Solar radiation assisted mixed convection MHD flow of nanofluids over an inclined transparent plate embedded in a porous medium

The present paper investigates analytically and numerically the magneto-hydrodynamic (MHD) mixed convection flow of nanofluid over a nonlinear stretching inclined transparent plate embedded in a porous medium under the solar radiation. The two-dimensional governing equations are obtained considering the dominant effect of boundary layer and also in presence of the effects of viscous dissipation and variable magnetic field. These equations are transformed by the similarity transformation to two coupled nonlinear transformed equations and then solved using a numerical implicit method called Keller-Box. The effect of various parameters such as nanofluid volume fraction, magnetic parameter, porosity, effective extinction coefficient of porous medium, solar radiation flux, plate inclination angle, diameter of porous medium solid particles and dimensionless Eckert, Richardson and Prandtl numbers have been studied on the dimensionless temperature and velocity profiles. Also the results are presented based on Nusselt number and Skin friction coefficient.     

Thermal behavior and entropy generation rate analysis of a viscous flow in MHD micropumps

Studying the effects of various parameters on the behavior of velocity, temperature and thus the entropy generation rate in the microfluidic systems to reduce loss power is very important. Minimization of entropy generation in the flow system enables us for the parametric optimization of the MHD micropumps operation. In the present study, a transient, laminar and fully developed electrically conductive fluid flow in MHD micropumps has been investigated and the temperature distribution and effects of dimensionless influencing parameters on the entropy generation rate has been presented. Pumping operator in MHD micropumps are the Lorentz forces, which is produced as a result of the interaction between magnetic and electric fields. Governing equations have been solved numerically using finite-difference (ADI) method. The results of simulation have shown good agreement with analytical results by ei-genfunction expansion method. In addition, the results are compared with experimental data from literature which confirms the accuracy of the model. The obtained results showed that aspect ratio, Hartman, Prandtl, Eckert numbers and Joule heating parameter have significant influences on the flow and temperature distribution as well as entropy generation rate in MHD micropumps that controlling them can lead us for optimized operation of MHD micropumps.

     

Entropy analysis for nanofluid flow over a stretching sheet in the presence of heat generation/absorption and partial slip

The boundary layer heat transfer and entropy generation of a nanofluid over an isothermal linear stretching sheet with heat generation/ absorption have been analyzed. In the nanofluid model, the development of nanoparticles concentration gradient due to slip mechanisms, the effects of Brownian motion and thermophoresis, is taken into account. The dependency of the local Nusselt number and entropy generation number on the non-dimensional parameters is numerically investigated. The results show that the increase of heat generation parameter, Brownian motion parameter, or thermophoresis parameter decreases the entropy generation number in the vicinity of the sheet.     

Influence of yield stress on free convective boundary-layer flow of a non-Newtonian nanofluid past a vertical plate in a porous medium

The effect of yield stress on the free convective heat transfer of dilute liquid suspensions of nanofluids flowing on a vertical plate saturated in porous medium under laminar conditions is investigated considering the nanofluid obeys the mathematical model of power-law. The model used for non-Newtonian nanofluid incorporates the effects of Brownian motion and thermophoresis. The governing boundary-layer equations are cast into dimensionless system which is solved numerically using a deferred correction technique and Newton iteration. This solution depends on yield stress parameter Ω, a power-law index n, Lewis number Le, a buoyancy-ratio number Nr, a Brownian motion number Nb, and a thermophoresis number Nt. Analyses of the results found that the reduced Nusselt and Sherwood numbers are decreasing functions of the higher yield stress parameter for each dimensionless numbers, n and Le, except the reduced Sherwood number is an increasing function of higher Nb for different values of yield stress parameter.     

Numerical study of natural convection and entropy generation of Cu-water nanofluid around an obstacle in a cavity

In this work, natural convection and entropy generation in a square cavity with an obstacle filled with Cu-water nanofluid is numerically studied. Horizontal walls of the cavity are adiabatic and vertical walls are maintained at a different constant temperature. The study has been done for the Rayleigh numbers between 10³ and 10⁶, the obstacle dimensions (W/L) of 0.1?C0.5 and for base fluid as well as nanofluid. It is found that, using the nanofluid overall leads to increase the flow strength, Nusselt number and entropy generation and decrease the Bejan number especially at high Rayleigh numbers. It is observed that by increasing the obstacle dimensions, the entropy generation increases and the Bejan number decreases, but the effect of the obstacle dimensions on Nusselt number depends on Rayleigh number. For the present thermal system, the increasing Nusselt number compared to increasing entropy generation due to increase obstacle dimensions is significant at low Rayleigh numbers.     

Effect of thermal non-equilibrium on transient hydromagnetic flow over a moving surface in a nanofluid saturated porous media

This work is made to study the effect of local thermal non-equilibrium (LTNE) on transient MHD laminar boundary layer flow of viscous, incompressible nanofluid over a vertical stretching plate embedded in a sparsely packed porous medium. The flow in the porous medium is governed by simple Darcy model. The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis. Three temperature model is used to represent the local thermal non-equilibrium among the particle, fluid, and solid-matrix phases. By applying similarity analysis, the governing partial differential equations are transformed into a set of time dependent nonlinear coupled ordinary differential equations and they are solved by Runge-Kutta Fehlberg Method along with shooting technique. Numerical results of the boundary layer flow characteristics for the fluid, particle and solid phases are obtained for various combinations of the physical parameters. It is found that the thermal non-equilibrium effects are strongest when the fluid/particle, fluid/solid Nield numbers and thermal capacity ratios are small. Moreover, the amount of heat transfer is maximum in nanoparticles than that of fluid and solid phases because of enhancement of thermal conductivity in nanofluids.     

Numerical analysis of wave energy dissipation by damping treatments in a plate with acoustic black holes

The reduction of vibration by acoustic black holes (ABHs) with damping treatments can be achieved in two stages: energy focalization and energy dissipation. The energy focalization is mainly due to changes of the local thickness by slowing down the flexural wave speed and energy dissipation can be achieved by using viscoelastic damping materials. In structures with embedded ABHs, the damping effectiveness can depend significantly on the types of damping treatments. In this paper, 4 different damping treatments according to the types of attached region are considered in order to estimate the effectiveness of damping treatments as 1) a fully-covered unconstrained damping treatment, 2) a fully-covered constrained damping treatment, 3) a partially-covered unconstrained damping treatment and 4) a partially- covered constrained damping treatment as well as no damping treatment as reference data. In this study, the performance of damping treatments is explored using numerical simulations of three-dimensional thin plate embedded truncated ABH(s). The wave energy in the ABH, the normalized total energy and the focalization ratio are introduced to compare the effectiveness of the damping treatments. The numerical results show that the fully-covered constrained damping treatment provides the most effective configuration in terms of the wave energy in ABH and the normalized total energy.     

直角弯管流道流场的数值模拟与分析

对直角弯管流道流场进行有限体积法数值模拟，分别给出了直角弯管的速度、流线、压力可视化图象，指出流体流动时直角弯管中涡旋产生的位置和大小。并描绘出进油口速度与进出油口两端压力差之间的关系曲线以及直角弯管内直管的摩擦阻力系数与雷诺数之间的关系曲线。     

Entropy analysis of flow and heat transfer caused by a moving plate with thermal radiation

This study examines the effects of thermal radiation on entropy generation in flow and heat transfer caused by a moving plate. The equations that govern the flow and heat transfer phenomenon are solved numerically. Velocity and temperature profiles are obtained for the parameters involved in the problem. The expressions for the entropy generation number and the Bejan number are obtained based on the profiles. Graphs for velocity, temperature, the entropy generation number, and the Bejan number are plotted and discussed qualitatively.     

Effect of variable viscosity on thermal boundary layer over a permeable flat plate with radiation and a convective surface boundary condition

In this paper, the combined effects of radiation, temperature dependent viscosity, suction and injection on thermal boundary layer over a permeable flat plate with a convective heat exchange at the surface are investigated. By taking suitable similarity variables, the governing boundary layer equations are transformed into a boundary value problem of coupled nonlinear ordinary differential equations and solved numerically using the shooting technique with sixth-order Runge-Kutta integration scheme. The solutions for the velocity and temperature distributions together with the skin friction coefficient and Nusselt number depend on six parameters; Prandtl number Pr, Brinkmann number Br, the radiation parameter Ra, the viscosity variation parameter a, suction/injection parameter f _w and convection Biot number Bi. Numerical results are presented both in tabular and graphical forms illustrating the effects of these parameters on thermal boundary layer. The thermal boundary layer thickens with a rise in the local temperature as the viscous dissipation, wall injection, and convective heating each intensifies, but decreases with increasing suction and thermal radiation. For fixed Pr, Ra, Br and Bi, both the skin friction coefficient and the Nusselt number increase with a decrease in fluid viscosity and an increase in suction. A comparison with previously published results on special case of the problem shows excellent agreement.     

某轻卡导流罩CFD分析及设计优化

以某型国产厢式轻型卡车为研究对象,建立几何模型、有限元模型,利用CFD软件对原模型进行数值模拟分析。分析得出的驾驶室与货箱之间高度差区域存在的明显正压区,即为文中空气动力学优化的关键。通过对驾驶室顶部加装导流罩后的模型进行数值模拟,得出导流罩使轻卡的气动阻力大幅减小。采用拉丁超立方试验设计方法继续对导流罩的尺寸位置进行优化,对决定导流罩尺寸的两水平因子设计试验,寻找导流罩的最优尺寸,得到最优导流罩模型的气动阻力系数为0.5486。     

Aspect ratio effects of an adiabatic rectangular obstacle on natural convection and entropy generation of a nanofluid in an enclosure

In the present study, aspect ratio (AR) effects of a centered adiabatic rectangular obstacle numerically investigated on natural convection and entropy generation in a differentially heated enclosure filled with either water or nanofluid (Cu-water). The governing equations are solved numerically with finite volume method using the SIMPLER algorithm. The study has been done for Rayleigh numbers between 10³ and 10⁶, the aspect ratio of 1/3, 1/2, 1, 2 and 3 and for base fluid as well as nanofluid. It is found that, using the nanofluid leads to increase the flow strength, average Nusselt number and entropy generation and decrease the Bejan number especially at high Rayleigh numbers. At low Rayleigh numbers entropy generation is very low. By increasing Rayleigh number, entropy generation and Bejan number increases. It is observed that the viscose entropy generation is more considerable than the thermal entropy generation and has dominant role in total entropy generation. The maximum entropy generation occurs at AR = 1/3 and 3 and the minimum entropy generation occurs at AR = 1 and 1/2. It is observed that the effect of AR on Nusselt number, entropy generation and Bejan number depends on Rayleigh number.     

Numerical analysis of heat generation and temperature field in reverse dual-rotation friction stir welding

A 3D model is developed for numerical analysis for heat generation, temperature field, and material flow in reverse dual-rotation friction stir welding (RDR-FSW) process. The reverse rotation of the assisted shoulder and the tool pin is considered to determine the heat generation rate. Friction heat, plastic deformation heat, and their partition coefficients are analyzed. Due to the tool pin and assisted shoulder being separated and reversely rotated independently, the temperature difference between the advancing and retreating sides is weakened. The reverse material flow is beneficial to the uniformity of both the temperature and microstructure at the advancing and retreating sides. The calculated temperature profiles agree well with the corresponding experimentally measured values.     

10MW工业汽轮机速关阀与调阀内流动和噪声计算分析

针对改进进汽段的设计、提高机组经济性、降低机组噪声的目的,用数值方法研究了10 MW给水泵汽轮机组速关阀和调阀系统的全开工况下的流动和噪声。求解了全三维N-S方程和k-ε湍流模型得到进汽系统内部的稳态流场,从流场的速度分布云图、湍动能分布云图和涡量分布云图出发,分析了压力损失产生的原因,将瞬态分析得到的流体边界压力随时间的脉动通过傅里叶变换,转换成频域下的声压值,得到进汽系统内各个壁面的二级子噪声源的分布云图,并分析了调阀喉部处各频率下的声压大小。研究结果表明,进汽系统内的总压损达6.06%,其中速关阀部分产生的压损为1.98%,调阀部分产生的压损为4.08%,调阀喉部及折弯处为气动噪声辐射的主要位置,噪声辐射能量最大的频率为30 Hz。     

Effect of gravity field,initial stress and rotation on the S-waves propagation in a non-homogeneous anisotropic medium with magnetic field

In this paper, we investigated the propagation of shear wave under the influences of the magnetic field, gravitational field, rotation and initially stressed in anisotropic non-homogeneous incompressible elastic medium. It is well known in the literature that the earth medium is not at all initial stress free and homogeneous throughout, but it is initially stressed and non-homogeneous. The frequency equation that determines the velocity of the shear waves has been obtained. Keeping these things in mind, we have discussed the frequency equation in an initially stressed, non-homogeneous medium with gravity field, magnetic field, and rotation. It has been observed that the inhomogeneity parameter, gravity field, magnetic field, and the initial stress play an important role in the propagation of S-waves propagation. The numerical values on the dimensionless phase velocities are calculated and presented graphically to illustrate the dependences upon gravity field, initial stress, magnetic field, anisotropy and rotation comparatively. The results indicate that the effects of gravity field, initial stress, magnetic field, anisotropy, and rotation are very pronounced.     

Influence of thermophoresis particle deposition and chemical reaction on unsteady non-Darcy MHD mixed convective flow over a porous wedge in the presence of temperature-dependent viscosity

An analysis is presented to investigate the effect of thermophoresis particle deposition and temperature dependent viscosity on unsteady non-Darcy MHD mixed convective heat and mass transfer of a viscous, incompressible and electrically conducting fluid past a porous wedge in the presence of chemical reaction. The wall of the wedge is embedded in a uniform non-Darcian porous medium in order to allow for possible fluid wall suction or injection. The results are compared with those known from the literature and excellent agreement between the results is obtained. The governing partial differential equations of the problem, subjected to their boundary conditions, are solved numerically by applying an efficient solution scheme for local nonsimilarity boundary layer analysis. Numerical calculations are carried out for different values of dimensionless parameter in the problem and an analysis of the results obtained show that the flow field is influenced appreciably by the applied magnetic field and thermophoresis particle deposition.     

Calculation and measurement of the magnetic field in a large diameter electromagnetic flow meter

An idealized magnet model previously used in a simple coil configuration is applied to a more complicated engineering design problem, where an electromagnetic flow meter in diameter of 500 mm is used with five pairs of coils. The numerical results are compared with measurement data. The difference between theory and experiment and the possible causes of errors are discussed. It is shown that the idealized magnet model is practical for the design and the analysis of the flow meter. The work also shows that the traditional uniform field design based on two dimensional (2D) analysis is not suitable for this kind of flow meter. Thus nonuniform field and 3D analysis is needed.     

Measurement and analysis of the flow field in a pulsatile ventricularassist device

A pneumatically driven ventricular assist device (VAD) of unconventional geometry, designed to mitigate adverse haemostatic phenomena by optimization of flow patterns, was investigated using two-component laser Doppler anemometry (LDA). Data were taken on a rectilinear grid over two orthogonal traverses, allowing synthesis of three-dimensional velocity vectors over most of the grid. The resulting data were examined by two-dimensional and three-dimensional static and animated computer graphic visualizations of the time-varying vector fields. This analysis revealed illuminating and previously unobserved features of the complex flow fields within pulsatile VADs and identified design considerations that bear upon minimization of turbulence and of flow recirculation and stasis. The findings of this study suggest that, while total abolition of undesirable flow phenomena in a diaphragm-type blood pump is probably impossible, comprehensive investigation in vitro can engender considerable improvements in the efficacy of a device.     

Numerical analysis of plume characteristics and liquid circulation in gas injection through a porous plug

Two phase flows have been numerically calculated to analyze plume characteristics and liquid circulation in gas injection through a porous plug. The Eulerian approach has been used for formulation of both the continuous and dispersed phases. The turbulence in the liquid phase has been modeled using the standardk−ɛ turbulence model. The interphase friction coefficient has been calculated using correlations available in the literature. The turbulent dispersion of the phases has been modeled by the “dispersion Prandtl number”. The predicted mean flows is compared well with the experimental data. The plume region area and the axial velocities are increased with the gas flow rate and with the decrease in the inlet area. The turbulent intensity also shows the same trend. Also, the space-averaged turbulent kinetic energy for various gas flow rates and inlet areas has been obtained. The results are of interest in the design and operation of a wide variety of materials and chemical processing operations.