Analysis of the performances of the CFD schemes used for coupling computation

Chen, Guangliang,Jiang, Hongwei,Kang, Huilun,Ma, Rui,Li, Lei,Yu, Yang,Li, Xiaochang Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.7

In this paper, the coupling of fine-mesh computational fluid dynamics (CFD) thermal-hydraulics (TH) code and neutronics code is achieved using the Ansys Fluent User Defined Function (UDF) for code development, including parallel meshing mapping, data computation, and data transfer. Also, some CFD schemes are designed for mesh mapping and data transfer to guarantee physical conservation in the coupling computation. Because there is no rigorous research that gives robust guidance on the various CFD schemes that must be obtained before the fine-mesh coupling computation, this work presents a quantitative analysis of the CFD meshing and mapping schemes to improve the accuracy of the value and location of key physical prediction. Furthermore, the effect of the sub-pin scale coupling computation is also studied. It is observed that even the pin-resolved coupling computation can also create a large deviation in the maximum value and spatial locations, which also proves the significance of the research on mesh mapping and data transfer for CFD code in a coupling computation.

Application of POD reduced-order algorithm on data-driven modeling of rod bundle

Huilun Kang,Zhaofei Tian,Guangliang Chen,Lei Li,Tianyu Wang 한국원자력학회 2022 Nuclear Engineering and Technology Vol.54 No.1

As a valid numerical method to obtain a high-resolution result of a flow field, computational fluid dynamics (CFD) have been widely used to study coolant flow and heat transfer characteristics in fuel rod bundles. However, the time-consuming, iterative calculation of Navier-Stokes equations makes CFD unsuitable for the scenarios that require efficient simulation such as sensitivity analysis and uncertainty quantification. To solve this problem, a reduced-order model (ROM) based on proper orthogonal decomposition (POD) and machine learning (ML) is proposed to simulate the flow field efficiently. Firstly, a validated CFD model to output the flow field data set of the rod bundle is established. Secondly, based on the POD method, the modes and corresponding coefficients of the flow field were extracted. Then, an deep feed-forward neural network, due to its efficiency in approximating arbitrary functions and its ability to handle high-dimensional and strong nonlinear problems, is selected to build a model that maps the non-linear relationship between the mode coefficients and the boundary conditions. A trained surrogate model for modes coefficients prediction is obtained after a certain number of training iterations. Finally, the flow field is reconstructed by combining the product of the POD basis and coefficients. Based on the test dataset, an evaluation of the ROM is carried out. The evaluation results show that the proposed POD-ROM accurately describe the flow status of the fluid field in rod bundles with high resolution in only a few milliseconds.

Investigation on the nonintrusive multi-fidelity reduced-order modeling for PWR rod bundles

Huilun Kang,Zhaofei Tian,Guangliang Chen,Lei Li,Tianhui Chu 한국원자력학회 2022 Nuclear Engineering and Technology Vol.54 No.5

Performing high-fidelity computational fluid dynamics (HF-CFD) to predict the flow and heat transferstate of the coolant in the reactor core is expensive, especially in scenarios that require extensiveparameter search, such as uncertainty analysis and design optimization. This work investigated theperformance of utilizing a multi-fidelity reduced-order model (MF-ROM) in PWR rod bundles simulation. Firstly, basis vectors and basis vector coefficients of high-fidelity and low-fidelity CFD results areextracted separately by the proper orthogonal decomposition (POD) approach. Secondly, a surrogatemodel is trained to map the relationship between the extracted coefficients from different fidelity results. In the prediction stage, the coefficients of the low-fidelity data under the new operating conditions areextracted by using the obtained POD basis vectors. Then, the trained surrogate model uses the lowfidelity coefficients to regress the high-fidelity coefficients. The predicted high-fidelity data is reconstructed from the product of extracted basis vectors and the regression coefficients. The effectiveness ofthe MF-ROM is evaluated on a flow and heat transfer problem in PWR fuel rod bundles. Two data-drivenalgorithms, the Kriging and artificial neural network (ANN), are trained as surrogate models for the MFROM to reconstruct the complex flow and heat transfer field downstream of the mixing vanes. The results show good agreements between the data reconstructed with the trained MF-ROM and the highfidelity CFD simulation result, while the former only requires to taken the computational burden oflow-fidelity simulation. The results also show that the performance of the ANN model is slightly betterthan the Kriging model when using a high number of POD basis vectors for regression. Moreover, theresult presented in this paper demonstrates the suitability of the proposed MF-ROM for high-fidelityfixed value initialization to accelerate complex simulation

Adsorption of phosphate by Mg/Fe-doped wheat straw biochars optimized using response surface methodology: Mechanisms and application in domestic sewage

Hao Wang,Jiangyue Dai,Huilun Chen,Fei Wang,Yangchen Zhu,Jia Liu,Beihai Zhou,Rongfang Yuan 대한환경공학회 2023 Environmental Engineering Research Vol.28 No.2

In this study, Mg/Fe-doped biochar (MFDB) was prepared using the impregnation pyrolysis method, and its preparation was optimized using response surface methodology (RSM). The competitive adsorption between dissolved organic matter (DOM) and phosphorus was also investigated. The best adsorption capacity was obtained with an ㎎ impregnation ratio of 3.17:1 (Mg: biomass, g:g), Fe impregnation ratio of 1.3:1 (Fe: biomass, g:g), and pyrolysis temperature of 491℃. The adsorption capacity of MFDB for phosphorus was 179.21 ㎎/g at 40℃, an initial phosphate concentration of 50 ㎎/g and pH 4. The phosphate adsorption by MFDB conformed to a pseudo-primary and secondary adsorption kinetic model, proving the coexistence of physical and chemical adsorption. The adsorption mechanisms, including ligand exchange, electrostatic interaction, and complexation reaction were revealed. As the pH increased, it weakened the electrostatic interaction of phosphate by MFDB and the ligand exchange between phosphate and OH⁻. When the pH was less than 3, the metal oxide dissolved. For pH values exceeding, OH⁻ competed with phosphate for adsorptio, which also weakened the complexation of phosphate and MFDB. The DOM in domestic wastewater had a slight effect on the phosphorus adsorption. The phosphorus removal rates were closely related to lignin-like humic acid and tryptophan.

Effects of sulfonamide antibiotics on digestion performance and microbial community during swine manure anaerobic digestion

Shaona Wang,Kang Du,Rongfang Yuan,Huilun Chen,Fei Wang,Beihai Zhou 대한환경공학회 2021 Environmental Engineering Research Vol.26 No.1

The effects of four types of sulfonamide antibiotics (SAs), including sulfaquinoxaline, sulfamethoxazole, sulfamethoxydiazine and sulfathiazole, on the digestion performance during anaerobic digestion process were studied using a lab-scale anaerobic sequencing batch reactor, and the changes of the community structure in the presence of SAs were investigated with the help of high throughput sequencing. The results indicated that when SAs were added, the hydrolytic acidification process was inhibited, and the accumulation of volatile fatty acids (VFAs) was induced, resulting in the suppression of methane production. However, the inhibition mechanism of different SAs was quite different. The inhibitory effect of high concentration of SAs on the hydrolysis of solid particulate matter into dissolved organic matter followed the order of sulfaquinoxaline > sulfamethoxydiazine > sulfathiazole > sulfamethoxazole. SAs have obvious inhibitory effects on acidification and methanation of dissolved organic matter, especially sulfathiazole. The richness and the community composition of the microorganism including bacteria and archaea in the digestion system were affected by SAs. Under the effect of SAs, the relative abundance of many microorganisms is negatively correlated with methane production, among which Methanobrevibacter, a kind of Archaea, had the greatest influence on methane production.

The mechanisms of conventional pollutants adsorption by modified granular steel slag

Shaona Wang,Sijian Yao,Kang Du,Rongfang Yuan,Huilun Chen,Fei Wang,Beihai Zhou 대한환경공학회 2021 Environmental Engineering Research Vol.26 No.1

This study was performed to investigate the removal of phosphorus, nitrogen, ammonia and dissolved organic matter (DOM) from domestic wastewater using modified granular steel slag (GSS) as adsorbent. The modification methods include acid modification, alkalinity modification and thermal modification. The GSS modified at 800°C for 1 h was easier to hydrolyze Ca<SUP>2+</SUP>, which could promote the precipitation of phosphates and the ion exchange process of ammonia. Therefore, the adsorptive capacity of GSS for phosphates and ammonia could be significantly improved by the thermal treatment. The acid-modified GSS promoted the adsorption capacity of nitrates by increasing surface protonation, specific surface area and pore size. The highest nitrates adsorption capacity was obtained when GSS was immersed in 1 mol/L HCl solution for 24 h. The presence of nitrates inhibited the adsorption of phosphates by GSS because the adsorption of nitrates and phosphates by GSS depended largely on electrostatic attraction and intermolecular force, and the competition between them reduced the adsorption capacity. Ammonia can promote the hydrolysis of metal ions on the surface of GSS, increase the concentration of metal ions in solution and promote the formation of phosphate precipitation, but ammonia also competed with phosphate for active sites on the surface of GSS. The effect of ammonia nitrogen on phosphate adsorption was the result of the interaction of the two mechanisms. For domestic wastewater, the thermally modified GSS showed the best adsorption rate of total phosphorus and total nitrogen, and the acid-modified GSS had better adsorption capacity for organic matter. The thermally modified GSS had a good application effect in laboratory subsurface flow constructed wetlands.