A numerical-experimental analysis of qualification assessment for mono-block plasma-facing component with flat heat sink

The heat removal capacity of a flat heat sink was studied using subcooled flow boiling experiments, to address the thermal peaking problem. Based on the Bowring criteria, the boiling curve is divided into a partially developed nucleate boiling regime (PDB) and fully developed nucleate boiling regime (FDB), and the existing heat transfer correlations for each flow regime are evaluated. In the PDB regime, the Baburajan correlation exhibited the highest prediction rate with an average error rate of 10.92%; however, the FDB regime heat transfer correlations exhibited high error rates at very high heat flux conditions. Therefore, the authors developed a new FDB correlation using the artificial intelligence technique by correlating the bubble agitation effect, which is a mechanism of the FDB regime, and then, evaluated the qualification assessment on this basis. The mono-block plasma-facing component with a flat heat sink was found to meet all criteria (except #1.2, shutdown plasma ratcheting), and to succeed in the actual fabrication.

Nusselt number correlation for turbulent heat transfer of helium–xenon gas mixtures

A gas-cooled nuclear reactor combined with a Brayton cycle shows promise as a technology for high-power space nuclear power systems. Generally, a helium–xenon gas mixture with a molecular weight of 14.5–40.0 g/mol is adopted as the working fluid to reduce the mass and volume of the turbomachinery. The Prandtl number for helium–xenon mixtures with this recommended mixing ratio may be as low as 0.2. As the convective heat transfer is closely related to the Prandtl number, different heat transfer correlations are often needed for fluids with various Prandtl numbers. Previous studies have established heat transfer correlations for fluids with medium–high Prandtl numbers (such as air and water) and extremely low-Prandtl fluids (such as liquid metals); however, these correlations cannot be directly recommended for such helium–xenon mixtures without verification. This study initially assessed the applicability of existing Nusselt number correlations, finding that the selected correlations are unsuitable for helium–xenon mixtures. To establish a more general heat transfer correlation, a theoretical derivation was conducted using the turbulent boundary layer theory. Numerical simulations of turbulent heat transfer for helium–xenon mixtures were carried out using Ansys Fluent. Based on simulated results, the parameters in the derived heat transfer correlation are determined. It is found that calculations using the new correlation were in good agreement with the experimental data, verifying its applicability to the turbulent heat transfer for helium–xenon mixtures. The effect of variable gas properties on turbulent heat transfer was also analyzed, and a modified heat transfer correlation with the temperature ratio was established. Based on the working conditions adopted in this study, the numerical error of the property-variable heat transfer correlation was almost within 10%.