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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

Revealing and predicting the long-term biomechanical response of orthokeratology by developing a patient-specific computational model

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Science China(Physics,Mechanics & Astronomy) 2025年第1期Mechanics & Astronomy) .卷 156-168页

作者： Yifeng Li Zhuoran Yang Ziming Yan Huibin Shi Zhanli Liu Kaijie Wang department of engineering Mechanics School of Aerospace Engineering Tsinghua University Beijing Tongren Eye Center Beijing Tongren Hospital Capital Medical University Beijing Ophthalmology & Visual Sciences Key Lab

Orthokeratology(OK) is widely used for effective myopia correction and control. However, the incomplete understanding of its biomechanical mechanisms makes OK lens fitting rely heavily on clinician judgment, complicating accurate predictions of treatment outcomes. In this paper, we performed clinical experiments and numerical analysis to study corneal deformation modes and long-term changes in central corneal thickness. Clinical experiments were conducted on 194 Chinese myopic patients under OK treatment for 3 months. Based on the experimental data, a patient-specific computational biomechanical model for OK was established and validated. Specifically, the anisotropic mechanical properties of the cornea were incorporated into the model to describe the significant difference between its shear modulus(29.5 kPa) and tensile modulus(768.4 kPa). Additionally, a viscohyperelastic material model with a prolonged corneal relaxation time of 5.6 h was developed to capture the long-term deformation response. The results show that corneal thickness reduction in OK is primarily due to out-of-plane shear deformation,influenced by the cornea's low shear resistance. Modeling the extended corneal relaxation time is crucial for predicting long-term biomechanical responses. The computational model effectively captures long-term changes in central corneal thickness, potentially improving OK lens fitting accuracy.

关键词： orthokeratology computational biomechanical model long-term viscoelasticity myopia correction

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

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

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

Optimization of wear parameters of binary Al-25Zn and Al-3Cu alloys using design of experiments

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International Journal of Minerals,Metallurgy and Materials 2018年第12期25卷 1465-1472页

作者： Sreejith J S.Ilangovan department of mechanical engineering Amrita School of Engineering

Zinc-aluminum alloys have been used as bearing materials in the past. In recent years, binary Al-Zn alloys and Al-Zn-Cu alloys are being used as an alternative to the Zn-Al alloys for bearing applications. In this study, both binary Al-25 Zn and Al-3 Cu were prepared using stir casting process. Homogenization of the as-cast alloys was performed at 350oC for 8 h and then, the alloys were furnace-cooled to 50oC. The homogenization led to the removal of the dendritic structure of the as-cast alloys. After homogenization, wear parameters optimization was carried out using Taguchi technique. For this purpose, L9 orthogonal array was selected, and the control parameters selected are load, velocity, and sliding distance. The optimum parametric condition was obtained using signal-to-noise(S/N) ratio analysis, and specific wear rate(SWR) is the selected response. The "smaller-the-better" is the goal of the experiment for S/N ratio analysis. After the optimization, confirmation tests were carried out using analysis of variance(ANOVA) from the developed regression equation. Finally, wear mechanism studies were conducted using scanning electron microscopy(SEM) and energy-dispersive X-ray spectroscopy(EDX) images.

关键词： specific wear rate micro-hardness Taguchi technique signal-to-noise ratio analysis of variance aluminum-zinc alloy aluminum-copper alloy

Machining studies of die cast aluminum alloy-silicon carbide composites

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International Journal of Minerals,Metallurgy and Materials 2010年第5期17卷 648-653页

作者： Thambu Sornakumar Marimuthu Kathiresan department of mechanical engineering Thiagarajar College of Engineering

Metal matrix composites （MMCs） with high specific stiffness, high strength, improved wear resistance, and thermal properties are being increasingly used in advanced structural, aerospace, automotive, electronics, and wear applications. Aluminum alloy-silicon carbide composites were developed using a new combination of the vortex method and the pressure die-casting technique in the present work. Machining studies were conducted on the aluminum alloy-silicon carbide （SiC） composite work pieces using high speed steel （HSS） end-mill tools in a milling machine at different speeds and feeds. The quantitative studies on the machined work piece show that the surface finish is better for higher speeds and lower feeds. The surface roughness of the plain aluminum alloy is better than that of the aluminum alloy-silicon carbide composites. The studies on tool wear show that flank wear increases with speed and feed. The end-mill tool wear is higher on machining the aluminum alloy-silicon carbide composites than on machining the plain aluminum alloy.

关键词： metal matrix composites aluminum alloys silicon carbide die casting milling surface roughness

Local and global Gabor features for raised character recognition

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Chinese Optics Letters 2008年第3期6卷 172-175页

作者：李建美路长厚李学勇李国平 department of mechanical engineering Shandong University department of mechanical engineering Ji'nan University

Conventional Gabor representation and its extracted features often yield a fairly poor performance in extracting the invariance features of objects. To address this issue, a global Gabor representation method for raised characters pressed on label is proposed in this paper, where the representation only requires few summations on the conventional Gabor filter responses. Features are then extracted from these new representations to construct the invariant features. Experimental results clearly show that the obtained global Gabor features provide good performance in rotation, translation, and scale invariance. Also, they are insensitive to illumination conditions and noise changes. It is proved that Gabor filters can be reliably used in low-level feature extraction in image processing and the global Gabor features can be used to construct robust invariant recognition system.

关键词： Feature extraction Image processing Invariance Lighting

A Computational Study of Thrust Vectoring Control Using Dual Throat Nozzle

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Journal of Thermal Science 2010年第6期19卷 486-490页

作者： Choon Sik Shin Heuy Dong Kim Toshiaki Setoguchi Shigeru Matsuo department of mechanical engineering Andong National University department of mechanical engineering Saga University

Dual throat nozzle (DTN) is fast becoming a popular technique for thrust vectoring. The DTN is designed with two throats, an upstream minimum and a downstream minimum at the nozzle exit, with a cavity in between the upstream throat and exit. In the present study, a computational work has been carried out to analyze the performance of a dual throat nozzle at various mass flow rates of secondary flow and nozzle pressure ratios (NPR). Two-dimensional, steady, compressible Navier-Stokes equations were solved using a fully implicit finite volume scheme. The present computational results were validated with available experimental data. Based on the present results, the control effectiveness of thrust-vectoring is discussed in terms of the thrust coefficient and the coefficient of discharge.

关键词： Compressible Flow Dual Throat Nozzle Thrust Vector Control Shock Wave Supersonic Flow