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Study and forecast of dynamic characteristics of heat exchangers with continuous spiral baffle plates

Reneng Dongli Gongcheng/Journal of engineering for Thermal Energy and power 2007年第2期22卷 190-196页

作者： Wu, Feng Wang, Qiu-Wang Chen, Qiu-Yang Xie, Gong-Nan National Key Laboratory on Multiple-phase Flow in Power Engineering Xi'an Jiaotong University Xi'an 710049 China

A system has been established to conduct the experimental study of dynamic characteristics of shell-and-tube heat exchangers. Through experimental methods, an experimental study has been performed of the dynamic characteristics of heat exchangers with continuous spiral baffle plates, which have water and oil to serve as heat exchange working media. With the inlet flow disturbance representing equal percentage flow rate characteristics, studied were the dynamic responses to water and oil temperature at the outlet in four modes of flow rate disturbance. In the meantime, the effect of fluid disturbing quantity on the temperature rise at heat exchanger inlet and outlet at a certain Re number was also studied with a correlation equation between the temperature rise at the inlet and outlet of the heat exchanger and fluid disturbing quantity being obtained. The tests show that the dynamic response to the temperature of a liquid-liquid heat exchange system needs a comparatively long time. It has been found through the study that under a disturbance with a positive or negative flow rate, the change of temperature at the inlet and outlet of spiral-baffle plate heat exchangers assumes a linear relationship and the variation curve featuring temperature rise at the inlet and outlet has a symmetric feature at a positive or negative flow rate disturbance. A finite-difference numerical forecast model and artificial neural network one have been established respectively to dynamically forecast the outlet temperature at the heat exchanger oil side. The forecast results are in good agreement with the test values. The forecast results obtained from the neural network is better than those from the numerical simulation with the absolute value of the deviation being less than 1.3%, indicating that artificial neural network has a definite merit for engineering reference and applications when performing the discrimination of complicated systems.

关键词： Artificial neural network Continuous spiral baffle plate Dynamic characteristics Dynamic forecast Numerical forecast Shell-and-tube heat exchanger

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Adsorption of Dibenzofuran by Modified Biochar Derived from Microwave Gasification

SSRN

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SSRN 2024年

作者： Ren, Jiyun Zhang, Yong Wang, Hui Huang, Xiaoming Jin, Xiaoling Zhang, Kai Li, Ruiyu Yang, Kaixuan Yue, Yang 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 Yantai Longyuan Power Technology Co. Ltd Yantai264000 China West Pipeline Company of PipeChina Urumchi830000 China Jinggangshan Power Plant Huaneng Power International Inc Jiangxi 343009 China Shunde Institute of Inspection Guangdong Institute of Special Equipment Inspection and Research Foshan528300 China Shanghai Power Equipment Research Institute Co. Ltd. Shanghai200240 China

Dioxins, emanating from the waste incineration, constitutes an organic pollutant that poses considerable risks to human health and environment. In this study, the corn straw char (CSC) and oak char (OC) derived from the electric heating and microwave gasification, and the coconut-shell activated carbon (AC) are employed as absorbents for the adsorption of dibenzofuran (DBF, dioxins model compound). Characterization techniques including BET, X-ray CT, SEM-EDS, FTIR, and XPS are performed to identify the DBF adsorption mechanism on biochar. The results show that the biochar prepared by the microwave gasification has a more well-developed pore structure than that of the electric heating gasification. Higher porosity (16.94%) and lower mineral content (1.75%) are responsible for the effective adsorption of DBF onto AC. The adsorption capacity of CSC is proportional to the modified concentration of KOH. It is mainly ascribed to the decrement of carboxyl and lactone groups and the enhancement of alkaline functional groups on the biochar surface, which augments the hydrophobicity and π–π electron donor–acceptor (EDA) interaction. Instead, DBF adsorption capacity on the biochar is adversely affected by HNO3 modification. For all biochar samples, the corresponding maximum adsorption ratios are AC (87.11%) > KOH-modified CSC (77.14%) > unmodified CSC (49.11%) > unmodified OC (39.70%) > HNO3-modified CSC (36.09%). The adsorption mechanisms of DBF on the gasified biochar encompass pore filling, hydrophobicity, and π–π EDA interaction. A desirable adsorption capacity of DBF on the biochar prepared by the microwave gasification is attainable through augmenting the specific surface area while diminishing the oxygen-containing groups of the surface simultaneously. © 2024, The Authors. All rights reserved.

关键词： Potassium hydroxide

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Research on a Poly-Generation System for Gas-Biochar-Heat-Electricity by Supercritical Water Gasification of Biomass Waste

SSRN

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SSRN 2024年

作者： Wang, Cui Jin, Hui School of Water and Environment Chang'an University Xi’an710054 China Key Laboratory of Subsurface Hydrology and Ecological Effect in Arid Region of the Ministry of Education Chang'an University Xi’an710054 China Key Laboratory of Eco-hydrology and Water Security in Arid and Semi-arid Regions of Ministry of Water Resources Chang’an University Xi’an710054 China State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi’an710049 China Ministry of Education of China Chongqing University Chongqing400044 China

Biomass energy is renewable and rich in the world, providing a solution for the shortage in fossil fuel and serious environmental pollution. Proposing efficient utilization method of biomass waste demands urgent attention. Supercritical water gasification (SCWG) process is a potential technology. In this work, a poly-generation system based on SCWG was developed to convert biomass waste to gas, biochar, heat and electricity. Firstly, mass, energy, and exergy flow were calculated at the typical condition. Subsequently, impact of various operating parameters, including gasification temperature, mass flowrate of preheated water, biomass concentration, on the hydrogen-rich syngas yield, generated electricity, thermodynamic performance of the system was investigated. The result demonstrated that the exergy loss primarily occurred on cooler, reactor, heat exchanger and preheater, accounting for more than 90% of total exergy loss under different conditions, arising from irreversible reaction, heat transfer and heat dissipation. Higher temperature, higher biomass concentration and more preheated water exerted a positive effect for hydrogen-rich gas production and supplied heat energy, while these parameters were disadvantageous to exergy efficiency. Biochar energy was primarily affected by biomass concentration. Energy efficiency increased with preheated water quantity and biomass concentration rising, and impact of biomass concentration was more significant. Conversely, evaluated gasification temperature displayed an adverse effect on energy efficiency. The maximal exergy efficiency reached about 58.3% at 550℃, biomass concentration of 33%, preheated water mass flowrate of 900 kg·h-1 © 2024, The Authors. All rights reserved.

关键词： Biomass

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Investigation on the flow distribution characteristics of a water-wall intermediate header at a supercritical pressure

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Reneng Dongli Gongcheng/Journal of engineering for Thermal Energy and power 2006年第3期21卷 299-302页

作者： Zhu, Yu-Qin Bi, Qin-Cheng Chen, Ting-Kuan State Key Laboratory of Power Engineering Multi-Phase Flow Xi'an Jiaotong University Xi'an 710049 China

An investigation was conducted of the flow distribution characteristics of distribution header water-wall tubes under a supercritical pressure for a home-made 600 MW once-through boiler. The test parameters can be listed as follows: pressure p=23-25 MPa, mass flow rate G=400-1200 kg/(m2·s), working medium temperature t=10-400°C. An experimental study has been conducted of the impact of working medium pressure, mass flow rate and working medium temperature on the vertical water-wall tube flow distribution characteristics of the distribution header. The test results show that with an increase in mass flow rate, the uniformity of flow distribution among the vertical water-wall tubes could be enhanced. The non-uniformity of flow distribution will undergo a step increase near the quasi-critical points. Moreover, with an increasing pressure, the above-mentioned step increase will become weaker. By employing a discrete model of the parallel-connected branch tubes of the distribution header, the flow distribution among the distribution header vertical water-wall tubes was calculated and the calculation results are in good agreement with the test ones.

关键词： Distribution header Once-through boiler Supercritical pressure Vertical water-wall tubes

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Pressure-velocity coupling algorithm on non-orthogonal non-staggered grid

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Jisuan Lixue Xuebao/Chinese Journal of Computational Mechanics 2006年第1期23卷 93-96页

作者： Xie, Gong-Nan Wang, Qiu-Wang Zhang, Dong-Sheng Tao, Wen-Quan State Key Laboratory of Multi-phase Flow in Power Engineering Xi'an Jiaotong University Xi'an 710049 China

In this paper, a new numerical procedure is proposed for the steady flow of a viscous, incompressible fluid based on SIMPLER algorithm on a non-orthogonal non-staggered grid, together with Cartesian velocity components as dependent variables in the momentum equations. The main feature of the algorithm is that the pressure and pressure correction equations are obtained by explicitly treating pressure cross-derivatives terms in interface contravariant velocities. A collocated arrangement of variables is introduced on numerical grids, and the cell face velocities are calculated by the momentum interpolation. It is proved that this algorithm can be effectively used to simulate fluid flow and heat transfer in complex geometry, by the validation calculation of flow inside branching channel.

关键词： Incompressible flow

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A 3d Ptco Degradation Model for Long-Term Performance Prediction of a Scaled-Up Pemfc Under Constant Voltage Operation

SSRN

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SSRN 2023年

作者： Yang, Yunjie Bai, Minli Zhou, Zhifu Wu, Wei-Tao Zhao, Jian Wei, Lei Li, Yang Li, Yubai Song, Yongchen Key Laboratory of Ocean Energy Utilization and Energy Conservation of Ministry of Education Dalian University of Technology Dalian116024 China State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'An710049 China School of Mechanical Engineering Nanjing University of Science and Technology Nanjing210094 China Center for Advanced Vehicular Systems Mississippi State University Starkville39762 United States Department of Mechanical and Energy Engineering Southern University of Science and Technology Shenzhen518055 China

The non-uniform distribution of reactants, pressure, temperature, and reaction rate, in a scaled-up proton exchange membrane fuel cell (PEMFC) can lead to different catalyst degradation rate, impacting the long-term performance of PEMFCs. However, the local catalyst degradation behaviors in a PEMFC stack have not yet been fully understood due to the lack of experimental approaches and catalyst degradation model. In the present study, a numerical model is established for a 200 cm2 commercial-sized PEMFC stack with realistic anode and cathode flow fields. PtCo is employed as the cathode catalyst, and a 3D PtCo catalyst degradation model is developed to analyze the non-uniform evolution of the electrochemical active surface area (ECSA), current density, and Co2+ in the catalyst layers under the constant voltage conditions. The modeling results demonstrated that catalyst degradation is more severe downstream as well as under land of the cathode flow field, and the cathode catalyst layer (CCL) is the area most contaminated by the Co2+. The non-uniform catalyst degradation as well as Co2+ contamination increased the activation losses and local oxygen transport resistance. The catalyst degradation leads to a total power loss of 43.3% after 80,000 hours operation. The aging model provides a better understanding for large scale PEMFC stacks regarding its nonuniform PtCo degradation and can assist the future design of commercial PEMFCs with better lifetime. © 2023, The Authors. All rights reserved.

关键词： Proton exchange membrane fuel cells (PEMFC)

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Strong Photo-Thermal Coupling Effect Boosts Co2 Reduction into Ch4 in a Concentrated Solar Reactor

SSRN

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SSRN 2023年

作者： Li, Naixu Xu, Lei Ren, Yuqi Liu, Maochang Zhu, Fengfan Cheng, Miao Zhou, Jiancheng Chen, Wenshuai Wang, Ke Wang, Nan School of Chemistry and Chemical Engineering Southeast University No.2 Dongnandaxue Road Jiangsu Nanjing211189 China International Research Center for Renewable Energy State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University No.28 Xianning West Road Shaanxi Xi'An710049 China Key Laboratory of Bio-Based Material Science and Technology Ministry of Education Northeast Forestry University No. 26 Hexing Road Harbin150040 China

This study is dedicated to solving the problems of low energy utilization and low yield in the conventional photocatalytic CO2 reduction process. In this work, a novel concentrated solar (light) reactor was established to improve solar energy utilization efficiency and CO2 conversion rate by concentrating light and heat (that is, by converting light into heat). The TF@TNT/0.4CoOx-0.1CuO monolithic photocatalyst based on titanium foam was designed and prepared. The results showed that the light intensity increased by ~10.6 times (from 400 mW/cm2 to 4266 mW/cm2) while the yield of CH4, the product of CO2 reduction driven by photo-thermal coupling effect, increased by ~220 times (from 0.53 µmol/cm2 to 116.4 µmol/cm2) in the concentrated solar (light) reactor. The results of CH4 yield, electrochemical measurement, and apparent activation energy calculation were investigated in the concentrator reactor under the conditions of concentrated and non-concentrated irradiation of simulated sunlight in different wavelength ranges. It can be found that the concentrated light and the induced photo-thermal coupling effect can significantly reduce the reaction barrier (from 41.62 to 31.51 kJ/mol) and improve the conversion efficiency of solar energy to chemical energy by ~15 times. This provides a potentially feasible method for efficient and green utilization of CO2 driven by solar energy. © 2023, The Authors. All rights reserved.

关键词： Solar energy

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Insight into the Interconversions of Three-Phase Products Through the Supercritical Water Gasification of Bark

SSRN

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SSRN 2023年

作者： Ge, Hui Yi, Lei Huang, Yong Peng, Pai Cao, Wen Chen, Yunan Qi, Xingang Guo, Liejin State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University No.28 Xianning West Road Xi'An710049 China International Institute for Innovation Jiangxi University of Science and Technology Jiangxi 341000 China Suzhou Academy Xi’an Jiaotong University No.99 Ren’ai Road Jiangsu Suzhou215123 China

The clean and efficient utilization of biomass waste for hydrogen production conforms to social development in the future. In this work, hydrogen production from supercritical water gasification (SCWG) of fir bark (FB) was investigated systematically at various reaction temperatures (500–750 °C), feedstock concentrations (5%–15%), and retention time (0–40 min). The gaseous, liquid, and solid products were analyzed comprehensively to determine the gasification mechanism. The results demonstrated that FB was the alternative feedstock for hydrogen production. The maximum CE and H2 selectivity of 95.34% and 0.99 were obtained at 700 °C-5%-40 min. High reaction temperature and prolonging retention time accelerated the conversions of phenolic compounds in liquid products and functional groups in solid products. High feedstock concentration also resulted in the bond-making between functional groups in solid products. The reaction mechanism was proposed based on the components of gaseous and liquid products and the variations of functional groups in solid products. © 2023, The Authors. All rights reserved.

关键词： Hydrogen production

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Investigation of Droplet Dynamic Behavior in Pemfcs Gas Diffusion Layer and Gas Channel with Micro-Ct and Lattice Boltzmann Method

SSRN

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SSRN 2024年

作者： Lv, Xuecheng Zhou, Zhifu Wu, Wei-Tao Wei, Lei Gao, Linsong Lyu, Jizu Hu, Chengzhi Li, Yang Li, Yubai Song, Yongchen Key Laboratory of Ocean Energy Utilization and Energy Conservation of Ministry of Education Dalian University of Technology Dalian116024 China State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'An710049 China School of Mechanical Engineering Nanjing University of Science and Technology Nanjing210094 China Department of Mechanical and Energy Engineering Southern University of Science and Technology Shenzhen518055 China School of Mechanical Engineering and Mechanics Xiangtan University Xiangtan411105 China School of Mechanical Engineering Guangdong Ocean University Zhanjiang524088 China

This study reconstructed the 3D structure for the gas diffusion layer (GDL) of proton exchange membrane fuel cells (PEMFCs) using the micro-CT technique and investigated the dynamic behavior of droplets inside the multi-scale space of GDL and gas channel (GC) using the lattice Boltzmann method (LBM). The prediction model for droplet detachment at the GDL-GC interface was developed. The results indicate that there is a significant difference between the breakage location of the liquid bridge and the trajectory of the liquid droplet after detaching from the GDL-GC interface in the multi-scale space of GC and GDL, compared to the single-scale GC space where GDL is ignored. The increase in gas velocity and internal contact angle of the GDL contribute to reducing the droplet detachment volume and increasing the droplet detachment frequency. At the internal contact angle of 120º-140º, GDL exhibited the most efficient removal of liquid water. A contact angle smaller than this range would hinder the detachment of droplets in the GC, while a contact angle larger than this range would lead to the accumulation of liquid water in the GDL. The surface force generated by the connection of liquid bridges in the analytical model for critical droplet detachment forms an angle with the gas flow direction, with the characteristic length determining this force being the minimum diameter at the necking of the liquid bridge. © 2024, The Authors. All rights reserved.

关键词： Contact angle

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Theoretical insights into the hydrophobicity of low index CeO2 surfaces

arXiv

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arXiv 2019年

作者： Fronzi, Marco N. Assadi, M. Hussein Hanaor, Dorian A.H. International Research Centre for Renewable Energy State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’anShaanxi710049 China 1-1 Namiki TsukubaIbaraki305-0044 Japan Chair of Advanced Ceramic Materials Institute for Materials Science and Technology Technische Universität Berlin Berlin10653 Germany

The hydrophobicity of CeO2 surfaces is examined here. Since wettability measurements are extremely sensitive to experimental conditions, we propose a general approach to obtain contact angles between water and ceria surfaces of specified orientations based on density functional calculations. In particular, we analysed the low index surfaces of this oxide to establish their interactions with water. According to our calculations, the CeO2 (111) surface was the most hydrophobic with a contact angle of Θ = 112.53° followed by (100) with Θ = 93.91°. The CeO2 (110) surface was, on the other hand, mildly hydrophilic with Θ = 64.09°. By combining our calculations with an atomistic thermodynamic approach, we found that the O terminated (100) surface was unstable unless fully covered by molecularly adsorbed water. We also identified a strong attractive interaction between the hydrogen atoms in water molecules and surface oxygen, which gives rise to the hydrophilic behaviour of (110) surfaces. Interestingly, the adsorption of water molecules on the lower-energy (111) surface stabilises oxygen vacancies, which are expected to enhance the catalytic activity of this plane. The findings here shed light on the origin of the intrinsic wettability of rare earth oxides in general and CeO2 surfaces in particular and also explain why CeO2 (100) surface properties are so critically dependant on applied synthesis methods. Copyright © 2019, The Authors. All rights reserved.

关键词： Density functional theory

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