2-DIMENSIONAL IMPINGING JET COOLING OF HIGH HEAT-FLUX SURFACES IN MAGNETIC CONFINEMENT FUSION-REACTORS

The divertor surface of a magnetic confinement fusion reactor is expos ed to strong radiation heating by high flux charged particles. Accordi ng to the standard design for the ITER, the heat flux on the divertor surface averages 15 MW m(-2) or more. In this study, cooling by a two- dimensional impinging jet flow is proposed to cool this surface. For a n impinging jet flow on a flat heated surface, a high critical heat fl ux (CHF) is obtained only in the limited surface region where the jet flow hits directly. Outside this region, the CHF decreases abruptly wi th distance from the center. The main reason is that the pressure decr eases abruptly away from the center region and the liquid flow is spre ad away from the heated surface region by the strong boiling. To overc ome these difficulties, we propose that the impinging jet is applied t o a heat transfer wall with a concave surface. In this study, the CHFs and the nucleate boiling curves for two-dimensional impinging jet coo ling were first obtained as a function of the distance from the center using a thin copper foil heater designed on the plastic sheet. Experi ments were done under various conditions of liquid subcooling, flow ve locity and surface curvature. Empirical correlations for the CHF inclu ding these parameters were obtained. It is clear that impinging jet co oling of the curved surface is useful to keep the CHF in the downstrea m region high. Finally, application of the two-dimensional jet to the cooling of a fusion divertor surface is assessed. When the jet velocit y is equal to 14.6 m s(-1), and the liquid subcooling is 80 K, a two-d imensional jet is able to cool a curved surface area 50 mm wide with a n average heat flux of 30 MW m(-2).