Verification of Thermal Performance Predictions of Prototypical Multi-jet Impingement Helium-cooled Divertor Module

An experimental investigation of the thermal performance of the He-Cooled Multi-Jet (HEMJ) modular divertor design developed by the Karlsruhe Research Center (FZK) was previously performed at Georgia Tech using air at Reynolds numbers (Re) spanning those at which the actual He-cooled divertor is to be operated. The electrically heated test section was constructed from a brass alloy with nearly the same thermal conductivity as the tungsten alloy from which the prototypical HEMJ is to be constructed. More recently, another experimental investigation was performed by the Georgia Tech group for a similar finger-type divertor module using both air and He as coolants. The results of these experiments suggest that, in addition to matching Re, dynamic similarity between the air and He experiments requires that a correction be made to account for the differences in the relative contributions of convection and conduction (through the divertor walls) to the overall heat removal rate by the module. This correction factor depends on the thermal conductivity ratio of the solid to the coolant. This investigation is aimed at quantifying the correction factor necessary to achieve dynamic similarity for the HEMJ to account for changes in the coolant and solid thermal conductivities. Experiments have been conducted using two (one each brass and steel) HEMJ test modules cooled with air, Ar, or He. The test modules were directly heated using an oxy-acetylene torch achieving heat fluxes up to 3 MW/m. The results of these experiments, together with data obtained using the aforementioned air-cooled experiments at lower heat fluxes (<1 MW/m) were used to develop a generalized correlation for the Nusselt number which accounts for changes in Re, as well as the solid to coolant thermal conductivity ratio. The correlation can be used to predict the performance of the actual He-cooled divertor at prototypical operating conditions.