Applicability of RANS models and pressure drop in edge subchannels for 19-pin wire-wrapped fuel bundle channel in CiADS.

The accelerator-driven subcritical system has a strong transmutation ability and high inherent safety, and it is internationally recognized as the most promising long-life nuclear waste disposal device. This study involves the construction of a Visual Hydraulic ExperimentaL Platform (VHELP) for the purpose of evaluating the applicability of Reynolds-averaged Navier-Stokes (RANS) models and analyzing the pressure distribution within the fuel bundle channel of China initiative accelerator-driven system (CiADS). Measurements of thirty differential pressures in edge subchannels within a 19-pin wire-wrapped fuel bundle channel were obtained under different conditions using deionized water. The pressure distribution in the fuel bundle channel at Reynolds numbers of 5000, 7500, 10,000, 12,500, and 15,000 was simulated using Fluent. The results show that RANS models obtained accurate results, and the shear stress transport k-ω model provided the most accurate prediction of the pressure distribution. The difference between the results of the Shear stress transport (SST) k-ω model and experimental data was the smallest, and the maximum difference was ±5.57%. Moreover, the error between the experimental data and numerical results of the axial differential pressure was smaller than that of the transverse differential pressure. The pressure periodicity in axial and transverse directions (one pitch) and a relatively three-dimensional pressure measurements were studied. The static pressure fluctuated and decreased periodically as the z-axis coordinate increased. These results can facilitate research on the cross-flow characteristics of liquid metal-cooled fast reactors.

Modulating the Coordination of Single Co Atoms to Trigger the Catalytic Oxidation of Formaldehyde at Room Temperature.

Designing efficient and stable non-precious metal catalysts remains a significant challenge for formaldehyde (HCHO) oxidation, which is an expected way to replace the employment of noble-metal catalysts. Herein, a series of atomically dispersed Co catalysts are optimized by evaporating nitrogen atoms and exploring their HCHO oxidation catalytic performance. The results show that the prepared temperature can effectively control the coordination regulation of the Co atomic site, which in turn affects the catalytic oxidation activity. Our best catalyst, the Co-N/C prepared at 1000 °C, exhibits superior activity with 92.8% of conversion at room temperature at a gas hourly space velocity (GHSV) of 72,000 mL·g-1·h-1. Extensive characterizations combined with theoretical calculations reveal that the high catalytic activity is attributed to the low-coordinated center, which can be tailored by pyrolysis temperature. This work provides an innovative strategy for catalyst design in the catalytic oxidation reaction.