An Investigation into Forced Convection of a Nanofluid Flowing in a Rectangular Microchannel under the Influence of a Magnetic Field

In line with recent studies,where it has been shown that nanofluids containing graphene have a stronger capacity to boost the heat transfer coefficient with respect to ordinary nanofluids,experiments have been conducted using water with cobalt ferrite/graphene nanoparticles.In particular,a circular channel made of copper subjected to a constant heatflux has been considered.As nanoparticles are sensitive to the presence of a magneticfield,different conditions have been examined,allowing both the strength and the frequency of such afield to span relatively wide ranges and assuming different concentrations of nanoparticles.According to thefindings,the addition of nanoparticles to thefluid causes its rotation speed to increase by a factor of two,whereas ultraviolet radiation plays a negligible role.The amount of time required to attain the maximum rotation speed of the nanofluid and the Nusselt number have been measured under both constant and alternating magneticfields for a ferrofluid with a concentration of 0.5%and atflow Reynolds number of 550 and 1750.

CHAOTIC TRANSIENTS IN A CURVED FLUID CONVEYING TUBE

The chaotic transients of a curved fluid conveying tube subjected to a nonlinear foundation are investigated. The assumption of the inextensibility of the tube is applied to derive the nonlinear differential equation of motion via the Newtonian approach, with the differential quadrature method used to discretize the curved tube model in the spatial domain. And the nonlinear dynamic motion equation is obtained. The numerical analysis shows that, the final steady states are sensitive to the initial system conditions in a large parameter region of the fluid speed. This phenomenon of chaotic transients is infrequent for fluid conveying tubes.

Peristaltic flow of MHD Jeffrey fluid through finite length cylindrical tube

The present investigation studies the peristaltic flow of the Jeffrey fluid through a tube of finite length. The fluid is electrically conducting in the presence of an applied magnetic field. Analysis is carried out under the assumption of long wavelength and low Reynolds number approximations. Expressions of the pressure gradient, volume flow rate, average volume flow rate, and local wall shear stress are obtained. The effects of relaxation time, retardation time, Hartman number on pressure, local wall shear stress, and mechanical efficiency of peristaltic pump are studied. The reflux phenomenon is also investigated. The case of propagation of a non-integral number of waves along the tube walls, which are inherent characteristics of finite length vessels, is also examined.

Heat transfer and friction factor of Therminol liquid phase heat transfer fluid in a ribbed tube

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.

Nonlinear waves in a fluid-filled thin viscoelastic tube

In the present paper the propagation property of nonlinear waves in a thin viscoelastic tube filled with incom- pressible inviscid fluid is studied. The tube is considered to be made of an incompressible isotropic viscoelastic material described by Kelvin-Voigt model. Using the mass conservation and the momentum theorem of the fluid and radial dynamic equilibrium of an element of the tube wall, a set of nonlinear partial differential equations governing the propagation of nonlinear pressure wave in the solid-liquid coupled system is obtained. In the long-wave approximation the nonlinear far-field equations can be derived employing the reductive perturbation technique （RPT）. Selecting the expo- nent c~ of the perturbation parameter in Gardner-Morikawa transformation according to the order of viscous coefficient 7, three kinds of evolution equations with soliton solution, i.e. Korteweg-de Vries （KdV）-Burgers, KdV and Burgers equations are deduced. By means of the method of traveling-wave solution and numerical calculation, the propagation properties of solitary waves corresponding with these evolution equations are analysed in detail. Finally, as a example of practical application, the propagation of pressure pulses in large blood vessels is discussed.

HEAT TRANSFER STUDIES OF HIGHLY VISCOUS NON-NEWTONIAN FLUIDS IN VERTICAL TUBES BY FINITE ELEMENT METHOD

A numerical method capable is developed for handling steady laminar flow and heat trans-fer of a highly viscous power-law fluid whose density,viscosity,specific heat and thermalconductivity,vary with temperature.The governing equations are found to be continuity,monmentumand energy expressions.Important effects such as varying viscosity,natural convection and viscousdissipation are incorporated in the theoretical model.These equations are being attracted by employing a decoupled finite element method.Galerkin’sprinciple is used to handle the momentum and continuity equations.Consistent(SU/PG)andnon-consistent(SU)streamline upwind methods are employed for the energy equation.Comparisonof calculated results and experimental data shows good agreement.Similar results are obtained withSU and SU/PG methods.Velocity and temperature profiles which provide insights into the processare also given.

Fallopian tube assessment of the peristaltic-ciliary flow of a linearly viscous fluid in a finite narrow tube

The present theoretical assessment deals with the peristaltic-ciliary trans- port of a developing embryo within a fallopian tubal fluid in the human fallopian tube. A mathematical model of peristalsis-cilia induced flow of a linearly viscous fluid within a fallopian tubal fluid in a finite two-dimensional narrow tube is developed. The lubrica- tion approximation theory is used to solve the resulting partial differential equation. The expressions for axial and radial velocities, pressure gradient, stream function, volume flow rate, and time mean volume flow rate are derived. Numerical integration is performed for the appropriate residue time over the wavelength and the pressure difference over the wavelength. Moreover, the plots of axial velocity, the appropriate residue time over wavelength, the vector, the pressure difference over wavelength, and the streamlines are displayed and discussed for emerging parameters and constants. Salient features of the pumping characteristics and the trapping phenomenon are discussed in detail. Yhrther- more, a comparison between the peristaltic flow and the peristaltic-ciliary flow is made as the special case. Relevance of the current results to the transport of a developing embryo within a fallopian tubal fluid from ampulla to the intramural in the fallopian tube is also explored. It reveals the fact that cilia along with peristalsis helps to complete the required mitotic divisions while transporting the developing embryo within a fallopian tubal fluid in the human fallopian tube.

ANALYTICAL SOLUTIONS FOR EQUATIONS OF UNSTEADY FLOW OF NON-NEWTONIAN FLUIDS IN TUBE

This paper presents analytieal solutions to the partial differential equations for unsteady flow of the second-order fluid and Maxwell fluid in tube by using the integral transform method. It can be used to analyse the behaviour of axial velocity and shear stress for unsteady flow of nun-Newtonian visco-elastie fluids in tube, and to provide a theoretical base for the projection of pipe-line engineering.

Analytical Modeling of Fluid Flow through a Deformable Tube

In this document,we analytically investigate fluid flow through a deformable tube.The fluid is considered to be Newtonian,incompressible and it moves along an elastic and isotropic tube wall.The study provides a review of recent modeling aimed at understanding the effects of fluid parameters over the elastic wall behavior.The unsteady fluid flow will be analyzed following the asymptotic approach process using to a large Reynolds number and a small aspect radio.Moreover,according to the small axisymmetric deformation,the wall is mathematically developed basing on the thin shell theory whose linear approach is applied.Lastly,the dynamic behavior of the tube is represented and discussed.

A Numerical Study on Fully Developed Fluid Flow and Heat Transfer in a Spiral Finned Tube

In this paper, the standard k-εtwo-equation model is adopted to numerically simulate fully developed fluid flow and heat transfer in a spiral finned tube within a cracking furnace for ethylene manufacturing. By variable transformation, the orlglnal 3-D problem is converted into a 2-D problem in spiral coordinates. The algorithm of SIMPLEC is used to study the fully developed fluld flow and heat transfer in the spiral finned tube at constant periphery temperature and constant axial heat flux, The computed results agree pretty well with the experimental data obtained from the industry, Further studies on the fluid flows and temperature profiles at different Reynolds numbers within straight and spiral finned tubes are conducted and the mechanisms involved are explored. It is found that with the spiral finned tube, pressure drop increases to a great extent whereas heat transfer tends to be decreased.

Computational fluid dynamic simulation of an inter-phasing pulse tube cooler

An inter-phasing pulse tube cooler (IPPTC) consists of two pulse tube units, which are connected to each other at hot ends of the pulse tubes through a needle valve. This paper presents the computational fluid dynamic (CFD) results of an IPPTC using a 2D axis-symmetrical model. General results such as the phase difference between pressure and velocity at cold end and hot end, the temperature profiles along the wall, the available lowest temperature as well as its oscillations and the coefficient of performance (COP) for IPPTC are presented. The formation of DC flow and its effects on the performance of the cooler are investigated and analyzed in detail. Turbulence, which is partially responsible for the poor overall performance of a single orifice pulse tube cooler (OPTC), is found to be much reduced in IPPTC and its performance is improved significantly compared with the single OPTC.

管束结构的阻尼控制型流弹失稳特性研究

尽管自2012年SONGS事故以来,流弹失稳对管束结构的危害性和重要性再次引起了重点关注,但对导致这种不稳定现象的根本因素仍未确定。为进一步研究流弹失稳的基本物理机制,以压水堆蒸汽发生器通常采用的平行三角形管束为对象,基于开源CFD(computational fluid dynamics)工具OpenFOAM,同时耦合管的动力学方程,求解具有移动边界的非定常Navier-Stokes(uRANS)方程,建立了研究阻尼控制型不稳定机制的数值模型,进而预测管束的流固耦合振动,揭示影响阻尼控制型不稳定机制的关键参数和流动响应;重点讨论了不同质量阻尼参数下,系统的响应特性、能量输入与耗散,升力与位移间的相干性、相位差、相关系数,升力的频谱特性,主导激励机理。进一步揭示了管束流弹系统中占主导地位的激励机理和关键流动现象,有助于理解管束与流体之间的相互作用机理,同时为工程中使用开源CFD工具OpenFOAM预测流弹失稳行为提供了参考。

螺旋扭曲扁管传热流阻性能及工艺计算方法研究

螺旋扭曲扁管是一种非标换热管,成熟的热交换器计算商业软件,如HTRI、Aspen EDR等目前均尚未提供对应的计算模型,现有计算方法存在不统一、偏差大等问题。以螺旋扭曲扁管为对象,通过数值模拟计算、实验测试对其进行传热及流阻性能研究,综合利用HTRI传热计算软件,建立了一套螺旋扁管传热及流阻性能的通用化计算方法。进行了通用化计算结果、数值模拟分析数据、实验测试数据的对比,验证了通用计算方法的准确性,对螺旋扭曲扁管的工艺设计具有指导意义。

低液量水平井连续油管气举产液剖面测井技术应用

产液剖面测试找水是了解生产层段产液状况,为油藏动态调整提供依据的重要手段,是油田开发的一项主要工作。针对低渗透油藏水平井单井产液低,常规产液剖面测试技术准确性差及分段生产测试效率低的问题,提出采用2 in^(*)预置式穿芯连续油管带测井仪器入井测试,通过氮气气举井筒排液,连续油管拖动井下测井仪器连续监测为核心的快速找水新方法。设计了制氮车+油管悬挂器+3½in普通油管+喇叭口的负压生产管柱,以及2 in穿芯连续油管+卡瓦连接器+测井连接工具串+测井仪器串的测试管柱,研制了连续油管测井连接工具、电滑环滚筒电缆密封固定器和FIT测井仪器等关键配套装置,形成了低液量水平井连续油管气举产液剖面测井快速找水技术。开展了6口井现场先导试验,试验过程中,井下测试信号无交流电干扰,保证了实时数据传输优势,真正做到了井下监测与地面实时可读同步。该技术可实现1天测试1口井,为定量快速解释低液量水平井产液分布状况提供了新的技术手段。

增强型中空纤维膜及MBR数值模拟的研究

中空纤维膜作为膜生物反应器(MBR),由于其高效性及灵活性被广泛应用于污水处理领域。文中介绍了纤维管增强型中空纤维膜,包括针织管增强膜、编织管增强膜及无纺管增强膜,综述了计算流体力学在MBR优化设计及膜污染清洗等方面的研究,并对增强型中空纤维膜及MBR数值模拟的应用前景进行展望。在未来的研究中,将计算流体力学与理论试验相结合可以提升研究效率,更好地解决水处理问题。

非球形湿颗粒导向管喷动流化床流动特性

实际工业生产中颗粒多为非球形颗粒,对颗粒形状效应和液相作用机制的研究不足,是导向管喷动流化床在颗粒涂层改性、包膜等工业应用的关键限制因素。选取粒径、密度相似的球形和圆柱形非球形颗粒为实验物料,对比两种颗粒在不同气速和雾滴引入量下的压力脉动信号频谱分析、信息熵分析,并结合床内气固流动对流型进行划分,绘制非球形湿颗粒流动相图,进而探究喷动流化过程中颗粒形状效应及液相作用机制。相比于球形颗粒,粒径、密度相似的非球形颗粒有较小的最小喷动速度,在喷动过程中有两个及以上较低的主频峰且信息熵较大,显示出非球形颗粒在系统内较高的混乱程度,颗粒之间摩擦、碰撞等降低了导向管内颗粒的固体循环速率。液体的引入增大了环形区颗粒间液桥力,使最小流化速度变大,但液体挥发引起喷动气量增大,使最小喷动速度与最小喷动流化速度减小。在喷动流化流型下引入液体,球形颗粒导向管两端压降ΔpDT的脉动主频降低,而非球形颗粒ΔpDT的主频升高。而且非球形颗粒黏附液体后频谱分析结果显示幅值较大的单一主频峰,表明非球形湿颗粒压力脉动规律性的增强。

“牛角管”式组合桨釜内中药膏剂的流动传热特性

为解决高黏度中药膏剂在搅拌釜内受热不均、混合效率低下等问题,设计了新型“牛角管”式组合桨。基于计算流体动力学(computational fluid dynamics,CFD)中的瞬态滑移网格法,对内盘管加热下搅拌釜流场进行数值模拟研究,并对其中一种工况进行了普适性的实验验证,探究搅拌釜内中药膏剂的流场情况及温度分布规律,分析了同一组合桨不同转速下以及同一转速下不同组合桨对流场情况的影响。结果表明:新型组合桨在转速300 r/min时釜内温度以及流场混合效率最高,在该转速下,将新型组合桨与传统组合桨进行对比,“涡轮叶片”式组合桨对釜内温度分布影响能力弱,不适用于工业生产,“大叶片”式组合桨机械搅拌功耗和釜内温差均大于新型组合桨,使得新型组合桨在多方面优于传统组合桨。研究结果为工业生产提供参考。

泵送灌注钢管混凝土流态数值模拟

钢管混凝土在国内外的桥梁工程建造中被广泛应用,管内混凝土泵管灌注过程中的匀质性控制是保证钢管混凝土组合构件具有良好力学性能的关键。混凝土中各组成原料在钢管的分布情况直接影响钢管混凝土的力学性能,为了探究泵送灌注时各组成原料在钢管中分布规律,将混凝土拌合物等效为气相(空气,主相)、液相(水介质,第2相)、固相(拟流体,第3相),用流体力学软件模拟了混凝土拌合物在钢管垂直布置和倾斜布置时各相流动行为和各相的体积分布规律。对于钢管道垂直布置,混凝土拌合物表现出来第2相和第3相以不同速度的整体顶升推移;对于钢管道倾斜布置,混凝土拌合物表现出来第2相和第3相以不同速度沿上升通道顶升推移和沿下降通道的沉降;两种布置方式均会导致近液面部分出现浮浆趋势,而在底部出现骨料下沉;泵送压力与高度成正比。以上结论可为钢管混凝土在工程上的应用提供参考。

气井环空液面下泄漏声场模拟

气井油套管环空液面下泄漏声波的产生及传播机理一直备受关注。为研究液面下泄漏声波声源特性,建立了井下油套管环空泄漏物理模型,联合STAR-CCM+软件对环空液面下气体泄漏状态进行了流场及声场的仿真分析,得到了泄漏流场的压力和相态云图及不同泄漏孔径、泄漏位置和泄漏速度下的声压频率曲线。研究结果表明:随着泄漏速度升高,泄漏气流冲击管壁且液面震荡剧烈,液面下泄漏声源主要以四极子声源为主;液面上泄漏声源主要由液面震荡破裂及液面下四极子声源共同产生,泄漏声波能量的主要频率分布在0~100 Hz区间;在单一变量条件下,泄漏声压级随泄漏孔径、泄漏速度及泄漏位置距底部距离的增大而增大。研究结果可为在井口应用声波法检测液面下泄漏奠定理论基础。

基于流-热-固耦合分析的数值模拟及结构优化

为解决等径T型管路应力过大问题,提出一种基于流-热-固耦合分析方法的优化方法对等径T型管结构进行优化。首先,基于流、固力学理论建立T型管多场耦合的数学模型和物理模型,对T型管内流体的速度温度变化情况和管路的等效应力的分布情况进行仿真模拟,在仿真结果的基础上对管路进行结构优化。仿真结果表明:冷热流体的压力差会导致流体产生逆流现象,从而导致管路的上游区等效应力值增大。等径T型管的最大等效应力值出现在主支管交汇的下游内壁面处。优化后管路内壁面最大等效应力值下降约14%,可以有效地延长管路的使用寿命。该方法对提高气体管路设计的可靠性具有一定的实践意义。