3D numerical study of natural convection heat transfer from a hollow horizontal cylinder placed on the ground

Abstract

In the present work, natural convection heat transfer from a thick hollow horizontal cylinder placed on ground is studied numerically. 3D numerical simulations have been performed by varying the Rayleigh number (Ra) from 104 to 108 (preferably within laminar regime). All the simulations have been carried out by varying length to outer diameter ratio (L/D) and thickness ratio (d/D) in the range of 0.2–20 and 0.4–0.9 respectively. Nusselt number, heat transfer rate and contribution to total heat transfer rate from different surfaces have been calculated and their variation with the above parameter is represented graphically. Similarly, thermal plume and velocity vector are shown pictorially at different sections of the cylinder and physical phenomenon of fluid flow and heat transfer could be described from such pictures. Later on effect of above parameters on cooling time is also discussed. It has been observed that with increase in thickness, Nu decreases at low L/D (L/D ≤ 2), whereas at higher L/D a reverse trend is observed. Heat transfer rate from the inner surface increases initially with increase in L/D and after a particular L/D, it attains constant value whereas for outer surface, it increases continuously. It has been also observed that at a particular L/D and d/D, contribution of heat transfer rate from inner surface increases with Ra, whereas reverse trend is observed for outer and side flat surface. A correlation for Nusselt number as a function of Rayleigh number, L/D and d/D has been developed which may be useful for industrial purposes.