Natural convection heat transfer from a cylinder covered with an orthotropic porous layer

The problem of laminar natural convection from a horizontal cylinder with an orthotropic porous layer on its outer surface was investigated numerically. The effect of several combinations of pressure loss coefficients and porous layer thickness on the normalized average Nusselt number was studied over a wide range of Rayleigh numbers. The results showed that the change in the normalized average Nusselt number was insensitive to the value of the radial pressure loss coefficient but decreased, nonlinearly, with the value of the tangential pressure loss coefficient. The optimal porous layer thickness for maximum reduction in the normalized average Nusselt number was inversely proportional to the Rayleigh number.