Experimental study on natural convection in the vertical enclosure of a double coaxial cylinder

This paper presents results of an experimental study on natural convection in the vertical enclosure of a double coaxial cylinder where the inner wall is at constant heat flux. It is the objective of this experiment to understand the basic characteristics of heat transfer under the condition of natural convection coupled with thermal radiation in a vertical enclosure. The range of Rayleigh numbers based on the width of the double coaxial cylinder is set to be 5.6 × 10 < Ra < 1.04 × 108, the radius ratio is 2.73, the aspect ratio is 3.43 (cylinder length divided by annular gap). The heat transfer coefficient of natural convection coupled with thermal radiation was obtained as function of the Rayleigh number, aspect ratio of the enclosure, and temperature of the hot and cold surfaces. The experimental results show that thermal radiation can’t be neglected in analyzing heat transfer of vertical annulus with natural convection. The results provide the basic data for the design and the performance assessment of the future passive cooling system used in a high-temperature engineering test reactor.