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A non-uniform pressure distribution model on the end face in screw expander and shaft seal leakage characteristics{fr}Etude des parametres de la Structure sur les fuites d'arbres dans un expandeur a vis base sur un nouveau modele de distribution de pression non uniforme sur la face d'extremite

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INTERNATIONAL JOURNAL OF REFRIGERATION 2023年 154卷 99-110页

作者： Tian, Yafen Wang, Zebin Geng, Yanting Chen, Xi Zhang, Hua He, Qize Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China Shanghai Fire Res Inst MEM Shanghai 200093 Peoples R China

Pressure distribution on the end face of screw expanders is the primary premise for calculating shaft seal leakage and axial force. Different from other types of expanders, pressure distribution on the screw expander end face is not only affected by operating conditions but also closely related to rotor geometric parameters. To illustrate the leakage characteristics of shaft seal in screw expanders, a non-uniform pressure distribution model on the end face was proposed, and a thermodynamic leakage model in the shaft seal was established. Labyrinth seal, the most widely used sealing assembly, was taken as an example to study the effects of shaft seal parameters on leakage. The influence of four main parameters, namely tooth tip clearance, cavity depth, cavity width, and clearance on the rotor end face, on the leakage of the shaft seal was studied. The results show that pressure on the screw expander end face is non-uniformly distributed, and the average pressure is far less than the highest operating pressure. Moreover, the leakage through the shaft seal rises rapidly with the increase of end face clearance and tooth tip clearance, and a 0.1 mm increment of them can lead to increased leakage up to 108.6% and 52.5%, respectively. And the leakage drops with the increment of cavity width. There is an optimal depth-to width ratio of about 0.13 for minimum leakage. Clearance on the rotor end face has the most significant influence on the leakage of the seal, followed by the tooth tip clearance, cavity width, and cavity depth.

关键词： Twin-screw expander End face pressure Structure parameters Leakage simulation Shaft seal

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Short-term load forecasting for multiple buildings: A length sensitivity-based approach

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ENERGY REPORTS 2022年 8卷 14274-14288页

作者： Chen, Yongbao Chen, Zhe Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Shanghai Key Lab Multiphase Flow & Heat Transfer Shanghai 200093 Peoples R China

With the rapid development of large-scale building energy monitoring platforms, it is of great significance to develop precise forecasting methods for buildings on a large scale to achieve better energy system design, system operation, energy management, and renewable energy integration in the grid. Traditionally, using all available historical data to train a data-driven model has been widely employed to ensure prediction performance because more historical information can be learned. However, this strategy may introduce more noise, especially for short-term load forecasting. Thus, this study proposes a novel approach for selectively utilizing building historical data to determine the amount of data that should be used to train the data-driven model. First, the CV(RMSE) curve of each building reflecting the relationship between training data length and forecasting accuracy is obtained using LightGBM. Second, clustering techniques such as k-means are used to identify buildings that are sensitive to the training data length based on CV(RMSE) curves. Finally, the optimal training data length for day-ahead forecasting is estimated for each building. The case study shows that approximately 20% of buildings in the Building Data Genome are labeled as length-sensitive buildings, and adopting appropriate training data lengths can reduce the prediction error of these buildings by up to 15%. (c) 2022 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://***/licenses/by- nc- nd/4.0/).

关键词： Short-term load forecasting Big data for buildings Data-driven models LightGBM Length sensitivity analysis

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A multi-step discharge/charge model of Li-O2 batteries coupled with electrolyte decomposition and carbon electrode corrosion reactions

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APPLIED ENERGY 2024年 376卷

作者： Wang, Yuanhui Dou, Shaojun Hao, Liang Yanshan Univ Hebei Engn Res Ctr Low Carbon Dev & Resource Utili Sch Vehicle & Energy Qinhuangdao 066004 Peoples R China Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

Electrolyte decomposition and electrode corrosion stand as two primary side reactions in lithium-oxygen (Li-O2) batteries during their discharge/charge cycles. In this work, a comprehensive Li-O2 battery model combining multi-step lithium peroxide (Li2O2) formation, electrolyte decomposition, and electrode corrosion is proposed. Based on this model, the deposition behaviors and cycling performance of the Li-O2 battery under deep discharge/charge cycles are investigated. The stop of discharge is mainly ascribed to the loss of active surface area for the battery using tetraethylene glycol dimethyl ether (TEGDME) electrolyte, while both O2 transport limitation and active surface area loss lead to the discharge termination for battery using dimethyl sulfoxide (DMSO) electrolyte. The incomplete decomposition of Li2O2 and lithium carbonate (Li2CO3) clogs electrode pores, leading to a continuous decline in the discharge capacity of the Li-O2 battery. For the TEGDMEbased battery, the undecomposed Li2CO3 gradually dominates the deposition with cycles, wherein electrode corrosion becomes the primary source of the undecomposed Li2CO3 after 3 cycles. For the DMSO-based battery, undecomposed Li2O2 is always a dominant trigger for battery discharge capacity degradation, although electrode corrosion remains a key contributor to Li2CO3 generation. Despite the DMSO-based battery exhibiting lower rates of electrolyte decomposition and electrode corrosion, it demonstrates poorer cyclic performance than the TEGDME-based battery due to the generation of more toroidal Li2O2. Moreover, when the charging cut-off voltage is reduced to 4.2 V, discharge capacity diminishes more rapidly due to the increased accumulation of undecomposed Li2O2, despite suppressed Li2CO3 deposition. Finally, the results confirm that thick electrodes lead to deteriorating cycling performance, stemming from increased discharge/charge overpotential and extended discharge/charge times, thus intensifying the side reac

关键词： Discharge/charge model Li-O-2 batteries Electrolyte decomposition Electrode corrosion Cycling performance

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Experimental study on a wet precooling system for fruit and vegetables with ice slurry

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INTERNATIONAL JOURNAL OF REFRIGERATION 2022年 133卷 9-18页

作者： Li, Xiang Wu, Weidong Li, Kun Ren, Xueming Wang, Zian Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Shanghai Key Lab Multiphase Flow & Heat Transfer Shanghai 200093 Peoples R China

Aiming at the application of fruit and vegetables precooling, an innovative wet precooling system with ice slurry as a cooling medium was proposed. A small wet precooling room performance test platform was built. With apples as the precooling subject, the temperature and relative humidity in precooling room, the cooling rate and weight loss of apples as indexes, by changing the weight concentration of ice slurry additives (0%-8%), the ice fraction (0%-10%) and the ice slurry flow rate (50-150 L h-1), the precooling experiments were carried out. The results showed that increasing the concentration of ice slurry additives (NaCl) could effectively reduce the equilibrium temperature in precooling room. For the ice slurry solution with the additive concentrations of 0%, 2%, 4%, 6% and 8%, the equilibrium temperature in precooling room were 4.3 degrees C, 1.7 degrees C, 0.4 degrees C, 0.0 degrees C and -0.7 degrees C, respectively. When the ice fractions increased from 0% to 10%, the precooling time decreased from 165 min to 96 min, and the weight loss decreased from 2.11% to 0.42%. When the ice slurry flow rate increased, the relative humidity in precooling room increased, and the cooling rate of apples firstly increased rapidly and then leveled off. When the flow rate reached 100 L h-1, the relative humidity remained above 90%. The precooling system has a strong applicability, easy to realize the stable environment of low temperature and high relative humidity (0 degrees C, >90%), so it has a large application space in the precooling and fresh-keeping of fruit and vegetables.

关键词： Wet precooling system Ice slurry Fruit and vegetables precooling Cooling rate Weight loss

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Unraveling the contribution of water to the discharge capacity of Li-O2 batteries from a modelling perspective

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APPLIED ENERGY 2024年 372卷

作者： Wang, Yuanhui Zhang, Tianci Hao, Liang Yanshan Univ Hebei Engn Res Ctr Low Carbon Dev & Resource Utili Sch Vehicle & Energy Qinhuangdao 066004 Peoples R China Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

Adding water (H2O) to the electrolyte improves discharge capacity by enhancing the solution mechanism, but the evolution of discharge capacity with H2O content growth remains divergent. In view of this, the contribution of H2O to discharge capacity is revealed by modelling a lithium-oxygen (Li-O2) battery coupled with the H2O reaction mechanism. With increasing H2O content in the electrolyte, the discharge capacity first rises thanks to the alleviation of surface passivation and then declines owing to the limitation of O2 diffusion. Although the promotion of solution mechanism is most pronounced with a small amount of H2O (below 2000 ppm) in the dimethoxyethane (DME)-based electrolyte, the enhancement of solution mechanism in the tetraethylene glycol dimethyl ether (TEGDME)-based electrolyte is more sensitive to changes in H2O contents (above 500 ppm) than DME- and DMSO (dimethyl sulfoxide)-based electrolytes. Hence the H2O contents corresponding to the maximum discharge capacity (defined as "optimized water content") of TEGDME- and DMSO-based electrolytes are 2000 ppm and 10,500 ppm based on the Super P carbon cathode, respectively. The evolutions of "optimized water content" and discharge capacity are more sensitive to changes in the porosity and initial carbon particle radius of the carbon cathode. Compared to the absence of H2O, the discharge capacities with the "optimized water content" increase by 360% and 346% at a porosity of 0.9, as well as by 268% and 290% for TEGDME- and DMSO-based electrolytes at an initial carbon particle radius of 70 nm, respectively. In consequence, the electrolyte composition and cathode structure codetermine the "optimized water content" and the maximum promotion of H2O to the discharge capacity.

关键词： Li-O (2) batteries H (2) O additive Discharge capacity O- 2 diffusion Surface passivation Cathode structure

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The assessment of energy-related greenhouse gas emissions in China's chemical industry

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SUSTAINABLE PRODUCTION AND CONSUMPTION 2023年 37卷 112-125页

作者： Li, Zeqiu Yang, Fan Huang, Beijia Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China Univ Shanghai Sci & Technol Coll Environm & Architecture Shanghai Peoples R China

The chemical industry has a large production scale, many products, and very complex processes, so estimating the greenhouse gas (GHG) it produces is not easy. Few comprehensive assessment models at the national level are studied. Emission sources of most models are not complete, and data are outdated. The paper conducts a com-prehensive assessment of GHG emissions in China's chemical industry. The emission sources cover direct and in-direct emissions. The chemical industry is divided into three main sub sectors to explore GHG flows. GHG flows are examined through chemical production and consumption, and then the emission reduction potential is pre-dicted based on technological developments. The assessment results show that crude oil and coal are the main sources of direct GHG emissions. The indirect GHG emissions are mainly from North China and Northwest China. GHG emissions in the power grid regions are directly related to the distribution of the chemical industry in China. Coal chemical industry has the most GHG emissions. The analysis of driving factors shows that the out-put effect is the main factor of GHG emissions. Scenario analysis shows that the baseline scenario will reach 6195.95 Mt in 2030. Under the technological improvement scenarios, 589.01 Mt emission reduction can be achieved by 2030 compared with the baseline scenario. Based on the results of the study, this paper provides some policy recommendations.(c) 2023 Institution of Chemical Engineers. Published by Elsevier Ltd. All rights reserved.

关键词： Chemical industry GHG Assessment model Driving factors

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Study on boiling heat transfer mechanism based on microlayer evaporation theory 6

Study on boiling heat transfer mechanism based on microlayer...

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6th International Conference on Fluid Mechanics and Industrial Applications, FMIA 2022

作者： Dong, Wu-Han Gao, Ming Shen, Zhong-Xiang Zhang, Li-Xin 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

Based on dynamic microlayer evaporation model. heat transfer mechanism of nuclear boiling and microlayer thickness under single bubble on heated surface. It has a lot to do with the temperature of the wall. Therefore, this paper studies the mechanism of bubble microlayer and makes comparative analysis with its experiments. It is helpful to master nuclear boiling heat transfer more comprehensively. In the study of individual bubble microlayer thickness. The effects of time and radius on wall temperature are considered in this paper. The theoretical formula of initial thickness of microlayer is deduced. The theoretical formula is compared with the experimental data of microlayer evaporation under the nucleation bubble. It was found that the experimental data fell within ±25% of the formula range. It is consistent with the previous experimental research. © Published under licence by IOP Publishing Ltd.

关键词： Evaporation

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Liutex identification on hairpin vortex structures in a channel based on msfle and moving-PIV

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Journal of Hydrodynamics 2021年第6期33卷 1119-1128页

作者： Xin-ran Tang Xiang-rui Dong Xiao-shu Cai Wu Zhou School of Energy and Power Engineering University of Shanghai for Science and TechnologyShanghai 200093China Key Laboratory of Multiphase Flow and Heat Transfer in Shanghai Power Engineering University of Shanghai for Science and TechnologyShanghai 200093China

The spatiotemporal evolution of hairpin vortex structures in a fully developed turbulent boundary layer is investigated qualitatively and quantitatively by using two image *** this paper,the moving single-frame and long-exposure(MSFLE)image method is used to intuitively track the evolution process of a hairpin vortex,while the moving particle image velocimetry(moving-PIV)method is applied for obtaining a moving velocity field for quantitative *** to the structural characteristics of the hairpin vortex,an inclined light sheet with an appropriate inclination of 53°is arranged to capture the complete hairpin vortex structure at Re_(θ)=97–*** addition,the core size and the rotational strength of a hairpin vortex are further defined and quantified by the Liutex vector *** evolution process of a complete hairpin vortex structure observed by MSFLE shows that the shear along the normal direction leads to an increasing strength of the hairpin vortex,accompanied by a lifting vortex head and a distance decrease between two vortex legs during the dissipation *** combining moving-PIV with the Liutex identification,the spatiotemporal evolution of four typical regions of a hairpin vortex projecting into a 53°cross-section is *** results show that the process from the generation to the dissipation of a single hairpin vortex can be well characterized and recorded by the Liutex based on the core size and rotational intensity,and the evolution process is consistent with the MSFLE *** to the statistics of vortex core size and rotation intensity along time,the evolution of the hairpin vortex necks and legs can be described as a process of enhancement followed by *** the vortex head,its evolution maintains longer attributed to its far-from-wall position,which consists of an absolute enhancement process(stage 1)with an increasing rotation strength and a constant core size,and an absolute dissipation(stage 2)with a dec

关键词： Turbulent boundary layer hairpin vortex moving single-frame and long-exposure moving particle image velocimetry(PIV) Liutex vortex identification method

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Comparative experimental study on dynamic characteristics of bubble microlayers in small channel flow boiling and pool boiling 6

Comparative experimental study on dynamic characteristics of...

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6th International Conference on Fluid Mechanics and Industrial Applications, FMIA 2022

作者： Shen, Zhongxiang Gao, Ming Dong, Wuhan Zhang, Lixin 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

The microlayer present at the bottom of the bubble plays a very important role in heat transfer during nucleation boiling. In this paper, the dynamic characteristics of microlayer at the bottom of boiling bubble in a small channel were studied by laser interferometry method and high speed camera, and the results were compared with pool boiling experiments. The results show that the bubbles have an obvious tendency to slip in the flow boiling. The microlayer interference fringe is deformed and no longer a complete Newtonian ring. By analyzing the thickness distribution of microlayer in different directions in flow boiling and the change of micro-contact angle in the flow direction, it was found that the micro-contact angle in the flow direction became larger with the growth of bubbles. © Published under licence by IOP Publishing Ltd.

关键词： Contact angle

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Electrospinning engineering of gas electrodes for high-performance lithium-gas batteries

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Carbon Energy 2024年第10期6卷 353-398页

作者： Jingzhao Wang Xin Chen Jianan Wang Xiangming Cui Ze Wang Guangpeng Zhang Wei Lyu Maxim Shkunov S.Ravi P.Silva Yaozu Liao Kai Yang Wei Yan State Key Laboratory of Multiphase Flow in Power Engineering Department of Environmental Science and EngineeringSchool of Energy and Power EngineeringXi'an Jiaotong UniversityXi'anChina Advanced Technology Institute University of SurreyGuildfordSurreyUK State Key Laboratory for Modification of Chemical Fibers and Polymer Materials College of Materials Science and EngineeringDonghua UniversityShanghaiChina

Lithium-gas batteries(LGBs)have garnered significant attention due to their impressive high-energy densities and unique gas conversion ***,the practical application of LGBs faces substantial challenges,including sluggish gas conversion kinetics inducing in low-rate performance and high overpotential,along with limited electrochemical reversibility leading to poor cycle *** imperative task is to develop gas electrodes with remarkable catalytic activity,abundant active sites,and exceptional electrochemical ***,a versatile and well-established technique for fabricating fibrous nanomaterials,has been extensively explored in LGB *** this work,we emphasize the critical structure-property for ideal gas electrodes and summarize the advancement of employing electrospun nanofibers(NFs)for performance enhancement in *** elucidating the fundamental principles of LGBs and the electrospinning technique,we focus on the systematic design of electrospun NF-based gas electrodes regarding optimal structural fabrication,catalyst handling and activation,and catalytic site optimization,as well as considerations for large-scale *** demonstrated principles and regulations for electrode design are expected to inspire broad applications in catalyst-based energy applications.

关键词： carbon nanofibers electrocatalyst electrospinning gas electrodes metal-gas batteries

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