The nano-fluids in view of the fabulous thermal conductivity enhancement have been recognized useful in several industrial and engineering applications. Present study provides an analytical investigation of the fluid flow, heat and mass transfer and entropy generation for the steady laminar non-Newtonian nano-fluid flow induced by a stretching sheet in the presence of velocity slip and convective surface boundary conditions using Optimal Homotopy Analysis Method (OHAM). In contrast to the conventional no-slip condition at the surface, Navier’s slip condition is applied. The governing partial differential equations (PDEs) are transformed into highly nonlinear coupled ordinary differential equations (ODEs) consist of the momentum, energy and concentration equations via appropriate similarity transformations. Entropy generation equations, for the first time in this problem, are derived as a function of velocity, temperature and concentration gradients. The current OHAM solution demonstrates very good correlation with those of the previously published studies in the especial cases. The influences of different flow physical parameters on fluid velocity component, temperature distribution and concentration profile as well as the entropy generation number are discussed in details. Increasing the Brownian motion parameter and thermophoresis parameter, Biot number, Reynolds number, and Brinkman number or decreasing the Casson parameter and velocity slip parameter cause an increase in the entropy generation number.
• MHD nanofluid flow in an inclined half-annulus is investigated. • CVFEM is used to solve this problem. • Nusselt number has direct relationship with and . • Nusselt number has reverse relationship with . • Inclination angle of the enclosure can be control parameter. In this paper, the effect of a magnetic field on natural convection in a half-annulus enclosure with one wall under constant heat flux using control volume based finite element method. The fluid in the enclosure is a water-based nanofluid containing Cu nanoparticles. The effective thermal conductivity and viscosity of nanofluid are calculated using the Maxwell–Garnetts (MG) and Brinkman models, respectively. Numerical simulations were performed for different governing parameters namely the Hartmann number, Rayleigh number and inclination angle of enclosure. The results indicate that Hartmann number and the inclination angle of the enclosure can be control parameters at different Rayleigh number. In presence of magnetic field velocity field retarded and hence convection and Nusselt number decreases.
Control of particle size and morphology has increasingly captured the attention of researchers for decades. The exploration of unique sizes and shapes as they relate to various properties has become a great quest for large field applications. To meet these demands, this review covers recent developments in particle processing. An aerosol-assisted self-assembly technique, with a spray-drying method as a representative of it, to create particles is thoroughly reviewed. Its popularity and its broad use in industry for producing particles are the main reason of this review; thus, elucidation of this method is important for the improvement of particle technology. A practical spray-drying method is described from the step-by-step process to the selection of apparatus types (merits and demerits). Elaboration of particle processing of several morphologies (sphere, doughnut, encapsulated, porous, hollow, and hairy) is discussed in terms of the selection of material types, the addition of supporting materials, and the change of process conditions. Controllable size is also discussed in terms of the adjustment of the droplet size, initial precursor concentration, and the addition of specific techniques. A comparison between a theoretical mechanism and current experimental results (over a 15-year period) are shown to clarify how particles with various sizes and morphologies are designed. This method must be considered an art rather than a science because of its advantages in creating wonderful and unique particle shapes. The performance of various particle morphologies is also demonstrated, which is essential for an understanding of the importance that shape can exert on practical use. Because the method outlined here can be broadly applied to the production of various types of functional materials, we believe that this report contributes new information to the field of chemical, material, environmental, and medical engineering.
To investigate the effects of the air volume ratio parameters (axial-to-radial flow ratio of the wall-attached air cylinder “δ” and the forced-to-exhaust ratio of the ventilation system “β”) on the air curtain dust suppression in a rock tunnel's fully-mechanized working face, the eastern belt fully-mechanized working face in Huipodi mining company (Shanxi Mineral Group Co., Ltd., China) was numerically simulated by CFD software in this study. First, a mathematical model for describing the airflow-dust migration in a fully-mechanized working face was established using the Euler-Lagrange method. A full-scale geometrical model of the tunnel was also developed. The effectiveness of the established models and the related parameter settings were then verified by making comparisons between the field measured values and the numerical simulation results. Finally, the airflow migration and dust dispersion rules under different ventilation conditions (δ = 5:5–1:9 and β = 0.5–1.5) were simulated. According to the simulation results, a decrease in δ and β contributed to the formation of an effective axial dust-suppression air curtain in the fully-mechanized excavating region. For eastern belt fully-mechanized working face and those under similar production conditions, an effective axial dust-suppression air curtain can be formed when δ = 1:9–2:8 and β = 0.5–0.75. When δ = 1:9 and β = 0.5–0.75, the high-concentration dust were blocked in the space in front of the driver of heading machine (i.e., within 7 m from the head-on section), which achieved a better dust suppression effect.
In this work, ZnTiO ceramics have been synthesized from the reaction of zinc acetate (Zn(CH COO) ·2H O), tetrabutyl titanate (Ti(OC H ) ) as precursors and ethanol as the solvent, in the presence benzene-1,3,5-tricarboxylic acid as a novel chelating agent by sol-gel method. The effect of various parameters such as reaction temperature, pH effect, effect of molar ratio of benzene-1,3,5-tricarboxylic acid to tetrabutyl titanate on morphology, size and purity of products was investigated. The as-prepared products were characterized by various analyses such as: X-ray diffraction (XRD), scanning and transmittance electron microscopy (SEM, TEM), X-ray energy dispersive spectroscopy (EDS), UV-vis and Fourier transform infrared spectroscopy (FT-IR) technique. The photocatalytic degradation was investigated using methyl orange (MO) under ultraviolet (UV) light irradiation. Application of this product as photocatalyst was investigated through degradation of methyl orange (MO) under UV irradiation and percentage of degradation obtained about 70% after 60 min.
Schematic of the analyzed configuration. This study numerically investigated the laminar mixed-convection heat transfer of different water-copper nanofluids inside a microtube with curvature angle of 90°, using a finite volume method. The Reynolds number of modeling was 10, nanoparticles volume fractions were chosen from 0.0% to 6.0% and Richardson numbers varied from 0.1 to 10. The findings were depicted for dimensionless axial velocity, coefficient of friction and Nusselt number profiles as well as dimensionless temperature contours. The validity of model was excellent compared to former numerical and experimental studies. The results showed that the heat transfer and hydraulics behavior of nanofluids in curved geometries is to some extent different with other geometries and flat surfaces due to presence of buoyancy and centrifugal forces at the same time. Especially, in the regions near and after 45° curvature angle, the behavior of heat transfer and nanofluid flow is unpredictable. In this region, increasing the nanoparticles volume concentration or transition from forced convection regime to free convection state, cause a decrease in Nusselt number and friction factor. That’s while for the entrance region of microtube, the results are completely opposite; increasing the Richardson number or nanoparticle concentration enhances the heat transfer as well as friction factor. Also, the velocity profile variations in the vertical and horizontal diameter of microtube is significant in areas of 60° ( /3) and the heterogeneity of this profile increases by rising Rayleigh number and volume fraction of solid particles.
FTIR spectra analysis (400–4000 cm ) for synthesized nanoparticles before adsorption are shown in the figure. In this figure, the most distinguishable peaks are shown for the NPs which are coded separately. All synthesized nanoparticles have relatively same peaks. In range between wave number 3400 and 3430 cm , the highest peak was appeared in region A which corresponds to polyphenols. These peaks show the prominent phenolic functional groups in FTIR analysis. The second strong peak in region E in the range of 1126–1190 cm , corresponds to carbonyl group which shows heterocyclic compounds resulting from proteins of plant extracts. Accordingly, the FTIR spectra of NPs exhibited another prominent peak in region C between 1628 cm and 1640 cm . This peak corresponds to resonance absorption of the C C in alkene groups belonging to the family of no-saturated hydrocarbon compounds. Another strong peak is observed in region G within the range of 615–617 cm , indicating aromatic compounds of alkanes. Other peaks can also be seen in regions F and D, which all correspond to organic, aromatic compounds, an also derivations of these compounds including polyphenols, alcohol or terpenoids, proteins and organic acids in plant extracts. According to the Fig, the intensity of peaks corresponding to TV-Fe is stronger than other synthesized NPs in almost all peaks, while for RD-Fe NPs the relationship is opposite. This shows the difference between stabilizing and reducing agents in extracts of different plants. The intensity of RD-Fe peak in region E is less than other NPs due to the presence of NPs which inhibit aggregation. In the present study, NZVI particles were synthesized from the plant extracts including Rosa damascene (RD), Thymus vulgaris (TV), and Urtica dioica (UD). The FTIR arspectshowed that polyphenols, proteins and organic acids which serve as reducing and stabilizing agents play a significant role in the synthesis of NPs and reduce the possibility of aggregation of NPs compared to chemical techniques of NPs synthesis. The amount and type of compounds in plant extracts affect the structure and also agglomeration of NPs after adsorption process. Based on the results, the highest removal efficiency occurred at pH 2. With increase in contact time and amount of dose, the percentage removal increases. Inversely, increase of initial concentration of Cr(VI) decreases the removal efficiency of the contaminant. These nanoparticles have a high adsorption capacity. Accordingly, by applying a dose of 0.2 g/l and contact time of 10 min, the three NPs yielded >90% removal efficiency. Also, for 1 min contact time, the percentage removal was 94.87%, 83.48% and 86.8% for RD-Fe, UD-Fe and TV-Fe, respectively. By an increase to 25 min, the removal percentage reached to 100% for TV-Fe and UD-Fe. Moreover, 30 min was required to remove Cr(VI) completely by RD-F.
Physical model of the problem. Nowadays graphene is emanating as one of the most encouraging nanomaterial due to its continuous electrical conducting behaviour even at zero carrier concentration. With this initiation, we investigate the flow and heat transfer nature of liquid film flow of magnetic-nanofluids over a stretching surface by considering the aligned magnetic field with non-uniform source/sink and thermal radiation. For this study, we considered the graphene (GP) nanoparticles embedded in water and water-ethylene glycol (EG) mixtures (i.e. 70%water + 30%EG and 50%water + 50%EG). With the assistance of similarity transformations, governed equations are transferred as ordinary differential equations. Numerical results are determined by applying the Runge-Kutta and Newton’s methods. Graphs are exhibited and explained for important parameters. The influence of non-dimensional parameters on reduced Nusselt number, flow and heat transfer is discussed with the assistance of graphs. It is found that aligned magnetic field regulates the local Nusselt number. It is also found that rising the volume fraction of nanoparticles effectively boosts the thermal conductivity of water + 50%EG + GP nanofluid when compared with water + GP and water + 30%EG + GP nanofluids.
Schematic of the problem. In present study, heat transfer and turbulent flow of water/alumina nanofluid in a parallel as well as counter flow double pipe heat exchanger have been investigated. The governing equations have been solved using an in-house FORTRAN code, based on finite volume method. Single-phase and standard k-ε models have been used for nanofluid and turbulent modeling, respectively. The internal fluid has been considered as hot fluid (nanofluid) and the external fluid, cold fluid (base fluid). The effects of nanoparticles volume fraction, flow direction and Reynolds number on base fluid, nanofluid and wall temperatures, thermal efficiency, Nusselt number and convection heat transfer coefficient have been studied. The results indicated that increasing the nanoparticles volume fraction or Reynolds number causes enhancement of Nusselt number and convection heat transfer coefficient. Maximum rate of average Nusselt number and thermal efficiency enhancement are 32.7% and 30%, respectively. Also, by nanoparticles volume fraction increment, the outlet temperature of fluid and wall temperature increase. Study the minimum temperature in the solid wall of heat exchangers, it can be observed that the minimum temperature in counter flow has significantly reduced, compared to parallel flow. However, by increasing Reynolds number, the slope of thermal efficiency enhancement of heat exchanger gradually tends to a constant amount. This behavior is more obvious in parallel flow heat exchangers. Therefore, using of counter flow heat exchangers is recommended in higher Reynolds numbers.
This article deals with the combined effects of heat and mass transfer on the peristaltic propulsion of two-phase fluid flow through a Darcy-Brinkman-Forchheimer porous medium with compliant walls. The Sisko fluid model together with small particles is considered in the presence of extrinsic magnetic field and chemical reaction. It is well-known that different biological fluids behave like a Newtonian or non-Newtonian fluid depending upon the shear rates. The non-Newtonian fluid models are more complicated than Newtonian fluid and difficult to express using the single constitutive relationship between stress and strain rate. These constitutive equations provide a complex mathematical formulation and become numerous challenges to find numerical and analytical solutions. Small magnetic particles are helpful to manipulate and control the two-phase flow by magnetic force. Moreover, it is also beneficial in drug targeting for the treatment of different diseases. Further, two-phase flow plays an important role to examine the muscular expansion and contraction during the propagation of various biological fluids. An appropriate approximation is considered such as long wavelength and creeping flow regime to model the governing equations. Analytical solutions are obtained using the perturbation method. Moreover, numerical computations are performed to determine the features of peristaltic pumping. The results of different rheological properties for particle and fluid phase are discussed mathematically as well as graphically for different sundry parameters. The current analysis has an extensive amount of applications in medical engineering and also significant importance of smart fluid pumping systems in various engineering processes.
The aim of present paper is to investigate the heat/mass and motile microorganisms transfer rates in the convective stretched flow of nanofluid consisting of nanoparticles and gyrotactic microorganisms. Magneto nanofluid in presence of an inclined magnetic field is adopted. Idea of microorganisms is employed just to stabilize the suspended nanoparticles through bioconvection which has been induced by combined effects of buoyancy forces and magnetic field. Further interesting aspects of Brownian motion, thermophoresis, viscous dissipation, Joule heating and stratification are examined. Convergent solutions for the obtained nonlinear differential systems are derived. Main attention through plots is given to the influences of sundry variables on the velocity, temperature, concentration and motile microorganisms density. Numerical values for the skin friction coefficient, local Nusselt number, Sherwood number and local density number of motile microorganisms are computed and analyzed. Comparison is also made with limiting published results from open literature and an excellent agreement is noticed.
A cavity filled with a porous medium saturated by a hybrid nanofluid with the size is depicted in Fig. 1. The top and bottom walls are well insulated, and the left and right walls are kept in the hot and cold temperature of and , respectively. Hybrid nanofluids are a new type of enhanced working fluids, engineered with enhanced thermo-physical properties. The hybrid nanofluids profit from the thermo-physical properties of more than one type of nanoparticles. The present study aims to address the free convective heat transfer of the Al O -Cu water hybrid nanofluid in a cavity filled with a porous medium. Two types of important porous media, glass ball and aluminum metal foam, are considered for the porous matrix. The experimental data show dramatic enhancement in the thermal conductivity and dynamic viscosity of the synthesized hybrid nanofluids, and hence, these thermophysical properties could not be modeled using available models of nanofluids. Thus, the actual available experimental data for the thermal conductivity and the dynamic viscosity of hybrid nanofluids are directly utilized in the present theoretical study. Various comparison with results published previously in the literature are performed and the results are found to be in excellent agreement. In most cases, the average Nusselt number is decreasing function of the volume fraction of nanoparticles. The results show the reduction of heat transfer using nanoparticles in porous media. The observed reduction of the heat transfer rate is much higher for hybrid nanofluid compared to the single nanofluid.
Bio-mediated synthesis of metal oxide nanoparticles using plant extract is a promising alternative of traditional chemical synthesis. The present study reports the synthesis of ZnO nanoparticles by biological method. Highly stable and hexagonal phase ZnO nanoparticles were synthesized using leaves extract and were characterized by XRD, UV–vis, DLS, SEM, TEM and FT-IR spectroscopy. The synthesized ZnO nanoparticles were confirmed by XRD and FTIR spectra. Morphology studies indicates spherical nature of the ZnO NPs and EDX shows the highly pure ZnO nanoparticles. The antibacterial activity of ZnO nanoparticles and ZnO nanoparticles coated cotton fabric were tested against (gram positive) and (gram negative) organisms by agar diffusion method. Finally, the current study has clearly demonstrated that the ZnO NPs are responsible for significant higher antibacterial activities. Therefore, the study reveals an efficient, ecofriendly and simple method for the green synthesis of multifunctional ZnO NPs using green synthetic approach.
Force convective heat transfer of alumina/water nanofluid inside a cooled parallel-plate channel in the creeping flow regime and the presence of heat generation is investigated theoretically. A modified two-component four-equation non-homogeneous equilibrium model is employed for the alumina/water nanofluid that fully accounts for the effects of nanoparticles volume fraction distribution. To impose the temperature gradients across the channel, the upper wall is subjected to a prescribed wall heat flux while the bottom wall is kept adiabatic. Moreover, due to the nanoparticle migration in the fluid, the no-slip condition of the fluid–solid interface at the walls is abandoned in favor of a slip condition that appropriately represents the non-equilibrium region near the interface. The results indicated that nanoparticles move from the adiabatic wall (nanoparticles depletion) toward the cold wall (nanoparticles accumulation) and construct a non-uniform nanoparticle distribution. Moreover, the anomalous heat transfer rate occurs when the Brownian motion takes control of the nanoparticle migration (smaller nanoparticles).
The multi-radial vortex airflow migration and dust diffusion rules were investigated by a self-designed experimental platform in this paper. Firstly, a multi-radial vortex airflow generator was designed; secondly, the experimental platform for simulation was designed; thirdly, experiment results of airflow migration and dust diffusion were analyzed. In order to control the diffusion of dusts towards the working area in an excavation face, a novel multi-radial vortex wind generator was designed and developed in this study. Using a self-designed simulation system, the multi-radial vortex airflow migration and dust diffusion rules were experimentally investigated. As to the airflow migration, it was easier to form the dust suppression air curtains with uniform airflow distribution at a longer distance away from the head-on section ( ), under smaller forced-to-exhaust ratio ( ), forced air flow rate ( ) and axial-to-radial-ratio ( ), with the airflow pointing to the head-on section. As to the control of dust diffusion, the dust concentration decreased gradually with the increase of . As the distance away from the head-on section increased, the control capacity of dust diffusion firstly weakened and then strengthened. The smaller values of forced-to-exhaust ratio and axial-to-radial ratio and the larger forced air flow rate would be beneficial to the control of dust diffusion. When the ventilation parameters were reasonably set, the airflow distribution of the dust suppression air curtain, the airflow direction and the hindrance on dust diffusion tended to be stable. Additionally, the optimal ventilation parameters were determined in this study, i.e., = 20 m, = 5:4, = 200 m /min and = 1:9. Under the optimal condition, the average removal ratios of total dusts and respirable dusts were as high as 96.02% and 95.51%, respectively.
In this paper, flow and heat transfer of MHD Go-water nanofluid between two parallel flat plates in the presence of thermal radiation are studied. One of plates is externally heated and cooled by coolant injection through the other plate, which also expands or contracts with time. A similarity transformation is used to transmute the governing momentum and energy equations into non-linear ordinary differential equations with the appropriate boundary conditions. The obtained non-linear ordinary differential equations are solved by Duan–Rach Approach ( ). This method allows us to find a solution without using numerical methods to evaluate the undetermined coefficients. This method modifies the standard Adomian Decomposition Method by evaluating the inverse operators at the boundary conditions directly. The impacts of various parameters such as the Reynolds number, the expansion ratio, the magnetic parameter, the power law index, the solid volume fraction and the radiation parameter are investigated on the velocity and temperature. Furthermore, the value of the Nusselt number is calculated and presented through figures. The results indicate that the temperature profile and the Nusselt number have a direct relationship with the solid volume fraction and have an inverse relationship with the radiation parameter. In addition, the limiting cases are gained and found to be in an excellent agreement with the previous works.
This article models the effects of magnetic field and nanoparticles in the three-dimensional flow of Sisko fluid. The flow is caused by a bidirectional stretching surface. Effects of Brownian motion and thermophoresis in the nanofluid model are considered. Sisko fluid is assumed electrically conducted through a constant applied magnetic field. Mathematical formulation in boundary layer regime is presented for a low magnetic Reynolds number. Newly constructed boundary condition subject to zero nanoparticles mass flux at the surface is employed. Nonlinear differential systems are solved for the convergent solutions. Effects of various physical parameters are studied and discussed. Numerical values of skin friction coefficients and Nusselt number are tabulated and analyzed. It is observed that the effects of Brownian motion and thermophoresis parameters on the nanoparticles concentration distribution are quite opposite. Further the temperature and nanoparticles concentration distributions are enhanced for the larger values of magnetic parameter.
The melting process of a nano-enhanced phase-change material is investigated in a square cavity with a hot cylinder located in the middle of the cavity in the presence of both single and hybrid nanoparticles. The dimensionless partial differential equations are solved numerically using the Galerkin finite element method using a grid with 6000 quadrilateral elements. The effects of the volume fraction of nanoparticles, the Fourier number, the thermal conductivity parameter, and the viscosity parameters are studied. The results show that the solid-liquid interface and the liquid fraction are significantly affected by the volume fraction of nanoparticles and the thermal conductivity parameter. Additionally, it is found that the melting rate is much larger when the Fourier number changes between 0 and 0.5 and a further increase in the Fourier number causes a reduction in the rate of the melting.
Chromium doped titanium dioxide (TiO ) nanocrystal films with various doping concentration have been successfully prepared by a sol–gel dip-coating process. These films have been characterized by XRD, XPS, AFM, and UV–vis absorption spectroscopy. It is found that Cr doping can effectively reduce the transition temperature of anatase to rutile phase as well as the grain size. The absorption edges of TiO thin films shift towards longer wavelengths (i.e. red shifted) from 375 nm to about 800 nm with increasing Cr concentration, which greatly enhances TiO nano-materials on the absorption of solar spectrum. The appearance of UV–vis absorption features in the visible region can be ascribed to the newly formed energy levels such as Cr 2p level and oxygen vacancy state between the valence and the conduction bands in the TiO band structure. The enhancement of the photocatalytic properties is observed for Cr-doped TiO thin film.
Chromium doped titanium dioxide (TiO2) nanocrystal films with various doping concentration have been successfully prepared by a sol-gel dip-coating process. These films have been characterized by XRD, XPS, AFM, and UV-vis absorption spectroscopy. It is found that Cr doping can effectively reduce the transition temperature of anatase to rutile phase as well as the grain size. The absorption edges of TiO2 thin films shift towards longer wavelengths (i.e. red shifted) from 375 nm to about 800 nm with increasing Cr concentration, which greatly enhances TiO2 nano-materials on the absorption of solar spectrum. The appearance of UV-vis absorption features in the visible region can be ascribed to the newly formed energy levels such as Cr 2p level and oxygen vacancy state between the valence and the conduction bands in the TiO2 band structure. The enhancement of the photocatalytic properties is observed for Cr-doped TiO2 thin film. (C) 2010 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.