed of a granular material (about 70 mm deep) is placed in a vertical glass column. A distribution chamber and an air distributor have been devised at the lower end of the column to ensure uniform air flow into the bed without causing excessive pressure drop. The air passes through the bed and leaves the system from the top after passing through a filter. The
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