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Numerical study of heat transfer characteristics of phase change materials reinforced with porous media based on hybrid mesh

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SUSTAINABLE ENERGY TECHNOLOGIES AND ASSESSMENTS 2024年 65卷

作者： Wang, Zilong Zhu, Liucan Zhang, Hua Yu, Guoxin Li, Jing Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China Qingdao Haier Smart Technol R&D Co Ltd 1 Haier Rd Qingdao Shandong Peoples R China

To address the drawbacks of inadequate energy density as well as utilization effectiveness in solar energy utilization, phase change energy storage offers a possible option. However, the low thermal conductivity of traditional phase change materials (PCMs) restricts the extent to which solar energy utilization can be enhanced. In this paper, the impact of the metal foam (MF) on the solid-liquid interface, the flow field, the enhancement heat transfer mechanism during the paraffin wax (PX) melting process and thermal storage characteristics was analyzed. Besides, a three-dimensional mathematical model of MF-PX using the hybrid mesh technique was established and software ANSYS-FLUENT was used for simulation. The results indicated that, the hybrid mesh exhibited a reduction of 52.75 % in mesh count compared to the unstructured mesh, resulting in 45 % reduction in computational time. Moreover, the hybrid mesh also showcased improved mesh quality that the unstructured mesh was mainly distributed in the range of 0.48-0.6, while within the range of 0.84-1.0 for the hybrid mesh. More important, the maximum relative error between experimental and simulation was 8.67 %, indicating that the model can make a reasonable prediction. With the proportions of MF increased from 0.11 % to 0.43 %, both the Rayleigh number (Ra) and its amplification decreased. At 800 s, the Ra decreased from 1.76E+07 to 1.20E+07, while the amplification of the Ra was reduced from 1.88E+07 to 1.30E+07. In addition, the natural convection proportions of CMF decreased from 96.31 % to 80.65 %. These observations indicated that natural convection was the primary heat transfer mechanism, and the conduction was enhanced by the increasing proportion of MF. Finally, in terms of heat storage characteristics, the heat storage capacity and heat storage rate of the composite PCM slightly decreased. The heat storage values decreased from 19.30 kJ to 18.66 kJ. Similarly, the heat storage rates decreased from 19.86 J/s

关键词： Phase change materials Numerical simulation Copper metal foam Hybrid mesh heat transfer enhancement

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Numerical Simulation Study on Two-Phase flow of Thermal Runaway Evolution and Jet Fire of 18650 Lithium-Ion Battery Under Thermal Abuse

SSRN

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SSRN 2023年

作者： Wang, Jia-Hao Mei, Mei Jiang, Ziqi Qiu, Huihe Wang, Ying Shanghai Key Laboratory of Multiphase Flow and Heat Transfer in Power Engineering School of Energy and Power Engineering University of Shanghai for Science and Technology Shanghai200093 China Department of Mechanical and Aerospace Engineering The Hong Kong University of Science and Technology Clear Water Bay Hong Kong

This study investigates the impact of particles on the external jet flame of 18650 lithium-ion batteries using a two-dimensional transient numerical simulation. The mixing characteristics of jet flames and particles generated by battery combustion are analyzed using a multi-component Navier-Stokes equation and Lagrangian method. The model is validated by comparing it with experimental measurements of flame height. The results show that particles have a significant impact on the jet flame's characteristics and dynamic behavior during the battery's thermal runaway process. The study includes an analysis of the velocity field, temperature field, flow field, component concentration distribution, and lift-off height. Two stages of the jet flame are identified: unstable and stable. The presence of particles causes the unstable flame height to be 1-2 times higher than the stable flame height. This research provides reference for the safety assessment of actual batteries. © 2023, The Authors. All rights reserved.

关键词： Lithium-ion batteries

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Sorption-enhanced chemical looping steam reforming of glycerol with CO2 in-situ capture and utilization

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CHEMICAL engineering JOURNAL 2023年第Part4期452卷

作者： Dou, Binlin Wu, Kai Zhang, Hua Chen, Bingbing Chen, Haisheng Xu, Yujie Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China Chinese Acad Sci Inst Engn Thermophys Beijing 100190 Peoples R China

Hydrogen production from chemical looping steam reforming using an oxygen transport catalyst is definitely enhanced by CO2 in-situ capture, which shifts the chemical equilibrium and reduces the energy demands. The utilization of CO2 from this process as a reactant for chemicals and fuels could help to improve economic reasons and mitigate its impact on climate. In this study, we proposed a sorption-enhanced chemical looping steam reforming of glycerol to realize the synergetic capture and conversion of CO2 in one integrated chemical looping hydrogen production process. The process is characterized to use the oxidized NiO/NiAl2O4 as a steam reforming catalyst, the reduced NiO/NiAl2O4 as a CO2-CH4 dry reforming catalyst, and the inexpensive dolomite as a CO2 sorbent. The surface carbon that would deactivate the catalyst is combusted by air after CO2-CH4 dry reforming and the Ni on the catalyst is re-oxidized. The coupling of these different processes of chemical looping steam reforming, CO2 in-situ capture, dolomite decomposition and CO2 in-situ utilization, results in simultaneous generation of high purity hydrogen and syngas. The results demonstrated that hydrogen of above 92.5% was one-step generated and CO2 was decreased to zero in the pre-CO2 breakthrough periods. The reduced NiO/NiAl2O4 catalysts favored the CO2-CH4 dry reforming at 850 degrees C. The syngas of H2-to-CO molar ratios of 0.8-1.1 through the conversion of CO2 from in-situ extraction of the absorbed CO2 dolomite, was produced. The NiO/Al2O4 with 15 wt% NiO gave the highest hydrogen and syngas yields, and maintained high performance for the proposed system. The catalysts and dolomite exhibited good stability with no obvious loss of activity in 10 cycles.

关键词： High-purity hydrogen production from sorption-enhanced chemical looping steam reforming (SE-CLSR) CO2 in-situ capture and utilization NiO Dolomite sorbent Syngas production from CO2-CH4 dry reforming (MDR)

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Numerical simulation study on two-phase flow of thermal runaway evolution and jet fire of 18650 lithium-ion battery under thermal abuse

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CASE STUDIES IN THERMAL engineering 2024年 53卷

作者： Wang, Jia-hao Jiang, Ziqi Mei, Mei Qiu, Huihe Wang, Ying Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China Hong Kong Univ Sci & Technol Dept Mech & Aerosp Engn Clear Water Bay Hong Kong 999077 Peoples R China

The influence of particles on the external jet flame generated by 18650 lithium-ion batteries dur-ing thermal runaway is considered. A model that employed multi-component Navier-Stokes equations to consider gas-phase flow, and used the Lagrangian method to consider solid particles, was applied to describe the mixing characteristics of the jet flames and particles generated by bat-tery combustion. The related combustion process, with and without particles, was compared and analyzed, and the flow lines outside the battery were obtained. Moreover, the effect of particles on the concentration of combustion components and the elevation of flame height are discussed. The results show that particles reduce the generation of external vortices outside the battery, making the external airflow more stable. The particles reduce the rate of concentration decrease outside the core, leading to an increase in the overall flame height. In the early stage of battery combustion, the flame has not yet stabilized, and the total flame height with the particles is on average 1-2 times higher than that without them. This article demonstrates that particles have a significant impact on the jet flame characteristics and dynamic behavior during thermal runaway process of batteries, providing a reference for the safety evaluation of actual batteries.

关键词： Lithium-ion battery Cell venting Thermal runaway Turbulent flow battery models Jet fire

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Characterization of the Temperature Profile near Contact Lines of an Evaporating Sessile Drop

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ENERGIES 2023年第6期16卷 2623页

作者： Zhang, Xiaodong Zhao, Yugang Wang, Dongmin Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai Peoples R China China Aerodynam Res & Dev Ctr Key Lab Icing & Anti Deicing Mianyang 621000 Peoples R China

Evaporation of a sessile drop is ubiquitous in nature and has many industrial applications. Despite extensive studies over recent decades, a critical issue, i.e., how temperature varies near contact lines, remains elusive. In this work, we report to date the first direct experimental measurement showing the microscopic temperature distribution near contact lines of an evaporating pinned sessile drop. Using a fluorescence-based thermometry, we find that the temperature at the free interface near contact lines varies drastically along the radial direction, engendering a concentric fringe pattern that evolves over the evaporation lifespan. The formation of such fringe patterns is attributed to a combined mechanism of locally enhanced evaporative cooling at the drop edge and the development of interfacial convective vortices due to Benard-Marangoni instability. We also study the evaporation dynamics at different initial contact angles and find that the characteristics of this fringe pattern vary as the initial contact angle decreases. Our experimental investigation and theoretical analysis in this work reveal insights to the understanding of droplet evaporation dynamics in various heat transfer systems.

关键词： drop evaporation Benard-Marangoni instability temperature measurement microscopic fluorescence-based thermometry

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Novel application of multi-model ensemble learning for fault diagnosis in refrigeration systems

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APPLIED THERMAL engineering 2020年 164卷 114516-000页

作者： Zhang, Zhan Han, Hua Cui, Xiaoyu Fan, Yuqiang Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer Shanghai 200093 Peoples R China

Despite the importance of fault diagnosis in refrigeration systems, the performance and improvement of most existing diagnostic models are limited by their reliance on a single method. This study proposes a novel application of ensemble learning that incorporates several intelligent ensemble members into an integrated model by means of majority voting. The ensemble members include k-nearest neighbour (KNN), support vector machine (SVM), decision tree (DT), random forest (RF) and logistic regression (LR). ASHRAE fault data were employed to establish the model. In addition, this study explores the integration of different subsets of ensemble members and revealed that the optimum subset combination comprised KNN, DT, and RF. Although the accuracy of this model was slightly lower than the model with all five ensemble members, it realised a substantial reduction in runtime. Compared to an SVM optimization model, the integrated model realised higher accuracy and reduced training time, without requiring parameter optimization. This achievement merits note as ensemble learning is traditionally associated high time-costs. Further investigation revealed that both the diversity and high accuracy of ensemble members are required to obtain an effective integrated model. These observations demonstrate the proposed model offers a promising alternative solution for fault diagnosis in refrigeration systems.

关键词： Refrigeration system Fault diagnosis Integrated model Majority voting Parameter optimization

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A green and efficient lignite-fired power generation process based on superheated-steam-dried open pulverizing system

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ENERGY 2024年 294卷

作者： Ma, Youfu Chi, Tonghui Yu, Yi Lyu, Junfu Wang, Zirui Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China Shanxi Res Inst Huairou Lab Taiyuan 030032 Peoples R China Tsinghua Univ Dept Energy & Power Engn Key Lab Thermal Sci & Power Engn Minist Educ Beijing 100084 Peoples R China

Currently, lignite -fired boilers often feature low thermal efficiency, difficult coal pulverizing and poor combustion stability owing to lignite having high water content. A novel lignite -fired power generation process is proposed in this paper with using a superheated -steam -drying open -pulverizing -system boiler (SSD-OPSB) and a deep utilization of waste heat from the steam for coal drying. Through using an open pulverizing system, the problems of low furnace temperature and low boiler efficiency are resolved. Meanwhile, the operation safety of the coal pulverizing system is ensured by using superheated steam as the drying agent. This paper described the working principle and engineering feasibility of the SSD-OPSB process, and established analysis model for its thermo-economic performance. Energy savings and environmental benefits of applying the process were calculated and discussed based on an in-service 600 MW supercritical power unit firing lignite with water content of 39.5% at its turbine heat acceptance condition. The result shows that for the power unit, applying the SSD-OPSB process can decrease coal consumption by 6.86% under the same power supply, meanwhile recovering water by 132.2 t/h and reducing CO2 emission by 27.78 t/h. It indicates that the SSD-OPSB process would significantly benefit lignite -fired power plants regarding energy -saving and environmental protection.

关键词： Thermal power plant Lignite Open pulverizing system Energy saving Water recovery

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Research of cooling tower filler based on radial basis function artificial neural network (RBF ANN)

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ENERGY SCIENCE & engineering 2023年第8期11卷 2885-2898页

作者： Zhang, Lixin Chen, Jie Zhao, Shunan Chen, Yongbao Song, Huijuan Liu, Jingnan Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China China Inst Water Resources & Hydropower Res Dept Hydraul Beijing Peoples R China

The filler is the core component of the cooling tower, filler performance refers to both its thermal and flow resistance characteristics, which use empirical formulas of tower characteristic N, volumetric mass transfer coefficient beta(xv), and pressure drop Delta P obtained through experimentation under specific conditions. However, the performance equations for identical countercurrent fillers can vary at different heights or seawater concentrations. Linear interpolation is the conventional method for obtaining the filler performance under different conditions, but its uncertainty limits the application. This paper explores the use of the radial basis function artificial neural network (RBF ANN) to analyze filler performance based on existing performance equations. The data set is generated by the filler performance equations. The results demonstrate that RBF ANN has a preferable prediction effect with high correlation (the determination coefficient R-2 > 0.99) and prediction accuracy (the proportion of relative error within 10% N-10 > 90%). Furthermore, the predicted results are consistent with the experimental results of the filler performance. Therefore, RBF ANN can accurately predict filler performance at varying heights and seawater concentrations, making it universal and providing a basis for cooling tower design.

关键词： cooling tower filler RBF ANN resistance performance thermal performance

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Constructing a ghost fluid layer for implementation of contact angle schemes in multiphase pseudopotential lattice Boltzmann simulations for non-isothermal phase-change heat transfer

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INTERNATIONAL JOURNAL OF heat AND MASS transfer 2023年 201卷

作者： Wang, Dongmin Cheng, Ping Univ Shanghai Sci & Technol Sch Energy & Power Engn Key Lab Multiphase Flow & Heat Transfer Shanghai P Shanghai 200093 Peoples R China Shanghai Jiao Tong Univ Sch Mech Engn Shanghai 200240 Peoples R China Suzhou Univ Sci & Technol Jiangsu Key Lab Micro & Nano Heat Fluid Flow Techn Suzhou 215009 Peoples R China

The PP scheme (primitive pseudopotential-based scheme), the MP scheme (modified pseudopotential-based scheme) and the IVD scheme (improved virtual-density scheme) are the three most widely used contact angle schemes in pseudopotential lattice Boltzmann (LB) models to simulate wetting character-istics of multiphase flow over solid surfaces under isothermal conditions. In this paper, we apply these schemes to simulate the problem of sessile droplet evaporation on a heated substrate, which is an ex-ample of non-isothermal phase-change heat transfer process. It is found that the substrate heating effect destabilizes algorithms of these schemes in certain ranges of contact angles of a heated substrate. The droplet interface shapes simulated by the PP scheme and the MP scheme are inaccurate at obtuse con-tact angles due to large fluid density variations near the wall. The spurious currents near the droplet triple-phase contact line are very large in the MP scheme, causing the deformation of the Marangoni vortex shape inside the droplet and the erroneous droplet interface temperature distribution near the triple-phase contact line. The addition of a special ghost fluid layer on the wall proposed in this study can improve numerical stability of the PP and the MP schemes for application under non-isothermal conditions as well as under high saturated liquid/vapor density ratios. Although the IVD Scheme (with the nearest fluid layer temperatures above the heated wall chosen for calculating the effective mass of wall nodes) is also stable at low liquid/vapor density ratios, its numerical stability at high density ra-tios is not as robust as those of the PP and the MP schemes if a special ghost fluid layer is added in these schemes. It is shown that by adding such a special ghost fluid layer on the wall, large near-wall fluid density variations diminish in the PP and MP schemes and accurate droplet interface shapes can be recovered at obtuse contact angles. The spurious current

关键词： Pseudopotential lattice Boltzmann model Droplet evaporation Contact angle scheme

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Editorial: multiphase flow in energy studies and applications—A special issue for MTCUE-2022

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Physics of Fluids 2023年第7期35卷 1-7页

作者： Zhu, Li-Tao Xu, Fei Jin, Hui Xiong, Qingang Department of Chemical and Biological Engineering University of British Columbia VancouverBCV6T 1Z3 Canada School of Chemistry and Chemical Engineering Shanghai Jiao Tong University Shanghai200240 China Electronics Business Unit Ansys Inc. AustinTX78746 United States State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China State Key Laboratory of Pulp and Paper Engineering South China University of Technology Guangzhou510641 China

Establishing a clean, low-carbon, and efficient energy system is paramount for the sustainable development of industries and human society. multiphase flows are encountered extensively in various energy applications, including transportation, conversion, and utilization of fossil, renewable, hydrogen, and nuclear energies. These flows encompass a wide range of phenomena, such as fluid flow, heat and mass transfer, combustion, and chemical reactions. However, multiphase flows are highly intricate due to the coexistence of multiple phases, states, and components, as well as the interactions among them that occur across diverse spatiotemporal scales. Consequently, both academia and industry face significant challenges in comprehending and harnessing multiphase flows. Thus, establishing connections between basic research and industrial applications in the field of multiphase flows is fundamental and indispensable for advancements in energy science and technologies. © 2023 Author(s).

关键词： multiphase flow

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