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Journal of Thermal Science 2015年第1期24卷 49-57页

作者： Wan Aizon W Ghopa Zambri Harun Ken-ichi Funazaki Takemitsu Miura department of mechanical and Materials engineering Universiti Kebangsaan Malaysia department of mechanical engineering Iwate University

The existence of a gap between combustor and turbine endwall in the real gas turbine induces to the leakages phenomenon. However, the leakages could be used as a coolant to protect the endwaU surfaces from the hot gas since it could not be completely prevented. Thus, present study investigated the potential of leakage flows as a function of film cooling. In present study, the flow field at the downstream of high-pressure turbine blade has been investigated by 5-holes pitot tube. This is to reveal the aerodynamic performances under the influenced of leakage flows while the temperature measurement was conducted by thermoehromic liquid crystal （TLC）. Expe- rimental has significantly captured theaerodynamics effect of leakage flows near the blade downstream. Further- more, TLC measurement illustrated that the film cooling effectiveness contours were strongly influenced by the secondary flows behavior on the endwall region. Aero-thermal results were validated by the numerical simulation adopted by commercial sottware, ANSYS CFX 13. Both experimental and numerical simulation indicated almost similar trendinaero and also thermal behavior as the amount of leakage flows increases.

关键词： endwall fllmcooling leakage flows secondary flows aerodynamic loss film cooling effectiveness

An Experimental Study of Condensation Heat Transfer in Sub-Millimeter Rectangular Tubes

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Journal of Thermal Science 2004年第4期13卷 350-357页

作者： Jeong Seob SHIN Moo Hwan KIM department of mechanical engineering POSTECH Pohang KoreaDepartment of Mechanical Engineering POSTECH Pohang Korea

The characteristics of local heat transfer and pressure drops were experimentally investigated using condensing R134a two-phase flow, in single rectangular tubes, with hydraulic diameter of 0.494, 0.658, and 0.972 mm. New experimental techniques were used to measure the in-tube condensation heat transfer coefficient especially for the low heat and mass flows. Tests were performed for a mass flux of 100, 200, 400, and 600 kg/m2s, a heat flux of 5 to 20 kW/m2, and a saturation temperature of 40℃. In this study, effect of heat flux, mass flux, vapor qualities, and hydraulic diameter on flow condensation were investigated and the experimental local condensation heat transfer coefficients and frictional pressure drop are shown. The experimental data of condensation Nusselt number are compared with previous correlations, most of which are proposed for the condensation of pure refrigerant in a relatively large inner diameter round tubes.

关键词： condensation hydraulic diameter rectangular in-tube multiphase flow.

Novel PA encapsulated PCL hybrid coating for corrosion inhibition of biodegradable Mg alloys:A triple triggered self-healing response for synergistic multiple protection

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Journal of Magnesium and Alloys 2023年第4期11卷 1440-1460页

作者： Navdeep Singh Grewal Uma Batra Kamal Kumar Anil Mahapatro department of Metallurgical and Materials engineering Punjab Engineering CollegeChandigarh 160012India department of mechanical engineering Punjab Engineering CollegeChandigarh 160012India department of biomedical engineering Wichita State UniversityWichitaKS 67260USA

Surface coatings have been extensively used to control the degradation rate of Mg alloys for bioimplant ***,these coatings only act as passive *** corrosive media,structural damage impairs their barrier properties,resulting in rapid degradation of Mg *** present study incorporates phytic acid(PA)as a healing agent in polycaprolactone(PCL)microcapsules with a unique honeycomb core matrix to obtain a self-healing PA-PCLcaps *** contact between simulated body fluid(SBF)and PA-PCLcaps coated ZM21 exhibited Cassie-Baxter interfacial states,resulting in significant hydrophobicity with a contact angle(CA)of *** corrosion potential(Ecorr)and current density(Icorr)were found to be-0.28 V and 1.1×10^(-9)A/cm^(2),respectively,for PA-PCLcaps coating,resulting in biosafe corrosion rate of 2.5×10^(-4)mm/*** mechanical scratching,rapid HA mineralization at scratched regions recovered the hydrogen evolution rate(HER,0.36 mL/cm^(2)/day)and pH change(pH 7.10)of scratched PA-PCLcaps coated ZM21 samples to corresponding unscratched samples within one day of *** coating’s self-healing ability could be attributed to PA released from punctured microcapsules,which facilitates HA *** pH-triggered(pH 10)and Mg(II)-triggered(5 mM)conditions enhanced PA release from PA-PCLcaps coating by 2.5 and 3.1 times,*** a result,dense HA mineralization occurred,which protects the coating from structural defects and ensures its durability in stimulating *** findings of present study provide new insight for design of multiple stimuli-feedback based self-healing coatings on biodegradable Mg alloys.

关键词： Self-healing coating Corrosion resistance Magnesium alloy Phytic acid Polycaprolactone microcapsules

Submicron particle sizing by aerodynamic dynamic focusing and electrical charge measurement

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Particuology 2015年第1期13卷 105-111页

作者： Zhongchao Tan Raheleh Givehchi Alena Saprykina department of mechanical & Mechatronics engineering University of Waterloo department of mechanical and Manufacturing engineering University of Calgary

Principles of a novel submicron particle sizing technology are first introduced followed by experimental validation. The sizing was accomplished by coupling aerodynamic particle focusing and maximum ion measurement. Experimental results showed that the prototype could detect particle sizes down to 40 nm in diameter. Comparison between the prototype and a scanning mobility particle sizer using identical polydisperse particles showed that the measurements agreed well for the tested particles.

关键词： Submicron particle Particle sizing Aerodynamic focusing Particle charging

Numerical investigation of grooves effects on the thermal performance of helically grooved shell and coil tube heat exchanger

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Chinese Journal of Chemical engineering 2022年第4期35卷 424-434页

作者： Mehdi Miansari Mehdi Rajabtabar Darvishi Davood Toghraie Pouya Barnoon Mojtaba Shirzad As'ad Alizadeh department of mechanical engineering Qaemshahr BranchIslamic Azad UniversityQaemshahrIran department of mechanical engineering Khomeinishahr BranchIslamic Azad UniversityKhomeinishahrIran department of mechanical engineering Department of Mechanical EngineeringBabol Noshirvani University of TechnologyBabolIran department of mechanical engineering Urmia UniversityUrmiaIran department of mechanical engineering College of EngineeringUniversity of ZakhoZakhoIraq

Heat exchangers are integral parts of important industrial units such as petrochemicals,medicine and power *** to the importance of systems energy consumption,different modifications have been applied on heat exchangers in terms of size and *** this study,a novel heat exchanger with helically grooved annulus shell and helically coiled tube was investigated by numerical *** grooves with the same pitch of the helical coil tube and different depth are created on the inner and outer wall of annulus shell to improve the thermal performance of heat *** the first section,thermal performance of the shell and coil heat exchanger with the helical grooves on its outer shell wall was compared with same but without helical *** the second section,helically grooves created on both outer and inner wall of the annulus shell with different groove *** results showed that the heat exchanger with grooves on both inner and outer shell wall has better thermal performance up to 20%compared to the heat exchanger with grooves on only outer shell *** highest thermal performance achieves at lower flow rates and higher groove depths whereas the pressure drop did not increase significantly.

关键词： Numerical simulation Heat transfer Turbulent flow Shell and coil Helically grooved shell Heat exchanger

An identifier-actor-optimizer policy learning architecture for optimal control of continuous-time nonlinear systems

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Science China(Physics,Mechanics & Astronomy) 2020年第6期63卷 42-53页

作者： Lin Cheng ZhenBo Wang FangHua Jiang JunFeng Li School of Aerospace engineering Tsinghua UniversityBeijing 100084China department of mechanical Aerospaceand Biomedical EngineeringUniversity of TennesseeKnoxville TN 37996USA

An intelligent solution method is proposed to achieve real-time optimal control for continuous-time nonlinear systems using a novel identifier-actor-optimizer(IAO)policy learning *** this IAO-based policy learning approach,a dynamical identifier is developed to approximate the unknown part of system dynamics using deep neural networks(DNNs).Then,an indirect-method-based optimizer is proposed to generate high-quality optimal actions for system control considering both the constraints and performance ***,a DNN-based actor is developed to approximate the obtained optimal actions and return good initial guesses to the *** this way,the traditional optimal control methods and state-of-the-art DNN techniques are combined in the IAO-based optimal policy learning *** to the reinforcement learning algorithms with actor-critic architectures that suffer hard reward design and low computational efficiency,the IAO-based optimal policy learning algorithm enjoys fewer user-defined parameters,higher learning speeds,and steadier convergence properties in solving complex continuous-time optimal control problems(OCPs).Simulation results of three space flight control missions are given to substantiate the effectiveness of this IAO-based policy learning strategy and to illustrate the performance of the developed DNN-based optimal control method for continuous-time OCPs.

关键词： continous-time nonlinear systems identifier-actor-optimizer architecture intelligent optimal control deep neural net-works

Numerical investigations on HCCI engine with increased induction induced swirl and engine speed

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Journal of Central South University 2015年第10期22卷 3837-3848页

作者： T.Karthikeya Sharma G.Amba Prasad Rao K.Madhu Murthy department of mechanical engineering NIT

Homogeneous charge compression ignition(HCCI) mode of combustion is popularly known for achieving simultaneous reduction of NOx as well as soot emissions as it combines the compression ignition(CI) and spark ignition(SI) engine features. In this work, a CI engine was simulated to work in HCCI mode and was analyzed to study the effect of induction induced swirl under varying speeds using three-zone extended coherent flame combustion model(ECFM-3Z, compression ignition) of STAR-CD. The analysis was done considering speed ranging from 800 to 1600 r/min and swirl ratios from 1 to 4. The present study reveals that ECFM-3Z model has well predicted the performance and emissions of CI engine in HCCI mode. The simulation predicts reduced in-cylinder pressures, temperatures, wall heat transfer losses, and piston work with increase in swirl ratio irrespective of engine speed. Also, simultaneous reduction in CO2 and NOx emissions is realized with higher engine speeds and swirl ratios. Low speeds and swirl ratios are favorable for low CO2 emissions. It is observed that increase in engine speed causes a marginal reduction in in-cylinder pressures and temperatures. Also, higher turbulent energy and velocity magnitude levels are obtained with increase in swirl ratio, indicating efficient combustion necessitating no modifications in combustion chamber design. The investigations reveal a total decrease of 38.68% in CO2 emissions and 12.93% in NOx emissions when the engine speed increases from 800 to 1600 r/min at swirl ratio of 4. Also an increase of 14.16% in net work done is obtained with engine speed increasing from 800 to 1600 r/min at swirl ratio of 1. The simulation indicates that there is a tradeoff observed between the emissions and piston work. It is finally concluded that the HCCI combustion can be regarded as low temperature combustion as there is significant decrease in in-cylinder temperatures and pressures at higher speeds and higher swirl ratios.

关键词： HCCI engine ECFM-3Z swirl ratio emissions and performance

Model for the static friction coefficient in a full stick elastic-plastic coated spherical contact

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Friction 2019年第6期7卷 613-624页

作者： Zhou CHEN Izhak ETSION department of mechanical engineering Technion

Finite element analysis is used to investigate an elastic-plastic coated spherical contact in full stick contact condition under combined normal and tangential loading. Sliding inception is associated with a loss of tangential stiffness. The effect of coating thickness on the static friction coefficient is intensively investigated for the case of hard coatings. For this case, with the increase in coating thickness, the static friction coefficient first increases to its maximum value at a certain coating thickness, thereafter decreases, and eventually levels off. The effect of the normal load and material properties on this behavior is discussed. Finally, a model for the static friction coefficient as a function of the coating thickness is provided for a wide range of material properties and normal loading.

关键词： contact mechanics elastic‐plastic contact spherical contact static friction hard coatings

An Experimental Study on Aerodynamic Sound Generated from Wake Interaction of Circular Cylinder and Airfoil with Attack Angle in Tandem

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Journal of Thermal Science 2008年第3期17卷 212-217页

作者： Mizue MUNEKATA Ryuta KOSHIISHI Hiroyuki YOSHIKAWA Hideki OHBA department of mechanical System engineering

In our previous study, the effects of the interval between the cylinder and the airfoil on the aerodynamic sound were investigated and compared with the cases of single circular and single airfoil. In this study, the effects of the attack angle of the airfoil located downstream on the characteristics of aerodynamic sound and the wake structure are investigated at a given interval between the cylinder and the airfoil. It is found that the sound pressure level of DFN and the peak frequency decrease with increasing attack angle of airfoil because of the diffusive wake structure due to the increased back pressure of circular cylinder, which is caused by the blocking effect of airfoil. It is shown that the sound sources are corresponded to the attack points of shedding vortex form the upstream circular cylinder to the downstream airfoil. We conclude that the pressure fluctuation at the airfoil surface effects on the sound pressure level, from the flow visualizations and the exploration test of sound source.

关键词： aerodynamic sound wake interaction circular cylinder airfoil Karman's vortex flow visualization

De Novo Assembly Methods for Next Generation Sequencing Data

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Tsinghua Science and Technology 2013年第5期18卷 500-514页

作者： Yiming He Zhen Zhang Xiaoqing Peng Fangxiang Wu Jianxin Wang the School of Information Science and engineering Central South University the Morehouse School of Medicine the department of mechanical engineering and Division of biomedical engineering University of Saskatchewan

The recent breakthroughs in next-generation sequencing technologies, such as those of Roche 454,Illumina/Solexa, and ABI SOLID, have dramatically reduced the cost of producing short reads of the genome of new species. The huge volume of reads, along with short read length, high coverage, and sequencing errors, poses a great challenge to de novo genome assembly. However, the paired-end information provides a new solution to these problems. In this paper, we review and compare some current assembly tools, including Newbler, CAP3, Velvet,SOAPdenovo, AllPaths, Abyss, IDBA, PE-Assembly, and Telescoper. In general, we compare the seed extension and graph-based methods that use the overlap/lapout/consensus approach and the de Bruijn graph approach for assembly. At the end of the paper, we summarize these methods and discuss the future directions of genome assembly.

关键词： next-generation sequencing genome assembly overlap/lapout/consensus de Bruijn graph