Experiments and simulations on flow and heat transfer behavior of Therminol-55 liquid phase heat transfer fluid have been conducted in a ribbed tube with the outer diameter and inner diameter 25.0 and 20.0 mm, pitch and rib height of 4.5 and 1.0 mm. respectively. Experimental results show that the heat transfer and thermal performance of Therminol-55 liquid phase heat transfer fluid in the ribbed tube are considerably improved compared to those of the smooth tube. The Nusselt number increase with the increase of Reynolds number. The increase in heat transfer rate of the ribbed tube has a mean value of 2.24 times. Also, the pressure drop results reveal that the average friction factor of the ribbed tube is in a range of 2.4 and 2.8 times over the smooth tube. Numerical simulations of three-dimensional flow behavior of Therminol-55 liquid phase heat transfer fluid are carried out using three different turbulence models in the ribbed tube. The numerical results show that the heat transfer of ribbed tube is improved because vortices are generated behind ribs, which produce some disruptions to fluid flow and enhance heat transfer compared with smooth tube. The numerical results prove that the ribbed tube can improve heat transfer and fluid flow performances of Therminol liquid phase heat transfer fluid.

基于优化气门通过能力的目的,利用多体动力学软件,文章对增大升程的凸轮方案工作应力进行了仿真,分别计算了凸轮和摇臂以及摇臂和气门接触区域的接触应力,并与基础方案进行了对比;依据仿真结果,进行了方案的差异分析和影响因素总结.

Heat transfer coefficient and friction factor of Therminol 55 liquid phase heat transfer fluid are measured and simulated in a ribbed tube with the outer and inner diameters of 19.0 and 15.0 mm, and the pitch and height of the rib of 4.5 and 1.0 mm, respectively. Compared to the heat transfer in the smooth tube, the measured heat transfer in the ribbed tube increases by 3.3-4.6 times for the laminar flow, and by 1.9-3.8 times for the turbulent flow. Comparing to the smooth tube, the measured friction factor in the ribbed tube increases by 2.0-3.1 times for the laminar flow and 3.0-3.9 times for the turbulent flow. Three-dimensional flow behavior and heat transfer is performed by means of FLUENT code in the ribbed tube. The distributions of velocity and temperature are predicted as a function of Reynolds number. The effect of rib height, pitch and rib width on heat transfer and friction factor is discussed. The simulated thermal enhancement factor and synergy angle prove that the ribbed tube can improve heat transfer and fluid flow performances of Therminol liquid phase heat transfer fluid. (C) 2015 Elsevier Inc. All rights reserved.

Experiments and simulations on flow and heat transfer behavior of Therminol 55 liquid phase heat transfer fluid have been conducted in a ribbed tube with outer and inner diameters of 25.0 and 20.0 mm, pitch and rib height of 12.0 and 1.0 mm respectively. Experimental results show that the increase in heat transfer rate of the ribbed tube has a mean value of 2.24 times in the turbulent flow and in a range of 33 -5.2 times in the laminar flow over the smooth tube at the test range. The measured average friction factor of the ribbed tube is in a range of 2.2-2.6 times over the smooth tube. The numerical results show that the heat transfer rate of the windward face wall is 1.34 times in excess of the heat transfer rate of the leeward face wall of ribs, which enhances heat transfer compared with smooth tube. In addition, correlations of the Nusselt number and friction factor in terms of Reynolds number and Prandtl number are determined, based on the curve fitting of the experimental data. (C) 2016 Elsevier Ltd. All rights reserved.

Vibration stress relief (VSR) is an effective and economic method for reducing residual stress in various welding components. Compared with other methods, it costs much less time and energy. In this study, finite element method (FEM) was used to assist VSR treatment of large DH36 steel welded tube by determining the 1st order vibration mode of the tube and the natural frequency of the tube in a hypothetic zero-stress state. According to the computational results, proper vibration exciting assembling and excitation strategy was selected. An effectiveness index, η, for fast and quantitative estimation of the residual stress decrease rate was proposed. η is determined by 1st order natural frequencies of the tube in three states, i.e. as-welded, VSR treated and a hypothetic zero-stress state. η in this study was 49.8 %, meeting well with the experimentally measured residual stress decrease rate, ~50 %. Thus, the validity of the effectiveness index was verified. This study provides a novel method for analysis of VSR effectiveness. In comparison, maximum residual stress was reduced by 20-57 % when traditional local post weld heat treatment (PWHT) was used. This indicates that VSR is a good stress relief method for DH36 welded structures.

The low-volume and high-variety shoes making enterprise is required by the increasingly fierce market to apply SMED to reduce production setup time and improve the flexibility of the production system. In this paper, production preparation process of injection machine is to be sorted out by the use of visualization tool of lean production - value stream mapping. According to the four sub-processes (material preparation, material change, mold change, machine adjust) in the VSM, auxiliary machinery, automation, standard operating and other methods are applied to reduce exchange-type time by 45%, shorten the production cycle, reduce labor intensity and improve equipment effectiveness with the SMED and Lean thinking.

采用有限差分方法开发了气冷涡轮气弹耦合求解器.该求解器分别在流动区域求解时间平均N-S方程.在固体区域求解振动方程,在流固边界则施加了气弹耦合边界条件.在流动问题求解中,采用了B-L代数湍流模型封闭时均N-S方程,采用三阶AUSMPW+差分格式离散对流项,并采用隐式LU-SGS格式求解离散后的代数方程;振动问题则采用显式格式求解;采用代数网格法进行固体区域动态网格生成.采用该耦合求解器对某涡轮级动叶的振动响应问题进行了数值仿真,研究表明:所开发的耦合求解器能够用于振动响应问题的分析,同时本算例中涡轮动叶的振动不存在发散现象,并且叶片振动对流动的影响很小.

The rapid development of sports has attracted much attention in the digital network today. People's health awareness and world intense sports competition makes sports records get more and more attention. The rapid development of computer and network technology provide various fields with a lot of convenience. In order to make computer technology serve the College Sports education better, this paper proposes to establish a school sports computer comprehensive managing system. The system is composed of seven modules: sports teaching, physical fitness tests, sports competitions, extra-curricular sports activities, files management, professional team training, venues and equipment management, etc.

Coupled heat transfer (CHT) simulations taking account of transition flow around vane surfaces are carried out in this research. First, a coupled solver with finite difference method was developed to compute the heat transfer, and the direct coupling method was employed to combine the N-S equation solver in the flow passage and the heat transfer module in the solid domain. The modified Abu-Ghannam and Shaw (AGS) algebraic transition model was used to predict the transition flow around the vane surfaces. Then, coupled heat transfer simulation was carried out and verified through testing the 5411 run of NASA-MARKII vane, a high-pressure turbine vane. The comparison between the numerical results and the tested ones has been shown that the AGS transition model is able to predict the transition model process in the boundary layer, and that the predicted vane thermal loads by such model are closer to the tested ones than those by full turbulence model. Finally the developed solver has been applied to the CHT simulations of a low-pressure air-cooled turbine with two cooling air channels and a slut in the trailing edge, and its vane thermal load could be analytically obtained.

The combustion system in a high specific power diesel was studied.Firstly,3D numerical simulation of the combustion process in the chamber was carried out by AVL-Fire.The WAVE model,the Dukowicz model and the Eddy Break Up model were utilized to predict the fuel atomization,evaporation and combustion processes,respectively,and the k-e two-equation turbulence model was employed to predict the turbulent flow.The predicted average pressure and effective power agree well with the measured ones,verifying the employed numerical models.Secondly the detailed analysis of the numerical three-dimensional flow field,thermal field and oil distribution during the combustion process were carried out,and the disadvantages of the original combustion system were found out..The structure of combustion system was modified on the basis of the above-mentioned analysis.Then The modified combustion system was also numerically simulated by using the same numerical models as the original chamber.Finally the numerical results of the original and the modified combustion system show that the performance of the combustion system is significantly affected by the shape of the combustion chamber,and that the combustion organization of the modified combustion system is significantly improved compared with that of the original one,resulting in great increase in the effective power and heat release rate of the combustion system.

This paper proposes a novel fault diagnosis scheme based on numerical differentiation. Specifically, wavelet transform is utilized to estimate the numerical derivatives of known signals. And then, based on the algebraic observability of the fault, fault estimation is achieved by certain algebraic operations on a set of known signals and their numerical derivatives. The proposed fault diagnosis method is not limited to estimate the magnitude of a single fault. When there are multiple faults occurred simultaneously, it is also effective. In this paper, the proposed fault diagnosis scheme is applied to estimate the gyroscope faults in a satellite attitude determination subsystem. Simulation results are given to demonstrate the performance of the proposed method.

Based on the thermo-mechanical coupling analysis of FEM,the joining process of high speed rail floor was studied,which was welded by seven pieces of large-scale hollow extruded shape of aluminum alloy.To enhance the calculation precision,the mechanical and thermal-physical properties of the aluminum alloy and its filler metal were tested between room temperature and their melting points,moreover,the moving double-ellipsoid heat source was employed to simulate the metal-inert gas welding.The measured as-welded deflection data of ten real rail floors at the production site was highly coincident with the numerical simulation results.The results proved that,the thermo-mechanical coupling analysis and the dynamic material properties were two essential factors in the high precision simulation of high speed rail floor,which could lay a digital workplace for the improvement of the current process and further development of the new-type assembly.

The study focuses on the flow in the intake port of a high-specific-power diesel with high pressure drop.A numerical model for such intake port was built by AVL BOOST and AVL FIRE.The model consists of a 1D unsteady model and a 3D steady one.3D steady flow of the gas intake port in the diesel with high pressure drop was analyzed.The intake valve flow coefficient of the 1D unsteady model was modified using the 3D numerical result.Then the intake port of such diesel was improved on the basis of the modified numerical model.It can be known from the high-pressure-drop steady flow test that the improved gas intake port provides a fine gas intake performance.

The developed coupled solver HIT-3D was applied to the coupled heat transfer simulations of an air-cooled turbine with single cooling channel.Different turbulence and transition models were utilized.The numerical results validated the ability of the developed solver in the engineering simulation.Then a method combining the coupled heat transfer and engineering design techniques was developed to reduce the computational loads of simulations of turbines with complex cooling systems.With the same test case mentioned above,such method was validated,and the influences of rough inner wall on the blade thermal load were investigated.The results show that the transition model predicts lower vane thermal load than the full turbulence models at the transition zones on the vane surface,and that the developed method can greatly reduce the computational load during the turbine design.

The effects of several numerical methods, including computational grids, coupling method, transition model and inner cooling air flow prediction, on the conjugate simulations were studied in the research. Firstly a finite difference conjugate solver was developed. Such solver included an N-S solver and a thermal conduction module for fluid flow and solid thermal conduction, respectively. Then conjugate simulations of an air cooling turbine were carried out. There were four kinds of conjugate simulations: the first one employs different types of computational grids, including H-type grids and O-type grids, for discretizing near-wall regions in fluid zone; the second one employs different coupling methods including indirect and direct ones; the third one employs different models including the B-L and q-ω turbulence models, and the AGS transition model; and the forth one employs different turbulence models for the prediction of flows in the cooling channels. All of the numerical results have been compared to the experimental result. Finally it concludes that to accurately predict thermal and aerodynamic load of the air cooled turbine, the conjugate simulation should employ O-type girds to discretize the near wall regions in the fluid zone, use the direct coupling method to transfer data between solid and fluid domains, and utilize the transition model to predict accurate flow details within the boundary layers, and also account for flows in the cooling air channels.

This work aims at the improvement of measurement accuracy of thermal conductivity and thermal diffusivity using a hot disk thermal constants analyser. The hot disk technique is based on the transient heating of a double spiral plane sandwiched between two pieces of investigated material. By researching the temperature change in the sensor surface, it is possible to deduce both the thermal conductivity and thermal diffusivity of the surrounding material from one single transient recording, provided the heating power and measuring time are appropriately chosen within the reasonable range defined by the theory and experimental situation. Based on the engineering application requirement for precision and efficacy, a new experimental method has been developed for high-accuracy measurement of thermal conductivity and thermal diffusivity in different experimental conditions. The standardized material Pyroceram 9606, with a thermal conductivity of 4.05 W/(mK), has been investigated and analyzed using the newly developed method. The measurement results show that the precision 5% estimated for thermal conductivity and 4% for thermal diffusivity at or around room temperature and under normal pressure, which indicate that the newly developed method has led to the high-accuracy measurement of thermal conductivity and diffusivity.

This paper presents a novel passive lossless snubber circuit for pulse-width modulation (PWM) inverters to achieve soft-switching purposes without an extra switch and additional control circuitry. This novel passive lossless soft-switching snubber employs an inductor/capacitor snubber circuit for each switching device in an inverter to achieve passive zero-current turn on and zero-voltage turn off. Furthermore, instead of conventional bulky transformer coupling for energy recovery, three inductors coupled tightly on a single core are used to losslessly recover snubber energy to the input in the proposed snubber. In addition, freewheeling of output phase current of inverters can be realized via energy storage components in the snubber in the dead-time and the effect of dead-time is reduced. The distortion ratio of the output phase current in low output frequency is also reduced. All components in the snubber circuit are passive, thus having a better price/performance ratio than their active counterparts. The snubber has been incorporated into a PWM inverter. Experimental results are given to demonstrate the validity and features of the snubber circuit.

Preheating and stretching process is the key step of the product process of geogrid. To improve temperature control effect, a single parameter PID adaptive control algorithm is used in this article, which can easily be realized by software, and a temperature-speed double control system is brought in which based on the temperature-speed relation in the process of stretching. The temperature and speed can be kept at a best joint point by the way of adjusting the temperature and speed automatically in this system. It can largely improve the stability of the system and the stretching speed.

The investigation is intended to verify a coupled solver developed for turbines to illustrate how transition exerts effects on the predicted thermal loads. The solver couples the N-S solver named HIT-3D, with a thermal conduction module using the finite difference method. Three operating conditions of the NASA-MarkII vane are selected to be the cases for tests. The models used in the simulations include Baldwin-Lomax (B-L) algebraic model, q-ωlow-Re model and B-L & Abu-Ghannam and Shaw (AGS) model. The predicted profile pressure distributions obtained in all the simulations agree well with the measured ones. The predicted profile temperatures acquired with different models in the turbulent zones and those with the B-L & AGS model in the laminar and transition zones accord with the measured ones. Therefore, in order to accurately predict the thermal loads on the turbine vane, it is necessary to take transition into account in the simulations.

Coupled heat transfer simulations with a FDM coupled solver were carried out to study the factors effecting the coupled simulation accuracy.Such factors included numerical grids around the blade wall,the turbulence and transition models,and the variation of Pradtl number.The difference scheme corresponding to the conjugate heat transfer dynamics differential equation and structured grids were employed to ensure the computational accuracy and speed.The comparison between numerical results and the measured ones shows that the grids quality around the blade wall and the transition model are essential for the coupled heat transfer simulations,and that the variation of Prandtl number affects slightly on the numerical results.