An experimental study on rheological behavior of a nanofluid containing oxide nanoparticle and proposing a new correlation

In this paper, the nanofluid dynamic viscosity composed of CeO 2-Ethylene Glycol is examined within 25-50 C with 5 C intervals and at six volume fractions (0.05, 0.1, 0.2, 0.4, 0.8 and 1.2%) experimentally. The nanofluid was exposed to ultrasound
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  An experimental study on rheological behavior of a nano fl uid containingoxide nanoparticle and proposing a new correlation Amir Hussein Saeedi a , Mohammad Akbari b , * , Davood Toghraie a a  Department of Mechanical Engineering, Khomeinishahr Branch, Islamic Azad University, Khomeinishahr, Iran  b  Department of Mechanical Engineering, Najafabad Branch, Islamic Azad University, Najafabad, Iran  A R T I C L E I N F O  Keywords: Experimental measurementViscosityNano fl uidVolume fractionTemperatureEthylene glycol A B S T R A C T In this paper, the nano fl uid dynamic viscosity composed of CeO 2 - Ethylene Glycol is examined within 25 – 50  Cwith 5  C intervals and at six volume fractions (0.05, 0.1, 0.2, 0.4, 0.8 and 1.2%) experimentally. The nano fl uidwas exposed to ultrasound waves for various durations to study the effect of this parameter on dynamic viscosityof the  fl uid. We found that at a constant temperature, nano fl uid viscosity increases with increases in the volumefraction of the nanoparticles. Also, at a given volume fraction, nano fl uid viscosity decreases when temperature isincreased. Maximum increase in nano fl uid viscosity compared to the base  fl uid viscosity occurs at 25  C andvolume fraction of 1.2%. It can be inferred that the obtained mathematical relationship is a suitable predictingmodel for estimating dynamic viscosity of CeO 2 - Ethylene Glycol (EG) at different volume fractions and tem-peratures and its results are consistent to laboratory results in the set volume fraction and temperature ranges. 1. Introduction Heat transfer plays major role in many  fi elds of industry; moreover,high-performance cooling is widely needed in industrial technologies.Nano fl uids are embryonic  fl uids that exhibit thermal properties superiorthan that of the conventional  fl uid. Rheological behavior of nano fl uids,besides thermophysical properties, is an important issue. Although addi-tion of nanoparticles to the base- fl uids alter thermal properties, and willalsoaffecttheviscosityofnano fl uids.Theviscosityisverycriticalfactorinindustry from economical point of view. This issue is directly associatedwith pumping power to share the nano fl uid inside the cooling system.Since there was less focus on viscosity of nano fl uids other than thermalconductivity, there was a need to consider viscosity to have a commercialview for these cooling media [1 – 3]. Moreover, many mechanism andmodels were suggested by different researches for viscosity of nano fl uids.Namburu et al. [4] measured the viscosity of copper oxide nano-particles dispersed in ethylene glycol and water mixture.Nguyen et al. [5] investigated the effect due to temperature andparticle volume concentration on the dynamic viscosity for the water- – Al 2 O 3  nano fl uid. They showed that the Einstein's formula and someother ones srcinated from the classical linear  fl uid theory seem to belimited to nano fl uids with low particle fractions.Garg et al. [6] investigated the thermal conductivity and viscosity of copper nanoparticles in Ethylene glycol. They concluded that the vis-cosity increase was almost four times of that predicted by the Einsteinlaw of viscosity.Duangthongsuk and Wongwises [7] measured temperature-dependent thermal conductivity and viscosity of TiO 2 -water nano fl uids.They proposed new thermophysical correlations for predicting thethermal conductivity and viscosity of nano fl uids.Masoumi et al. [8] obtained a new model for calculating the effectiveviscosity of nano fl uids. Their predicted results are compared with otherexperimental results for different nano fl uids.Yu et al. [9] investigated the thermal conductivity and viscosity of ethylene glycol based ZnO nano fl uid. The rheological behaviors of thenano fl uidsshowthatZnO-EGnano fl uidswithlowvolumeconcentrationsdemonstrate Newtonian behaviors,Lee et al. [10] investigated viscosity and thermal conductivity of SiCnano fl uids for heat transfer applications. They concluded that the vis-cosity of SiC/DIW nano fl uids increases with an increase of particle vol-ume fraction.Yang et al. [11] investigated the thermal conductivity and shearviscosity of viscoelastic- fl uid-based nano fl uids. The results show thatviscosityof themeasurednano fl uidsisslightlylargerthanits viscoelasticbase  fl uid and it increases with the increase of nanoparticles volumefraction and decreases with the increase of temperature. * Corresponding author.  E-mail address: (M. Akbari). Contents lists available at ScienceDirect Physica E: Low-dimensional Systems and Nanostructures journal homepage: 8 October 2017; Received in revised form 2 February 2018; Accepted 16 February 2018Available online 17 February 20181386-9477/ ©  2018 Elsevier B.V. All rights reserved.Physica E: Low-dimensional Systems and Nanostructures 99 (2018) 285 – 293  Jamshidi et al. [12] investigated the viscosity of nano fl uids. Theydiscussed about the effect of cooling and heating process on the viscosityof nano fl uid.Sundar et al. [13] measured thermal conductivity and viscosity of sta-bilizedethyleneglycolandwatermixture-Al 2 O 3 nano fl uidsforheattransferapplications. They found that nano fl uid prepared in higher viscosity base fl uid exhibits more enhancement compared to low viscosity base fl uid.Beheshti et al. [14] investigated the effect of oxidized multi walledcarbon nanotubes on transformer oil thermophysical properties. Theviscosities of pure oil and nano fl uids as a function of temperature werealso measured.Hemmat Esfe et al. [15] studied the effect of diameter on thermalconductivity and dynamic viscosity of Fe/water nano fl uids. Theyconcluded that the nano fl uid viscosity ratio increases with an increase inparticle concentration and nanoparticle's diameter.Shanbedi et al. [16] investigated stability and thermophysical prop-erties of carbon nanotubes suspension in the presence of different sur-factants. They found that viscosity and shear stress decreased as theconcentration of the surfactant increased.HemmatEsfeetal.[17]measuredThermalconductivityandviscosityof Mg (OH) 2 -Ethylene glycol nano fl uids experimentally. They measuredthermal conductivity and viscosity of nano fl uids with volume fractionsby 2% in the temperature range of 25 – 55  C.Hemmat Esfe et al. [18] studied the viscosity of alumina-engine oiland investigated the effects of temperature and nanoparticles concen-tration. Their results indicated that the maximum viscosity enhancementof nano fl uid was 132% compared with that of base  fl uid.Abbasi et al. [19] investigated the rheological behavior and viscosityof decorated multi-walled carbon nanotubes with TiO 2  nanoparticles/-water nano fl uids. They found that viscosity decreases by increasing theattached TiO 2  nanoparticles.Ahammed et al. [20] investigated the effect of volume concentrationand temperature on viscosity of Graphene – water nano fl uid. Theyconcluded that the viscosity showed stronger dependency on volumeconcentration than temperature.Akbari et al. [21] studied the rheological behavior of ethylene glycolbased nano fl uid and proposed a new correlation as a function of silicaconcentration and temperature.Zy ł a [22] predicted Viscosity and thermal conductivity of MgO – EGnano fl uids. They showed that with increasing volume fraction of nano-particles viscosity of the material increases.In the present study, the nano fl uid dynamic viscosity composed of CeO 2 - Ethylene Glycol is examined experimentally. To the author'sknowledge, there is no comprehensive and thorough investigation topredict the dynamic viscosity of the supposed nano fl uid. 2. Preparation of nano fl uid  2.1. Properties The following materials were used in preparing the tested nano fl uid:1. Ethylene glycol produced by the German Company Merck used as thebase  fl uid (Table 1)2. Cerium dioxide nanoparticles to prepare the nano fl uid (characteris-tics presented in Table 2)  2.2. Description of the experiment  The nano fl uid used in the experiment was prepared in two stages.Fig. 1 presents the TEM image of CeO 2  nanoparticles. To prepare thestable nano fl uid, the solution was fi rst mixed using a magnetic stirrer for2h, then the agglomerated particles were broken up using 400W ultra-sonic power at the frequency of 24kHz for 6h, and the nanoparticleswere completely dissolved in the base  fl uid. X-ray diffraction (XRD) wasused to test the dry samples of cerium dioxide nanoparticles and ensuretheir structure and size. The size and structure of the nanoparticles wereprovedusingtheXRDdiagramandtheSchererequation.Fig.2showstheXRD diagram of the nanoparticles. Table 1 EG properties. Value ParameterCombustion temperature 410 (  C)Saturation density (air) 0.15 (gr/m 3 )Melting point   13 (  C)Molar mass 62.07 (gr/mol)Density 1.11 (gr/m 3 )pH level 6 – 7.5Boiling point 197.6 (  C)Vapor pressure 0.053 (kPa) Table 2 Properties of CeO 2  nanoparticle. PropertiesMolecular formula CeO 2 Shape SphericalSize 10-30nmPurity 99.97%Appearance pale yellow solidDensity 7.132g/cm 3 Surface area to volume ratio 30-50m 2 /g Fig. 1.  TEM image of CeO 2  nanoparticles. Fig. 2.  XRD image of CeO 2  nanoparticle.  A.H. Saeedi et al. Physica E: Low-dimensional Systems and Nanostructures 99 (2018) 285 –  293 286  Each experiment was repeated three times to achieve greater accu-racy in studying the rheological behavior of the nano fl uid. The experi-mentwascarriedoutatsixtemperaturerangesfrom25to50  Cwith5  Cintervals and at six volume fraction (0.05, 0.1, 0.2, 0.4, 0.8 and 1.2%).After collecting the experimentaldata, the average of the three replicatesof each experiment was recorded as the viscosity number. The speed of theBrook fi eldviscometerstartedat50andendedat500rpmtostudytheNewtonian behavior of the nano fl uid. The accuracy and repeatability of the viscometer were  5% and  2%, respectively. 3. Results and discussion 3.1. Studying the rheological behavior of the nano  fl uid  The rheological behavior of the base  fl uid is evaluated  fi rst bymeasuring its viscosity at different speeds of the viscometer (Table 3) atambient temperature.If viscosity is constant at different shear rates, then the  fl uid isNewtonian.In otherwords,if there isa linear relationshipbetweenshearstress and shear rate, the  fl uid of interest is a Newtonian one. Fig. 3clari fi es this point. As shown in Fig. 3, the base  fl uid exhibits Newtonianbehavior.The rheological behavior of the nano fl uid of interest must then bestudied.Figs.4 – 7suggestthatthereisalinearrelationshipbetweenshearstress and shear rate at different temperatures and volume fraction of 1.2%. As seen in these  fi gures, the nano fl uid had Newtonian behavior atthis volume fraction and as a result, the nano fl uid behavior is Newtonianin all smaller volume fractions. 3.2. Effects of volume fraction on nano  fl uid viscosity  Fig. 8 shows the effect of temperature on dynamic viscosity indifferent volume fractions. As shown in Fig. 8, nano fl uid viscosity in-creases with increases in the volume fraction of the nanoparticles at aconstant temperature, which is as expected because other researchers innumerousexperimentsreportedthesamething.Fig.8indicatesthatbase fl uid viscosity was 0.144 Poise at 25  C, but the nano fl uid viscosityincreasedto0.173Poisewhennanoparticleswereaddedandreachedthevolume fraction of 0.2 and increased by 0.195 and 0.295 Poise at thevolume fractionsof 0.4 and 1.2%,respectively. At the mentioned volumefractions, nano fl uid viscosity, respectively, increased by 20, 35, and104% compared to the base  fl uid.At a constant temperature, nano fl uid viscosity increases with in-creasesinthevolumefractionofthenanoparticles.Thefollowingreasons Table 3 Viscosity of base- fl uid at different speeds of the viscometer at ambienttemperature. Temp (  C) Shear Rate Viscosity Shear Stress(dyne/cm 2 )rpm 1/s cP Poise25 20 24.48 14.4 0.144 3.5251230 36.72 14.2 0.142 5.2876850 61.2 14.3 0.143 8.812860 73.44 14.1 0.141 10.57536100 122.4 14.2 0.142 17.6256 Fig. 3.  Relationship of shear rate with shear stress of base  fl uid at ambienttemperature. Fig. 4.  Relationship of shear rate with shear stress of nano fl uid in volumefraction of 1.2% at T ¼ 25  C. Fig. 5.  Relationship of shear rate with shear stress of nano fl uid in volumefraction of 1.2% at T ¼ 30  C.  A.H. Saeedi et al. Physica E: Low-dimensional Systems and Nanostructures 99 (2018) 285 –  293 287  are expressed for this phenomenon:1  Brownian motion:  This random motion of nanoparticles in the base fl uid is one of the factors in fl uencing viscosity. It is generated due tothe constant collisions between nanoparticles and molecules of thebase  fl uid. We can assume that nanoparticles are larger than themolecules of the base  fl uid and nanoparticles move with the meankinetic energy equivalent to that of molecules of the base fl uid. Whenthe volume fraction increases; that is, when the presence of nano-particles in the base  fl uid increases, and since viscosity is the resis-tance of a  fl uid to  fl ow, we basically increase resistance to  fl ow whenwe addnanoparticlesto thebase fl uid.This meansthatmoreparticlescollide with each other due to the random motion of thenanoparticles.2 Whenweaddnanoparticlestothebase fl uid,theyaredispersedinthebase  fl uid and form symmetrical and larger nanoparticles clustersunderthein fl uenceofvanderWaalsforcesbetweenthenanoparticlesand the base  fl uid. These nanoclusters prevent the movement of ethylene glycol molecules on each other and, hence, viscosityincreases.3 As the surface to volume ratio is extremely high in nanostructures,properties such as density change due to nanonization and buoyancyforce, weight lose their importance because of the extremely smallsize and mass, and intermolecular and surface forces becomeimportant.Ifitisassumedfromthisperspectivethatthenano fl uidisatwo-phase  fl uid consisting of a liquid and a solid (of course, if it isassumed), in that case nanoparticles may slide against each other andagainst the base  fl uid due to the forces that are applied on them. Thiswill increase the volume fraction and resistance to  fl ow will becomegreater and, hence, viscosity will increase.4 Viscosity is a resistive property that generates shear stress because of the force that is appliedon the nano fl uid. In fact, viscosity is the mainfactor of transmitting momentum between nano fl uid layers and ap-pears when a motion is generated between its layers. This motionresultsfromintermolecularforces.Thepresenceofnanomaterialsina fl uid increases these forces and, hence, viscosity will increase. In amoving  fl uid, layers move at different speeds; that is, the  fl uid has avelocitypro fi le.Viscosityresultsfromshearstressbetweenlayersand fl uid shear stresses inside the nanoparticles will increase with in-creasesinvolumefractionofnanoparticlesinthebase fl uidleadingtoincreases in nano fl uid viscosity. If the nanomaterial increases in agiven volume of the base  fl uid (that is, if the volume fraction in-creases), shear stress will gradually increase. Therefore, increases inthe volume fraction of nanotubes and nanoparticles in the base  fl uidwill increase viscosity of the hybrid nano fl uid. 3.3. Effects of temperature on nano  fl uid viscosity  Fig. 9 shows the effects of temperature on nano fl uid viscosity atdifferent volume fractions.As shown in this  fi gure, nano fl uid viscosities are 0.198, 0.140, and0.118 Poise at volume fractions of 0.8% at 30, 40, and 50  C, respec-tively. Therefore, at a given volume fraction, nano fl uid viscosity de-creases when temperature is increased. The reasons are as follows:Viscosity results from adhesive forces between molecules of liquids and Fig. 7.  Relationship of shear rate with shear stress of nano fl uid in volumefraction of 1.2% at T ¼ 40  C. Fig. 8.  Effect of temperature on dynamic viscosity in different volume fractions. Fig. 6.  Relationship of shear rate with shear stress of nano fl uid in volumefraction of 1.2% at T ¼ 35  C.  A.H. Saeedi et al. Physica E: Low-dimensional Systems and Nanostructures 99 (2018) 285 –  293 288  molecular collisions in gases. This property varies with changes in tem-perature. When temperature increases, the viscosity of liquids decreases,butthatofgasesincreases.Inliquids,moleculesarein fl uencedbygreaterenergies resulting from higher temperatures and can overcome theintermolecular adhesive forces and, hence, molecules with energy canmovemoreeasily.Ingases,intermolecularforcescanbeignored,andgasmolecules move randomly and at greater speeds at higher temperatures.Consequently, the greater number of collisions between gas moleculesper unit volume and per unit time creates greater resistance to  fl ow.Reduced intermolecular forces caused by increased temperature de-creases resistance to  fl ow and, therefore, viscosity of Newtonian nano- fl uids decreases with increases in temperature. Also, the effects of Brownian motion on nano fl uid viscosity with increases in temperaturecan also be explained. When temperature increases, there will be freemolecular motion of nanoparticles and base fl uid and fewer nanoparticlemolecules will collide with each other. Finally, intermolecular spacesbetween nanoparticles increase at higher temperatures and, hence,resistance to  fl ow declines leading to reduced viscosity.Figs. 10 and 11 show changes in relative viscosity caused by changesin temperature and volume fractions. The  fi gures suggest that maximumincreaseinnano fl uidviscositycomparedtothebase fl uidviscosityoccursat 25  C and volume fraction of 1.2%. 3.4. Comparison of data obtained from the experiment with analyticrelationships introduced by researchers Researchers have presented various analytic relationships for calcu-lating nano fl uid viscositythatwill bediscussedhere.Relationships1 and2 were used by Bachelor [23] and Wong [24], respectively, to predict viscosities of various nano fl uids. Fig. 9.  Effect of volume fraction on dynamic viscosity at different temperatures. Fig. 10.  Relative viscosity at different volume fractions and temperatures. Fig. 11.  Relative viscosity in different volume fractions and temperatures. Fig. 12.  Comparison of experimental data with Batchelor model [23] andWang's model [24].  A.H. Saeedi et al. Physica E: Low-dimensional Systems and Nanostructures 99 (2018) 285 –  293 289
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