Modeling of a Solar Water Collector with Water‐Based Nanofluid Using Nanoparticles

The pressure‐velocity form of the Navier–Stokes equations, energy equation, and concentration equation are used to represent the mass, momentum, energy, and concentration conservations of the nanofluid medium in the solar collector. The governing equations and corresponding boundary conditions are converted to dimensionless form and solved numerically by the finite element method. The physical domain is discretized by triangular mesh elements with six nodes. The working fluid is water‐based nanofluid with two nanoparticles, namely, silver (Ag) and copper oxide (CuO). The study includes computations for different values of buoyancy ratio (Nr) and Schmidt number (Sc). Flow, heat, and mass transfer characteristics are presented in the forms of streamlines, isotherms, and iso‐concentrations. In addition, results for the average radiative, convective heat and mass transfer, mean temperature and concentration of nanofluid, mid‐height horizontal‐vertical velocities, and subdomain average velocity field are offered and discussed for the above‐mentioned parametric conditions. Results show that the effects of Nr and Sc on the convective‐radiative heat and mass transfer phenomenon inside the collector are significant for all values of Nr and Sc studied. Comparison and validation with the standard experimental/numerical data is given in brief. The variation of the obtained result is presented as 34% with the result of experimental data. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 43(3): 270–287, 2014; Published online 30 September 2013 in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21080     

Convective instability in binary nanofluids with an internal heat source in the presence of thermodiffusion and nanoparticles

This paper investigates the effect of internal heat source on the convective instability under the effect of thermodiffusion of nanoparticles and solute in binary nanofluids theoretically using stability criterion based on linear stability theory. A horizontal layer of binary nanofluid at constant and different temperatures is considered, and the problem is modeled by the system of highly nonlinear partial differential equations. These coupled equations are transformed into ordinary differential equations using nondimensional variables. To study the convective instability of a binary nanofluid, the Rayleigh numbers are derived analytically for stationary and oscillatory convections and the addition factor F_a is proposed. The comparison of the obtained results is favorable with previously published results. The Brinkman model for viscosity and the Bruggeman model for thermal conductivity are used to study the effect of nanoparticle on the system. The effects of various parameters, namely internal Rayleigh number, volume fraction of nanoparticles, Soret coefficients of nanoparticles, and solute on the system are shown through graphs. To check the variation in stability, we have considered NH₃/H₂O+Ag binary nanofluid and the effect of addition factor on the concentration profiles are explained with the help of a graph.     

Effects of Thermal‐Diffusion,Diffusion‐Thermo,and Space Porosity on MHD Mixed Convective Flow of Micropolar Fluid in a Vertical Channel with Viscous Dissipation

This paper examines thermal‐diffusion and diffusion‐thermo effects on the fully developed MHD flow of a micropolar fluid through a porous space in a vertical channel with asymmetric wall temperatures and concentrations. The homotopy analysis method (HAM) is adopted to obtain the approximate analytical solution for the velocity, micro‐rotation, temperature, and concentration field. The convergence and the accuracy of the solutions are discussed. The role of pertinent parameters on the heat and mass transfer characteristics of the flow are presented graphically. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 43(6): 561–576, 2014; Published online 11 November 2013 in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21100     

On the Performance of Ag/Oil Nanofluids in Heat Transfer Enhancement in a Sinusoidal Tube: Constant Heat Flux Boundary Condition

The present work provides an empirical investigation on the thermal characteristics of Ag/oil nanofluids flow inside a sinusoidal tube under a constant heat flux boundary condition. Ag/oil nanofluids have been prepared in low‐volume concentrations of 0.011%, 0.044%, and 0.171%. The average size of the nanoparticles was 20 nm. A heated coil was attached to the upper and lower surface of the tube that satisfied the constant thermal boundary condition of 204 W. The experiment has been pursued at low Reynolds numbers less than 160. A loop was designed to keep the flow hydrodynamically fully developed during the experiment. The test case was a sinusoidal tube. Upper and lower surfaces of the tube have been designed sinusoidally. Moreover, the width of the plates was long enough, so the problem was not considerably affected by the three‐dimensional releasing effect. Convective heat transfer coefficient and Nusselt number were calculated. It has been observed that based on the acquired data of the present work, convective heat transfer coefficient increased up to 23% for the best case (nanofluid with a volume concentration of 0.171%) compared to the base fluid. This happened while the rise of the friction factor was very low. In addition, a comparison between the new results and the previous work by authors showed the positive performance of sinusoidal tubes in increasing the convective heat transfer coefficient (the average increase was calculated to be about 82%) compared to the annular tube.     

纳米流体稳定性及其导热性能研究

为了探究影响纳米流体稳定性和导热系数的因素,采用一步法和两步法分别制备了SiO2-EG/DW(50∶50)纳米流体和SiO2-EG纳米流体,探讨团聚体等效直径对纳米流体稳定性的影响.基于瞬态热线法的原理,测量一步法纳米流体的导热系数,分析温度和纳米颗粒质量分数对其导热系数的影响.结果表明:相比一步法制备的纳米流体,两步...     

Triple solutions of micropolar nanofluid in the presence of radiation over an exponentially preamble shrinking surface: Convective boundary condition

In this study, we attempt to obtain all probable multiple solutions of the magnetohydrodynamic (MHD) steady flow of micropolar nanofluid on an exponentially shrinking surface by the consideration of concentration slip, thermal radiation, and convective boundary condition with help of the revised model of Buongiorno. The significance of the mass suction on the existence of multiple solutions is integrated. The suitable pseudo‐exponential similarity variables have been adopted to transfer the system of nonlinear partial differential equations into a system of nonlinear quasi‐ordinary ordinary differential equations. The resultant system has been solved by employing the Runge–Kutta fourth‐order method along with the shooting method. Three different ranges of solutions are noticed, namely triple solutions and single solution. When ranges of the suction parameter are $S\ge S_{c1}$ and $S\ge S_{c2}$, then there exist triple solutions otherwise there exists only single solution. The effect of the numerous emerging parameters on the velocity profile, angular velocity profile, temperature profile, concentration profile, coefficient of skin friction, and local Nusselt and Sherwood numbers are demonstrated graphically. Results reveal that the velocity of the rotating fluid particles near the rigid surface declines regularly by the rise of the micropolar parameter $K$ in the second and first solutions.     

Effects of the viscous dissipation and chemical reaction on Casson nanofluid flow over the permeable stretching/shrinking sheet

A steady two‐dimensional Casson nanofluid flow over the permeable stretching/shrinking sheet along the viscous dissipation and the chemical reaction is studied in this article. The convective boundary condition is incorporated in energy equation. Similarity variables are applied to convert the governing partial differential equations into ordinary differential equations. The numerical solutions of the equations are obtained by using the shooting method with Maple implementation. The numerical findings indicate occurrence of the dual solutions for a certain range of stretching/shrinking and suction parameters. Therefore, a stability analysis is done to find the solution that is stable and physically realizable. The effects of the pertinent physical parameters on velocity, temperature, and concentration profiles are investigated graphically. Numerical results of various parameters involved for skin friction coefficient, the local Nusselt as well as Sherwood numbers are determined and also discussed in detail. The Casson and suction parameters decrease the velocity in the first solution, whereas they increase it in the second solution. The rate of heat transfer increases in both solutions with an increment in Eckert number, Biot number, thermophoresis, and Brownian motion parameters. Thermophoresis and Brownian motion parameters show opposite behavior in the nanoparticle's concentration. The nanoparticle concentration decreases in both solutions with increment in Schmidt number, Brownian motion, and chemical reaction parameters.     

Soret Effect on Darcy–Brinkman Convection in a Binary Viscoelastic Fluid‐Saturated Porous Layer

A linear and weakly nonlinear stability analyses is performed to study the onset of Darcy–Brinkman double diffusive convection in a binary viscoelastic fluid‐saturated porous layer in the presence of the Soret effect. The modified Darcy–Brinkman–Oldroyd model including the time derivative term is employed for the momentum equation. The expressions for stationary, oscillatory, and finite amplitude Rayleigh number are obtained as a function of the governing parameters. There is a competition between the processes of the Soret coefficient, viscoelasticity, thermal diffusion, and solute diffusion that causes the convection to set in through an oscillatory mode rather than a stationary mode. The effects of the Soret parameter, Darcy number, relaxation and retardation parameters, and Darcy–Prandtl number on the stationary, oscillatory, and finite amplitude convection is shown graphically. The weakly nonlinear theory is based on truncated representation of the Fourier series method and is used to find the Nusselt and Sherwood numbers. Further, the transient behavior of the Nusselt and Sherwood numbers is investigated by solving the nonlinear system of ordinary differential equations numerically using the Runge–Kutta method. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 43(4): 297–320, 2014; Published online 3 October 2013 in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21076     

Effects of multislip and distinct heat source on MHD Carreau nanofluid flow past an elongating cylinder using the statistical method

This study focuses on studying the impact of multiple slip effects on the hydromagnetic Carreau nanofluid flow over an elongating cylinder considering a linear heat source and exponential space-based heat source. Suitable transformations are used in converting the highly nonlinear system of partial differential equations governing the flow into a system of ordinary differential equations and hence resolved using the Runge–Kutta method of order four coupled with the shooting method. BVP5C and RKF45 are used to compare the numerical accuracy and an excellent agreement is noted. The parallel effect of parameters on Nusselt number is studied using surface plots and the corresponding effects are scrutinized using multiple linear regression. It is observed that the linear heat source parameter, thermal slip parameter and exponential space-based heat source parameter demote the heat transfer rate. The consequence of different parameters on drag coefficient and mass transfer are quantified using a linear regression slope.     

纳米流体在车用机油冷却器中的强化换热试验研究

为了探求新型冷却介质--纳米流体的换热效果,制备了不同粒子体积分数的氧化铝有机纳米流体,并在车用机油冷却器中进行了换热性能的试验研究.研究结果表明:添加纳米粒子能够有效提高纳米流体基础液体的换热能力,且换热能力随着粒子体积分数的增加 而增高.在不同温度和温差条件下,粒子体积分数为5%的纳米流体的传热量和换热系数均超过常规冷却介质(水和防冻液).纳米流体的黏度和流动阻力亦随着粒子体积分数增加而增加.当冷、热介质的进口温差不变时,提高冷却介质的进口温度能在明显增强换热能力的同时大幅度降低流动阻力,并且纳米流体换热能力的增幅要高于防冻液和基础液体.     

Numerical simulation of Dufour and Soret impacts on MHD Williamson nanofluid flow through an inclined surface

The carry-outs of Dufour and Soret, as well as radiation, and chemical response on a non-Newtonian MHD Williamson nanofluid flow through an inclined extended plane are discussed in this article. Keller-box analysis is being used to explore the influence of the Williamson factor here on the fluid domain quantitatively. Ordinary differential equations (ODEs) are recovered from boundary flow equations using appropriate similarity transformations. These ODEs are numerically addressed. Graphs and comparisons are used to simulate and study the features of flow characteristics such as velocity, temperature, and concentration of Williamson nanofluids distributions in response to various emerging parameters. The numerical computations show that our results are in reasonable harmony with previous studies. The numerical computations revealed that for the time being, the density of the momentum fluid layers is diminishing for the values of $ᴦ$, Le, $\Omega$, M, and increasing for Gc, Gr. The thickness of the thermal boundary layer is decreasing for Sr, Df, Pr, Gc, and Gr. M, $ᴦ$, $\Omega$, R, N, and Le are all on the rise. The concentration profile for R, Le, Nb, Nt, Gr, Gc, and N is decreasing, while Pr, Df, Sr, M, $ᴦ$, and $\Omega$ are increasing.     

Numerical Modeling of Fluid Flow and Thermal Behavior of Different Nanofluids on a Rotating Disk

The thermal and velocity profiles of various nanofluid systems on a rotating disk are simulated. Finite difference method, the orthogonal collocation method, and the differential quadrature method (DQM) of numerical approaches are used to solve the governing equations and are compared to determine the faster and more accurate solution procedure. Five nanoparticles Al, Al₂O₃, Cu, CuO, and TiO₂ solved in three base fluids water, ethylene glycol, and engine oil are considered to be used on the disk at different volume fractions. A new general algorithm is presented for solving equations of a rotating‐disk problem quickly and accurately and it is found that the DQM method is the best approach for this numerical simulation. Heat transfer performance of a rotating disk would be much better enhanced with water based Al nanofluid. A wide range of results for different base–fluid combinations with nanoparticles is presented with untransformed 3D results and effects of the variation of different parameters provides comprehensive insight and prevents inaccurate deductions.     

Heatline Analysis on Heat Transfer and Convective Flow of Nanofluids in an Inclined Enclosure

This article presents a heatline method to analyse the transport mechanism of heat transfer and convective flow of nanofluids in an inclined square enclosure, where a heated thin plate located in the middle of the enclosure. The fluid flow, heat transfer, and heat transport characteristics are illustrated using streamlines, isotherms, Nusselt number and heatlines. Results show that fluid flow and temperature fields strongly depend on Rayleigh number, inclination angle, solid volume fraction, types of nanoparticles and the plate length, and the maximum strength of heatfunction increases as the inclination angle and Rayleigh number increase.     

Thermophoresis and Brownian motion effects on Williamson nanofluid flow past a stretching surface with thermal radiation and chemical reaction

The heat transfer mechanism of nanofluids has numerous industrial applications owing to the non-Newtonian behavior and has been exercised as a thermophysical phenomena in presence of thermal radiation. The present paper deals with the thermal transfer characteristics of time-independent magnetohydrodynamics Williamson fluid past a stretching surface in presence of the reaction of chemical equilibrium is dealt. The flow constitutive nonlinear partial differential coupled equations are transmitted into ordinary differential equalities by employing relevant similarity transmutations. These deduced equations are determined by using the Runge–Kutta numerical technique with a shooting approach with the aid of MATLAB software. Influences of distinct pertinent flow parameters like an inclined uniform magnetic field, Soret number, heat generation/absorption, and Schmidt number constrained to convective boundary condition is displayed through graphs with relevant physical interpretations. Computed numerical values for the friction factor coefficient, local Nusselt parameter, and Sherwood number are tabulated.      

Mixed Convection Effect on Melting from a Vertical Plate Embedded in Porous Medium with Soret and Dufour Effects

The present work analyzed the impact of mixed convection on melting from a vertical flat plate embedded in porous medium in the presence of Dufour and Soret effects. The partial differential equations governing the problem under consideration have been transformed by a similarity transformation into a system of ordinary differential equation which is solved numerically by Runge–Kutta–Gill methods. Dimensionless velocity, temperature, and concentration profiles are presented graphically for various values of the Dufour number (Df), Soret number (Sr), melting parameter (M), and buoyancy parameter (Gr/Re). During the investigation, it was found that the melting phenomenon decreases the local Nusselt number and local Sherwood number at the solid–liquid interface. Also, it is interesting to note that the velocity as well as temperature increases while the concentration decreases with an increase in the Dufour number Df (or simultaneous decrease in the Soret number Sr). © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 43(7): 667–676, 2014; Published online 3 October 2013 in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21113     

活塞内冷油腔中纳米流体振荡流动与传热特性影响因素研究

采用计算流体力学的方法,研究了分别含Al₂O₃、Cu O、Si O₂的3种纳米机油在纳米颗粒体积分数为1%、3%、5%时相对于传统机油的振荡传热能力和机油在油腔内流动的规律。结果表明,纳米颗粒的加入改变了流体的物性参数,纳米流体的传热效果比传统机油更好,且内冷油腔的传热系数随着纳米流体体积分数的增加而增加,但对内冷油腔内瞬态机油的瞬态分布和充油率的影响不大;纳米流体的黏度、密度、导热系数、比热容都能影响内冷油腔的传热性能,密度的增加会使流体对壁面的冲击作用更强,从而增强油腔的传热能力;在纳米颗粒体积分数为5%时CuO纳米机油的传热系数比Al₂O₃、SiO₂纳米机油分别高8.2%和14.6%。     

Brownian Motion Effects on Natural Convection of Alumina–Water Nanofluid in 2‐D Enclosure

This article reports a numerical study of natural convection heat transfer in a differentially heated enclosure filled with a Al₂O₃–water nanofluid. Fluent v6.3 is used to simulate nanofluid flow. Simulations have been carried out for the pertinent parameters in the following ranges: the Rayleigh number, Ra = 10⁶, 10⁷, and the volumetric fraction of alumina nanoparticles, ? = 0 ? 4%. The effect of Brownian motion on the heat transfer is considered and examined. The numerical results show a decrease in heat transfer with an increase in particle volume fraction. Similar to experimental results, the Nusselt number increases with the Rayleigh number in the numerical results. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21121     

Effects of Soret diffusion on the exergy losses in hydrogen laminar premixed flames

The analysis of the exergy loss is an effective tool for evaluating second-law irreversibility in laminar flames. However, despite numerous studies underlining the importance of taking into account thermal diffusion in laminar flame studies, especially in hydrogen/air flames, this phenomenon is usually neglected in the exergy analysis of these flames. Therefore, this work investigates the effect of Soret diffusion on the exergy loss in laminar premixed flames for hydrogen/air mixtures using a detailed reaction mechanism and the multicomponent transport model. The study starts from conditions in which the importance of the Soret effect is well established in the scientific literature. It is found that, while the exergy losses directly due to the Soret effect are negligible, the Soret effect can appreciably affect the other exergy loss contributions and hence the total exergy loss. Hence, the Soret effect, unlike what has usually been assumed, is not negligible in flame calculations at least when this effect is known to affect laminar flame speed.     

Modeling and CFD Simulation of a Mixed‐Convection Flow of Regular Fluids and Nanofluids in Vertical Porous and Regular Channels

In this article, the problem of combined forced and free convection in vertical porous and regular channels for both regular fluids and nanofluids has been solved using the CFD technique in the entrance regions of momentum and heat transfer taking into account the influences of viscous heating and inertial force. In this regard, various types of viscous dissipation models reported in the literature such as the Darcy model, the power of the drag force model, and the clear fluid‐compatible model were applied. In the case of nanofluid flow, both the Brownian and thermophoresis molecular transfer mechanisms were considered. The dimensionless distributions of velocity, temperature, and the volume fraction of nanoparticles were determined in terms of corresponding dimensionless numbers such as the Grashof, Reynolds, Forchheimer, Brinkman, and Darcy numbers. The predicted results were validated using fully‐developed distributions of velocity and temperature. In addition, the influences of the Grashof number value on the temperature and velocity distributions in the entrance and fully‐developed regions were examined carefully. In addition, temperature and velocity distributions of nanofluids and regular fluids in porous and regular channels were compared. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 43(3): 243–269, 2014; Published online 30 September 2013 in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21079     

Soret,viscous dissipation,and thermal radiation effects on MHD free convective flow of Williamson liquid with variable viscosity and thermal conductivity

The flow model of heat and mass transport of a Williamson liquid through a porous stretching sheet with radiation, viscous dissipation, Soret effect, and chemical reaction has been explored. The motion starts from the slot to the free stream. The present study is unique, because it examines the flow of a Williamson fluid under the influence of variable viscosity and thermal conductivity. The Williamson fluid term as added to the momentum and energy equation is considered in a nonlinear form as compared with other studies in literature. The flow model is a set of coupled highly nonlinear partial differential equations that are simplified and lead to coupled nonlinear total differential equations by employing sufficient similarity variables. The simplified equations are later solved by utilizing the spectral homotopy analysis method. Our experiment shows that the injected variable viscosity, together with thermal conductivity, has a great impact on the fluid profiles. An increase in the Williamson parameter (β) leads to a decrease in the thickness of the hydrodynamic thermal layer. Our numerical calculations were compared with earlier published work, and they were discovered to be correct.