The analysis and the conceptual design of an experimental apparatus for the determination of pressure drop across heat transfer surfaces in a fluidized bed

An analysis of the pressure drop across a fluidized bed with immersed heat transfer surfaces was performed. The analysis was for an isothermal bed in which no net transport of particles occurs. A momentum equation was written for a control volume of the bed and the effects of the weight and the drag forces of the fluidizing gas on the tubes, and the containing walls were evaluated. The analysis included considerations of the effective viscosity for the fluidized beds.

The conceptual design of an experimental apparatus for the measurement of the pressure drop in a fluidized bed was also completed. The bed is rectangular in shape (2 ft x 1 ft) with two opposite sides of plywood and two sides of plexiglass to permit visual observation. The heat transfer tubes are horizontal and are sealed at the end to avoid ieakage. The distributor plate consists of 288 nozzle buttons made from standard size bolts.

Sample calculations are presented for the total pressure drop using l020 microns (0.040 in.) diameter glass bead particles in the bed with k in. diameter heat transfer tubes using air as the fluidizing gas. Both in-line and staggered tube arrangements are considered. For a typical geometry considered, configuraticn 1 (tubes on 1 in. centers, 17 rows), the total pressure drop was 18.45 ins. of water with the bed weight contributing 99.3 percent and the tube drag and wall drag contributing 0.8 percent and O.0l percent respectively.

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iv The effect of pressure drop on larger heat transfer tube diameters was also evaluated. With lk im. diameter tubes, a typical total pressure drop of 18.43 ins. of water was obtained for configuration 7 (tubes on 2 in. centers, 9 rows). The bed weight contributed 99.5 percent and the tube drag and wall drag contributed 0.5 percent and O.oll percent of the total pressure drop.

This analysis showed that the pressure drop due to the drag on the tubes and walls did not contribute significantly to the total pressure drop with immersed heat transfer surfaces.