Question

1. Gas flow through a fixed bed A regenerative heater is a device where “waste" energy from a hot fluid is stored in some type of thermal storage medium before it is transmitted to a cold fluid. In this problem, you will analyze the flow of the cold fluid across a hot packed bed as it picks up the stored energy. This is a fluid flow problem, not a heat transfer problem. A packed bed of cubes (with side =0.6 mm) is used for this type of regenerator. The cubes are poured into a cylindrical column to a depth of 8 m. The porosity of the bed & =0.44. Air flows at a mass velocity of 3000 kg/hr.m² through the bed entering at 27°C and 0.7 MPa, and leaving at 205°C. Notes: • The viscosity of air varies with temperature, and this should be taken into account in evaluating the Reynolds no in the packed bed Rep.b. at the inlet and outlet ends. • The density of air varies with temperature and this should be taken into account in evaluating the superficial velocity at the inlet and outlet. a) Find the superficial air velocity at the inlet, at the outlet, and as the average between the two ends. b) Use the average Reynolds no. to evaluate the friction factor fpt for the packed bed. b) Using the average superficial velocity, and the friction factor from (b), evaluate the pressure drop across the packed bed. c) What would you expect to happen to the pressure drop if the particles were smaller (cubes with a side of 0.3 mm say)? Would it increase or decrease? Explain your rationale.

Answer 1

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