Numerical investigation of laminar heat transfer and nanofluid flow between two porous horizontal concentric cylinders

In this study, the laminar heat transfer and nanofluid flow between two porous horizontal concentric cylinders was investigated. The problem is investigated in two different geometries and the Re=10, 25, 50, 75, 100 and volume fraction 0, 0.2%, 0.5%, 2% and 5% that related to copper nanoparticles, and porous medium porosity of 0.5 and 0.9. Compared to the first geometry, the convective coefficient in the second geometry increases by 8.3%, 7% and 5.5% at Reynolds numbers of 100, 75 and 50, respectively. Comparison of the outlet temperatures for two heat fluxes of 300 and 1200 W/m^2 indicates a 2.5% temperature growth by a fourfold increase in the heat fluxes. Also, the higher Nusselt number is associated with the second geometry occurring at porosities of 0.9 and 0.5, respectively. In both geometries, the Nusselt number values at the porosity of 0.9 are higher, which is due to the increased nanofluid convection at higher porosities. The velocity of the nanofluid experiences a two-fold increase at the outlet compared to its inlet velocity in the first geometry and for both porosities. Similarly, a three-fold increase was achieved in the second geometry and for both porosities.

An analytic solution and investigation of character of viscoelastic fluids in double-gap concentric cylinder rheometer

An analytical solution to annular pipe flow of the second fluid and Maxwell fluid is given using Weber integral transform. The formulas can be used to analyse the behavior of unsteady flow of viscoelastic fluid in annular pipe, especially to analyse the flow character of double-gap concentric cylinder rheometer. It is found by computation that when the outer cylinder is in simple periodic motion, there are step junctions along the history curve of Maxwell fluid’s velocity and shear stress, and at step junctions both amplitude and phase of oscillatory wave vary sharply; when the outer cylinder makes uniform rotation, the velocity and shear stress of Maxwell fluid exhibit rhombic wave oscillation, and its period is in close parabolic relation with material constant H.

Analysis of general second-order fluid flow in double cylinder rheometer

The fractional calculus approach in the constitutive relationship model of second-order fluid is introduced and the flow characteristics of the viscoelastic fluid in double cylinder rheometer are studied. First, the analytical solution of which the derivative order is 1/2 is derived with the analytical solution and the reliability of Laplace numerical inversion based on Crump algorithm for the problem is verified, then the characteristics of second-order fluid flow in the rheometer by using Crump method is analyzed. The results indicate that the more obvious the viscoelastic properties of fluid are, the more sensitive the dependence of velocity and stress on fractional derivative order is.

Wave Loading on Concentric Porous Cylinders with Varying Porosity

Wave diffraction of two concentric porous cylinders with varying porosity was studied by using an analytical method based on eigenfunction matching.The fluid domain around the cylinders is divided into three sub-domains and in each sub-domain an eigenfunction expansion of the velocity potential is obtained by satisfying the Laplace equation,the boundary conditions on the free surface and on the sea bed.The unknown coefficients of eigenfunction expansions are determined by boundary conditions on the porous hulls.In the paper,the boundary conditions are based upon the assumption that the flow in the porous medium is governed by Darcy's law.Two porous-effect parameters applied on two porous cylinders are functions of the vertical coordinate instead of the constant.Wave loading on the outer and inner cylinder is presented in the numerical results.

Geometric shapes of the interface surface of bicomponent flows between two concentric rotating cylinders

In this paper, the shape problem of interface of bicomponent flows between two concentric rotating cylinders is investigated. With tensor analysis, the problem is reduced to an energy functional isoperimetric problem when neglecting the effects of the dissipative energy caused by viscosity. We derive the associated Euler-Lagrangian equation, which is a nonlinear elliptic boundary value problem of the second order. Moreover, by considering the effects of the dissipative energy, we propose another total energy functional to characterize the geometric shape of the interface, and obtain the corresponding Euler-Lagrangian equation, which is also a nonlinear elliptic boundary value problem of the second order. Thus, the problem of the geometric shape is converted into a nonlinear boundary value problem of the second order in both cases.

基于5G通信技术的变电站SF_(6)气瓶智能管理系统设计

为确保变电站六氟化硫(SF_(6))气瓶智能管理的时效性和可靠性,设计基于5G通信技术的变电站SF_(6)气瓶智能管理系统。通过SF_(6)气体采集器等装置,感知并采集变电站SF_(6)气瓶的状态数据。将该数据通过由5G通信技术构建的5G传输模块,传送至管理模块,并采用5G切片技术划分网络,以实现按需通信。管理模块接收经由5G传输模块传送的数据后,基于非分光红外差分检测方法,在线智能检测SF_(6)气瓶的泄漏浓度,并校核SF_(6)气体在线监测结果,以实现SF_(6)气瓶的智能管理。测试结果表明:网络传输平均速率在8~10 Gbit/s之间,极大程度接近传输速率峰值,通信的实时性良好;能够实时监测SF_(6)气瓶运行状态,在线监测精度较高,平均偏移程度低于0.035。该系统可全面呈现气体的泄漏情况,以及发生泄漏的时间和泄漏气体的浓度情况。

纸机车间尾气检测及处理系统

通过对纸机生产线压榨部真空泵尾气及烘干部烘缸气罩尾气指标进行检测分析,对比各废气治理技术优缺点,确定用于真空泵尾气及烘缸气罩收集尾气治理的最佳处理工艺,满足国标及民标对废气治理要求,改善造纸企业周边环境。

一起500 kV液压弹簧机构GIS断路器频繁打压原因浅析

液压弹簧操作机构作为高电压等级的主要操作机构,容易出现频繁打压等故障,严重时会导致断路器闭锁,进而扩大故障范围。通过对一起500 kV GIS断路器频繁打压问题分析,现场检查储能控制回路无异常,解体后发现工作缸内壁存在裂纹,导致高压区域与低压区域连通,打压频繁。通过宏观检查、金相检测、能谱分析、材质复核、机械性能检测等方法,深入研究裂纹原因,结合液压机构动作原理及工作缸材料对比,最终确定机构频繁打压原因为工作缸加工质量不佳,成品材料存在相对较多的微观组织缺陷,造成轴向应力集中,导致工作缸出现裂纹。给出了同类型断路器处理方案,以避免相同问题导致设备停运,保证电力系统的安全运行。

Magnetophotothermal interaction in a rotating solid cylinder of semiconductor silicone material with time dependent heat flow

A mathematical model linking thermoelasticity to photothermal experiments is proposed with the consideration of the photothermal effect.The system equations for coupled plasma,heat conduction with phase-lags(PLs),and motion equations are introduced and solved by using the Laplace transform technique.The photothermal,thermal,and elastic waves in a rotating solid cylinder of semiconductor material are analyzed with the proposed model.The cylinder surface is constrained and subjected to a time-dependent pulse heat flux.The sensitivity of the physical fields for the angular velocity,PLs,and thermal vibration parameters is investigated.In addition,the effects of the effective parameters on the physical quantities are graphically illustrated and discussed in detail.

A semi-analytical solution for electric double layers near an elliptical cylinder

A theoretical analysis on the electric double layer formed near the surface of an infinite cylinder with an elliptical cross section and a prescribed electric potential in an ionic conductor was performed using the linearized Gouy–Chapman theory. A semi-analytical solution in terms of the Mathieu functions was obtained. The distributions of the electric potential, cations, anions, and electric field were calculated. The effects of various physical and geometric parameters were examined. The fields vary rapidly near the elliptical boundary and are nearly uniform at far field. Electric field concentrations were found at the ends of the semi-major and semi-minor axes of the ellipse. These concentrations are sensitive to the physical and geometric parameters.

Quenching Phenomena Due to a Concentrated Nonlinear Source in an Infinitely Long Cylinder

This article studies a semilinear parabolic first initial-boundary value problem with a concentrated nonlinear source in an infinitely long cylinder. We study the effects of the strength of the source on quenching. Criteria for global existence of the solution and for quenching are investigated.

Effect of Generating Heat on Ozone Generation in Dielectric Cylinder-Cylinder DBD Ozone Generator

A cylinder-cylinder dielectric-barrier discharge (DBD) ozone generator has been developed. The ozone concentration was measured at an oxygen pressure of 1.02 atm and an oxygen flow rate of 12 L/min. The heat generated in the ozone tube during the operation of the ozone generator was investigated using a thermal camera. The infrared (IR) images and corresponding temperatures of the ozone tube surfaces at different operating times were observed. The IR images showed the generating of the inhomogeneous heat-up along the ozone tube surface which results in the decrease of the ozone production efficiency.

气缸体裂纹缺陷的分析与解决

介绍了16 L气缸体铸件的工艺过程和性能要求。分析了试制过程中在气缸体通风口位置产生的裂纹缺陷情况,结合软件模拟计算结果认为,铸件壁厚差大形成集中应力、砂型退让性差和浇注温度过高是引起裂纹的主要原因。通过改进铸件设计结构、树脂加入量由1.5%调整至1.3%、浇注温度降低20℃、延长开箱时间等措施,获得了合格铸件。

导弹同心筒发射时导弹头部压强环境研究

为了研究导弹发射时头部的压强环境,利用计算流体动力学软件Fluent对导弹发射时同心筒内流场进行数值仿真。建立前盖不加装凸台结构的计算模型,分析发射过程中导弹头部的压强环境,并把仿真结果与试验结果进行对比,仿真结果与试验结果吻合较好。然后建立前盖加装凸台结构的计算模型,并改变凸台结构的直径、高度和截面形状,研究这些参数对导弹头部压强环境的影响,发现前盖加装凸台结构能明显减弱导弹头部顶端的压强集中现象,通过优化凸台结构的直径、高度和截面形状,可以最大化减小导弹头部的压强峰值,为后续导弹头部压强环境的优化设计提供参考。

填孔电镀不良能力提升研究

随着电子产品朝高速化、高频化、高密度方向的发展,印制电路板的盲孔填孔工艺越来越受到大家关注。目前,盲孔填孔电镀面临的最大问题是填孔深度不符,其中填孔深度不符的缺陷大部分是填孔漏填。造成填孔漏填的原因是填孔电镀的驱动力不足,导致起镀时间延后与爆发阶段受阻。填孔漏填会影响到产品的交付品质,而且一旦流入到客户端产品上将产生严重不良影响。控制填孔漏填的关键方法是在前处理、铜缸温度、电流分布,改善除油浓度、铜缸温度和电流分布环节中提升填孔电镀的深镀能力。

40Cr钢油缸断裂原因

采用宏观观察、化学成分分析、金相检验、扫描电镜和能谱分析、显微硬度测试等方法分析了40Cr钢油缸断裂的原因。结果表明:油缸断裂主要与硫元素含量超标、硫化物聚集、表面凹坑缺陷及热处理不均匀有关;硫元素易产生“热脆”,聚集的条状夹杂物破坏了基体的连续性,使油缸产生微裂纹,在表面凹坑处产生应力集中,热处理不均匀使组织产生内应力,萌生的裂纹及表面凹坑在以上因素的作用下不断扩展,最终导致油缸断裂。

关于AERScreen模型估算结果与地形之间规律的研究

以杭州三捷公司的大气AERScreen模型估算软件的AERScreen模型为基础,通过设置排气筒所在地的不同地形,得出最大浓度占标率P_(max)、D_(10%)最远距离与排气筒所在地的地形之间的规律。

Comparison of Rheometric Devices for Measuring the Rheological Parameters of Debris Flow Slurry

Soil samples with clay content ranging from 15% to 31%, were taken from three debris flow gullies in Southwest China. Three debris flow slurry samples were prepared and tested with four measuring systems of an Anton Paar Physica MCR301 rheometer, including the concentric cylinder system,the parallel-plate system, the vane geometry, and the ball measuring system. All systems were smoothwalled. Flow curves were plotted and yield stress was determined using the Herschel-Bulkley model,showing differences among the different systems.Flow curves from the concentric cylinder and parallelplate systems involved two distinct regions, the low shear and the high shear regions. Yield stresses determined by data fitting in the low shear region were significantly lower than the values from the inclined channel test which is a practical method for determining yield stress. Flow curves in the high shear region are close to those from the vane geometry and the ball measuring system. The fitted values of yield stress are comparable to the values from the inclined channel test. The differences are caused by wall-slip effects in the low shear region.Vane geometry can capture the stress overshoot phenomenon caused by the destruction of slurry structure, whereas end effects should be considered in the determination of yield stress. The ball measuring system can give reasonable results, and it is applicable for rheological testing of debris flow slurries.

聚甲丙烯酸铵酯Ⅱ黏度测定方法

目的研究聚甲丙烯酸铵酯Ⅱ的流体特性并建立其动力黏度测定方法。方法采用马尔文Kinexus Ultra同轴圆筒式流变仪,温度20℃,剪切速率10 s-1条件下测定动力黏度。结果 6%聚甲丙烯酸铵酯Ⅱ的75%乙醇溶液为牛顿流体,动力黏度为5.06 mPa.s,30次测定的RSD为0.25%。结论该方法简便、准确、重复性好,适用于测定聚甲丙烯酸铵酯Ⅱ的动力黏度。

聚丙烯酸树脂Ⅱ动力黏度的测定方法

目的:研究聚丙烯酸树脂Ⅱ的流体特性,并建立测定其动力黏度的方法。方法:用马尔文Bohlin Gemini HRnano同轴圆筒式流变仪,在温度20℃,剪切速率10s-1条件下测定动力黏度。结果:聚丙烯酸树脂Ⅱ为牛顿流体,3批样品的动力黏度分别为70.9、71.8和71.1mPa/s,RSD分别为0.3%、0.3%和0.5%(n=28)。结论:该方法简便、准确、重复性好,适用于测定聚丙烯酸树脂Ⅱ的动力黏度。