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Journal of Thermal Science 2021年第2期30卷 432-440页

作者： WANG Haitao TAO Tao MEI Xuesong WANG Haijun GU Hongfang State Key Laboratory for Manufacturing Systems Engineering Xi'an Jiaotong UniversityXi'an 710049China Shaanxi Key Laboratory of Intelligent Robots School of Mechanical EngineeringXi'an Jiaotong UniversityXi'an 710049China State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong UniversityXi'an 710049China

In this paper,the condensation heat transfer characteristics of parallel flow and counter flow inside an inclined wave-finned flat tube is investigated *** condensation heat transfer coefficients are analyzed based on the experimental *** of experiments show that condensation heat transfer coefficient decreases as the temperature difference Δt=ts-tw increases and mass flow rate *** parallel flow has a similar development with the counter flow,and the condensation heat transfer coefficient of counter flow is less than that of parallel flow under the same air cooling *** addition,condensation heat transfer coefficient correlations are also obtained under experimental *** calculations agree well with the measured data and the agreement is seen to be within ±4% for the parallel flow and ±5% for the counter flow.

关键词： condensation heat transfer wave-finned fiat tube modified model parallel flow counter flow

Verification and validation plus uncertainty quantification of heat transfer simulation for liquid metal in wire-wrapped rod assembly

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International Communications in Heat and Mass Transfer 2025年 165卷

作者： Liu, Zhenglong Zhong, Peiling Qiu, Hanrui Wang, Mingjun Tian, Wenxi Su, Guanghui State Key Laboratory of Multiphase Flow in Power Engineering Department of Nuclear Science and Technology Xi'an Jiaotong University Xi'an710049 China

A complete CFD best practice process is proposed, including Phenomena Identification and Ranking Table (PIRT), Verification and Validation (V&V), and Uncertainty Quantification (UQ). The heat transfer of liquid metal within a rod assembly under both normal and blocked conditions is used as an example to demonstrate the full CFD process. key flow and heat transfer phenomena are identified, and model sensitivity analyses are performed based on these phenomena. Turbulent Prandtl models, porous blockage models and different meshing strategies sensitivity analysis are conducted. Uncertainty quantification is performed. The discretization uncertainty is calculated using the Grid Convergence Index (GCI). The convergence orders are greater than unity for all cases except the fluid temperature in the blocked condition using meshing strategy 2. The input parameter uncertainty is estimated using finite difference. The model uncertainty is derived. Under normal condition, the model uncertainty of the wall and fluid temperatures are 2.88 K and 3.37 K, respectively. Under blocked condition, the model uncertainty of wall temperature is slightly higher than fluid temperature. The wall temperature uncertainty for strategies 1 and 2 are 8.46 K and 9.03 K, while the fluid uncertainty of strategy 1 and 2 are 3.57 K and 3.06 K, respectively. © 2025 Elsevier Ltd

关键词： Liquid metals

Numerical study of specific C-shaped heat exchanger using porous medium and coarse mesh coupling method

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International Journal of Thermal Sciences 2025年 210卷

作者： He, Shaopeng Wang, Shiqi Wang, Mingjun Tian, W.X. Qiu, S.Z. Su, G.H. State Key Laboratory of Multiphase Flow in Power Engineering School of Nuclear Science and Technology Xi'an Jiaotong University Xi'an710049 China

Porous medium method is an effective simplified approach for the heat exchanger simulation when the numerous tubes and complex structures bring unacceptable computational resources to full-scale simulation. However, for the specific C-shaped heat exchanger, the tube side resistance and flow distribution characteristics that significantly affects the heat transfer and natural circulation performance cannot be obtained by the traditional porous medium method coupled with the one-dimensional node model for tube side. It is urgent to develop a new coupling method that can not only simplify modeling and calculation, but also obtain tube side high-resolution flow heat transfer characteristics. This study presents a novel calculation method which couples the porous medium mesh and the tube side coarse mesh. The coupling method was then applied to a typical C-shaped passive residual heat removal heat exchanger (PRHR HX), which is significant to the stable operation and the mitigation of accident conditions in the nuclear power plant. The coupling calculation method was validated against the full-scaled simulation and data from scaled-down experiment. The average relative error of heat transfer power is 2.1 % under steady state conditions. Under transient conditions, the average absolute error of the fluid temperature and wall temperature are less than 6 K. Then the 3D thermal-hydraulic characteristics of PRHR HX was studied. Owing to a greater gravitational pressure head, the mass flow rates in the extended tubes surpass those in the shorter tubes by a relative deviation of 27.4 %. The upper horizontal tube's heat exchange capacity constitutes approximately 70 % of the total power, leading to enhanced natural circulation. The outlet temperatures from various tubes tend to equalize. The boiling area gradually extended down along the heat transfer tubes. Our work would present an innovative calculation method to the numerical study and design optimization of the C-shaped heat

关键词： Nuclear power plants

Experimental Study on flow Boiling and Circumferential Non-Uniform Heat Transfer Characteristics in Helically-Coiled Tube Under Coupled Heat Transfer Conditions

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SSRN 2024年

作者： Wang, Hengyuan Xuan, Qiyu Lei, Hailin Li, Xi Li, Zhibin Li, Huixiong State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xi’an Jiaotong University Xi’an710049 China

Because of its compact structure and high energy conversion efficiency, helically-coiled tube steam generator has been widely used in nuclear reactor, energy power, petrochemical and other systems. In the liquid metal reactor, the liquid metal on the primary side of the helically-coiled tube steam generator washes the helically-coiled tube bundles, and exchanges heat with the water on the secondary side. Due to the coupled heat transfer between liquid metal and water, the distribution of the wall temperature or heat transfer coefficient of helically-coiled tube are significant different in the circumference direction of the tube cross-section. An experimental system of helically-coiled tube steam generator was set up in this paper. The non-uniform heat transfer characteristics of secondary side fluid of helically-coiled tube steam generator were studied under the coupled heat transfer conditions between the heat transfer of primary side and secondary sides fluid. It was found the local wall temperature or local heat transfer coefficient in the circumferential direction of the tube cross-section was significantly different, and they showed different change trends with the change of the parameters such as subcooling degree, mass flux of the secondary side fluid, system pressure of secondary side fluid, heating temperature of primary side fluid, etc. Secondly, ηt and ηh were defined to represent the degree of local non-uniformity of local wall temperature or local heat transfer coefficient in the circumferential distribution of the tube cross-section, respectively. δt and δh were defined to characterize the degree of overall non-uniformity of wall temperature or heat transfer coefficient in the circumferential distribution of the tube cross-section, respectively. The variation rules of ηt and ηh, δt and δh with subcooling degree、system pressure、mass flux of primary side fluid、mass flux of secondary side fluid and heating temperature of primary side fluid were obtained.

关键词： Steam generators

Experimental Investigation on Product and Temperature Distribution in a Continuous flow Packed-Bed Reactor for Dodecahydro-N-Ethylcarbazole Dehydrogenation

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SSRN 2024年

作者： Xue, Jingwen Li, Pengzhao Yu, Pengfei Yi, Jinhao Ma, Tao Liu, Hu Che, Defu State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xi'an Jiaotong University Xi'An710049 China

The dehydrogenation of dodecahydro-N-ethylcarbazole (H12-NEC) generates enormous gas accompanied by intense heat absorption, affecting heat and mass transfer in porous catalysts. A packed-bed reactor equipped with a temperature measurement device was designed to investigate the continuous flow dehydrogenation of H12-NEC. The effects of weight hourly space velocity (WHSV), reaction temperature, catalyst particle size, and pressure were evaluated. The results reveal that the volume flow rate of hydrogen will increase with the increase of WHSV. And the generation of hydrogen enhances heat transfer by strengthening the perturbation of flow. As the temperature rises, the hydrogen yield increases along with more by-products. The decrease of catalyst particle size improves the hydrogen yield and a more uniform temperature distribution can be created within the reactor due to the weakened wall effect. 456 K and 2 mm of catalyst particle size are determined to be the optimal reaction conditions in the study, achieving the hydrogen production rate of 9.61 [[EQUATION]]. With pressure increasing, the hydrogen yield gradually decreases, but the decreased evaporation of H12-NEC results in a smaller temperature difference between the reactor and heating wall. A comparison with the thermodynamic equilibrium model reveals that the effect of pressure on chemical equilibrium may be more significant than the temperature. © 2024, The Authors. All rights reserved.

关键词： Temperature distribution

Experimental Study on Yield and Quality of Tar from Tar-Rich Coal Under the Simulated In-Situ Conditions

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SSRN 2024年

作者： Ning, Xing Huang, Xiaole Xue, Xiangyu Wang, Chang'an Deng, Lei Che, Defu State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xi’an Jiaotong University Xi’an710049 China

Tar-rich coal is considered to have a great potential to extract a large body of liquid fuels through thermal treatment. In this study, an experimental system in which the in-situ conditions can be simulated was built to investigate the yield and the quality of the tar from tar-rich coal. The simulated conditions include in-situ stress, pyrolysis temperature, heating rate, and moisture content. The results indicate that the tar yield increases from 0.83 % to 10.13 % in the temperature range of 200-500 ℃, but a considerable drop of the yield occurs around 600 ℃ due to the cracking of the tar. The heating rate is decreased from 16 °C/min to 2 °C/min, the tar yield is increased from 4.63 % to 10.3 % during the simulated in-situ pyrolysis of tar-rich coal. At low heating rates, the tar yield can be boosted owing to the difference in coal size and underground environment, in contrast to the high heating rate required in traditional coal pyrolysis. Moreover, the ether bonds connected with the oxygenated compounds in the tar under in-situ stress are cleaved, increasing the light components. For other simulated conditions, the low ratio of chain hydrocarbons to aromatic hydrocarbons leads to a decrease in the heavy components. Component variation in the tar under pyrolysis condition promotes the formation of light oil while preventing the synthesis of heavy oil, improving the quality of the tar from the simulated in-situ pyrolysis of tar-rich coal. © 2024, The Authors. All rights reserved.

关键词： Pyrolysis

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

Effects of Residual Carbon on Slag flow Characteristics of Zhundong High-Alkali Coal Under Oxy-Fuel Condition

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SSRN 2024年

作者： Wang, Chang'an Chen, Yuanmao Luo, Maoyun Zhao, Lin Zhao, Pengbo Che, Defu State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xi’an Jiaotong University Xi’an710049 China

The implementation of oxy-fuel combustion technology in slag-tapping cyclone furnace holds significant promise for addressing the challenges associated with the combustion of Zhundong high-alkali coal. However, the flow characteristics of the Zhundong high-alkali coal slag under oxy-fuel condition remain unclear, while the influences of residual carbon have yet to be fully understood. In the present study, a high-temperature flow experimental system was designed to investigate the effects of residual carbon content, degree of graphitization of residual carbon, and atmosphere on the high-temperature flow behaviors of the high-alkali coal slag. The scanning electron microscopy (SEM) with energy dispersive spectrometer (EDS) was utilized to further analyze the microscopic characteristics and elemental distribution within the slag samples. The results reveal that under oxy-fuel condition, the flow length of slag diminishes as the content of residual carbon increases. The slag samples blended with residual carbon exhibit rougher and looser surfaces, with numerous particles adhering to them. In addition, the higher the degree of graphitization in the residual carbon, the lesser its impact on the flowability of the slag. The slag samples in oxy-fuel atmosphere display relatively smooth surfaces with dense structures and extensive liquid-phase areas. On the contrary, slag samples under inert condition feature fewer smooth surfaces, with adherent particles visible along the edges of the structure. The present research provides valuable insights into the high-temperature flow behaviors of slag in oxy-fuel combustion for Zhundong high-alkali coal in slag-tapping boilers, which can contribute to clean and efficient energy production. © 2024, The Authors. All rights reserved.

关键词： Coal

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

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