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

Abstract

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.