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Transient Cooling Performance of R134a Flash-Evaporation Spray Enhanced by Cold Air Jet: A Novel Heat Transfer Enhancement Method in Laser Dermatology

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SSRN 2022年

作者： Li, Bufa Wang, Junfeng Tian, Jiameng Chen, Bin Xu, Haojie School of Energy and Power Engineering Jiangsu University Zhenjiang212013 China State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Shaanxi Xi’an710049 China

Nevus of Ota is a dermal hyperplastic pigmented disease with a morbidity rate of 0.1%–0.6% in the Asian population. Laser surgery with the assistance of cryogen spray cooling (CSC) is a potential clinical treatment for nevus of Ota. However, for Asians with high melanin content, it is necessary to enhance cooling capability without the increment of refrigerant amount. In this study, a R134a flash-evaporation cryogen spray cooling coupled with cold air jet (CSC-CAJ) was developed to improve the cooling capacity. Epoxy resin was employed as a skin phantom to investigate the heat transfer characteristics of CSC-CAJ with different air jet parameters. Air jet parameters of CSC-CAJ are recommended to be T a = -7 °C, V a = 3 m 3 /h Z a = 10 mm and Φ a = 30°. Compared to CSC, CSC-CAJ could reduce the minimum surface temperature from -39 °C to -42.1 °C, and the average value of convection heat transfer coefficient ( h ) of CSC-CAJ could increase from 8 W/(m 2 ·k) to 12.9 W/(m 2 ·k) or 61.3% for the recommended parameters. The liquid film residence time ( τ ) decreases from 301 ms to 234 ms or 23.3%. In addition, based on the visualization observation and surface heat transfer measurement, the frost formation phenomenon on the surface and the heat transfer enhancement mechanisms are well understood. Four modes, including Leidonfrost mode, no runoff mode, runoff mode and evaporation mode, are proposed to describe the four stages of CSC-CAJ. A non-dimensional correlation of normalized Nusselt number ( Nu *) and time ( t *) is summarized. The primary heat transfer enhancement mechanism of CSC-CAJ is found to be the increase in cryogen evaporation rate and the ratio of heat removal from the phantom surface to phase change latent heat. © 2022, The Authors. All rights reserved.

关键词： Evaporation

Tuning the local electronic structure of oxygen vacancies over copper-doped zinc oxide for efficient CO_(2) electroreduction

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eScience 2022年第5期2卷 518-528页

作者： Ke Wang Dongyu Liu Limin Liu Jia Liu XiaoFei Hu Ping Li Mingtao Li Andrey S.Vasenko Chunhui Xiao Shujiang Ding Xi'an Key Laboratory of Sustainable Energy Materials Chemistry School of ChemistryEnergy Storage Materials and Chemistry of Shaanxi University Engineering Research CenterXi'an Jiaotong University28 Xianning West RoadXi'an710049China International Research Center for Renewable Energy(IRCRE) State Key Laboratory of Multiphase Flow in Power Engineering(MFPE)Xi'an Jiaotong University28 Xianning West RoadXi'anShaanxi710049China HSE University 101000MoscowRussia College of Materials and Environmental Engineering Hangzhou Dianzi UniversityHangzhou310018PR China CNNC Shaanxi Uranium Enrichment Co. Ltd.HanzhongChina

Oxygen vacancies in metal oxides can serve as electron trap centers to capture CO_(2) and lower energy barriers for the electrochemical CO_(2) reduction reaction(CO_(2)RR).Under aqueous electrolytes,however,such charge-enriched active sites can be occupied by adsorbed hydrogen(H∗)and lose their effectiveness for the CO_(2)***,we develop an efficient catalyst consisting of Cu-doped,defect-rich ZnO(Cu–ZnO)for the CO_(2)RR,which exhibits enhanced CO Faradaic efficiency and current density compared to pristine *** introduced Cu dopants simultaneously stabilize neighboring oxygen vacancies and modulate their local electronic structure,achieving inhibition of hydrogen evolution and acceleration of the CO_(2)*** a flow cell test,a current density of more than 45mAcm^(−2) and a CO Faradaic efficiency of>80%is obtained for a Cu–ZnO electrocatalyst in the wide potential range of−0.76V to−1.06V *** Hydrogen Electrode(RHE).This work opens up great opportunities for dopant-modulated metal oxide catalysts for the CO_(2)RR.

关键词： CO_(2)electroreduction Oxygen vacancy Heteroatom doping Metal oxide catalysts

A Comprehensive Review on Multi-Dimensional Heat Conduction of Multi-Layer and Composite Structures:Analytical Solutions

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Journal of Thermal Science 2021年第6期30卷 1875-1907页

作者： AMIRI DELOUEI Amin EMAMIAN Amin SAJJADI Hasan ATASHAFROOZ Meysam LI Yueming WANG Lian-Ping JING Dengwei XIE Gongnan Department of Mechanical Engineering University of BojnordBojnordIran Mechanical Engineering Department Shahrood University of TechnologyShahroodIran Department of Mechanical Engineering Siijan University of TechnologySiijanIran School of Aerospace Engineering Xi’an Jiaotong UniversityXi’an 710049China Guangdong Provincial Key Laboratory of Turbulence Research and Applications Center for Complex Flows and Soft Matter Research and Department of Mechanics and Aerospace EngineeringSouthern University of Science and TechnologyShenzhen 518055China Department of Mechanical Engineering University of DelawareNewarkDelaware19711USA International Research Center for Renewable Energy State Key Laboratory of Multiphase Flow in Power EngineeringXi’an Jiaotong UniversityXi’an 710049China Department of Mechanical and Power Engineering Northwestern Polytechnical UniversityXi'an 710072China

Heat conduction in multi-layer and composite materials is one of the fundamental heat transfer problems in many industrial *** to different materials types,interface conditions,and various geometries of these laminates,the heat conduction mechanism is more complicated than that of one-layer isotropic *** solutions are the best ways to study and understand such problems in *** this study,different existing analytical solutions for heat conduction in multi-layer and composite materials are reviewed and classified in rectangular,cylindrical,spherical,and conical *** boundary conditions,internal heat source,and thermal contact resistance as the most critical parameters in the solution complexity investigated in the literature,are discussed and summarized in different *** types of multi-layer structures such as isotropic,anisotropic,orthotropic,and reinforced laminates are included in this *** is found that although more than half a century has passed since the beginning of the research on heat transfer in multi-layer composites,new researches that can help with a better understanding in this area are still being *** challenges and shortcomings in this area are also discussed to guide future researches.

关键词： multi-dimensional heat conduction composite laminates multi-layer structures analytical solutions interface contact resistance

Prediction of Pressure Drop in Heavy Oil-Water Ring Two-Phase flow Based on Modified Two-Fluid Model

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SSRN 2024年

作者： Fu, Jiqiang Du, Mingjun Jing, Jiaqiang Sun, Jie Liu, Huichao Chen, Yongjiu State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China China Petroleum Engineering & Construction Corp North Company Heibei Renqiu062552 China School of Oil & Natural Gas Engineering Southwest Petroleum University Sichuan Chengdu610500 China

Accurate prediction of pressure drop of the heavy oil-water ring flow in pipeline is of great significance for establishing an optimal drag reduction model and ensuring safe production. The effects of different factors on the flow pattern and pressure drop of heavy oil-water annular two-phase flow were systematically analyzed, and a standard two-fluid pressure drop prediction model for annular flow was established. By modifying the shear stress equation of oil-water interface and introducing the wave-flow theory to modify the shear stress equation of water wall, a pressure drop prediction model for the generalized concentric water ring was obtained to calculate the periodic fluctuations of oil phase. Furthermore, by introducing the comprehensive Reynolds number expression of eccentric water ring, the pressure drop prediction model for the generalized eccentric water ring was obtained to calculate the periodic fluctuations of oil phase. The results show that the pressure drop prediction accuracy of the concentric water ring for ultra-heavy oil is improved by 80 % by using the modified pressure drop prediction model. The comprehensive Reynolds number expression of eccentric water ring can effectively reflect the influence of eccentric effect on shear stress of water wall and the calculation error is less than 20 % by predicting the pressure drop of the generalized eccentric water ring with different density differences. © 2024, The Authors. All rights reserved.

关键词： Two phase flow

Thermodynamics analyses on a novel CHP system integrated with multi-grade thermal energy storage

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Journal of Energy Storage 2025年 106卷

作者： Liu, Rongtang Zhang, Kezhen Qin, Yuanzhi Wan, Kaidi Xu, Can Liu, Ming Ningbo Institute of Technology Beihang University Ningbo315800 China Xi'an Thermal Power Research Institute Co. Ltd. Xi'an710054 China State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China Dongfang Boiler Co. Ltd. of Dongfang Electric Group Chengdu611731 China

The high penetration level of intermittent renewable power necessitates the crucial requirement for combined heat and power systems to possess both high efficiency and flexibility. However, the heat-controlled operation modes of traditional combined heat and power systems impose limitations on their efficiency and flexibility. Therefore, it is of great significance to develop a heat-power decoupling technology that exhibits exceptional efficiency and flexibility. A novel combined heat and power system integrated with multi-grade thermal energy storage is proposed in this study. Thermodynamic analysis models of all operational conditions are developed, and the comprehensive characteristics of efficiency and operational flexibility for the proposed system are assessed by taking a 330 MW system as an example. Results show that the proposed system can decrease/increase 16.05 MW/30.96 MW power loads comparing with the reference system during the charging/discharging periods under the design condition. Energy efficiency of the proposed system can reach 49.40 %, which is improved by 1.66 percentage points. Exergy analysis reveals the exergy destruction order for the proposed system, and shows that the combustion and heat transfer in the boiler are the major process of exergy dissipation. Moreover, operation strategies of the proposed system during charging-discharging cycle are explored and formulated under off-design condition, suggesting that thermodynamic performances of the novel system under various conditions even extreme conditions exhibits exceptional properties. The maximum heat load of the proposed system can be improved by 46.78 % comparing with the reference system, and the maximum improvement of power load capacity during charging-discharging cycle is 14.58 percentage points. This study provides a promising approach for multi-grade thermal energy storage to improve the comprehensive characteristics of combined heat and power systems. © 2024

关键词： Charge storage

Thermal-Hydraulic Characteristics of Helical Cruciform Single Rod Based on Cfd Investigation

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SSRN 2024年

作者： Chen, Yiwen Zhang, Dalin Jiang, Dianqiang Deng, Jian Zhang, Xisi Wang, Xinan Tian, Wenxi Qiu, Suizheng Su, Guanghui State Key Laboratory of Multiphase Flow in Power Engineering Shaanxi Key Laboratory of Advanced Nuclear Energy and Technology School of Nuclear Science and Technology Xi’an Jiaotong University Xi’an710049 China Nuclear Power Institute of China 328 Changshun Avenue Chengdu610213 China Science and Technology on Reactor System Design Technology Laboratory Nuclear Power Institute of China Chengdu610213 China China Institute of Atomic Energy Beijing611731 China

To increase power density in nuclear reactors, the helical cruciform fuel (HCF) is designed as a fundamental element. HCF takes advantages of strong mixing effects, self-supporting features, and strengthened heat transfer, potential to increase the fuel performance in nuclear reactors. In this paper, friction factor and heat transfer coefficient empirical correlations of HCF single rod cooled by water were proposed using a geometric dimensionless number based on numerical simulation. The velocity field, and temperature distribution were obtained to discuss influences of geometric sizes on the fuel performance. Finally, correlations with a geometric dimensionless number were validated with various cases, whose application conditions were also proposed and discussed. This paper provides a guide for study of heat transfer and fluid flow in helical structures, and a reference for establishment of reactor system model using helical cruciform fuels. © 2024, The Authors. All rights reserved.

关键词： Heat transfer coefficients

Comparison of Lifetime Performance of Pemfc Stacks with Two Cooling Strategies Under Different Humidity

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SSRN 2024年

作者： Yang, Yunjie Bai, Minli Zhou, Zhifu Wu, Wei-Tao Lv, 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 School of Mechanical Engineering Guangdong Ocean University Zhanjiang524088 China

While reducing the size and Pt loading can achieve a lower proton exchange membrane fuel cell (PEMFC) stack cost, it is also very important to focus on the performance changes of the PEMFC stack during the long-term operation. A 3D PtCo catalysts long-term performance model is established in this study, and PEMFC stacks with one cooling unit per cell (1-cell stack) and three cells (3-cell stack) are employed as the computational domains, respectively. The effective area of each cell is 50 cm2, and the changes in current density as well as effective catalytic area of PEMFC stacks with two cooling strategies before and after long-term operation under different humidity conditions are investigated at low Pt loadings. The results show that there are large differences in the output voltage and current density distributions between the three cells due to the poor membrane hydration affected by the non-uniform temperature distribution, although the 3-cell stack can significantly reduce the size. Localized catalyst degradation in both 3-cell and 1-cell stacks is closely related to the geometry of the cathodic flow field, and non-uniform catalyst degradation is found to increase the activation and mass transfer losses and change the distribution of current density within the membrane. In addition, the 3-cell stack is found to perform even better in terms of durability, especially under high humidity conditions, which provides a potential solution to improve the durability of PEMFC stacks operating in harsh conditions. © 2024, The Authors. All rights reserved.

关键词： Durability

A kinetics and dynamics study on the auto-ignition of dimethyl ether at low temperatures and low pressures 38th

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A kinetics and dynamics study on the auto-ignition of dimeth...

38th International Symposium on Combustion, 2021

作者： Huang, Wenlin Zhao, Qian Huang, Zuohua Curran, Henry J. Zhang, Yingjia State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an 710049 China Combustion Chemistry Centre School of Chemistry Ryan Institute MaREI Nui Galway Ireland

Dimethyl ether (DME)/air mixtures at various equivalence ratios from lean (0.5) to extremely rich (5.0) were ignited behind reflected shock waves at a fixed pressure (3.0 atm) over the temperature range 625 K– 1200 K. The ignition behavior was different from that at high-pressures, with a repeatable ignition delay time fall-off feature observed experimentally in the temperature transition zone from the negative temperature coefficient (NTC) regime to the high-temperature regime. The fall-off behavior showed strong equivalence ratio dependence and disappeared completely at an equivalence ratio of 5.0. A local ignition kernel postulate was implemented numerically to quantifiably examine the inhomogeneous premature ignition. At low temperature, no pre-ignition occurs in the mixture. A conspicuous discrepancy was observed between the measurements and constrained UV simulations at temperatures beyond the NTC regime. A third O₂ addition reaction sub-set was incorporated into AramcoMech 3.0, together with related species thermochemistry calculated using the G3/G4/CBS-APNO compound method, to explore the low-temperature deviation. The new reaction class did not influence the model predictions in IDT, but the updated thermochemistry does. Sensitivity analyses indicated that the decomposition of hydroperoxy-methylformate plays a critical role in improving the low-temperature oxidation mechanism of DME.

关键词： Ethers

Steam Entrainment and Heat Transfer Characteristic of Steam Submerged Jet Condensation within Steam-Water Mixture Layer

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SSRN 2022年

作者： Zhao, Quanbin Fu, Pengfei Chong, Daotong Chen, Weixiong Liu, Jiping Yan, Junjie State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China MOE Key Laboratory of Thermal Fluid Science and Engineering Xi'an Jiaotong University Xi'An710049 China

Steam-water interface and mixture layer are the key window for understanding the heat and mass transfer mechanism of steam submerged jet condensation. In this paper, the steam-water two-phase mixture layer is captured and the interfacial vortex is observed with a quasi-two-dimensional submerged steam jet visualization experimental platform. Then, the volume heat transfer capacity of steam-water mixture layer and heat transfer coefficient with steam-water inner interface are obtained. Furthermore, a new turbulent eddy entrainment model is developed to calculate the local entrainment mass rate and local condensation heat transfer coefficient. Both the local entrainment mass rate and local condensation heat transfer coefficient increases along steam jet direction, and reaches the maximum value at the tail of the mixture layer. The calculated condensation heat transfer coefficient ranges from 0.88 to 2.94 MW·m -2 ·K -1 , which is about the half of the value of hypothetical heat transfer coefficient with inner interfacial area. © 2022, The Authors. All rights reserved.

关键词： Condensation