Abstract

Heat transfer characteristics around an elliptic heated tube immersed in fluidized bed were studied experimentally. Experiments were carried out under uniform heat flux condition, with air as a fluidizing gas and pulverized coal as a bed material of Geldart D. An elliptic tube was heated by using a cartridge heater of 16 mm OD and 200 mm length. The heated tube had a total surface area of As ≈ 0.015 m2, and length of 200 mm. The local as well as average heat transfer coefficients were calculated at different superficial air velocities, particles sizes of 2, 4 and 6 mm, and static bed height of 250 mm. Various values of fluidization number, Usup/Umf, based on hydraulic diameter of the heated tube are utilized in the experiments which are ranged from 1 to 1.4.

The results showed that, the minimum fluidization velocity increased with the increase in bed particles diameter. The local Nusselt number was quasi-uniform and having a maximum value at the sides of the heated tube and minimum at the stagnation, ϑ=0°, and top, ϑ=180°, of the tube. The local and average Nusselt numbers increase with the increase of the fluidization velocity and decrease in particles diameter.

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