Experimental Investigation of Heat Transfer From Elliptic Tube Immersed in a Fluidized Bed

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 outer diameter (OD) and 200 mm length. The heated tube had a total surface area of As ≈ 0.015 m2 and a length of 200 mm. The local as well as average heat transfer coefficients were calculated at different superficial air velocities, particle sizes of 2, 4, and 6 mm, and a 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 deg, and top, θ = 180 deg, of the tube. The local and average Nusselt numbers increase with the increase of the fluidization velocity and decrease in particle diameter. A correlation equation for the average Nusselt number with the fluidization number and tube to particle diameter ratio is deduced.