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

The problem of laminar natural convection from a horizontal cylinder with a n orthotropic porous layer on its outer surface was investigated numericall y. The effect of several combinations of pressure loss coefficients and por ous layer thickness on the normalized average Nusselt number was studied ov er 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 r adial pressure loss coefficient but decreased, nonlinearly, with the value of the tangential pressure loss coefficient. The optimal porous layer thick ness for maximum reduction in the normalized average Nusselt number was inv ersely proportional to the Rayleigh number.