抄録
Natural convection heat transfer from a vertical cylinder in liquid sodium was experimentally studied. Two test cylinders of different dimensions were used. They were 7.62 and 17.51 mm in diameter, and 186 and 257 mm in heated length, respectively. The surface heat flux was ranged from 2×104 to 2×106 W/m2 at the bulk liquid temperatures of 673, 773 and 873 K. The local heat transfer coefficients on the cylinders were obtained systematically at various heights, x, from the leading edge of the heated section. On the other hand, theoretical equations for laminar natural convection heat transfer from a vertical cylinder were numerically solved by using PHOENICS code for the same conditions as the experimental ones considering the temperature dependence of thermo-physical properties concerned. The local Nusselt numbers, Nux, on the vertical cylinders obtained experimentally were compared with the corresponding theoretical values on the Nux versus modified local Rayleigh number, Rf [=Grx*Pr2/(4+9Pr1/2+10Pr)], graph. The experimental values of Nux are almost in agreement with the corresponding theoretical values of Nux with the deviations less than 20 % for the range of Rf tested here. The Nux on the rod diameter of a heat exchanger for a power plant, D=31.8 mm, were numerically analyzed by using this code. A correlation, which can describe the effects of the cylinder diameter and the cylinder height, was given based on the experimental and theoretical values. This correlation can describe the experimental and theoretical values of Nux for Rf ranging from 1.5×102 to 4.7×106 within 20 % difference.
