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Effect of catalyst layer mesoscopic pore-morphology on cold start process of PEM fuel cells

Ahmed Mohmed DAFALLA, Fangming JIANG

《能源前沿（英文）》 2021年 第15卷 第2期   页码 460-472 doi: 10.1007/s11708-021-0733-4

摘要： Water transport is of paramount importance to the cold start of proton exchange membrane fuel cells (PEMFCs). Analysis of water transport in cathode catalyst layer (CCL) during cold start reveals the distinct characteristics from the normal temperature operation. This work studies the effect of CCL mesoscopic pore-morphology on PEMFC cold start. The CCL mesoscale morphology is characterized by two tortuosity factors of the ionomer network and pore structure, respectively. The simulation results demonstrate that the mesoscale morphology of CCL has a significant influence on the performance of PEMFC cold start. It was found that cold-starting of a cell with a CCL of less tortuous mesoscale morphology can succeed, whereas starting up a cell with a CCL of more tortuous mesoscale morphology may fail. The CCL of less tortuous pore structure reduces the water back diffusion resistance from the CCL to proton exchange membrane (PEM), thus enhancing the water storage in PEM, while reducing the tortuosity in ionomer network of CCL is found to enhance the water transport in and the water removal from CCL. For the sake of better cold start performance, novel preparation methods, which can create catalyst layers of larger size primary pores and less tortuous pore structure and ionomer network, are desirable.

关键词： cold start     energy conversion     fuel cells     mesoscale morphology     tortuosity     water management    

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汽油压燃发动机低负荷燃烧稳定性和冷机着火性能的试验研究 Article

周磊, 华剑雄, 卫海桥, 韩义勇

《工程（英文）》 2019年 第5卷 第3期   页码 558-567 doi: 10.1016/j.eng.2018.12.010

摘要：

汽油压燃（GCI）是一种极具发展前景的低排放、高效率燃烧技术。然而，低负荷燃烧稳定性和冷启动是GCI燃烧面临的两大挑战。为了解决这些问题，研究人员提出了负气门重叠角（NVO）、喷油策略优化、燃油重整和进气预热等策略，然而，冷启动难题却仍然有待解决。本文的目标正是研究实现GCI发动机冷启动的切实可行的方法。本研究结合了NVO、缸内燃油重整和进气预热，以实现在冷机和冷边界条件下GCI发动机的着火和随后的热机工况。结果表明，喷油开始时刻（SOI）在进气冲程时具有最佳的燃油经济性；SOI在压缩冲程期间可有效拓展发动机小负荷极限；SOI在NVO期间则可实现发动机在冷进气和冷却液未预热条件下的稳定燃烧。考虑到NVO喷油策略具有未燃混合气活性强、缸内热积累速度快的特点，该策略非常适合用于实现GCI的冷机着火。在冷启动过程中，实现GCI发动机的着火还需要一些辅助措施，如进气加热，以启动第一个着火循环。通过NVO策略、缸内燃油重整和进气预热的组合，本文实现了GCI发动机在5个燃烧循环内的成功着火。启动过程结束后，发动机无需再采用进气预热即可实现稳定运行。

关键词： 汽油压燃     冷起动     热机工况     喷油策略     燃烧稳定性    

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HHT-based crack identification method for start-up rotor

Bing LI, Chunlin ZHANG, Zhengjia HE

《机械工程前沿（英文）》 2012年 第7卷 第3期   页码 300-304 doi: 10.1007/s11465-012-0328-1

摘要：

This paper presents a crack identification method for start-up rotor based on the Hilbert-Huang transform (HHT). With this method, the instantaneous frequency (IF) of each intrinsic mode function is obtained through the Hilbert transform, and the spectrum of IF is calculated accordingly. The influence of acceleration and crack depth on the rotor is analyzed through experiments. HHT is employed to detect the shallower crack, and is then tested during the start-up process of the rotor. The results of the experiment show that HHT is a better tool for crack detection than fast Fourier transform.

关键词： cracked rotor     start-up     Hilbert-Huang transform (HHT)    

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氢能列车投入运营

Chris Palmer

《工程（英文）》 2022年 第11卷 第4期   页码 9-11 doi: 10.1016/j.eng.2022.02.003

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review on technologies with electricity generation potentials using liquified natural gas regasification cold

《能源前沿（英文）》 2023年 第17卷 第3期   页码 332-379 doi: 10.1007/s11708-023-0863-y

摘要： In modern times, worldwide requirements to curb greenhouse gas emissions, and increment in energy demand due to the progress of humanity, have become a serious concern. In such scenarios, the effective and efficient utilization of the liquified natural gas (LNG) regasification cold energy (RCE), in the economically and environmentally viable methods, could present a great opportunity in tackling the core issues related to global warming across the world. In this paper, the technologies that are widely used to harness the LNG RCE for electrical power have been reviewed. The systems incorporating, the Rankine cycles, Stirling engines, Kalina cycles, Brayton cycles, Allam cycles, and fuel cells have been considered. Additionally, the economic and environmental studies apart from the thermal studies have also been reviewed. Moreover, the discussion regarding the systems with respect to the regassification pressure of the LNG has also been provided. The aim of this paper is to provide guidelines for the prospective researchers and policy makers in their decision making.

关键词： liquified natural gas     cold energy     power generation    

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Optimization of cold-end system of thermal power plants based on entropy generation minimization

《能源前沿（英文）》 2022年 第16卷 第6期   页码 956-972 doi: 10.1007/s11708-021-0785-5

摘要： Cold-end systems are heat sinks of thermal power cycles, which have an essential effect on the overall performance of thermal power plants. To enhance the efficiency of thermal power plants, multi-pressure condensers have been applied in some large-capacity thermal power plants. However, little attention has been paid to the optimization of the cold-end system with multi-pressure condensers which have multiple parameters to be identified. Therefore, the design optimization methods of cold-end systems with single- and multi-pressure condensers are developed based on the entropy generation rate, and the genetic algorithm (GA) is used to optimize multiple parameters. Multiple parameters, including heat transfer area of multi-pressure condensers, steam distribution in condensers, and cooling water mass flow rate, are optimized while considering detailed entropy generation rate of the cold-end systems. The results show that the entropy generation rate of the multi-pressure cold-end system is less than that of the single-pressure cold-end system when the total condenser area is constant. Moreover, the economic performance can be improved with the adoption of the multi-pressure cold-end system. When compared with the single-pressure cold-end system, the excess revenues gained by using dual- and quadruple-pressure cold-end systems are 575 and 580 k$/a, respectively.

关键词： cold-end system     entropy generation minimization     optimization     economic analysis     genetic algorithm (GA)    

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Current understanding and applications of the cold sintering process

Tong Yu, Jiang Cheng, Lu Li, Benshuang Sun, Xujin Bao, Hongtao Zhang

《化学科学与工程前沿（英文）》 2019年 第13卷 第4期   页码 654-664 doi: 10.1007/s11705-019-1832-1

摘要： In traditional ceramic processing techniques, high sintering temperature is necessary to achieve fully dense microstructures. But it can cause various problems including warpage, overfiring, element evaporation, and polymorphic transformation. To overcome these drawbacks, a novel processing technique called “cold sintering process (CSP)” has been explored by Randall et al. CSP enables densification of ceramics at ultra-low temperature (≤300°C) with the assistance of transient aqueous solution and applied pressure. In CSP, the processing conditions including aqueous solution, pressure, temperature, and sintering duration play critical roles in the densification and properties of ceramics, which will be reviewed. The review will also include the applications of CSP in solid-state rechargeable batteries. Finally, the perspectives about CSP is proposed.

关键词： cold sintering process     processing variables     solid-state rechargeable batteries    

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新企业寻求加快核聚变商业化

Mitch Leslie

《工程（英文）》 2022年 第8卷 第1期   页码 6-8 doi: 10.1016/j.eng.2021.11.006

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Application of cold spraying for flux-free brazing of aluminium alloy 6060

Kirsten BOBZIN, Lidong ZHAO, Thomas SCHLAEFER, Thomas WARDA,

《机械工程前沿（英文）》 2010年 第5卷 第3期   页码 256-260 doi: 10.1007/s11465-010-0095-9

摘要： In the present study, samples of aluminium alloy 6060 were coated by cold spraying with a powder of brazing alloy Al12Si. The influence of the process gas temperature on particle velocities and coating build-up was investigated. The coated samples were heat-treated in air and under argon atmosphere to investigate the wetting behaviour of the deposited Al12Si and the diffusion processes between Al12Si coatings and substrates. Coated samples were brazed flux-free under argon atmosphere by an induction heating system. The microstructure of the coated, heat-treated, and brazed samples was investigated. The shear strength of the brazed joints was determined. The results show that the brazing alloy Al12Si could be very well deposited on the substrate by cold spraying. The particle velocity increased with increasing process temperature. Correspondingly, the thickness of Al12Si coatings increased with increasing process temperature. The heat treatments showed that a very good metallurgical bond between the Al12Si coatings and the substrate could be realized by the deposition using cold spraying. The coated samples could be well brazed without fluxes. The coating thickness and overlap width influenced the shear strength of the brazed joints. The highest shear strength of brazed joints amounts to 80 MPa.

关键词： aluminium alloy     flux-free brazing     cold spraying     shear strength    

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A fully solid-state cold thermal energy storage device for car seats using shape-memory alloys

《能源前沿（英文）》 2023年 第17卷 第4期   页码 504-515 doi: 10.1007/s11708-022-0855-3

摘要： Thermal energy storage has been a pivotal technology to fill the gap between energy demands and energy supplies. As a solid-solid phase change material, shape-memory alloys (SMAs) have the inherent advantages of leakage free, no encapsulation, negligible volume variation, as well as superior energy storage properties such as high thermal conductivity (compared with ice and paraffin) and volumetric energy density, making them excellent thermal energy storage materials. Considering these characteristics, the design of the shape-memory alloy based the cold thermal energy storage system for precooling car seat application is introduced in this paper based on the proposed shape-memory alloy-based cold thermal energy storage cycle. The simulation results show that the minimum temperature of the metal boss under the seat reaches 26.2 °C at 9.85 s, which is reduced by 9.8 °C, and the energy storage efficiency of the device is 66%. The influence of initial temperature, elastocaloric materials, and the shape-memory alloy geometry scheme on the performance of car seat cold thermal energy storage devices is also discussed. Since SMAs are both solid-state refrigerants and thermal energy storage materials, hopefully the proposed concept can promote the development of more promising shape-memory alloy-based cold and hot thermal energy storage devices.

关键词： shape-memory alloy (SMA)     elastocaloric effect (eCE)     cooled seat     cold thermal energy storage    

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Tracking in urban wastewater treatment plants in a cold region: Occurrence, species and infectivity

《环境科学与工程前沿（英文）》 2022年 第16卷 第9期 doi: 10.1007/s11783-022-1533-8

摘要：

• Cryptosporidium in WWTPs in a cold region was investigated in different seasons.

关键词： WWTPs     Cryptosporidium     Occurrence     Species     Infectivity     Low temperature    

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Survey of thermal comfort in residential buildings under natural conditions in hot humid and cold wet

Changhai PENG

《结构与土木工程前沿（英文）》 2010年 第4卷 第4期   页码 503-511 doi: 10.1007/s11709-010-0095-1

摘要： Comfort standards (ISO 7730, ASHRAE 55) specify the exact physical criteria for producing acceptable thermal environments, such as temperature, air movement, and humidity limits. These, however, are often difficult to comply with, particularly in hot humid and cold wet seasons in Nanjing, China. Changing expectations of comfort is important in evaluating comfort, since naturally conditioned buildings in Nanjing are not typically air-conditioned. For this objective, a field study was conducted during the summer of 2000 and the winter of 2001. A total of 600 participants each answered a subjective questionnaire. Analyzing these field data shows that in natural conditions, the influence of gender and age on people’s thermal sensations is insignificant compared with six main variables. In addition, people’s thermal discomfort rapidly increases along with growth in relative humidity. Further, the variation of people’s hot or cold sensations is in proportion to that of air movement, and the effect in winter is greater than that in summer. The range of acceptable temperatures in hot humid and cold wet Nanjing is between 14.14°C and 29.42°C.

关键词： thermal comfort     naturally conditioned     hot humid     cold wet     Nanjing    

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A critical literature review of bioretention research for stormwater management in cold climate and future

Hannah Kratky, Zhan Li, Yijun Chen, Chengjin Wang, Xiangfei Li, Tong Yu

《环境科学与工程前沿（英文）》 2017年 第11卷 第4期 doi: 10.1007/s11783-017-0982-y

摘要： Bioretention is a popular best management practice of low impact development that effectively restores urban hydrologic characteristics to those of predevelopment and improves water quality prior to conveyance to surface waters. This is achieved by utilizing an engineered system containing a surface layer of mulch, a thick soil media often amended with a variety of materials to improve water quality, a variety of vegetation, and underdrains, depending on the surrounding soil characteristics. Bioretention systems have been studied quite extensively for warm climate applications, but data strongly supporting their long-term efficacy and application in cold climates is sparse. Although it is apparent that bioretention is an effective stormwater management system, its design in cold climate needs further research. Existing cold climate research has shown that coarser media is required to prevent concrete frost from forming. For spring, summer and fall seasons, if sufficient permeability exists to drain the system prior to freezing, peak flow and volume reduction can be maintained. Additionally, contaminants that are removed via filtration are also not impacted by cold climates. In contrary, dissolved contaminants, nutrients, and organics are significantly more variable in their ability to be removed or degraded via bioretention in colder temperatures. Winter road maintenance salts have been shown to negatively impact the removal of some contaminants and positively impact others, while their effects on properly selected vegetation or bacteria health are also not very well understood. Research in these water quality aspects has been inconsistent and therefore requires further study.

关键词： Bioretention     Cold climate     Low impact development     Stormwater    

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Fabrication of form stable NaCl-Al2O3 composite for thermal energy storage by cold sintering process

Bilyaminu Suleiman, Qinghua Yu, Yulong Ding, Yongliang Li

《化学科学与工程前沿（英文）》 2019年 第13卷 第4期   页码 727-735 doi: 10.1007/s11705-019-1823-2

摘要： A form stable NaCl-Al O (50-50 wt-%) composite material for high temperature thermal energy storage was fabricated by cold sintering process, a process recently applied to the densification of ceramics at low temperature ˂ 300°C under uniaxial pressure in the presence of small amount of transient liquid. The fabricated composite achieved as high as 98.65% of the theoretical density. The NaCl-Al O composite also retained the chloride salt without leakage after 30 heating-cooling cycles between 750°C–850°C together with a holding period of 24 h at 850°C. X-ray diffraction measurements indicated congruent solubility of the alumina in chloride salt, excellent compatibility of NaCl with Al O , and chemical stability at high temperature. Structural analysis by scanning electron microscope also showed limited grain growth, high density, uniform NaCl distribution and clear faceted composite structure without inter-diffusion. The latent heat storage density of 252.5 J/g was obtained from simultaneous thermal analysis. Fracture strength test showed high sintered strength around 5 GPa after 50 min. The composite was found to have fair mass losses due to volatilization. Overall, cold sintering process has the potential to be an efficient, safe and cost-effective strategy for the fabrication of high temperature thermal energy storage materials.

关键词： cold sintering process     composite fabrication     thermal energy storage     phase change materials    

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Optimization of turbine cold-end system based on BP neural network and genetic algorithm

Chang CHEN,Danmei XIE,Yangheng XIONG,Hengliang ZHANG

《能源前沿（英文）》 2014年 第8卷 第4期   页码 459-463 doi: 10.1007/s11708-014-0335-5

摘要： The operation condition of the cold-end system of a steam turbine has a direct impact on the economy and security of the unit as it is an indispensible auxiliary system of the thermal power unit. Many factors influence the cold-end operation of a steam turbine; therefore, the operation mode needs to be optimized. The optimization analysis of a 1000 MW ultra-supercritical (USC) unit, the turbine cold-end system, was performed utilizing the back propagation (BP) neural network method with genetic algorithm (GA) optimization analysis. The optimized condenser pressure under different conditions was obtained, and it turned out that the optimized parameters were of significance to the performance and economic operation of the system.

关键词： optimization     turbine     cold-end system     BP neural network     genetic algorithm    

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标题 作者 时间 类型 操作

Effect of catalyst layer mesoscopic pore-morphology on cold start process of PEM fuel cells

Ahmed Mohmed DAFALLA, Fangming JIANG

期刊论文

汽油压燃发动机低负荷燃烧稳定性和冷机着火性能的试验研究

周磊, 华剑雄, 卫海桥, 韩义勇

期刊论文

HHT-based crack identification method for start-up rotor

Bing LI, Chunlin ZHANG, Zhengjia HE

期刊论文

氢能列车投入运营

Chris Palmer

期刊论文

review on technologies with electricity generation potentials using liquified natural gas regasification cold

期刊论文

Optimization of cold-end system of thermal power plants based on entropy generation minimization

期刊论文

Current understanding and applications of the cold sintering process

Tong Yu, Jiang Cheng, Lu Li, Benshuang Sun, Xujin Bao, Hongtao Zhang

期刊论文

新企业寻求加快核聚变商业化

Mitch Leslie

期刊论文

Application of cold spraying for flux-free brazing of aluminium alloy 6060

Kirsten BOBZIN, Lidong ZHAO, Thomas SCHLAEFER, Thomas WARDA,

期刊论文

A fully solid-state cold thermal energy storage device for car seats using shape-memory alloys

期刊论文

Tracking in urban wastewater treatment plants in a cold region: Occurrence, species and infectivity

期刊论文

Survey of thermal comfort in residential buildings under natural conditions in hot humid and cold wet

Changhai PENG

期刊论文

A critical literature review of bioretention research for stormwater management in cold climate and future

Hannah Kratky, Zhan Li, Yijun Chen, Chengjin Wang, Xiangfei Li, Tong Yu

期刊论文

Fabrication of form stable NaCl-Al2O3 composite for thermal energy storage by cold sintering process

Bilyaminu Suleiman, Qinghua Yu, Yulong Ding, Yongliang Li

期刊论文

Optimization of turbine cold-end system based on BP neural network and genetic algorithm

Chang CHEN,Danmei XIE,Yangheng XIONG,Hengliang ZHANG

期刊论文