%0 Journal Article %A Klimenta, Dardan %D 2017 %I Begell House %K empirical correlation, evacuated tube collector, fundamental dimensionless number, inclination angle, natural convection %N 1 %P 23-34 %R 10.1615/HeatTransRes.2016008323 %T MODELING THE INFLUENCE OF INCLINATION ANGLE ON NATURAL CONVECTION AROUND AN EVACUATED TUBE SOLAR COLLECTOR %U https://www.dl.begellhouse.com/journals/46784ef93dddff27,293227985b205145,269e47ed7d3ac3e4.html %V 48 %X The main purpose of this paper is to propose a procedure for modeling heat transfer by natural convection for both laminar and turbulent flows around an evacuated tube collector at inclination angles of 0−90°. Using the experimental results obtained by Heo and Chung (2012) for different cylinders and inclinations, the heat transfer correlations based on the fundamental dimensionless number for natural convection have been derived. Their experiments included measurements for solid circular cylinders having diameters of 0.01, 0.034, and 0.067 m, and lengths of 0.1, 0.25, and 0.45 m, as well as for a Prandtl number of 2094 in either laminar or turbulent conditions. Introducing the correlations based on the fundamental dimensionless number for natural convection, the studies performed on inclined cylinders were generalized for the whole range of Prandtl numbers. A modified Nusselt number, which represents the mean of the heat transfer correlations based on the cylinder diameter and on the cylinder length, was introduced and applied to estimate the heat transfer coefficients for natural convection on the outer surface of an evacuated tube collector surrounded by air. The results obtained by applying the proposed correlations were also compared to the results obtained using existing ones for various Prandtl numbers. %8 2016-11-10