Apparatus to study the onset of free convection about vertical and inclined hot wires

This article describes a methodology and an apparatus used to evaluate the onset time of free convection in hot-wire experiments. The evaluation of the onset time is useful to obtain a measurement interval that is suitable to estimate the thermal properties of a fluid. If a pure conduction regime is present, the hot-wire temperature increment versus time is a straight line in a semilog plot, whereas the convection effect induces a deviation from this trend. An algorithm based on the F test is proposed to evaluate the onset time of free convection. The experimental facility has the particular feature of allowing an easy change of the hot-wire inclination angle up to 118.3 mrad. The wire is kept in a tilted position by a permanent horseshoe magnet, and the tilting angle from the vertical is measured by a theodolite. Some testing results using water are discussed for vertical and inclined wires. A good agreement between the experimental onset times and the theoretical ones is found in the case of a vertical wire.     

Experimental assessment on the performance of hot wire anemometry in and around a permeable medium by comparison with Particle Image Velocimetry

The air flow through a test section partially obstructed by a permeable array of wires was measured simultaneously by Hot Wire Anemometry (HWA) and Particle Image Velocimetry. The objective of the study was the assessment of the suitability of HWA for the measurement of flow velocities amid and adjacent to groups of small obstacles. In the present case the obstacles are set in a regular array configuring a highly permeable structure. The probe was placed at three characteristic positions: in the free flow close to the wire array, inside the permeable medium, and at the interface between the permeable structure and the free flow. The measurements were performed with the hot wire operating under natural convection and mixed convection heat transfer, and operating the hot wire at different overheat ratios. Natural convection plumes extending over several permeable volume elements were detected when the hot wire was under natural convection, in some cases reaching velocities up to 60 mm/s downstream from the hot wire position. For low velocity flows, natural convection can be regarded as a flow velocity offset, which becomes negligible at local velocities higher than 0.03 m/s. For higher velocities, in the mixed convection regime, the intrusivity of the HWA probe becomes relevant. Furthermore, the flow in the test section used in the study presents a linear instability that produces velocity fluctuations. Availing ourselves of this phenomenon we verified the dynamic response of the HWA at the lowest velocity where the flow shows periodic fluctuations; for a local mean velocity of (0.131 ± 0.012) m/s the HWA showed a satisfactory dynamic response up to 20 Hz.     

形状记忆合金丝驱动器冷却方法理论分析及实验研究

形状记忆合金(SMA)丝驱动器的冷却时间直接影响驱动器的响应速度。提出了一种以压缩空气为冷却气源的套管式强制空气对流冷却方案,可在不影响其他SMA丝的情况下实现对单根SMA丝的快速冷却。建立了自然冷却换热和强制对流换热的数值分析理论模型,并且对直径为1mm的NiTi合金SMA丝分别进行了自然对流和强制对流换热实验,实验结果验证了数学模型的准确性。     

On the thermal elastohydrodynamic lubrication of tilting roller pairs

In order to investigate thermal effect of tilting roller pairs, a numerical solution for TEHL of tilting roller pairs has been presented. Variations in the lubricating performance with tilting angle have been investigated. Comparison between thermal and isothermal solutions has been made. Effects of the end profile radius, the velocity, and the maximum Hertzian pressure have been discussed. Profile modification of the roller generatrix has been assumed. Results show that all of the highest temperature, the maximum pressure, and the minimum film thickness occur at the load-carrying end. Larger tilting angle results in more evident thermal effect.     

A new method for determining the preload in a wire race ball bearing

This paper explores a numerical method to calculate the frictionless three-dimensional non-conforming contact problem associated with a wire race ball bearing used in a certain aircraft simulating rotary table, for challenging the conventional method on the determination of the preload magnitude. A computer program based on the Hertz elastic contact theory and a mathematical model of two critical loading conditions was performed in MATLAB^® by using an example of a wire race ball bearing having an approximately 900 mm diameter. The normal contact forces, the contact deformation, the maximum contact pressure, the semi-major axes and the semi-minor axes of contact ellipses of the ball-wire race were computed. The analytic results show that the overturning moment, the pitting corrosion and the shear failure due to combined stresses can be avoided by controlling preload values in the range 11.3–169.9 μm. The experimental results are closely in agreement with the theoretical results, and verify the availability of the numerical method. The research provides theoretical support for the development and further application of wire race ball bearings with large diameters.     

Heat loss investigation from spherical cavity receiver of solar concentrator

The heat losses are mainly affects on the performance of cavity receiver of solar concentrator. In this paper, the experimental and numerical study is carried out for different heat losses from spherical cavity receiver of 0.385 m cavity diameter and 0.154 m opening diameter. The total and convection losses are studied experimentally to no wind and wind conditions for the temperature range of 150 °C to 300 °C at 0°, 30°, 45°, 60° and 90° inclination angle of cavity receiver. The experimental set up mainly consists of copper tube material cavity receiver wrapped with nichrome heating coil to heat the cavity and insulated with glasswool insulation. The numerical analysis was carried out with Fluent Computational fluid dynamics (CFD) software, to study connective heat losses for no wind condition only. The numerical results are compared with experimental results and found good agreement with maximum deviation of 12 %. The effect of inclination angle of cavity receiver on total losses & convection losses shows that as the inclination angle increases from 0o to 90o, both losses decreased due to decreased in convective zone into the cavity receiver. The effect of operating temperature of cavity shows that as the temperature of cavity receiver increases, the total and convective losses goes on increasing. The effect of external wind at 2 m/s and 4 m/s in two directions (side-on wind and head-on wind) is also studied experimentally for total and convective heat losses. The result shows that the heat losses are higher for head-on wind condition compared to side-on wind and no wind condition at all inclination angle of cavity receiver. The present results are also compared to the convective losses obtained from the correlations of Stine & Mcdonald and M. Prakash. The convective loss from these correlations shows nearest prediction to both experimental and numerical results.

     

装载机线控转向系统的设计与分析

针对装载机转向系统能源消耗大,使用成本高,驾驶室工作条件差和驾驶易疲劳的缺点,设计了线控转向系统。该系统采用变量泵,系统采用容积控制,能耗较定量泵低,去除了方向盘与转向系统之间的机械连接,转向非常轻便,工作室环境得到了改善。首先设计了整体的线控转向系统方案,然后建立了数学模型,在数学模型中加入PID模糊控制,最后在MATLAB/Simulink中仿真。结果证明,该系统具有非常好的稳定性,方向盘转角与转向马达转角随动性很好。     

Analysis of Pulsed wire measurements on bi-harmonic undulator

In this paper we report measurement of bi-harmonic undulator in a Pulsed wire bench. The pulsed wire data for field integral is compared with Hall probe data. It is observed that the wire rigidity and stiffness of the thick wire do not affect the bi harmonic undulator field measurement and gives comparable results with Hall probe data.     

Performance characteristics of a therapeutic ultrasound wire waveguide apparatus

Therapeutic ultrasound angioplasty has been investigated, clinically, by a number of researchers and represents a potentially promising therapy for the treatment of atherosclerotic lesions. To date, there has been no detailed analysis of the effect of mechanical design parameters, such as wire geometry or damping characteristics, on wire waveguide performance. An apparatus capable of delivering therapeutic ultrasound down small diameter nickel–titanium (NiTi) wire waveguides is described. The output peak-to-peak (p–p) displacements at the distal tip of a 1.0 mm diameter waveguide were measured experimentally, by means of an optical microscope and image analysis software. The output was measured for a range of waveguide lengths from 118 to 303 mm. Wire waveguide distal tip displacements as high as 98 μm (p–p) at 23.5 kHz were measured. For the range of lengths tested, the experimental measurements show the critical relationship between the length of the waveguide and the output distal tip displacements. A finite element model that can predict the resonant frequencies and distal tip displacements of various wire waveguide geometries and configurations, including the effect of damping, is presented. This numerical model has been validated against the experimental displacement data obtained. This will be a valuable design tool for ensuring the safety and effectiveness of therapeutic ultrasound angioplasty procedures.     

An experimental apparatus measuring convective heat transfer coefficient from a heated fine wire traversing in nanofluids

Most of the previous convection experiments for nanofluids have been performed for internal tube flow with constant heat flux boundary condition. In contrast, a simple experimental apparatus measuring convective heat transfer coefficient from a heated wire to external nanofluids is proposed and its working principles are explained in detail. The convective heat transfer coefficient provided by the present system might be used as a useful indication justifying the adoption of prepared nanofluids as new efficient heat transfer fluids. Validation experiments by comparing convective heat transfer coefficients between the conventional correlation and measured values are carried out for base fluids. Also the effect of increased thermal conductivity of nano lubrication oil on the enhancement of convective heat transfer coefficient is investigated.     

Effect of thermal radiation on convection heat transfer in cooling channel of photovoltaic thermal system

The effect of thermal radiation on convection heat transfer in flat-box type cooling channel of photovoltaic thermal system with tilt angle of 30 degree was studied by 3D numerical simulation under constant heat flux boundary condition. The temperature contours and velocity fields of fluid near the outlet were obtained. The variations of wall temperature and convection Nusselt number along flow direction for all the separate walls composing the cooling channel were compared and analyzed. The results show that due to thermal radiation, the deflection of the maximum velocity region to heated top wall, together with the asymmetry of temperature field is weakened. For natural convection, radiation promotes the formation of multi-vortices. For mixed convection, heat transfer on all the cooling channel walls is enhanced under the condition of lower heat flux while heat transfer on heated top wall is deteriorated when the heat flux is relative high. Also, pressure re-rising is promoted by thermal radiation.     

新型节能抽油机的设计

新型节能抽油机采用柔性与刚性相结合的传动方案，根据渐开线的特性，设计出变径天轮与定径天轮组合的结构，优化了平衡相位角，极位夹角和结构尺寸。针对易损件钢丝绳的失效机理，提出了提高钢丝绳使用寿命的具体措施。     

高深宽比微细结构电铸时传质过程数值分析

针对高深宽比微细结构电铸时存在严重传质受限的问题,以微深槽特征为分析对象建立液相传质两种数学模型——维扩散模型和二维对流—扩散模型,并分别用Matlab专用工具箱和Fluent 6.2流体仿真软件进行数值求解,依次分析以扩散、强制对流－扩散、复合对流(强制对流和自然对流)－扩散等为主导传质模式作用下微细电铸时,流场和离子浓度场的空间变化规律及其对液相传质效果的影响,并进行试验验证。结果表明：微细结构电铸时,单一扩散作用仅能用于深宽比小于2且电流密度小于2 A/dm2的液相传质场合;槽外强制对流只能对深宽比小于2的微槽内电解液产生一定搅拌作用;强化槽内自然对流作用并与槽外强制对流协同配合时,槽(深宽比为5)内可形成独特的单个或多个占据整个槽空间的涡流循环胞,涡流流速约为强制对流流速的1/20～1/2,明显改善传质效果,试验结果与此相印证。     

Automated thermal conductivity measurement algorithm for the transient hot wire method

Even after more than 20 years of research, establishment of a nanofluid thermal conductivity enhancement mechanism is impeded by differences in research results among researchers. Thermal conductivity measurement results may differ considerably depending on the selection of the temperature history range used to estimate thermal conductivity. This range should be selected carefully considering factors such as the hot wire specifications and the applied heat, but comparisons between researchers’ choices have rarely been reported.

To resolve this problem, herein we present an algorithm that estimates test fluid thermal conductivity based upon the inputs of various hot wire specifications, wire resistance history, and applied voltage. We confirm that the proposed algorithm gives more accurate and precise results comparing with the cases of selecting the range based on solely on the determination coefficient R² and is effective in eliminating data affected by the errors. The proposed method for fluid thermal conductivity measurement is robust to differences in measurement conditions including operator skill level, applied voltage, and hot wire specifications. It is expected that the discrepancies noted across the results of different research groups would be greatly reduced by adopting the proposed method.

     

Measurement,simulation on dynamic characteristics of a wire gauze–fluid damping shock absorber

A new kind of shock absorber with Coulomb–fluid damping through coupling oil, wire gauze, rubber and spring by ingenious tactics is designed for reinforcement of electronic-information equipment in atrocious vibration and impact. The physical mechanism of the shock absorber is systematically investigated. The key-model machine shows complex non-linear dynamic characteristics in multi-parameter coupling dynamic test; otherwise, it has a good dynamic performance for attenuating vibration and resisting violent impact. Based on this, the non-linear dynamic model for attenuating vibration mode of the shock absorber is presented by analysing coupling physical mechanism of fluid and Coulomb friction and other factors for designing the shock absorber with high validity. The analytical results obtained in experimental data have been compared with the numerical ones obtained by performing the Runge–Kutta method with the mathematical model. As the model results agree well with the test data, it can be used for engineering design.     

多道次拉丝设备的道次切除技术

针对因工艺要求、原料与成品材料的不同，多道次拉丝设备有可能只要求其中的几个道次运行而切除其它的道次的情况，对最前面道次被切除、中间某一道次被切除以及最后一个道次被切除这3种情况进行了详细分析。在采用线速度法的基础上，利用归一化处理简化了计算与编程工作量。最后，得出了任意道次切除时的计算流程。实验结果表明，采用该方法使控制器在任意道次切除后仍具有良好的控制效果。     

The measurement of the axial internal stress in steel wire

Apparatus is described for the measurement of the approximate axial internal stress distribution in wires typically 0·3–0·4 mm diameter. A sensitive optical system measures the change of length of the wire as its diameter is reduced at a rate of about 0·3 μm per minute by dissolution in 0·012 M nitric acid maintained at a constant temperature. The change of area of cross section of the wire is deduced from measurement of its electrical resistance. The adoption of a continuous thinning process makes it possible to measure the internal stress at the original wire surface. The method is not able to take account of the effect on the axial strain of the relief of circumferential and radial stresses. This leads to the axial stress being underestimated by about 30%. Internal stress measurements are reported on patented and drawn steel wire which confirm the wide range of internal stress intensity that can be generated in this material by changing and drawing conditions.     

Free abrasive wire saw machining of ceramics

Currently, many kinds of ceramics are used in advanced industrial fields due to their superior mechanical properties, such as thermal, wear, corrosion resistance, and lightweight features. Wire saw machining ceramic (Al₂O₃) was investigated by ultrasonic vibration in this study. Taguchi approach is a powerful design tool for high-quality systems. Material removal rate, wafer surface roughness, steel wire wear, kerf width, and flatness during machining ceramic were selected as quality character factors to optimize the machining parameters (swinging angle, concentration, mixed grain and direction of ultrasonic vibration) to get the larger-the-better (material removal rate) and the smaller-the-better (wafer surface roughness, steel wire wear, kerf width and flatness) machining characteristics by Taguchi method. The results indicated that wire swinging produces a higher material removal rate and good wafer surface roughness. Ultrasonic vibration improved material removal rate, without affecting the flatness under different machining conditions. Experimental results show that the optimal wire saw machining parameters based on grey relational analysis can be determined effectively and material removal rate increases from 2.972 to 3.324 mm²/min, wafer surface roughness decreases from 0.37 to 0.34 μm, steel wire wear decreases from 0.78 to 0.77 μm, kerf width decreases from 0.352 to 0.350 mm, and flatness decreases from 7.51 to 7.22 μm are observed.     

激光自混合干涉角度测量参数优化及旋转方向判别

对反射旋转体引起聚焦激光自混合干涉信号位相与旋转角度的非线性关系进行了研究,提出了一个实验参数的优化方法来降低该非线性效应引起的非线性角度测量误差。重新评估了自混合干涉角度测量在测量范围扩大后的物理近似条件,从理论上分析了实验参数给角度测量带来的误差影响并进行了模拟仿真,提出了利用该非线性关系判别反射体旋转方向的方法。最后,进行了激光自混合干涉角度测量实验并给出若干个实验参数条件下分别得到的角度测量结果。实验结果表明,实验参数优化后,角度测量误差大幅减少;在最优情况下,比未优化方法的测量精度提升了一个数量级,可达10-5 rad,证明了提出的实验参数优化方法和反射体旋转方向判别方法的有效性。实验结果还显示,使用提出的方法在提高测量范围的同时仍能进行高精度的角度测量,从而进一步拓宽了基于反射体旋转引起的激光自混合干涉效应的应用范围。     

Inertia Effect on the Load Capacity of Large Water-Lubricated Thrust Bearing

With an assumption that the profile of the velocity is not affected by the inertia force, a numerical model based on an extended Reynolds equation, which takes the full inertia effect and turbulence into account, is established. A finite deference method is used to solve the equation and the numerical results are validated with numerical and experimental results. A simplified expression is derived theoretically and modified by the numerical results of the established model. Finally, a study of a large water-lubricated tilting pad thrust bearing is presented. The analytical results and numerical results agree well. A quantitative analysis of inertia effects on load capacity is made in this article.