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BackgroundReactor core computational fluid dynamics (CFD) plays a crucial role in identifying core vulnerabilities, optimizing feature structures, and improving safety and economic in nuclear reactors. However, conventional pressurized water reactor fuel assemblies often feature a multitude of spacer grids with mixing vanes, leading to challenges in mesh generation and numerical solution instability, excessive computational resource requirements. The current momentum source model established on the basis of the mechanism of fluid-structure interaction has not considered the effect of the low-pressure region on the fluid downstream of the mixing vanes, leading to significant errors in predicting the axial flow distribution downstream of the mixing vanes. Furthermore, it is challenging to identify the solid domain of the mixing vanes and to add momentum source terms.PurposeThis study aims to present a joint simulation scheme based on detailed porous media and momentum source modeling to simulate coolant flow in 5×5 rod bundle channels with mixing vanes, hence to reduce cells, lower mesh generation difficulty, and enhance numerical stability during the CFD solving process.MethodsThis scheme employed a detailed porous media approach in the spacer zone, while adopting Global Momentum Source Model in the vane zone. Simultaneously, a domain identification scheme was developed to determine the placement of momentum sources and detailed porous media models. The position of mixing vanes within the fluid domain was accurately located by this approach and established detailed porous media and momentum source models based on the fluid-structure interactions in the grid spacer zone and leeward side and windward side of mixing vanes. To simulate the flow field distribution within the spacer zone, a detailed porous media model was employed to enhance local flow resistance, thereby achieving an accurate simulation of the flow field distribution in the spacer zone. Finally, validation against experimental and body-fitted mesh simulations was performed to examine the effectiveness of this scheme in simulating flow blockage, fluid flow, mixing, and vortex shedding.ResultsThis scheme, compared to the momentum source scheme, exhibits stronger numerical stability. In the vane zone, the established momentum source model simultaneously considers the effects of the leeward side and the windward side of mixing vanes, leading to a more accurate prediction of axial flow velocity and heat transfer downstream of the mixing vanes. This approach allows for modeling without needing to consider the structure of the spacer grids with mixing vanes, thus greatly simplifying mesh generation. It achieves complete structured mesh modeling, significantly reducing the number of cells, and enhancing computational efficiency. Validation confirm the effectiveness of this scheme and results in a 90% reduction in cells and a 60% decrease in computational time for modeling and simulation of a 5×5 rod bundle channel with mixing vanes.ConclusionsThis scheme offers simplicity in modeling, reduces CFD computation time, insensitivity to mesh, and superior robustness. Furthermore, when identifying larger-scale components, the approach involves identifying the multi-span fuel components, since the mixing vanes form a regular array in both axial and transverse directions. Therefore, domain identification at a larger scale can be achieved by modifying coordinates, applying momentum source model developed in this paper.

This paper presents a frequency-domain method for transforming a class of high-order linear systems with high-order derivatives of input into the corresponding full-actuated system (FAS) models. Based on the coprime factorisation theory, it is proved that under the condition that the factorisation polynomial matrix is column reduced, a direct method can be given to transform the original system into an FAS model. Regard the non-square problem faced by the direct method, two different methods are given to present the explicit expression of the transformed state. The first one is given for the case the order of system is higher than that of input, in which the system is transformed into the corresponding observability canonical form. The other one considers the opposite case, in which the model reduction method is adopted. Three numerical examples are given to illustrate the proposed theories. [ABSTRACT FROM AUTHOR]

To broaden the applications of yttria‐stabilized zirconia (YSZ) in mobile phone back panels and high‐end decorative materials, the 3 mol% YSZ (3YSZ) ceramics doped with erbium oxide (Er2O3) as colorant were successfully sintered at 1250 and 1350°C in air. The influences of Er2O3‐doping concentration and sintering temperature on the phase, microstructure, color, and mechanical properties of the pink Er2O3‐3YSZ ceramics were investigated. As the Er2O3 concentration increased, the redness value a* gradually increased, while the yellowness value b* and the lightness value L* gradually decreased. The highest value a* and b* of Er2O3‐3YSZ ceramics reached absolute values of 15.2 and 4.5, respectively. The effect of Er2O3 concentration is also depicted in detail, which also affects the mechanical properties including hardness and fracture toughness of the ceramics. The maximum hardness and fracture toughness of Er2O3‐3YSZ ceramics reached 13.9 ± 0.3 GPa and 6.21 ± 0.20 MPa·m1/2, respectively. The hardness of the ceramics exceeds 12.5 GPa, which is the required market index for further practical application. This work provides a method for preparing 3YSZ ceramics with excellent mechanical properties and bright pink color, which has the potential to be used in the fields of advanced and superior electronics in particular. [ABSTRACT FROM AUTHOR]

Wuyi Rock Tea (WRT) is cherished for its exceptional "rock flavor" and its quality shows obvious regional differences. However, the flavor characteristics of Primary Wuyi Rock Teas (PWRTs) from different production areas remain unclear. Here, the Camellia sinensis var. sinensis cv. 'Rougui' and 'Shuixian', two quintessential cultivars for making WRT, planted in Zhengyan, Banyan, at high elevations, and Waishan production areas were used to make PWRTs. We conducted a comprehensive comparison of the sensory attributes, volatile organic compounds (VOCs), and macro-compositions of PWRTs of 'Rougui' and 'Shuixian' cultivars from different producing areas. Sensory evaluation indicated that both 'Rougui' and 'Shuixian' PWRTs from Zhengyan exhibited the best flavor qualities, followed by those from Banyan, at high altitudes, and Waishan production areas. The results of the determination and analysis of VOCs showed 680 VOCs in 'Rougui' and 'Shuixian' PWRTs, and that the different production areas mainly influenced the quantitative pattern of VOCs and rarely the qualitative composition. Integrated multivariate statistical analysis methods revealed that benzyl alcohol, hotrienol, butanoic acid, 2-methyl-, hexyl ester, benzene, (2-nitroethyl)-, and geranyl isobutyrate may be the key VOCs affecting the aroma differences in PWRTs from different production areas. In addition, water-extractable substances, tea polyphenols, caffeine, and free amino acids may be the important macro-compositions that distinguish PWRTs from different production areas. The metabolite basis for differences in the flavor qualities of PWRTs across production areas was elucidated, which may be helpful for the production of high-quality WRT. [ABSTRACT FROM AUTHOR]

Tb3Al5O12 (TAG) ceramics with high optical quality were fabricated successfully by a solid‐state reaction method combined with hot isostatic pressing (HIP) post‐treatment. The microstructure, optical transmittance, Verdet constant, and thermo‐optical properties were investigated. The obtained TAG ceramics showed a dense microstructure, and the in‐line transmittance reached 82.8% at 1070 nm after laser‐grade polishing. The Verdet constant of TAG ceramics was measured to be 50.9 rad·T1·m−1 at 1070 nm, which is higher than that of commercial Tb3Ga5O12 crystals. The Faraday isolator based on TAG ceramics can provide an isolation ratio of 30 dB with a laser power of more than 1 kW. With excellent optical quality, high Verdet constant, and maximum working power, TAG transparent ceramics are promising for applications of kilowatt‐level Faraday isolators. [ABSTRACT FROM AUTHOR]

The enzymatic reaction stage (ECS) of oolong tea processing plays an important role in the formation of the flavor quality of the oolong tea. To investigate the dynamic changes in the volatile and non-volatile components in the leaves of oolong tea during the ECS, metabolomic studies were carried out using the leaf samples collected at different stages of the ECS of Aijiao oolong tea. Out of the identified 306 non-volatile metabolites and 85 volatile metabolites, 159 non-volatile metabolites and 42 volatile metabolites were screened out as key differential metabolites for dynamic changes during the ECS. A multivariate statistical analysis on the key differential metabolites showed that the accumulations of most metabolites exhibited dynamic changes, while some amino acids, nucleosides, and organic acids accumulated significantly after turning-over treatment. The evolution characteristics of 27 key precursors or transformed VOCs during the ECS of Aijiao oolong tea were clarified, and it was found that the synthesis of aroma substances was mainly concentrated in lipids as precursors and glycosides as precursor pathways. The results revealed the dynamic changes in the flavor metabolites in the ECS during the processing of Aijiao oolong tea, which provided valuable information for the formation of the characteristic flavor of Aijiao oolong tea. [ABSTRACT FROM AUTHOR]