Experimental Study on Convective Heat Transfer of Water Flow in Tubes under Natural Circulation

Abstract

This paper reports on an experimental study on convective heat transfer of single phase water in an upflow heated tube, an upflow cooled tube and a downflow cooled tube under natural circulation conditions. In the experiments the average heat transfer coefficients in the three test tubes were obtained. The experimental data were compared with the predictions by a forced flow correlation available in the literature. The comparisons show that free convection caused by buoyancy in the tubes has great influence on heat transfer under natural circulation condition. By using the Grashof number Gr which can represent the influence of free convection on heat transfer in natural circulation to modify the known correlations for the calculation of heat transfer in forced flow, the empirical correlations for the calculation of convective heat transfer in tubes under natural circulation condition have been developed. The empirical correlations are in good agreement with the experimental data.