纳米流体液滴内的光驱流动实验及其解析解

在光透过性的流体介质中添加具有高光响应特性的纳米颗粒,可以形成光驱动纳米流体,实现对光能的高效利用.本文针对光驱纳米流体流动行为开展实验观察和理论分析研究,这是实现光驱纳米流动精确调控的理论基础.首先利用粒子图像测速技术对液滴中直径为300 nm的Fe3O4颗粒在不同光源照射下受Marangoni效应诱导的运动进行了实验观测,研究光能向动能的高效转化机制.实验结果表明,当颗粒浓度大于临界数密度时,可诱导出垂向具有对称结构的涡,在液滴底部颗粒由四周向中心运动,顶部则由中心向四周运动,光源频率和颗粒数密度是这一过程的主导因素.随后,针对光强高斯分布的紫外光驱动下大颗粒数密度、特征流速约mm/s的光驱纳米流体,通过Stokes方程和表面张力梯度边界条件实现了其流场分布的解析求解,理论获得的流场分布解析解与实验测量结果保持一致,证实定量理论分析的有效性.最后,讨论了引入表面张力与在液滴底部引入表面压力及体相中集中引入光辐射力的不同驱动模式之间的相关性.这一研究成果为光微流控系统中流动行为的精确调控及光能的高效转化等提供了理论支持.     

Heat generation/absorption effect on MHD flow of hybrid nanofluid over bidirectional exponential stretching/shrinking sheet

The idea of hybrid nanofluid has triggered many researchers because of its credential in improving the thermal characteristics. Hence, this study performed a mathematical analysis to evaluate the heat generation/absorption effect on magnetohydrodynamics (MHD) flow towards bidirectional exponential stretching/shrinking sheet of hybrid nanofluid. A system of ordinary differential equations was attained through a simplification of governing partial differential equations by employing appropriate similarity transformation and numerically determined via the bvp4c function in MATLAB programming system. The results revealed that the volume fraction of nanoparticle and magnetic parameter applied to the hybrid nanofluid improved the skin friction coefficient in the current work. The rate of heat transfer was strengthened by the intensity of the suction parameter, whereas the appearance of heat generation reduced the heat transfer rate performance. The results are proven to have dual solutions and lead to stability analysis implementation, hence confirming the first solution's achievability.     

Entropy generation applications in flow of viscoelastic nanofluid past a lubricated disk in presence of nonlinear thermal radiation and Joule heating

Entropy generation is the loss of energy in thermodynamical systems due to resistive forces,diffusion processes, radiation effects and chemical reactions. The main aim of this research is to address entropy generation due to magnetic field, nonlinear thermal radiation, viscous dissipation, thermal diffusion and nonlinear chemical reaction in the transport of viscoelastic fluid in the vicinity of a stagnation point over a lubricated disk. The conservation laws of mass and momentum along with the first law of thermodynamics and Fick's law are used to discuss the flow, heat and mass transfer, while the second law of thermodynamics is used to analyze the entropy and irreversibility. The numbers of independent variables in the modeled set of nonlinear partial differential equations are reduced using similarity variables and the resulting system is numerically approximated using the Keller box method. The effects of thermophoresis,Brownian motion and the magnetic parameter on temperature are presented for lubricated and rough disks. The local Nusselt and Sherwood numbers are documented for both linear and nonlinear thermal radiation and lubricated and rough disks. Graphical representations of the entropy generation number and Bejan number for various parameters are also shown for lubricated and rough disks. The concentration of nanoparticles at the lubricated surface reduces with the magnetic parameter and Brownian motion. The entropy generation declines for thermophoresis diffusion and Brownian motion when lubrication effects are dominant. It is concluded that both entropy generation and the magnitude of the Bejan number increase in the presence of slip. The current results present many applications in the lubrication phenomenon,heating processes, cooling of devices, thermal engineering, energy production, extrusion processes etc.     

Entropy analysis on unsteady MHD biviscosity nanofluid flow with convective heat transfer in a permeable radiative stretchable rotating disk

We examine the entropy analysis in three-dimensional hydromagnetic flow and convective heat transport of a biviscosity nanofluid over a rotating porous disk with a time-dependent stretching rate in the direction of the radius of the circular disk. We also examine the influence of thermal radiation and viscous dissipation due to nanoparticles and applied magnetic field. We invoked suitable self-similar transformations to covert the modeled coupled nonlinear PDEs into a set of nonlinear ODEs. The transformed system of equations is then worked out numerically by a well-known shooting technique and the fourth-order Runge–Kutta–Fehlberge method. The rotating phenomenon yields an additional parameter known as a rotation parameter, which controls the disk’s rotation. The study shows that the fluid motion is accelerated along the radial and cross-radial directions with an increase in the rotation of the disk. The skin-friction and the heat transfer rate at the disk strongly depend on the rotation of the disk, permeability of the porous medium, thermal radiation, and nanoparticle size. The Bejan number quantifies the entropy production of the system. It has a considerable impact on the magnetic field, rotation of the disk, thermal radiation, and Biot number. The efficient performance of the system is possible by a suitable choice of the physical parameters discussed in this article.     

Models base study of inclined MHD of hybrid nanofluid flow over nonlinear stretching cylinder

Focus of the present analysis is on the stagnation point flow of hybrid nanofluid with inclined magnetic field over a moving cylinder. The extended version of two models (e.g. Xue model and Yamada-Ota model for hybrid nanofluids) are considered in this study). A mathematical model of hybrid nanofluid flow is developed under certain flow assumptions. Boundary layer approximations are also utilized to model a system of partial differential equations. The systems of partial differential equations are further converted to dimensionless systems of ordinary differential equations by means of suitable similarity transformations. A numerical solution is obtained by applying bv4c technique. Effects of variation in physical parameters involved are depicted through graphs. Skin friction coefficient and Nusselt number are highlighted through tables. Our main objective is to investigate the heat transfer rate on the surface of the nonlinear stretching cylinder. The results of Xue model and Yamada-Ota model for the hybrid nanofluid due to nonlinear stretching cylinder are computed for comparison. In both cases, velocity and temperature profiles are best compared to the decay results.     

Entropy generation in radiative motion of tangent hyperbolic nanofluid in presence of activation energy and nonlinear mixed convection

In this communication, an optimization of entropy generation is performed through thermodynamics second law. Tangent hyperbolic nanomaterial model is used which describes the important slip mechanism namely Brownian and thermophoresis diffusions. MHD fluid is considered. The novel binary chemical reaction model is implemented to characterize the impact of activation energy. Nonlinear mixed convection, dissipation and Joule heating are considered. Appropriate similarity transformations are implemented to get the required coupled ODEs system. The obtained system is tackled for series solutions by homotopy method. Graphs are constructed to analyze the impact of different flow parameters on entropy number, nanoparticle volume concentration, temperature and velocity fields. Total entropy generation rate is calculated via various flow variables. It is noticed from obtained results that entropy number depend up thermal irreversibility, viscous dissipation and Joule heating irreversibility and concentration irreversibility. Decreasing behavior of concentration is witnessed for higher estimations of chemical reaction variable. Entropy number is more for higher Hartmann number, Weissenberg number and chemical reaction variable while contrast behavior is noted for Bejan number.     

Z箍缩聚变裂变混合堆包层中子学分析

作为一种有竞争力的能源系统,Z箍缩聚变裂变混合堆（Z-FFR）正在开展概念研究,包层研究正是其中重要的一部分。建立了Z-FFR包层设计模型,分析了包层影响因素、中子平衡、通量与功率密度、燃耗等方面,表明该包层设计在50年内能量放大因子、氚增殖比和燃料增殖比的平均值分别为14.91, 1.294和5.140,满足设计要求。针对聚变源的脉冲特性进行了包层的瞬态中子学分析,发现燃料区中子脉冲可分为聚变中子、瞬发裂变中子和缓发裂变中子脉冲三个部分,绝大部分热量约在0.01 s内沉积。结果较完整地给出了Z-FFR包层的中子学参数,为概念研究提供了基础。     

Z箍缩聚变裂变混合堆包层中子学分析

作为一种有竞争力的能源系统,Z箍缩聚变裂变混合堆(Z-FFR)正在开展概念研究,包层研究正是其中重要的一部分。建立了Z-FFR包层设计模型,分析了包层影响因素、中子平衡、通量与功率密度、燃耗等方面,表明该包层设计在50年内能量放大因子、氚增殖比和燃料增殖比的平均值分别为14.91,1.294和5.140,满足设计要求。针对聚变源的脉冲特性进行了包层的瞬态中子学分析,发现燃料区中子脉冲可分为聚变中子、瞬发裂变中子和缓发裂变中子脉冲三个部分,绝大部分热量约在0.01s内沉积。结果较完整地给出了Z-FFR包层的中子学参数,为概念研究提供了基础。     

纳米强化氨水发生过程机理分析

提出一种可以直接测试有、无纳米氨水溶液氨气发生量的氨水纳米降膜发生实验装置,通过有、无纳米的氨水溶液对比实验,发现添加合适纳米颗粒能够增加氨气发生率。结合氨水纳米溶液降膜发生过程试验结果,以及前人关于纳米颗粒强化传热传质方面的研究,分别从纳米粒子的微运动、界面效应、Marangoni效应、纳米流体物性等方面进行强化发生机理分析,证明纳米流体的粒子微运动和纳米流体的物性是纳米流体强化氨水降膜发生的两大主要因素。     

Non-similar mixed convection analysis for magnetic flow of second-grade nanofluid over a vertically stretching sheet

The aspiration of this research is to explore the impact of non-similar modeling for mixed convection in magnetized second-grade nanofluid flow. The flow is initiated by the stretching of a sheet at an exponential rate in the upward vertical direction. The buoyancy effects in terms of temperature and concentration differences are inserted in the $x$-momentum equation. The aspects of heat and mass transfer are studied using dimensionless thermophoresis, Schmidt and Brownian motion parameters. The governing coupled partial differential system (PDEs) is remodeled into coupled non-similar nonlinear PDEs by introducing non-similar transformations. The numerical analysis for the dimensionless non-similar partial differential system is performed using a local non-similarity method via bvp4c. Finally, the quantitative effects of emerging dimensionless quantities on the non-dimensional velocity, temperature and mass concentration in the boundary layer are conferred graphically, and inferences are drawn that important quantities of interest are substantially affected by these parameters. It is concluded that non-similar modeling, in contrast to similar models, is more general and more accurate in convection studies in the presence of buoyancy effects for second-grade non-Newtonian fluids.     

Magnetohydrodynamic flow and heat transfer of a hybrid nanofluid over a rotating disk by considering Arrhenius energy

This research work explores the effect of hybrid nanoparticles on the flow over a rotating disk by using an activation energy model. Here, we considered molybdenum disulfide and ferro sulfate as nanoparticles suspended in base fluid water. The magnetic field is pragmatic normal to the hybrid nanofluid flow direction. The derived nonlinear ordinary differential equations are nondimensionalized and worked out numerically with the help of Maple software by the RKF-45method. The scientific results for a non-dimensionalized equation are presented for both nanoparticle and hybrid nanoparticle case. Accoutrements of various predominant restrictions on flow and thermal fields are scanned. Computation estimation for friction factor, local Nusselt number and Sherwood number are also executed. Results reveal that the reduction of the heat transfer rate is greater in hybrid nanoparticles when compared to nanoparticles for increasing values of Eckert Number and the thermal field enhances for the enhanced values of volume fraction.     

Influences of Marangoni convection and variable magnetic field on hybrid nanofluid thin-film flow past a stretching surface

Investigations on thin-film flow play a vital role in the field of optoelectronics and magnetic devices. Thin films are reasonably hard and thermally stable but quite fragile. The thermal stability of a thin film can be further improved by incorporating the effects of nanoparticles. In the current work, a stretchable surface is considered upon which hybrid nanofluid thin-film flow is taken into account. The idea of augmenting heat transmission by making use of a hybrid nanofluid is a focus of the current work. The flow is affected by variations in the viscous forces, along with viscous dissipation effects and Marangoni convection. A time-constrained magnetic field is applied in the normal direction to the flow system. The equations governing the flow system are shifted to a non-dimensional form by applying similarity variables. The homotopy analysis method is employed to find the solution to the resultant equations. It is noticed in this study that the flow characteristics decline with augmentation of magnetic, viscosity and unsteadiness parameters while they increase with enhanced values of thin-film parameters. Thermal characteristics are supported by increasing values of the Eckert number and the unsteadiness parameter and opposed by the viscosity parameter and Prandtl number. The numerical impact of different emerging parameters upon skin friction and the Nusselt number is calculated in tabular form. A comparison of current work with established results is carried out, with good agreement.     

Electro-osmotic nanofluid flow in a curved microchannel

Biological mechanisms offer significant improvement in the efficiency of next generation energy systems. Motivated by new developments in distensible pumping systems, ionic electro-kinetic manipulation and nanoscale liquids (”nanofluids”), in the present study a mathematical model is developed to simulate the entropy generation and electro-osmotic transport of nanofluids in a curved deformable microchannel driven by peristaltic transport. Both thermal and species (nano-particle) buoyancy effects are included and Soret and Dufour cross-diffusion effects. The appropriate conservation equations are normalized with scaled variables and the resulting dimensionless nonlinear boundary value problem is solved in a transformed coordinate system. Simplification of the mathematics is achieved via lubrication approximations and low zeta potential (Debye Hückel linearization). The effects of various parameters, i.e. electro-osmotic velocity, EDL (electrical double layer) thickness and zeta potential ratio on velocity profile and temperature profiles are computed. The effects of Brinkman number (viscous heating parameter) and Joule (electrical field heating) parameter on nano-particle concentration profiles are also simulated. The micro-channel curvature effects on the nanofluid flow characteristics and thermal characteristics are also computed. Furthermore, streamline patterns, temperature contours, nano-particles concentration contours and entropy generation rate contours are plotted for various curvature parameters. Results indicate that the curvature of the channel and electro-osmotic body force influence strongly the sources of entropy generation rate. The study finds applications in bio-inspired electro-osmotic nanofluid pumping in microscale energy applications.     

Heat and mass transfer analysis of time-dependent tangent hyperbolic nanofluid flow past a wedge

The candid intension of this article is to inspect the heat and mass transfer of a magnetohydrodynamic tangent hyperbolic nanofluid. The nanofluid flow has been assumed to be directed by a wedge on its way. In addition, the collective stimulus of the convective heating mode with thermal radiation is inspected. The governing set of PDEs is rendered into that of the coupled nonlinear ODEs. The resulting ordinary differential equations are then solved by the well known shooting technique for two different cases; the flow over a static wedge and flow over a stretching wedge. The impact of intricate physical parameters on the velocity, temperature and concentration profiles is analyzed graphically. It is noticed that the intensifying values of the generalized Biot number, Brownian motion parameter, thermophoresis parameter and Weissenberg number enhances the dimensionless temperature profile.     

Thermal-hydraulic characteristics of nanofluid flow in corrugated ducts

This study aims are to present effects of periodic corrugations in rectangular ducts on the thermal-hydraulic behaviors of nanofluids. The applied corrugations were rectangular cavities with a constant cavity length. In this regard, three various dimensionless cavity shaped corrugation widths such as S/H = 0.1, 0.2, and 0.3 were investigated. Computations were carried out at different Reynolds numbers in the range of 500≤Re≤2000. Alternatively, for further improvement of thermal characteristics, effects of an alumina–water nanofluid flow on the aforementioned corrugated ducts were investigated using the constant nanoparticle size d_p = 25 nm and various nanoparticle volume concentrations in the range of 1%≤ Φ ≤8%. The governing equations were solved numerically by means of the finite volume method. The obtained results revealed that application of periodic corrugations in ducts develops the turbulent flow all over the duct, which results in the higher flow mixing and thermal efficiency compared with the plain duct. Furthermore, rates of turbulence intensity and flow mixing change as a function of S/H. In addition, it was demonstrated that application of alumina–water flow in such corrugated ducts enhances the rate of heat transfer and thermal efficiency index compared with water flow. It is hoped that the obtained results arouse interest for thermal designer.