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Convective heat transfer in helical coils for constant-property and variable-property flows with high Reynolds numbers

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中国能源与动力工程前沿 2010年第4期4卷 546-552页

作者： Yufei MAO Liejin GUO Bofeng BAI Ximin ZHANG State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an 710049 China

Forced convection heat transfer of single-phase water in helical coils was experimentally studied. The testing section was constructed from a stainless steel round tube with an inner diameter of 10?mm, coil diameter of 300?mm, and pitch of 50?mm. The experiments were conducted over a wide Reynolds number range of 40000 to 500000. Both constant-property flows at normal pressure and variable-property flows at supercritical pressure were investigated. The contribution of secondary flow in the helical coil to heat transfer was gradually suppressed with increasing Reynolds number. Hence, heat transfer coefficients of the helical tube were close to those of the straight tube under the same flow conditions when the Reynolds number is large enough. Based on the experimental data, heat transfer correlations for both incompressible flows and supercritical fluid flows through helical coils were proposed.

关键词： convective heat transfer helical coils high Reynolds number supercritical pressure variable property

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Load cycling rate of power-to-heat molten salt thermal storage and power generation system: Dynamic modeling and performance evaluation

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Journal of Energy Storage 2025年 125卷

作者： Wenting Hu Ming Liu Jihong Zhang Shunqi Zhang Junjie Yan State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an 710049 China Xi'an Thermal Power Research Institute Co. Ltd. Xi'an 710054 China

To develop a low-carbon power system with high renewable energy penetration, this study proposes a novel power-to-heat energy storage and power generation (P2HES-PG) system, which utilizes molten salt thermal storage technology to achieve flexible heat-power decoupling and rapid load regulation. By establishing dynamic models, the rapid load cycling dynamic characteristics and exergy destruction evolution of the P2HES-PG system under different load ranges were investigated. The results demonstrate that, within a 25% THA amplitude, the maximum load down rates in the high, medium, and low load ranges are 15%, 12%, and 11% P e min −1 , respectively, while the maximum load up rates reach 17%, 14%, and 11% P e min −1 , exceeding the ramping rate of conventional power units. During load cycling processes, significant fluctuations in molten salt circulation flowrate were observed, directly affecting the thermal storage/release dynamics of the steam generator (SG) and the system's thermal performance. Dynamic exergy analysis indicates the condenser maintains a stable 20% exergy destruction share, while turbine and mechanical contributions increase with higher loads, and the regenerative system peaks at 13.97% during the low-load range loading down process. The SG exhibits lower exergy destruction than ideal conditions during the loading down process and higher destruction during the loading up process, providing a theoretical basis for optimizing system control strategies and improving system variable load energy efficiency.

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A volume of fluid simulation of the steady deformation and the drag of a single droplet in a flowing gas

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Journal of Hydrodynamics 2021年第2期33卷 334-346页

作者： Zhi-bin Wang Zhong-wei Yang Lie-jin Guo Ren-jie Zhao State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation Southwest Petroleum UniversityChendu 610500China State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong UniversityXi'an 710049China

A method is proposed to investigate the steady deformation and the drag of a single droplet in a flowing gas at a high Reynolds *** volume of fluid(VOF)method is used to model the droplet surface *** direct numerical simulation(DNS)method is used to model the gas flow *** order to avoid the effect of the droplet acceleration on the drag and reduce the computation cost,a body force is added to the droplet to make it fixed at a constant *** body force is determined by using the Newton iteration *** simulated droplet aspect ratio and the drag coefficient agree well with the published experimental ***,the sources of the drag are analyzed and the effect of the Reynolds number and the Weber numbers on the droplet deformation and the drag are *** drag mainly comes from the pressure difference between the droplet-leading zone and the trailing zone,and the turbulence wake would increase the drag.

关键词： Droplet deformation steady drag volume of fluid(VOF) turbulent flow drag force

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Simulation of combustion in spark-ignition engine fuelled with natural gas-hydrogen blends combined with EGR

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中国高等学校学术文摘·能源与动力工程 2009年第2期3卷 204-211页

作者： Jie WANG Zuohua HUANG Bing LIU Xibin WANG State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an 710049 China

A numerical simulation of the influence of different hydrogen fractions, excess air ratios and EGR mass fractions in a spark-ignition engine was conducted. Good agreement between the calculated and measured in-cylinder pressure traces as well as pollutant formation trends was obtained. The simulation results show that NO concentration has an exponential relationship with temperature and increases sharply as hydrogen is added. EGR introduction strongly influences the gas temperature and NO concentration in the cylinder. The difference in temperature will lead to even greater difference in NO concentration. Thus, EGR can effectively decrease NO concentration. NO concentration reaches its peak value at the excess air ratio of 1.1 regardless of EGR mass fraction. The study shows that natural gas-hydrogen blend combined with EGR can realize a stable combustion and low NO emission in a spark-ignition engine.

关键词： natural gas hydrogen NO exhaust gas recirculation numerical simulation

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Quantitative Evaluation of Clinical Efficacy of Laser Thermotherapy for Port-Wine Stains Through Reflectance Spectra Measurements and an Inverse Radiation Algorithm

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Zhongguo Jiguang/Chinese Journal of Lasers 2025年第9期52卷

作者： Li, Dong Li, Xiaoyang Zhang, Pengfei Chen, Bin Ying, Zhaoxia State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Shaanxi Xi’an710049 China Shaanxi Provincial Institute for Skin Disease and STD Control Shaanxi Xi’an710003 China

Objective Port-wine stains (PWS) are congenital vascular malformations caused by the abnormal dilation of capillaries and venules in the skin. Affecting 0.3%‒0.5% of newborns, PWS typically manifest as pinkish patches on the face and neck that darken and thicken over time, significantly impacting patients’physical and mental well-being. Pulsed dye laser (PDL) therapy, based on selective photothermolysis, is the gold standard for PWS treatment. By targeting hemoglobin in abnormal blood vessels with specific wavelengths, PDL induces thermal damage to the vasculature while sparing surrounding tissues. However, due to variability in skin types, lesion depths, and laser parameters, clinical outcomes often depend on subjective evaluations and physician experience. These limitations underscore the urgent need for objective, quantitative, and noninvasive methods to assess skin structure and monitor treatment efficacy. This study integrates reflectance spectroscopy with an inverse Monte Carlo radiation method to quantify changes in key skin parameters before and after laser treatment. By measuring and reconstructing parameters such as epidermal thickness, melanin volume fraction, blood volume fraction, and blood oxygen saturation, this study establishes a robust framework for evaluating treatment outcomes and optimizing laser parameters. Additionally, it investigates differences in treatment responses between pediatric and adult patients, providing critical insights for personalized therapeutic strategies. Methods Eleven patients with PWS underwent pulsed dye laser (PDL) therapy at a wavelength of 595 nm, with an energy density of 8 J/cm2 and a fixed spot diameter of 7 mm. Reflectance spectra of the skin were measured before and after treatment using an HR400 CG-UV-NIR spectrometer (Fig. 1). To enhance efficacy, a double-irradiation strategy was employed, in which the second laser exposure followed the first after five minutes. For spectral analysis, an inverse Monte Carlo r

关键词： Hemoglobin oxygen saturation

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Experimental study on the laminar flame speed of hydrogen/natural gas/air mixtures

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Frontiers of Chemical Science and engineering 2010年第4期4卷 417-422页

作者： Chen DONG Qulan ZHOU Xiaoguang ZHANG Qinxin ZHAO Tongmo XU Shi’en HUI State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong UniversityXi’an 710049China

Laminar flame speeds of hydrogen/natural gas/air mixtures have been measured over a full range of fuel compositions(0-100%volumetric fraction of H_(2))and a wide range of equivalence ratio using Bunsen *** sensitivity scientific CCD camera is use to capture the image of laminar *** reaction zone area is employed to calculate the laminar flame *** initial temperature and pressure of fuel air mixtures are 293 K and 1 *** laminar flame speeds of hydrogen/air mixture and natural gas/air mixture reach their maximum values 2.933 and 0.374 m/s when equivalence ratios equal to 1.7 and 1.1,*** laminar flame speeds of hydrogen/natural gas/air mixtures rise with the increase of volumetric fraction of ***,the increase in laminar flame speed as the volumetric fraction of hydrogen increases presents an exponential increasing trend versus volumetric fraction of *** formulas to calculate the laminar flame speeds of hydrogen,natural gas,and hydrogen/natural gas mixtures are also *** these formulas,the laminar flame speed at different hydrogen fractions and equivalence ratios can be calculated.

关键词： laminar flame speed experimental study Bunsen flame

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Hydrodynamic Pattern in Drying Saline Droplet with Suspended Nanoparticles

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Journal of Bionic engineering 2020年第4期17卷 802-808页

作者： Junheng Ren Xin Zhong Lu Shen Fei Duan School of Mechanical and Aerospace Engineering Nanyang Technological UniversitySingapore 639798Singapore State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong UniversityXi'an 710049China

Evaporation of multicomponent droplets has gained much attention nowadays because of their complex flow fields and various deposition *** we observe strong flows in evaporating sodium chloride saline droplets with suspended alumina oxide *** evolution of flow pattern was studied by tracking the trajectories of particles and the velocity field was investigated with Particle Image Velocimetry *** non-uniform evaporation rate along the droplet surface leads to a concentration gradient which induces the convection *** the evaporation process before crystallization happens,evolution of the flow can be divided into two *** Regime I,a centrosymmetric convection recirculation is formed *** RegimeⅡ,the convection recirculation migrates to the droplet edge and evolves into several small *** the late evaporation stage,crystallization could induce strong convection *** is shown that the flow tends to become more chaotic with a lower salt concentration.

关键词： convection flow concentration gradient saline droplet crystallization

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CdS nanocrystallites sensitized ZnO nanorods with plasmon enhanced photoelectrochemical performance

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Chinese Chemical Letters 2019年第12期30卷 2363-2367页

作者： Li Cai Yuanchang Du Xiangjiu Guan Shaohua Shen International Research Center for Renewable Energy State Key Laboratory of Multiphase Flow in Power Engineering (MFPE) Xi’an Jiaotong University (XJTU)

A novel architecture of CdS/ZnO nanorods with plasmonic silver(Ag) nanoparticles deposited at the interface of ZnO nanorods and CdS nanocrystallites,was designed as a photoanode for solar hydrogen generation,with photocurrent density achieving 4.7 mA/cm^2 at 1.6 V(***),which is 8 and 1.7 times as high as those of pure ZnO and CdS/ZnO nanorod films,***,with optical absorption onset extended to^660 nm,CdS/Ag/ZnO nanorod film exhibits significantly increased incident photo-tocurrent efficiency(IPCE) in the whole optical absorption region,reaching 23.1% and 9.8% at 400 nm and500 nm,*** PEC enhancement can be attributed to the one-dimensional ZnO nanorod structure maintained for superior charge transfer,and the extended visible-light absorption of CdS ***,the incorporated plasmonic Ag nanoparticles could further promote the interfacial charge carrier transfer process and enhance the optical absorption ability,due to its excellent plasmon resonance effect.

关键词： ZnO nanorods Plasmonic Ag nanoparticles CdS nanocrystallites Photoelectrochemical water splitting Synergistic effect

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Heavy Metal Migration Characteristics of Co-Combustion between Sewage Sludge and High Alkaline Coal on Circulating Fluidized Bed

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Journal of Thermal Science 2022年第6期31卷 2178-2188页

作者： LI Yaode YANG Dong ZHOU Xihong DONG Le SUO Lihui SUN Wenbo State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong UniversityXi'an Jiaotong UniversityXi'an 710049China College of Energy&Power Engineering Northeast Electric Power UniversityJilin 132000China

The migration characteristics of heavy metals in co-combustion of sewage sludge and high alkali coal in circulating fluidized bed were studied by experiments and simulations. Temperature plays a crucial role in thermodynamic equilibrium distribution and migration characteristics of heavy metals. At the temperature range of 700℃-1200℃, Hg is completely gaseous and the proportion of Pb, Ni, and Cd in the gas phase is also high. As is mainly elemental in the system, and the proportion of Cr in the solid phase is large. Zn compounds are diverse and mostly solid materials. The volatility of Cu is not strong, and it will become gaseous when the temperature exceeds 1700℃. The proportion of heavy metals in the gas phase decreases as the excess air ratio increases. In an oxygen-rich atmosphere, most of Zn and Ni are converted to oxides;Pb and Cd are converted to crystalline silicate;Cu is converted to partial aluminate;Cr compound is decomposed to form Cr_(2)O_(3);they are good for the solidification and controlling of heavy metals. The elemental Hg is converted to HgCl_(2) and the elemental As is converted to AsCl_(3). Temperature also has a great influence on the volatilization rate of heavy metals. The higher the temperature, the shorter the time they reach the maximum volatility.

关键词： co-combustion heavy metal migration circulating fluidized bed sewage sludge high alkali coal

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Impacts of Startup,Shutdown and Load Variation on Transient Temperature and Thermal Stress Fields within Blades of Gas Turbines

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Journal of Thermal Science 2022年第3期31卷 727-740页

作者： CAI Liuxi HOU Yanfang LI Fang LI Yun WANG Shunsen MAO Jingru School of Chemical Engineering and Technology Xi’an Jiaotong UniversityXi’an710049China State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong UniversityXi’an710049China

Based on the actual operation parameters and temperature-dependent material properties of a gas turbine unit,composite cooling blade model and corresponding reliable boundary conditions were *** thermal-fluid-solid coupling simulations were then comprehensively conducted to analyze the transient flow and the temperature field of the blade under startup,shutdown,and variable loads *** with the obtained transient temperature data,the non-linear finite element method was exploited to examine the effect of these transient operations on the turbine blade thermal stress *** show that the temperature and pressure on the blade surface increase with the load level and vice *** the startup process progresses,the film cooling effectiveness and the heat convection of airflows inside the blade continuously grow;high-temperature areas on the pressure surface and along the trailing edge of the blade tip gradually *** high-temperature zones with the maximum of 1280 K are generated at the air inlet and outlet of the blade platform and the leading edge of the blade *** high thermal stresses detected on the higher temperature side of the temperature gradient are commonly generated in places with large temperature gradients and significant geometry *** the startup/shutdown process,the rate of increase/decrease of the thermal stress is positively correlated with the load variation rate.A slight variation rate of the load(1.52%/min)can lead to an apparent alteration(41%)to the thermal *** operations under action of the variable load,although thermal stress is less sensitive to the load variation,the rising or falling rate of the exerted load still needs to be carefully controlled due to the highly leveled thermal stresses.

关键词： composite cooling blade thermal-fluid-solid coupling method transient temperature field load variation thermal stress

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