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Improvement on Numerical Simulation of Supercritical Water flow in Horizontal Tubes: A Buoyancy-Tuned Turbulence Prandtl Number Model

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SSRN 2024年

作者： Hou, Zhenghui Guo, Xinyang Liang, Zhicheng Yang, Kuang Yang, Chaofan Wang, Haijun State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

To improve the predictive accuracy of numerical simulations for supercritical water, the effect of turbulence Prandtl number (Prt) on supercritical water heat transfer was extensively studied using the Shear-Stress Transport (SST) k-ω turbulence model. The efficacy of typical turbulence Prandtl number models for predicting heat transfer in horizontal tubes with supercritical water was evaluated based on wall temperatures measured experimentally and fluid temperatures obtained from multi-point temperature measurement devices. These models successfully demonstrated the phenomenon of thermal stratification due to physical property variations, but their predictive performance near the pseudocritical temperature, particularly in the top wall region, was not satisfying. Building upon this, a new turbulence Prandtl number model suitable for horizontal supercritical water tubes, named the SWBT model, was developed through constant calibration and the addition of buoyancy tuned. This model effectively replicates severe heat transfer deterioration (HTD) and buoyancy-induced improvements in heat transfer, showing robust predictive capabilities with a wide array of experimental data from both the authors and other researchers. The model was tested across ranges of P=24.5-26.5 MPa, q/G=0.11-0.67, and tube diameters of 7.5 mm, 26 mm and 43 mm. Additionally, the model's performance was benchmarked against experimental results of axially non-uniform heat flux conducted by the authors, successfully reproducing the variations in wall temperature due to changes in heat flux. This study substantially enhances the accuracy of numerical simulations for supercritical water in horizontal tubes, offering valuable insights for the engineering applications of supercritical water and the design of heat exchangers. © 2024, The Authors. All rights reserved.

关键词： Prandtl number

Evaluation of Load Following Control Strategy for Heat Pipe-Cooled Microreactor Coupled with Closed Brayton Cycle System

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SSRN 2024年

作者： Qian, Yiran Liu, Tao Zhang, Yan Leng, Yuyang Shi, Tianrun Song, Meihui Chen, Weixiong State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

Heat pipe-cooled reactors (HPCRs), with their straightforward and compact design and inherent safety features, are considered a promising option for mobile nuclear power sources. However, the coupling between the HPCR and the energy conversion system complicates load tracking control. In this study, a comprehensive dynamic model of an HPCR coupled with a closed-air Brayton cycle (CABC) is developed. This model integrates a neutron kinetics point reactor model, a thermal resistance network model for the heat pipe, and a CABC model representing the power conversion system. To achieve effective load tracking, a control scheme for the Brayton cycle power is proposed, combining turbine bypass control with inventory control. The system’s response to load variations, from 100% full power (FP) to 50% FP at a rate of 5% FP/min, is analysed, considering reactor power self-regulation. The results indicate that the reactor power exhibits an overshoot of -4.36% and stabilizes after 2100s, while the fuel average temperature fluctuates within ±4.6°C and stabilizes at 2240s. Building on the dynamic performance of the HPCR-CABC system, a reactor power control scheme is developed by adjusting control drums to introduce external reactivity. This scheme successfully controls reactor power at a steady state within 720s, without fluctuation. However, the fuel average temperature fluctuates by more than 10°C, stabilizing after 9450s. To improve control effectiveness, a temperature correction channel is incorporated into the reactor power control system. As a result, the fuel average temperature fluctuates within ±0.3°C and stabilizes at the design value of 699.4°C within 860s. Compared to previous control schemes, the improved cascade reactor power control scheme results in a shorter stabilization time for the fuel average temperature. To assess the adaptability of the proposed HPCR-CABC coordination control strategy, simulations are conducted for load reductions from 100% FP to 80%, 60%,

关键词： Brayton cycle

Experimental Investigation of Pressure Pulsation and Noise Due to Thermodynamic Effects on Cavitation in High-Temperature Water

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SSRN 2024年

作者： Xu, Bo Hu, Hongfei Yang, Kuang Wang, Haijun State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

In power systems or equipment, water is often in a state of high temperature and high pressure. The thermodynamic effects are non-negligible during cavitation. The orifice plate, as one of the most fundamental structures in cavitation flow, is used as a research object in cavitation experiment to analyze the thermodynamic effects of high-temperature water. In this study, the variational mode decomposition is improved by using the center frequency and correlation coefficient of the intrinsic mode functions, thus developing an adaptive variational mode decomposition method (AVMD). This method effectively decomposes the pressure pulsations and radiated noise during cavitation and can reasonably classify different cavitation stages. The results indicate that periodic turbulence pulsation frequencies of 5-15 Hz are observed in non-cavitating regions. With the onset of cavitation, the flow field exhibits high-frequency pseudo-periodic frequencies, and the turbulence pulsation frequency gradually decreases, with Strouhal number (St) reducing from 0.2 to 0.1. In regions of severe cavitation, the St of turbulence pulsation frequency exceeds 0.4. Under the same cavitation number, during the development stage of cavitation, as the degree of subcooling decreases, the temperature drop in the cavitation region gradually increases, and the maximum is 2.5 K. The amplitude of pressure pulsations also declines, with the maximum reduction reaching 49.7%. In the severe cavitation stage, the temperature drop in the cavitation region reaches a maximum of 2.87K and is no longer affected by the degree of subcooling. The radiated noise sound pressure level exhibited similar trends as the pressure pulsations inside the pipe when the cavitation number changed. The noise was dominated by low frequencies, with a sound pressure level around 82dBA. The mid-frequency component had a sound pressure level around 79dBA, while the high-frequency component corresponded to a level around 77dBA. At the s

关键词： Variational mode decomposition

Research on Full-Day Operation Strategies of Virtual power Plants Integrating Interruptible Loads Energy Storage to Adapt to Various Weather Changes

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SSRN 2024年

作者： Chong, Daotong Tian, Zeyu Wang, Zhu Du, Guanghan Yan, Hui State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi’an710049 China

Interruptible load energy storage (ILES) represents a novel energy storage technology with the dual functionality of load and storage. The storage aspect of an ILES facilitates flexible and controllable scheduling. In contrast, the load attribute offers widespread energy storage potential. ILES surpasses traditional storage methods, particularly at large scales, by efficiently utilizing existing resources, reducing investment needs, and avoiding energy decay. However, the dual nature of ILES presents challenges in its direct application to power grids, necessitating its integration into virtual power plants (VPPs) as an indirect but crucial scheduling tool. This study develops a dynamic simulation model for a large-scale VPP incorporating an industrial-scale ILES. A control strategy is proposed, focusing on the efficient and flexible use of ILES and ensuring the VPP's safe, stable operation. This strategy includes a method for determining the dispatching time and range of the ILES and introduces three schemes—power universality, power enhancement, and power attenuation—to compute the dispatching power of the ILES and develop a dispatch plan tailored to varying needs. Additionally, the strategy enhances existing control systems by generating optimized signals to increase the dispatch rate and ensure operational safety. Simulation analysis of three typical scenarios assesses the dispatching parameters of the ILES, VPP operation safety, and system capacity for grid ancillary service participation. The findings show that while maintaining safety and stability, the ILES dispatch rate improved from 10 MW/min to 40 MW/min, diminishing energy losses and enhancing efficiency. Adjustments in dispatching times increased the ILES dispatching power from 53.7 MW to 101.8 MW and the VPP output power from 16.9 "MW∙h" to 96.7 "MW∙h", significantly boosting system flexibility and ancillary service capabilities. The variability in dispatching power, under scheme modifications, ranged

关键词： Energy storage

Thermal mechanical response analysis of the first wall in laser initial confinement fusion reactors

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International Journal of Advanced Nuclear Reactor Design and Technology 2025年第2期7卷 147-155页

作者： Li, Xinze Zhang, Bingqian Tong, Chengcheng Chen, Ronghua Zhang, Dalin Tian, Wenxi Qiu, Suizheng State Key Laboratory of Multiphase Flow in Power Engineering Shaanxi Key Laboratory of Advanced Nuclear Energy and Technology School of Nuclear Science and Technology Xi'an Jiaotong University Xi'an710049 China

This paper investigates the thermo-mechanical response characteristics of the first wall of a laser initial confinement fusion reactor under periodic transient heat flux loads. The first wall of the reactor experiences extremely high instantaneous heat loads during the target compression process, leading to temperature and thermal stress oscillations, which can cause material fatigue damage. Finite element analysis is employed to model the first wall under various chamber sizes and target energies, and the thermal-mechanical response characteristics of W, W/Cu functional gradient materials, and blanket materials are studied under thermal shock and cyclic loading conditions. The results indicate that W/Cu functional gradient materials can effectively alleviate thermal stresses on the first wall, especially in addressing the stress concentration at the interface. Fatigue life of the first wall is assessed using the Basquin model, and it is found that increasing the chamber size and increasing the target frequency can significantly reduce temperature oscillations and thermal stresses, thus extending the service life of the first wall. This study provides valuable design references for the optimization and design of the first wall in laser initial confinement fusion reactor. © 2025 Xi'an Jiaotong University

关键词： Thermal fatigue

Revised Control Strategy for Coal-Fired power Plants During Transient Processes Considering Heat Transfer Deterioration of Cooling Wall: Flexibility Enhancement and Security Operation

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SSRN 2024年

作者： Wang, Dengliang Zhao, Yongliang Gao, Wei Chen, Weixiong Wang, Chaoyang Yan, Junjie State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

Increasing share of power generation from intermittent renewable energy has resulted in an expanding demand for deep peaking and operational flexibility of thermal power plants. Under this circumstance, it causes an enormous threat to the safe operation of the boiler, especially cooling wall. So it is crucial to focus on the thermo-hydraulic performance of the cooling wall during transient processes. In this paper, a 1100 MW ultra-supercritical thermal power plant is used as the research object. A one-dimensional dynamic model of the cooling wall is constructed based on the conservation of mass, conservation of momentum, conservation of energy, state, metal heat storage and heat transfer equations. The temperature distributions of working fluid, inner and outer wall along the height direction of the cooling wall are obtained. Dry-out phenomenon of the cooling wall during the load cycling process is observed. It is found that heat transfer deterioration is a key reason for metal wall temperature intermittent fluctuation. When the load cycling rates are 2.5% Pe/min and 3.0% Pe/min, the maximum temperatures of metal tube wall during the loading up process reach 527.9°C and 557.3°C, respectively. Furthermore, a revised control strategy is proposed based on the heat transfer deterioration characteristics of the cooling wall. During the loading up process, the highest wall temperature is significantly reduced from 557.3°C to 502.2°C at 3.0% Pe/min. The maximum power ramp rate is increased from 2.5% Pe/min to 3.0% Pe/min when the revised control strategy is adopted. © 2024, The Authors. All rights reserved.

关键词： Fossil fuel power plants

Data-Driven Dimensional Analysis of Critical Heat Flux in Subcooled Vertical flow: A Two-Stage Machine Learning Approach

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SSRN 2024年

作者： Yang, Kuang Liang, Zhicheng Xu, Bo Hou, Zhenghui Wang, Haijun State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

This study pioneers a machine learning-based method designed for automating dimensional analysis to refine critical heat flux (CHF) prediction. Addressing the limitations of traditional dimensional analysis, this approach not only enhances the precision in identifying and quantifying dimensionless numbers but also provides valuable insights for CHF modeling. By integrating the Buckingham Pi theorem with modern computational methods, including the active subspace method and automatic differentiation (AD), the research represents a hopeful methodological advancement in thermal hydraulics. Application of this algorithm to a dataset from subcooled departure from nucleate boiling (DNB) conditions in vertical tube experiments has led to the identification of the most significant dimensionless number, showing a strong negative correlation with the boiling number Bochf. This key discovery underpins the development of a simplified dimensionless correlation, exhibiting improved predictive accuracy over existing models. The contribution of this research lies in its potential to deepen the understanding of physical phenomena, such as CHF, and to mitigate the reliance on empiricism in complex physical modeling. The methodological innovation introduced in this study provides a more systematic and insightful approach to thermal phenomena analysis, potentially enhancing the precision and applicability of predictive models in a wide range of thermal management and design optimization applications. While the initial results are promising, the full impact and breadth of this methodology necessitate further exploration through extensive application and rigorous validation in various CHF scenarios. © 2024, The Authors. All rights reserved.

关键词： Heat flux

Thermodynamic Modeling and Analysis of the Hydrogen and Combustible Gas Production in Supercritical Water Partial Oxidation System of Coal

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SSRN 2024年

作者： Li, Yifeng Xing, Guowei Liu, Shi Guo, Shenghui Ge, Zhiwei Guo, Liejin State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

Supercritical water partial oxidation (SCWPO) is an eco-friendly coal treatment technology that lowers the temperature needed for complete gasification of coal, promotes hydrogen output, enables targeted regulation of gaseous product composition, and eliminates gaseous pollutants. Current researches mainly focus on experiments and numerical simulations, with limited exploration in thermodynamics. he present study establishes an auto-thermal SCWPO cogeneration system for Hongliulin coal, employs sensitivity analysis to refine system parameters, and utilizes Life Cycle Assessment to evaluate environmental impact of hydrogen production system. As the outlet temperature of the reactor increases and the preheating water flow and equivalence ratio (ER) increase, the fraction of hydrogen in the gas product rises;conversely, the fraction of the combustible gas (CH4+CO+H2) rises. The SCWPO system can be precisely tailored to yield high-purity hydrogen or combustible gas by modulating the amount of oxygen input. The system of combustible gas production is capable of generating 241.67 GJ·h-1 of energy and attaining a cold gas efficiency of 81.62% when the ER is 0.25. The hydrogen production system can produce 1004.38 kg·h-1 of hydrogen and 206 t·h-1 of heated water at 0.5 MPa and 150℃ for an ER of 0.6. The optimum hydrogen production system achieved an energy efficiency of 90.97%, showing an improvement of 11.12% to 46.76% compared to previous hydrogen production systems. The standard Global Warming Potential of the system through carbon capture technology is 0.0087. The system developed in this paper benefits the industrial application of SCWPO and the optimization of subsequent processes. © 2024, The Authors. All rights reserved.

关键词： Thermolysis

Thermodynamic Analysis of a Supercritical Water Partial Oxidation Autothermal Cogeneration System of Coal

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SSRN 2024年

作者： Xing, Guowei Li, Yifeng Ren, Changyifan Ge, Zhiwei Guo, Liejin State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

Supercritical water partial oxidation (SCWPO) is a very efficient technology for the environmentally sound treatment of resources. Currently, there are few thermodynamic studies of SCWPO cogeneration system. In this study, a new supercritical water partial oxidation autothermal cogeneration system of coal is proposed. The system was evaluated for energy and exergy under typical operating conditions. The efficiencies achieved were 86% for energy and 47.6% for exergy. Due to the mixed working fluid is a mixture of H2O and CO2, the CO2 is very easy to capture. The exergy analysis revealed that the most significant exergy loss within the system occurred in the SCWPO reactor, which accounted for 78.2%% of the total exergy loss. Further sensitivity analysis of the system indicates that optimum values identified for both back pressure and carbon capture and storage unit (CCS) first stage pressure (PV-pump1), which are 8.5 kPa and 0.03 MPa. Additionally, increasing both the flow rate and temperature of preheated water can significantly enhance system efficiency. An increase in the flow rate of preheated water can lead to a reduction of the maximum system temperature;however, an elevation in the temperature of preheated water may cause a significant rise of the maximum system temperature, which is not conducive to the stable operation of the system. Finally, this paper compares the proposed system with the systems that have been reported in the literature. The results show that the system represents an innovative cogeneration solution with considerable advantages. © 2024, The Authors. All rights reserved.

关键词： Exergy