Experimental investigation on flow and heat transfer characteristics of high temperature helium-xenon mixture in monoblock fuel element

Helium-xenon (He-Xe) mixtures demonstrate exceptional potential as heat transfer media in nuclear micro-reactor systems due to their superior heat transfer properties and compressibility. This study investigates the thermal-hydraulic behavior of a 19.26 g/mol He-Xe mixture through a dedicated high-temperature experimental loop designed for solid-core portable microreactor applications. Systematic experiments were performed under controlled conditions, with Reynolds numbers ranging from 5632 to 10,312, inlet temperatures from 417 K to 704 K, wall temperatures from 482 K to 1003 K, and heat flux densities from 4443 W/m² to 21,027 W/m². The results indicate that the friction pressure drop is highly sensitive to variations in inlet temperature and heat flux, primarily due to the high aspect ratio channel of the monoblock structure. Notably, thermal flux enhancement (compared to inlet temperature adjustment) more effectively enhances convective heat transfer coefficients when maintaining equivalent average fluid temperature rise, attributed to intensified flow acceleration from elevated heat fluxes. The research establishes empirical correlations for Darcy friction factors along with total and local Nusselt numbers specific to the He-Xe mixture. Validation of these correlations reveals average deviations of 2.7 %, 3.4 %, and 16.8 %, respectively, demonstrating superior accuracy compared to existing predictive models. Moreover, the newly derived local Nusselt number correlation, unlike existing ones, exhibits wall temperature independence, thereby extending its application range.