HEAT-TRANSFER AND FLUID-DYNAMICS OF HIGH HEAT-FLUX FUEL-ROD FOR VHTR HEAT-TRANSFER AUGMENTATION BY SQUARE RIBBED SURFACE

Experimental studies on the heat transfer and fluid dynamics of a high heat flux fuel rod for a very high temperature reactor (VHTR) were performed using a single channel test rig of a fuel stack test section (T1-s) installed in a helium engineering demonstration loop (HENDEL). The fuel rod has been developed in order to enhance the turbulent heat transfer coefficient than that of the standard fuel rod obtained by the previous experiment. Two-dimensional square ribs were settled on the outer surface of the fuel rod axially to improve the heat transfer. The configuration of a square rib is 0.5 mm in width(w), 0.5 mm in height(h) and 5 mm in pitch(p): p/h = 10. The experiment were carried out under the helium gas conditions of high temperature and pressure simulated the VHTR operation. For the turbulent region of Reynolds number 2,500 approximately 8,000 of the VHTR core flow condition, it was found that the heat transfer coefficient of the fuel rod and the friction factor of the fuel channel became about 120 approximately 140% and 200 approximately 250% higher than those of the standard fuel rod for the turbulent region, respectively. The studies also derived the heat transfer correlation of the fuel rod and clarified the effect on square ribs contribution as the turbulence promoter to the heat transfer augmentation.