An experimental correlation approach for predicting thermal conductivity of water-EG based nanofluids of zinc oxide

In this study, the effects of temperature (20 °C<T<50 °C) and volume fracti°n (0<φ<4%) on the thermal conductivity of zinc oxide/ethylene glycol-water nanofluid have been presented. Nanofluid samples were prepared by a two-step method and thermal conductivity measurements were performed by a KD2 pro instrument. Results showed that the thermal conductivity increases uniformly with increasing solid volume fraction and temperature. The results also revealed that the thermal conductivity of nanofluids significantly increases with increasing solid volume fraction at higher temperatures. Moreover, it can be seen that for more concentrated samples, the effect of temperature was more tangible. Experimental thermal conductivity enhancement of the nanofluid in comparison with the Maxwell model indicated that Maxwell model was unable to predict the thermal conductivity of the present nanofluid. Therefore, a new correlation was presented for predicting the thermal conductivity of ZnO/EG-water nanofluid.     

The effect of velocity and dimension of solid nanoparticles on heat transfer in non-Newtonian nanofluid

In this investigation, the behavior of non-Newtonian nanofluid hydrodynamic and heat transfer are simulated. In this study, we numerically simulated a laminar forced non-Newtonian nanofluid flow containing a 0.5 wt% carboxy methyl cellulose (CMC) solutionin water as the base fluid with alumina at volume fractions of 0.5 and 1.5 as the solid nanoparticle. Numerical solution was modelled in Cartesian coordinate system in a two-dimensional microchannel in Reynolds number range of 10≤Re≤1000. The analyzed geometrical space here was a rectangular part of whose upper and bottom walls was influenced by a constant temperature. The effect of volume fraction of the nanoparticles, Reynolds number and non-Newtonian nanofluids was studied. In this research, the changes pressure drop, the Nusselt number, dimensionless temperature and heat transfer coefficient, caused by the motion of non-Newtonian nanofluids are described. The results indicated that the increase of the volume fraction of the solid nanoparticles and a reduction in the diameter of the nanoparticles would improve heat transfer which is more significant in Reynolds number. The results of the introduced parameters in the form of graphs drawing and for different parameters are compared.     

Experimental Investigation on the Thermal Conductivity and Viscosity of Silver-Deionized Water Nanofluid

Abstract

This article presents an experimental investigation where the thermal conductivity and viscosity of silver-deionized water nanofluid is measured and studied. The mixture consists of silver nanoparticles of 0.3, 0.6, and 0.9% of volume concentrations and studied for temperatures between 50°C and 90°C. The transient hot-wire apparatus and Cannon-Fenske viscometer are used to measure the thermal conductivity and kinematic viscosity of nanofluid, respectively. The thermal conductivity increases with the increase in temperature and particle concentrations. A minimum and maximum enhancement of 27% at 0.3 vol% and 80% at 0.9 vol% are observed at an average temperature of 70°C. The viscosity decreases with the increase in temperature and increases with the increase in particle concentrations. The effect of Brownian motion and thermophoresis on the thermo-physical properties is discussed. Thus, an experimental correlation for thermal conductivity and viscosity, which relates the volume concentration and temperature, is developed, and the proposed correlation is found to be in good agreement with the experimental results.     

利用格子Boltzmann方法模拟矩形腔内纳米流体Raleigh-Benard对流

利用格 子 Boltzmann方法模拟矩形腔内纳米流体Rayleigh-Benard对流, 得到温度场和流线分布, 比较分析不同Ra数、体积分数、粒径下纳米流体对流换热的变化情况. 结果表明: 在相同的Ra 数和体积分数下, 纳米流体的对流换热随着粒径的增大而减弱; 在相同的Ra数和粒径下, 纳米流体的对流换热随着体积分数增大而增强. 关键词： 纳米流体 Raleigh-Benard 多相流 格子Boltzmann方法     

Numerical simulation of Electrokinetically Driven Peristaltic Pumping of Silver-Water Nanofluids in an asymmetric microchannel

This article intends to focus on the theoretical and numerical investigation of the peristaltic pumping of water-based silver nanofluid in the presence of electroosmotic forces. The investigation is carried out in an asymmetric microchannel subject to the influence of mixed convection and viscous dissipation. No-slip boundary conditions for velocity, temperature, and nanoparticle volume fraction are imposed on channel walls. The lubrication approach is utilized to simplify the normalized constitutive equations. The distribution of electric potential in the electric double layer is characterized by Poisson-Boltzmann ionic distribution which is further linearized by Debye-Hückel approximation. Nanofluid properties are predicted by a combination of the Buongiorno two-phase mixture model and homogeneous flow model. Additionally, the effective thermal conductivity and dynamic viscosity of silver-water nanofluid are characterized by the Corcione model. Silver nanoparticles of 20nm diameter are utilized in this suspension. The transformed set of nonlinear and coupled equations is numerically executed for axial velocity, temperature, and nanoparticle volume fraction by employing the mathematical software Maple 17. Pumping and trapping phenomena are also investigated. A comparison between the thermal conductivity of nanofluid predicted by the Corcione model and the Maxwell model is further presented. The influence of various flow parameters is outlined through graphical results. It has been observed that the thermal conductivity of silver-water nanofluid enhances with increasing nanoparticle volume fraction and temperature but decreases for larger sized nanoparticles. Moreover, the heat transfer rate rises significantly when smaller silver nanoparticles are suspended in water. Furthermore, the temperature of nanofluid is directly related to the Debye length parameter and the Helmholtz- Smoluchowski velocity parameter.     

小通道扁管内纳米流体流动与传热特性

建立了测量小通道扁管内纳米流体流动与对流换热性能的实验系统,测量了不同粒子体积份额的水-Cu纳米 流体的管内对流换热系数和摩擦阻力系数,实验结果表明,在相同雷诺数条件下,小通道扁管内纳米流体的对流换热系数 大于纯液体,且随粒子的体积份额的增加而增大,而纳米流体的阻力系数并未明显增大。     

Natural Convection of Fe_3O_4-Ethylene Glycol Nanofluid under the Impact of Electric Field in a Porous Enclosure

Free convection of Fe_3O_4-Ethylene glycol nanofluid in existence of Coulomb forces is studied. Effect of thermal radiation is taken into account. Properties of nanofluid are varied with supplied voltage and shape of nanoparticles. The bottom wall is considered as positive electrode. Control Volume based Finite Element Method is used to obtain the results, which are the roles of Darcy number(Da), radiation parameter(Rd), Rayleigh number(Ra), nanofluid volume fraction(φ), and supplied voltage(?φ). Results indicate that Nusselt number is an enhancing function of supplied voltage and Darcy number. Maximum values for temperature gradient are occurred for platelet shape nanoparticles.     

KKL correlation for simulation of nanofluid flow and heat transfer in a permeable channel

Hydrothermal behavior of nanofluid fluid between two parallel plates is studied. One of the plates is externally heated, and the other plate, through which coolant fluid is injected, expands or contracts with time. The effective thermal conductivity and viscosity of nanofluid are calculated by KKL correlation. The effects of the nanoparticle volume fraction, Reynolds number, Expansion ratio and power law index on Hydrothermal behavior are investigated. Results show that heat transfer enhancement has direct relationship with Reynolds number when power law index is equals to zero but opposite trend is observed for other values of power law index.     

纳米流体对流换热的实验研究

建立了测量纳米流体对流换热系数的实验系统,测量了不同粒子体积份额的水-Cu纳米流体在层流与湍流状态下的管内对流换热系数,实验结果表明,在液体中添加纳米粒子增大了液体的管内对流换热系数,粒子的体积份额是影响纳米流体对流换热系数的因素之一。综合考虑影响纳米流体对流换热的多种因素,提出了计算纳米流体对流换热系数的关联式。     

Reconstruction model for temperature and concentration profiles of soot and metal-oxide nanoparticles in a nanofluid fuel flame by using a CCD camera

This paper presents a numerical study on the simultaneous reconstruction of temperature and volume fraction fields of soot and metal-oxide nanoparticles in an axisymmetric nanofluid fuel sooting flame based on the radiative energy images captured by a charge-coupled device(CCD) camera. The least squares QR decomposition method was introduced to deal with the reconstruction inverse problem. The effects of ray numbers and measurement errors on the reconstruction accuracy were investigated. It was found that the reconstruction accuracies for volume fraction fields of soot and metaloxide nanoparticles were easily affected by the measurement errors for radiation intensity, whereas only the metal-oxide volume fraction field reconstruction was more sensitive to the measurement error for the volume fraction ratio of metaloxide nanoparticles to soot. The results show that the temperature, soot volume fraction, and metal-oxide nanoparticles volume fraction fields can be simultaneously and accurately retrieved for exact and noisy data using a single CCD camera.     

Dependence of the viscosity of nanofluids on nanoparticle size and material

The viscosity of nanofluids as a function of nanoparticle size and material is modeled and analyzed. Dependences of the viscosity of nanofluids based on liquid argon with aluminum and lithium nanoparticles are obtained. The nanoparticle size ranges from 1 to 4 nm. The volume concentration of nanoparticles is varied from 1% to 12%. It is shown that the viscosity of the nanofluid increases with decreasing nanoparticle size and, in addition, depends on the nanoparticle material.     

Dependence of Nanofluid Viscosity on Particle Size and pH Value

We investigate the viscosity of silicon dioxide nanofluid at different particle sizes and pH values considering nanoparticle aggregation. The experimental and simulation results indicate that nanoparticle size is of crucial importance to the viscosity of the nanofluid due to aggregation. As the nanoparticle size decreases, the viscosity becomes much more dependent on the volume fraction. Moreover, when the nanoparticle diameter is smaller than 2Ohm, the viscosity is closely related to the pH of the nanofluid, and fluctuates with pH values from 5 and 7.     

Investigating the effects of nanoparticles mean diameter on laminar mixed convection of a nanofluid through an inclined tube with circumferentially nonuniform heat flux

In this study, laminar mixed convection of a water-based nanofluid containing Al₂O₃ nanoparticles in an inclined copper tube, which is heated at the top half surface, is investigated numerically. A heat conduction mechanism through the tube wall was implemented. Three-dimensional equations using a two-phase mixture model were solved to investigate the hydrodynamic and thermal behaviors of the nanofluid over a wide range of nanoparticle volume fractions. To verify the model, the results were compared with previous works and a good agreement between the results was observed. The effect of nanoparticles diameter on the hydrodynamic and thermal parameters over a wide range of Grashof numbers is presented and discussed for a particle volume fraction and Reynolds number. It is shown that the diameter of nanoparticles affects the particle distribution in the cross section perpendicular to the tube axis, heat transfer coefficient, and shear stress.     

Transient electrohydrodynamic convective flow and heat transfer of MWCNT - Dielectric nanofluid in a heated enclosure

A computational research was performed to analyze the electrohydrodynamic (EHD) convective heat transfer in a differentially heated dielectric-MWCNT nanofluid layer. The study was conducted on a square enclosure subjected to a temperature gradient between these two vertical walls as well as a potential difference between these horizontal walls. The enclosure was filled with MWCNT oil-based nanofluid; the MWCNT nanoparticles were dispersed in a perfectly insulating thermal oil with a volume fraction of hardly exceeded 0.4%. The governing equations were derived with the assumption of homogeneous nanofluid and were solved with employing finite volume method. Based on the obtained results, it was found that the increase of Rayleigh number, electric Rayleigh number and nanoparticle concentration enhanced the heat transfer. For high thermal and electric Rayleigh number values, the flow and heat transfer became time dependent and accordingly a frequency study was also performed. It was found that the inclusion of an electric field with the addition of nanoparticles led to a significant heat transfer enhancement of about 43%.     

Experimental Assessment of Latent Heat of Evaporation for Hybrid Nanofluids

Innovative use of nanoparticles in synthesis to form hybrid nanofluids is of great interest recently. This generation of nanofluids is known to improve some thermal characteristics deliberately. In the present study, evaporative behavior of hybrid nanofluids is investigated experimentally. In boiling-mode cooling systems, longer lengths of dryouts are more preferred. In this regard, enhancing the value of heat of evaporation is a target. The experiments are implemented at temperature ranging from 90 to 155?C and in the solid volume fraction range of 0–3%. It is found that the use of hybrid nanofluids to enhance the fluid stability and in consequence the fluid latent heat of evaporation (LHE) is rational just at high working pressures (higher than 400 kPa). The most effective hybrid nanofluid in this study is 2% Ag–Au, which results in max increase of 8.7% in the latent heat of evaporation.     

Peristaltic transport of magneto-nanoparticles submerged in water: Model for drug delivery system

Recent development in biomedical engineering has enabled the use of the magnetic nanoparticles in modern drug delivery systems with great utility. Nanofluids composed of magnetic nanoparticles have the characteristics to be manipulated by external magnetic field and are used to guide the particles up the bloodstream to a tumor with magnets. In this study we examine the mixed convective peristaltic transport of copper–water nanofluid under the influence of constant applied magnetic field. Nanofluid is considered in an asymmetric channel. Aside from the effect of applied magnetic field on the mechanics of nanofluid, its side effects i.e. the Ohmic heating and Hall effects are also taken into consideration. Heat transfer analysis is performed in presence of viscous dissipation and heat generation/absorption. Mathematical modeling is carried out using the lubrication analysis. Resulting system of equations is numerically solved. Impact of embedded parameters on the velocity, pressure gradient, streamlines and temperature of nanofluid is examined. Effects of applied magnetic field in presence and absence of Hall effects are studied and compared. Results depict that addition of copper nanoparticles reduces the velocity and temperature of fluid. Heat transfer rate at the boundary enhances by increasing the nanoparticles volume fraction. Increase in the strength of applied magnetic field tends to decrease/increase the velocity/temperature of nanofluid. Further presence of Hall effects reduces the variations brought in the state of fluid when strength of applied magnetic field is increased.     

Entropy generation and MHD natural convection of a nanofluid in an inclined square porous cavity: Effects of a heat sink and source size and location

The effects of a heat sink and the source size and location on the entropy generation, MHD natural convection flow and heat transfer in an inclined porous enclosure filled with a Cu-water nanofluid are investigated numerically. A uniform heat source is located in a part of the bottom wall, and a part of the upper wall of the enclosure is maintained at a cooled temperature, while the remaining parts of these two walls are thermally insulated. Both the left and right walls of the enclosure are considered to be adiabatic. The thermal conductivity and the dynamic viscosity of the nanofluid are represented by different verified experimental correlations that are suitable for each type of nanoparticle. The finite difference methodology is used to solve the dimensionless partial differential equations governing the problem. A comparison with previously published works is performed, and the results show a very good agreement. The results indicate that the Nusselt number decreases via increasing the nanofluid volume fraction as well as the Hartmann number. The best location and size of the heat sink and the heat source considering the thermal performance criteria and magnetic effects are found to be D?=?0.7 and B?=?0.2. The entropy generation, thermal performance criteria and the natural heat transfer of the nanofluid for different sizes and locations of the heat sink and source and for various volume fractions of nanoparticles are also investigated and discussed.     

Transient thin film flow of nonlinear radiative Maxwell nanofluid over a rotating disk

In this letter, a mathematical model for transient nature thin film flow of Maxwell nanofluid over a rotating disk is studied in the presence of a uniform magnetic field and non-linear thermal radiation. The Brownian motion and thermophoresis features due to nanofluid are captured by adopting the Buongiorno model. The prime emphasize is to explore the temperature field and nanoparticles volume fraction in nanofluid thin film flow. The reduced system of differential equations is solved numerically by finite difference based method namely bvp4c. The numerical outcomes regarding film thickness, Nusselt number, Sherwood number, velocity, temperature, and concentration are revealed for varying estimation of involved physical parameters. It is shown that the film thickness decreases with increasing values of the magnetic number. Further, the impact of thermophoresis and thermal radiation parameters is worthwhile in enhancing the fluid temperature. The Solute concentration is found to decrease with Brownian motion and Schmidt number.     

Evaluation of thermal conductivity of MgO-MWCNTs/EG hybrid nanofluids based on experimental data by selecting optimal artificial neural networks

In this paper, the thermal conductivity ratio of MgO-MWCNTs/EG hybrid nanofluids has been predicted by an optimal artificial neural network at solid volume fractions of 0.05%, 0.1%, 0.15%, 0.2%, 0.4% and 0.6% in the temperature range of 25–50 °C. In this way, at the first, thirty six experimental data was presented to determine the thermal conductivity ratio of the hybrid nanofluid. Then, four optimal artificial neural networks with 6, 8, 10 and 12 neurons in hidden layer were designed to predict the thermal conductivity ratio of the nanofluid. The comparison between four optimal ANN results and experimental showed that the ANN with 12 neurons in hidden layer was the best model. Moreover, the results obtained from the best ANN indicated the maximum deviation margin of 0.8%.     

Impacts of ultrasonication time and surfactants on stability and optical properties of CuO,Fe3O4, and CNTs/water nanofluids for spectrum selective applications

The prime objective of the present experimental work is to evaluate the impact of ultrasonication time and surfactants on the optical characteristics (transmittance and absorbance) and stability of CuO/water, CNTs/water, and Fe₃O₄/water nanofluids to be used in spectrum selective applications. Two-step method with various ultrasonication times (30 min, 60 min, and 90 min) was employed to prepare nanofluids (having volume fractions of 0.004 % and 0.0004 %). Furthermore, various surfactants (anionic, cationic, and polymer) were added to the base fluid. The study results revealed that surfactants have a significant effect on the stability of nanofluids over ultrasonication time. The nanofluids prepared using sodium dodecylbenzene sulfonate (SDBS) have the highest zeta potential values than other surfactants used in the experimentation. The increase in transmittance of nanofluid was more prominent for lower concentration (0.0004 %) after one week of preparation. The concentration of nanoparticles, ultrasonication time, temperature, and surfactants influenced the optical characteristics of nanofluids. The most stabled CNTs nanofluid with 0.004 % concentration and 90 min of ultrasonication obtained an average of 67.6 % and 74.6 % higher absorbance than stabled CuO and Fe₃O₄ nanofluids, respectively. The irradiance transmitted through nanofluid was strongly dependent on the concentration and type of nanoparticles.