Behavior Of Nanofluids Research Articles

Exact solutions via Prabhakar fractional approach to investigate heat transfer and flow features of hybrid nanofluid subject to shape and slip effects

The core devotion of this study is to develop a generalized model by means of a recently proposed fractional technique in order to anticipate the enhancement in the thermal efficiency of engine oil because of the dispersion of graphene and magnesia nanoparticles. In addition to investigating the synergistic attributes of the foregoing particles, this work evaluates shape impacts for column, brick, tetrahedron, blade, and lamina-like shapes. In the primary model, the flow equation is coupled with concentration and energy functions. This classical system is transmuted into a fractional environment by generalizing mathematical expressions of thermal and diffusion fluxes by virtue of the Prabhakar fractional operator. In this study, ramped flow and temperature slip conditions are simultaneously applied for the first time to examine the behavior of a hybrid nanofluid. The mathematical analysis of this problem involves the incorporation of dimension-independent parameters into the model and the execution of the Laplace transform for the consequent equations. By doing so, exact solutions are derived in the form of Mittag–Leffler functions. Multiple illustrations are developed by dint of exact solutions to chew over all aspects of temperature variations and flow dynamics. For the preparation of these illustrations, the details of parametric ranges are as follows: 0.00 le varUpsilon le 0.04, 2.0 le Gr_1 le 8.0, 0.5 le Sc le 2.0, 0.1 le uptau le 4.0, 0.1 le d le 0.6, 0.2 le lambda _1 le 1.5, and 1.0 le Gr_2 le 7.0. The contribution of differently shaped nanoparticles, volume proportions, and fractional parameters in boosting the heat-transferring attributes of engine oil is also anticipated. In this regard, results for Nusselt number are provided in tabular form. Additionally, a brief analysis of shear stress is carried out for fractional parameters and various combinations of magnesia, graphene, and engine oil. This investigation anticipates that engine oil’s hybridization with magnesia and graphene would result in a 33% increase in its thermal performance, which evidently improves its industrial significance. The enhancement in Schmidt number yields an improvement in the mass transfer rate. An increment in collective volume fraction leads to raising the profile of the thermal field. However, the velocity indicates a decreasing behavior. Nusselt number reaches its highest value (Nu=8.1363) for the lamina shape of considered particles. When the intensity of the buoyancy force augments, it causes the velocity to increase.

Solvent-free carbon sphere nanofluids towards intelligent lubrication regulation

AbstractBy simply switching the electrical circuit installed on steel/steel contact, the tribological behaviors of nanofluids (NFs) can be regulated in real time, thereby achieving the desired performance of friction reduction and wear resistance. Herein, solvent-free carbon spherical nanofluids (C-NFs) were successfully prepared for intelligent lubrication regulation. C-NFs with excellent lubrication performance can immediately reduce the coefficient of friction (COF) despite applying a weak electric potential (1.5 V). Moreover, polyethylene glycol 400 (PEG400) containing 5.0 wt% C-NFs remained responsive to electrical stimulation under the intermittent voltage application with an average coefficient of friction (ACOF) reduction of 20.8% over PEG400. Such intelligent lubrication regulation of C-NFs under an external electric field (EEF) mainly depends on the orderly arranged double-electric adsorption film of ion canopy-adsorbed carbon spheres (CSs). The intermittent electrical application can continuously reinforce the adsorption film and its durability for real-time controlling the sliding interfaces. Electrical-stimulation-responsive intelligent lubricants provide a new technical support for realizing intelligent stepless control of devices.

Obtaining the optimal lubrication conditions by investigating the viscosity of MWCNT (25%)-TiO2(75%)/ oil SAE40 hybrid nanofluid by response surface methodology

The behavior of hybrid nanofluid (HNF) based on SAE40 oil has been investigated using response surface methodology (RSM) in this study. Laboratory conditions in this study are temperature T = 25–50 °C, SVF= 0.0625–1% and SR= 666.5–9331 s−1. The purpose of this study is to select the best-predicted model and creates optimal lubrication conditions in a cold environment (or starting car). The statistical-mathematical analysis of the performance of various modelers and their comparison, as well as the non-unification of laboratory behavior on a real scale in the past literature, were the motivations of the present work. Four different models (2FI, quadratic, cubic, and quartic models) have been evaluated. One of the innovations of this study is the investigation of various statistical aspects of these modeling functions and their comparison. Statistical findings show that the quartic model has double accuracy in presenting the HNF properties compared to other models. The model evaluation indicators are compared based on the R2, C.D%, C.V%, and P-value. The values of these indices are for the quartic model 0.9990, − 6.337 < C.D < 6.64%, 1.399196276e-216% and 1.76%, respectively. The optimum mode of viscosity of HNF for lubrication in a cold environment (T = 31.395 °C, SVF = 0.063% and SR = 666.510 s−1) is suggested as 212.360 MPa.sec.

Investigation of nanofluid physical behavior inside porous container utilizing mathematical numerical method

The numerical method for modeling the behavior of nanofluid within the closed container in the presence of Lorentz force was dissected in this paper. The working fluid contains water and two shapes of nanoparticles. The porous geometry has one sinusoidal inner surface which faces constant heat flux. Influences of gravity and vertical Lorentz was complicated in modeling and momentum equations have been edited with adding related source terms. The precision of code was tested and respectable agreement has been obtained. The influences of loading nanomaterial and strength of two important forces (gravity and buoyancy) have been analyzed in the result section. Loading nanoparticles leads to a growth of Nu around 26.99% and 41.04% when [Formula: see text] and 15. Increasing buoyancy leads to augment of Nu about 44.34% and 1.46% in the absence and existence of Ha. Applying Lorentz force makes Nu to decrease about 40.39% when [Formula: see text].

The unified impact of thermal radiation and heat source on unsteady flow of tangent hyperbolic nanofluid through a permeable shrinking sheet

The tangent hyperbolic nanofluid behaviour is observed in multiple practical applications and extensively used in different laboratory experiments. It motivates to focus on the two-dimensional boundary layer flow of tangent hyperbolic nanofluid past a shrinking sheet. The goal of this article is to scrutinize the mass and heat transport of an unsteady flow of non-Newtonian tangent hyperbolic nanofluid past a shrinking surface under the influences of a source of heat, thermal radiation and chemical reaction. The flow model is mathematically framed through a coupled nonlinear partial differential equations. To transform the non-linear PDEs to ODEs, we use the similarity transformations and reduced ODEs are solved by RK-IV (Runge-Kutta method of order four) with shooting technique using the computational software MATHEMATICA. The novelty which emerges from the flow pattern lies in the fact that there exist dual solutions for certain parametric domain and the range of the existing solution may be expanded by increasing the power-law index (n) and shortened by increasing the Weissenberg number (We). Another remarkable conclusion which can be drawn from the temporal stability analysis that among these two solutions, first solution is stable and realistic whereas the second solution is not physically realistic. A diversity of the parameter estimates were used to provide solution for velocity f′(η), temperature θ(η) and concentration profiles ϕ(η) of this fluid model. In addition to the above findings, there are graphs and tables with explanation for the skin friction coefficient, the Nusselt number and the Sherwood number. These characteristics of a tangent hyperbolic nanofluid are not reported yet and may be useful in the development of existing technology.

Bioconvective radiative unsteady Casson nanofluid flow across two concentric stretching cylinders with variable viscosity and variable thermal conductivity

The role of variable viscosity and variable thermal conductivity in nanofluid flows is significant, as they can strongly influence the flow behavior and heat transfer performance of nanofluids. Keeping in mind the importance of these effects of variable characteristics, our motivation in this study is to investigate the role of nonlinear radiative heat flux on unsteady Casson nanofluid flow across two concentric stretched cylinders in the presence of temperature-dependent viscosity and thermal conductivity. A convective condition on the inner cylinder wall is also considered. In addition, the nanofluid is immersed with microorganisms that can swim and move independently. The addition of microorganisms has a significant role in the stability of the nanofluid flow. The influence of thermophoresis and Brownian motion on the flow, heat, mass, and microorganisms are scrutinized by employing the Buongiorno model. The governing flow equations are converted into a system of differential equations engaging similarity transformations, and the bvp4c method is employed to solve it numerically. Engineering parameters are computed and tabulated numerically. The findings demonstrate that as the unsteadiness parameter upsurges, the radial profile intensifies while the axial profile diminishes near the outer cylinder surface. It is also comprehended that both Lewis and bioconvective Lewis numbers reduce the motile density profiles. The accuracy of the presented model is also given in a graphical illustration by comparing it with a published result in a limiting case.

Viscosity behavior for zirconia and γ-alumina nanoparticles in different electrolytic solutions: An experimental investigation

Viscosity modification of injected fluids is a vital mechanism for successful oil recovery from an oil reservoir. Various studies have demonstrated that nanoparticles (NPs) possess the tendency to alter the wettability of reservoir rocks, reduce the interfacial tension between injected fluids and crude oil, and modify the viscosity of injected fluids. Zirconia (ZrO2) and γ-alumina (γ-Al2O3) NPs have demonstrated huge prospects for enhanced oil recovery (EOR) in various studies. Recently, experimental investigations have attributed the viscosity behavior of silica nanofluids to the interaction between the ions of the silica NPs and electrolytes at the electrical double layer. Therefore, this study investigates the viscosity behavior of ZrO2 and γ-Al2O3 NPs with their increasing concentrations in different aqueous solutions present in reservoir brine by employing techniques such as dynamic light scattering and transmission electron microscopy in addition to viscosity and pH measurements at ambient conditions of approximately 25℃ and 1 atm. The viscosity behavior of spherical particles in suspensions is well suited for the viscosity profile of the nanofluids with increasing concentrations of ZrO2 and γ-Al2O3 NPs. The viscosity of the ZrO2 and γ-Al2O3 nanofluids containing the chloride salts increases in the order of Ca2+ > Na+ > K+ while those containing the sulfate salts increase in the order Mg2+ > Na+ > K+. Comparatively, the model proposed by Williams et al. predicts the viscosities of the electrolyte-based zirconia and γ-Al2O3 nanofluids with percentage absolute average deviation (%AAD) of 2.07 and 2.52 %, respectively, whereas those by Einstein’s model records %AAD of 3.15 and 3.68 %, respectively. The findings from this study provide experimental data and illuminate the understanding of the viscosity behavior of the nanofluids containing electrolytic ions and set the stage for further investigations, which are relevant for EOR purposes.

Infinite Shear Rate Viscosity Model of Cross Fluid Flow Containing Nanoparticles and Motile Gyrotactic Microorganisms Over 3-D Cylinder

Cross nanofluidic model yields extraordinary results and describes the behaviour of nanofluid at very high and very low shear rate. In this paper infinite shear rate viscosity model of cross nanofluid flow containing nanoparticles and motile gyrotactic microorganisms over three dimensional horizontal cylinder is taken. In this attempt simultaneous utilization of nanoparticles along with motile microorganisms attached mathematical model of cross fluid and three-dimensional geometry of cylinder has been carried out as an innovation. For the inspection of velocity profile of cross nanofluid inclined magnetic field is scrutinized. Temperature of Cross nanofluid and its concentration is also carried out with several facts. Mass flux and heat flux values for motile microorganisms and nanoparticles are calculated through statistical graphs. This attempt reveals that small variation of Brownian motion parameter gives lower concentration of nanoparticle about 80.21% and 78.44% reduction is found in concentration of motile microorganisms.

Mathematical modeling of thermophysical behavior of carbon nanotube nanofluid through porous container for mechanical systems with gradient influences

A mathematical theory was developed to simulate how magnetic force causes hybrid nanopowder to move through space. This numerical approach was created by combining the FEM and FVM, and triangular elements were used to create the grid. Iron oxide and MWCNT mixture were dispersed in water, and the hybrid nanomaterial’s properties were assessed using earlier empirical formulas. Gravity force can participate in the phenomena because there is a hot, wavy wall on the bottom side. Radiation flux impact was added, and different permeability spaces were used. A counterclockwise eddy is formed inside the domain as an output of gravity force and with the increase of Da, it divides into two vortexes. Additionally, increasing Da causes about a 75% increase in eddy power and increases iso-temperature distortions. The velocity decreases by between 82.5% and 90% as Lorentz terms are considered for flow equations, depending on the amount of Da. When Ra is taken into account at [Formula: see text], [Formula: see text], Nu increases by about 27.75%. When [Formula: see text], Nu increases by about 10.59% as permeability increases. With the use of MHD, Nu decreases by 43.26% when Ra and permeability are at their highest points.

Elaboration of thermophysical performance enhancement mechanism of functionalized boron nitride/graphite hybrid nanofluids

This study mainly investigated the physicochemical characteristics of ethylene glycol/ water (EG/W) based hydroxyl-functionalized boron nitride (BN-OH) and graphite (G) hybrid nanofluids. A novel simple and efficient annealing method was proposed to have hexagonal boron nitride (h-BN) nanoparticles functionalized to improve the synergistic role between hybrid G/BN-OH nanoparticles. Meanwhile, the dispersion stability, thermal stability, and rheological behavior of diverse nanofluids (h-BN, BN-OH, G, G/BN and G/BH-OH) were comprehensively evaluated. The results showed that the G/BN-OH hybrid nanofluids demonstrate both better dispersion stability and thermal stability, as well as a lower increase in viscosity. In addition, the thermal conductivity of G/BN-OH hybrid nanofluids was increased by up to 18.05% with a concentration of 0.2 wt% when compared to the base fluid. Ultimately, the complicated theoretical mechanism of thermophysical performance augment for G/BH-OH hybrid nanofluids was reliably presented. The enhanced thermal conductivity of nanofluids may be attributed to the formation of adsorption layers and the synergistic effect of the thermal conductivity network.

Three-Dimensional Swirling Flow of Nanofluid with Nanoparticle Aggregation Kinematics Using Modified Krieger–Dougherty and Maxwell–Bruggeman Models: A Finite Element Solution

The current study explores a three-dimensional swirling flow of titania–ethylene glycol-based nanofluid over a stretchable cylinder with torsional motion. The heat transfer process is explored subject to heat source/sink. Here, titania–ethylene glycol–water-based nanofluid is used. The Maxwell–Bruggeman models for thermal conductivity and modified Krieger–Dougherty models for viscosity are employed to scrutinize the impact of nanoparticle aggregation. A mathematical model based on partial differential equations (PDEs) is developed to solve the flow problem. Following that, a similarity transformation is performed to reduce the equations to ordinary differential equations (ODEs), which are then solved using the finite element method. It has been proven that nanoparticle aggregation significantly increases the temperature field. The results reveal that the rise in Reynolds number improves the heat transport rate, whereas an increase in the heat source/sink parameter value declines the heat transport rate. Swirling flows are commonly found in many industrial processes such as combustion, mixing, and fluidized bed reactors. Studying the behavior of nanofluids in these flows can lead to the development of more efficient and effective industrial processes.

A molecular dynamics study of thermal conductivity and viscosity in colloidal suspensions: From well-dispersed nanoparticles to nanoparticle aggregates

This study investigates the microscopic transport behavior of nanofluids addressing some debatable points including the anomalous thermal conductivity (κ), against the predictions of classical effective medium theories. International Nanofluid Property Benchmark Exercise (INPBE) [J. Buongiorno et al., J. Appl. Phys. 106 (2009) 094312] has shown that no such anomaly found in well-dispersed nanofluids after conducting experiments for range of different types of nanofluids. However, a number of molecular dynamics based studies reported otherwise making inconsistent conclusion with INPBE. In this work, it is argued that the over predicted κ values reported in previous computational studies can be attributed to the ill-defined partial enthalpy formulation of the Green-Kubo method for multicomponent systems. Present study begins by addressing this issue via non-equilibrium molecular dynamics and shows that the results are in agreement with the conclusions of INPBE. Further, it is shown that the contribution of potential micro-mechanisms such as micro-convection due to Brownian motion, and the solid-like liquid layering are either absent or suppressed by the interface thermal resistance. The observed decreasing trend of viscosity enhancement to thermal conductivity enhancement ratio (Cη/Cκ) with increasing particle size indicates the improved heat transfer performance in nanofluids with larger nanoparticles. The effect of nanoparticle aggregation, the proposed originative mechanism of anomalous κ, is evaluated arranging nanoparticles as chain-like structures. A 67% improvement in κ is achieved with negligible viscosity variation. This rapidly reduces Cη/Cκ indicating better heat transfer performance with the presence of conductive paths due to the aggregation or in general extended nanostructures.

Viscosity of Fe2O3-water nanofluids by molecular dynamics simulations: Effects of nanoparticle content, temperature and size

In this study, Molecular Dynamics (MD) Simulations are used to calculate the viscosity of Fe2O3-water nanofluid within the Green-Kubo framework considering the influence of nanoparticle volume fraction (2.05, 4.08, 6.08 vol%), nanofluid temperature (T = 5, 25, 45 and 65 °C), and size (d = 1, 1.24, and 1.44 nm). First, by screening some existing water models, SPC/E model is found to be the winning candidate for viscosity calculation under the temperature range. Second, the simulation method and parameters for Fe2O3-Water nanofluid interactions are developed and verified against experimental studies. Fe-O (RDF) of Fe2O3 nanoparticle first peak occurs at r = 1.879 Å with the maximum error of 7.4% in comparison to experimental and density functional theory (DFT) reported values. Simulation results show that the viscosity of Fe2O3-water nanofluid is significantly larger compared to that of the water base fluid (>57%). It is also demonstrated that the viscosity of the nanofluid increases with the particle volume fraction and decreases with temperature and size of nanoparticles with local sensitivities of about 0.69, −0.65, and −0.37, respectively. A second order polynomial regression analysis is performed on various volume fractions to express the relationship between the volume fraction and the viscosity. Our results are in agreement with existing experimental results. It was found that the presence of nanoparticles created a structured water layer near the nanoparticle surface, and that the interactions between water molecules and iron oxide nanoparticles were prominent in the Fe_Ow (iron-oxygen of water) pair interactions. Parameters such as SASA (Solvent Accessible Surface Area), surface to volume ratio, moment of inertia around principal axes, radius of gyration, and RDF are used to provide insights into the behavior of Fe2O3-water nanofluids and the underlying mechanisms. To the authors’ best knowledge, this is the first MD simulation of Fe2O3 nanofluids conducted to date.

Simulation of magneto mixed convective flow and thermal behavior of hybrid nanofluid in a partially heated wavy cavity

This study is an attempt to address numerically the thermal performance of magneto mixed convection in a wavy cavity filled with Cu-Al2O3(50%–50%) hybrid nanoparticles suspended in water under the influence of magnetic field dependent viscosity. A focus is made on the nonuniform partial heating from the left. The role of geometric parameters on the thermal performance is scrutinized thoroughly by changing surface waviness of the right wall, heating location and the direction of motion of the top and bottom walls. Based on these lid motion, the analysis is conducted by considering four geometrical set up. The transformed governing Navier–Stokes equations in dimensionless form are written in stream function-vorticity and energy transport equations. These equations are solved by using an inhouse computing code written in the compact finite difference approach. This study encompasses the effects of different physical pertinent parameters such as Richardson number, Hartmann number, magnetic orientation, solid concentrations, magnetic number. Simulations show the significant enhancement of thermal performance with the increase of magnetic orientation, undulation of the waviness and solid concentration of nanoparticles while it decreases with the increase in magnetic intensity. It is also seen that Case-I (single wall motion) and Case-III (parallel wall motion) can be an optimal configuration to get the strongest heat transfer inside the partially heated wavy enclosure.

Free Electrothermo-Convective Instability in a Dielectric Oldroydian Nanofluid Layer in a Porous Medium

For the last few years, thermal instability of non-Newtonian nanofluids becomes a prominent field of research because it has various applications in automotive industries, energy-saving, nuclear reactors, transportation, electronics etc. and suspensions of nanoparticles are being developed in medical applications including cancer therapy. In this paper, a free electrothermo-convective instability in a dielectric nanofluid layer in a porous medium is studied. An Oldroyd’s constitutive equation is used to describe the behaviour of nanofluid and for porous medium, the Darcy model is employed. The equation of conservation of momentum of fluid is stimulated due to the presence of an AC electric field, stress-relaxation parameter and strain-retardation parameter. The stability of the system is discussed in stationary and oscillatory convections for free–free boundaries. For the case stationary convection, it is found that the Oldroydian Nanofluid behaves like an ordinary nanofluid as the stationary Rayleigh number is independent of the stress-relaxation parameter, the strain-retardation parameter and Vadasz number. The effect of stress-relaxation-time parameter, strain-retardation-time parameter, Vadasz number, nanoparticles Rayleigh number, modified diffusivity ratio, medium porosity, Lewis number and electric Rayleigh number examined numerically and graphs have been plotted to analyse the stability of the system. It is observed that the electrical Rayleigh number has destabilizing influence whereas nanoparticles Rayleigh number, porosity and modified diffusivity ratio have stabilizing effect on the system. The oscillatory convection is possible for the values of the stress-relaxation parameter less than the strain-retardation parameter for both top-heavy/bottom-heavy distributions of nanoparticles.

Synthesis, stability, and heat transfer behavior of water and graphene nanoplatelet-based nanofluid for cool thermal storage applications

This study aims to synthesize stable nano-enhanced phase change materials (NEPCM) using deionized (DI) water and graphene nanoplatelets (GNPs) with the aid of three different surfactants (CTAB, SDBS, and GA). The study also investigates the dynamic behavior of the NEPCM during solidification and melting in a spherical encapsulation. GA-GNP dispersion showed prolonged stability based on zeta potential distribution (ZP) and UV–vis absorbance after 60 days of preparation. The effect of GNP concentration (0.25, 0.50, 0.75, and 1.00 wt%) on the heat transfer properties of the NEPCM was investigated using differential scanning calorimetry (DSC), temperature-time (T-t) profiles, and TC measurements. The maximum energy storage density decreased by 8.56 % and 15.3 % for 1.00 wt% GNPs added to DI-water during melting and crystallization, respectively, at a heating rate of 5 K/min. The thermal conductivity (TC) increased by 59.1 % and 10.8 % in the solid and fluid circumstances, correspondingly. Transient temperature results showed that GA significantly reduced super cooling (SC) by 47.6 % and eliminated it completely at a concentration of 1.00 wt% GNP-NEPCM. The maximum reduction in solidification rate was 26.4 % with 1.00 wt% GNP-NEPCM at a −7 °C constant heat transfer fluid (HTF) temperature. The melting duration was reduced by 33 % by adding 0.50 wt% GNPs, while the melting duration was prolonged at a concentration of 1.00 wt% due to the viscosity augmentation of molten layers. In conclusion, the proposed stable NEPCM formulation has great potential for use as an energy-efficient storage medium in the CTES system.

A mathematical study on thermal performance of aluminum and titanium alloys based hybrid nanofluid using a multiparametric fractional operator

The principal aim of this article is to establish a new fractional model for an all-inclusive analysis of heat transfer and flow dynamics of hybrid nanofluids. For the case study, a hybrid nanofluid composed of kerosene oil and aluminum and titanium alloy nanoparticles is investigated. This work also examines the role of shape factors for blade, lamina, hexahedron, cylinder, and column-like shapes, in addition to evaluating the synergistic properties of preceding particles. Natural convection, generalized thermal slip condition, and ramped velocity function are fundamental factors behind flow instigation. Initially, the mathematical relation for the thermal flux is generalized for the development of a fractional model, and to serve this purpose, Fourier law is exposed to the Prabhakar operator. The partial coupling of heat and velocity equations further leads to the incorporation of generalized thermal flux into the flow equation, which transforms the classical governing system into a fractional one. The acquirement of exact solutions for the formulated fractional system involves two major steps: the inclusion of adequate dimensionless parameters, followed by the application of the Laplace transform. Various graphical illustrations are supplied using these solutions to interpret variations occurring in thermal and flow behaviors of the under-investigation hybrid nanofluid due to several associated parameters. Moreover, the influences of relevant contributing factors such as volume concentration, fractional parameters, and shape constants on shear stress and thermal efficacy are elucidated by tabulating the numerical outcomes. The results indicate that the thermal efficiency of kerosene oil can be enhanced up to 26.5% by hybridizing it with uniform fractions of aluminum and titanium alloys. The velocity of flow reduces as the collective volume concentration of considered alloys increases. It is observed that lamina-shaped nanoparticles are the most significant in terms of improving thermal characteristics. The temperature function is attenuated as a result of positive alterations to fractional parameters. Furthermore, the increase in buoyancy force strength causes the flow to accelerate significantly.

Experimental study of the rheological behavior of TiO2-Al2O3/mineral oil hybrid nanofluids

The characterization of the rheological properties of hybrid nanofluids plays an important role in determining their effectiveness as thermofluids for heat transfer applications. The present study experimentally determines how the particle concentration, nanoparticle composition, ratio of the hybrid nanoparticle mixture, and temperature affect the overall viscosity and the rheological characteristics of Al2O3-TiO2/MO hybrid nanofluids. Nanoparticles used for the experimentation are Al2O3 (5 nm) and TiO2 (5 nm) with paraffin oil (white, CAS No: 8020-83-5) as the base fluid. Nanofluids containing single and mixture of nanoparticles at 0.2–1.5 % volumetric concentrations are prepared using two-step method, and viscosity is measured using a Brookfield Dv2T rotational viscometer with a cone (CPA-40Z) and plate apparatus. Flow behavior indices for the Al2O3-TiO2/MO hybrid nanofluids tested tended to approach a value of one, which indicated a more Newtonian flow behavior when compared to the conventional Al2O3/MO and TiO2/MO nanofluids. While Brownian motion best describes the microstructural changes in the nanofluid that result in the observed non-Newtonian behavior of conventional nanofluids, it appears that the competing nonhydrodynamic forces from the constituent nanoparticles in hybrid nanofluids negate these effects and result in a more Newtonian, rheological behavior. It was also observed that the ratio of the hybrid mixture of constituent nanoparticle components did affect the rheological characteristics in an intuitive way, resulting in two observed relationships: 1) the hybrid mixture composition of 50% Al2O3/50% TiO2 tended to present a peak value relative to the other hybrid compositions and was exhibited primarily at particle volume fractions of 0.5% and 1.0% and at all temperatures, and 2) there was a general decrease in flow behavior index with increasing ratio of TiO2 in the Al2O3/TiO2 hybrid mixture and was exhibited primarily at particle volume fractions of 0.2% and 1.5% and at all temperatures less than 60 °C.

Heat transfer improvement of hybrid nanofluid with use of twisted tapes within a heat exchanger

Influence of utilizing porous zone on behavior of hybrid nanofluid through a duct was scrutinized by applying of FVM approach. Darcy model in three dimensional steady flow forms has been applied and related terms have been incorporated in momentum equations. Mixture of nanoparticles (MWCNT + Al2O3) and H2O creates hybrid nanofluids which were utilized as testing fluid. To improve the absorbing heat, helical tape was incorporated. The test section of duct is middle 40 cm of the duct where the porous zone and helical tapes were mounted. Validation base of previous published work and studying the grid leads to the most accurate outputs with lowest computing price. Impacts of Da, ϕ and Re on treatment of working fluid have been examined. Selecting greater amounts of ϕ and Re makes Nu intensify by 7.27% and 35.58%. As permeability of zone increases, fluid can moves faster along the axial direction and Nu declines about 6.78%.

Convection behaviour of mono and hybrid nanofluids containing B4C and TiB2 nanoparticles

Hybrid nanofluids are intended to improve heat transfer due to possible synergistic effects between nanoparticles. Detailed studies comparing convection within hybrid nanofluids and equivalent mono nanofluids are still required to understand these effects, especially under turbulent flow. Boron carbide and titanium diboride are ceramics with interesting thermal properties that have not been commonly used in nanofluid design. A propylene glycol/water mixture at 20/80 wt% protects against freezing down to −7 °C and is frequently used as working fluid in cooling applications. This experimental study evaluates the behaviour of the heat transfer coefficient, pressure drop and performance index of B4C and TiB2 mono nanofluids and TiB2/B4C hybrid nanofluid based on a propylene glycol/water mixture at 20/80 wt% through a double pipe heat exchanger. Three average temperatures in the range 25–45 °C and different flow rates in the range 300–700 L/h (turbulent regime) are studied. Dimensionless analyses are performed using Nusselt, Prandtl, and Reynolds numbers and Darcy friction factor. The TiB2/B4C hybrid nanofluid shows the highest heat transfer coefficient improvements, up to 13%, and the highest performance index ratio, up to 1.03. This could be explained by potential nanoparticle synergistic effects that are especially evidenced through the dynamic viscosity.