Conjugate heat transfer due to conduction, natural convection, and radiation from a vertical hollow cylinder with finite thickness

A comprehensive numerical study is performed on a vertical hollow cylinder of finite thickness for natural convection with surface radiation effect. The prime aim is to find out the heat transfer rate due to both natural convection and radiation from both the inner and outer walls of the tube. Also, an attempt is made to estimate the cooling time, the time required to bring down the cylinder temperature from a prescribed temperature to atmospheric temperature. Numerical solution of Navier-Stokes equation, energy equation, and radiation equation is solved, taking the finite volume approach of ANSYS-Fluent 18 around a vertical tube for determining flow and heat transfer characteristics around it. Different relevant parameters are chosen for the numerical analysis, such as Rayleigh number (from 5.7 x 10(3) to 5.7 x 10(7)), inner surface temperature (from 350 K to 550 K), and aspect ratio (L/D) of the tube (from 0.5 to 20). To catch the effect of surface radiation, emissivity (from 0 to 1) is also varied. A comparison is made for natural convection and fluid flow characteristics with and without surface radiation effect.