Rheological Properties Of Nanofluids Research Articles

Review on Nanofluids: Preparation, Properties, Stability, and Thermal Performance Augmentation in Heat Transfer Applications.

Nanoparticles play a crucial role in enhancing the thermal and rheological properties of nanofluids, making them a valuable option for increasing the efficiency of heat exchangers. This research explores how nanoparticle characteristics, such as concentration, size, and shape, impact the properties of nanofluids. Nanofluids' thermophysical properties and flow characteristics are essential in determining heat transfer efficiency and pressure loss. Nanoparticles with high thermal conductivity, such as metallic oxides like MgO, TiO2, and ZnO, can significantly improve the heat transfer efficiency by around 30% compared to the base fluid. The stability of nanofluids plays a crucial role in their usability. Various methods, such as adding surfactants, using ultrasonic mixing, and controlling pH, have been employed to enhance the stability of nanofluids. The desired thermophysical properties can be achieved by utilizing nanofluids to enhance the system's heat transfer efficiency. Modifying the size and shape of nanoparticles also considerably improves thermal conductivity, affecting nanofluid viscosity and density. Equations for determining heat transfer rate and pressure drop in a double-pipe heat exchanger are discussed in this review, emphasizing the significance of nanofluid thermal conductivity in influencing heat transfer efficiency and nanofluid viscosity in impacting pressure loss. This Review identifies a trend indicating that increasing nanoparticle volume concentration can enhance heat transfer efficiency to a certain extent. However, surpassing the optimal concentration can reduce Brownian motions due to higher viscosity and density. This Review offers a viable solution for enhancing the thermal performance of heat transfer equipment and serves as a fundamental resource for applying nanofluids in heat transfer applications.

Thermal Transport and Rheological Properties of Hybrid Nanofluids Based on Vegetable Lubricants.

Nanofluids based on vegetal oil with different wt.% of carbon nanotubes (CNT), hexagonal boron nitride (h-BN), and its hybrid (h-BN@CNT) were produced to investigate the effects of these nano-additives on the thermal conductivity and rheological properties of nanofluids. Stable suspensions of these oil/nanostructures were produced without the use of stabilizing agents. The dispersed nanostructures were investigated by SEM, EDS, XRD, and XPS, while the thermal conductivity and rheological characteristics were studied by a transient hot-wire method and steady-state flow tests, respectively. Increases in thermal conductivity of up to 39% were observed for fluids produced with 0.5 wt.% of the hybrid nanomaterials. As for the rheological properties, it was verified that both the base fluid and the h-BN suspensions exhibited Newtonian behavior, while the presence of CNT modified this tendency. This change in behavior is attributed to the hydrophobic character of both CNT and the base oil, while h-BN nanostructures have lip-lip "bonds", giving it a partial ionic character. However, the combination of these nanostructures was fundamental for the synergistic effect on the increase of thermal conductivity with respect to their counterparts.

Numerical simulation of a thermally enhanced EMHD flow of a heterogeneous micropolar mixture comprising (60%)-ethylene glycol (EG), (40%)-water (W), and copper oxide nanomaterials (CuO)

In the past decades, the thermal and rheological properties of nanofluids have attracted much attention from many investigators due to their numerous applications as promising enhanced working fluids. The present numerical analysis intended to evidence the main hydro-thermal and mass transport appearances featuring the convective flows of an exceptional non-homogeneous micropolar mixture (i.e., 60% of ethylene glycol, 40% of pure water, and copper oxide nanomaterials) over an impermeable horizontal electromagnetic surface (i.e., Riga plate), which is heated convectively in the presence of a particular variable heat source. For this purpose, several admissible physical theories and hypotheses are adopted herein to derive the foremost conservation equations based on the renovated Buongiorno's formulation and some more realistic boundary conditions. Further, the leading partial differential equations (PDEs) are transformed into a system of ordinary differential equations (ODEs), which are tacked thereafter numerically using an efficient GDQNRM procedure. After performing multiple validations with the recent literature results, the aspects of the studied EMHD convective micropolar nanofluid flow are spotted accordingly and then discussed comprehensively via multiple figures and tables. As prominent results, it is found that the micropolarity and electrically conducting trends of the nanofluidic medium play an important role in the hastening of the nanofluid motion. Also, it is explored that the thermally enhancing influence of the thermophoresis diffusive mechanism can be reinforced more by the existence of an internal heat source along with an appropriate convective heating process.

Study on Rheological Properties of Nanofluids

Based on the previous research on the rheological properties of nanofluids by many scholars at home and abroad, to solve the problem that the viscosity of conventional polymer water control agents is large and cannot meet the demand for increasing production capacity in the process of tight gas reservoir exploitation, this paper takes self-made nanofluids as the research object, tests the rheological properties of self-made nanofluids by rheological experiment, and systematically studies the effects of concentration, temperature and shear action on the viscosity of nanofluids, and the dynamic viscoelasticity and thixotropy of nanofluids were discussed. The results show that the rheological type of nanofluid belongs to power-law fluid, but it is related to the shear rate. The viscosity of nanofluids increases with the increase of concentration; when the temperature increases, the viscosity of nanofluids decreases and the fluidity increases; under the shear action, the viscosity of nanofluid changes very little and has good shear resistance; the dynamic viscoelastic test shows that the storage modulus G´ of the nanofluid is larger than the loss modulus G”, showing elastic characteristics; the thixotropy test shows that when the shear rate is accelerated, the viscosity decreases with time, and when the shear rate is slowed down, the viscosity recovers rapidly with time, which has good thixotropy. The research results provide an important theoretical basis for further research on the application of nanomaterials in tight oil and gas reservoirs.

Effect of epoxidation and nanoparticle addition on the rheological and tribological properties of canola oil

The paper investigates the lubricating properties of epoxidised canola oil. The epoxidation is carried out to decrease the unsaturated bonds present in canola oil. Further, metal dichalcogenide nanoparticles (molybdenum disulphide and tungsten disulphide) are mixed in modified canola oil and their effect on rheological and tribological properties is evaluated. The tribological investigation is carried out on a pin-on-disc tribometer with aluminium alloy and steel as tribopairs. The rheological properties of nanofluids have been studied. It is observed that the modification of the canola oil improves the tribological properties of virgin canola oil. The addition of nanoparticles into the modified canola increases the viscosity of the oil with a 1 wt% concentration of nanoparticles. Further, enhancement in the tribological properties is observed with the addition of nanoparticles. A maximum of 54.6% and 30% decrease in coefficient of friction is observed with the use of tungsten disulphide and molybdenum disulphide nanoparticles, respectively.

An experimental/numerical hydrothermal-Second law analysis of a finned/tubular heat exchanger using Bhatnagar–Gross–Krook Lattice Boltzmann (BGKLBM) and rheological-thermal behavior of Fe2O3-water

Purpose The purpose of this study is analysis of the natural convection and entropy production in a two-dimensional section of the considered heat exchanger. For this purpose, the lattice Boltzmann method which is equipped with Bhatnagar–Gross–Krook model is used. This model proposes a significant accurate prediction for thermal and hydro-dynamical behaviors over free convection phenomenon. The heat exchanger is filled with Fe2O3-water nanofluid. To improve the accuracy of prediction, it is neglected to use the theoretical models for properties of nanofluid. At this end, some experimental observations are conducted, and the required rheological and thermal properties of nanofluid are measured based on laboratory work.. Design/methodology/approach The present work focuses on the influence of different factors on the thermal behaviors and entropy production of a heat exchanger. The heat exchanger is consisted by an inner tube, an outer tube and some fins which are implanted at the surface of inner tube. Findings The effects of various factors like structure of inner fins, nanoparticle concentration and Rayleigh number over the heat transfer rate, local and volumetric entropy production, Bejan number, flow configuration and temperature distributions are provided. Originality/value The originality of this work is using a new-developed numerical method for treating natural convection and experimental measurements for thermal and rheological properties of nanofluid.

Influence of Six Carbon-Based Nanomaterials on the Rheological Properties of Nanofluids.

Nanofluids, dispersions of nanosized solid particles in liquids, have been conceived as thermally-improved heat transfer fluids from their conception. More recently, they have also been considered as alternative working fluids to improve the performance of direct absorption solar thermal collectors, even at low nanoadditive concentrations. Carbon-based nanomaterials have been breaking ground in both applications as nanoadditives during the last decade due to their high thermal conductivities and the huge transformation of optical properties that their addition involves. In any application field, rheological behavior became a central concern because of its implications in the pumping power consumption. In this work, the rheological behavior of four different loaded dispersions (0.25, 0.50, 1.0, and 2.0 wt%) of six carbon-based nanomaterials (carbon black, two different phase content nanodiamonds, two different purity graphite/diamond mixtures, and sulfonic acid-functionalized graphene nanoplatelets) in ethylene glycol:water mixture 50:50 vol% have been analysed. For this purpose, a rotational rheometer with double cone geometry was employed, which included a special cover to avoid mass losses due to evaporation at elevated temperatures. The flow curves of the twenty-four nanofluids and the base fluid were obtained by varying the shear rate between 1 and 1000 s−1 for seven different temperatures in the range from 283.15 to 353.15 K. The shear-thinning behaviors identified, as well as their dependences on carbon-based nanomaterial, concentration, and temperature, were analyzed. In addition, oscillatory tests were performed for samples with the clearest Non-Newtonian response, varying the deformation from 0.1 to 1000% with constant frequency and temperature. The dependence of the behaviors identified on the employed carbon-based nanomaterial was described.

Influence of ultrasonication duration on rheological properties of nanofluid: An experimental study with alumina–water nanofluid

Nanofluid is being considered as a promising fluid for heat transfer and other applications. The performance of nanofluid is depends on its preparation processes, including the ultrasonication period. The objective of this study was to analyze the influence of ultrasonication period on rheological properties of nanofluids. A 0.5vol.% of Al2O3 nanoparticle was suspended in distilled water and ultrasonicated for the periods of 0 to 5h. Before and after dispersion, micrographs of nanoparticles were observed by electron microscopes. Rheological properties as viscosity at different shear rates were measured for different temperatures from 10°С to 50°С. Other flow characteristics as the flow behavior index and consistency index were also studied for the nanofluids prepared by different periods of ultrasonication. Better colloidal dispersion and lower viscosity were observed for the increase of sonication time. Furthermore, with the increase of temperature, viscosity decreased rapidly, but moved towards non-Newtonian fluids. The research concluded that better colloidal dispersion as well as lower viscosity could be achieved with the use of possible higher periods of ultrasonication.

Experimental research on microscale grinding temperature under different nanoparticle jet minimum quantity cooling

ABSTRACTTo solve the limited cooling capacity of drip cooling technique in current clinical grinding orthopedic surgery, this paper carried out a nanoparticle jet minimum quantity cooling grinding experiment by using hydroxyapatite, SiO2, Fe2O3, carbon nanotubes nanofluids. The mass fraction of each nanofluids was 2%, 4%, 6%, 8%, 10%, respectively. Grinding temperature during the grinding process was measured, and results show that the temperature peak of bone micro-grinding isn’t always proportional to the mass fraction of nanofluids. The measured temperature peak shows an inversely proportional relationship with the mass fraction of nanofluids within a certain mass fraction range, but a proportional relationship beyond this mass fraction range. Such a critical mass fraction varies when using different types of nanoparticles. Combined with heat transfer enhancement of nanofluids, the influence law of nanofluids type and concentration on grinding temperature was disclosed from the rheological properties of nanofluids and the micromechanisms of nanoparticles in the grinding zone. The bigger the mass fraction, the more easily it displays rheological properties. As for hydroxyapatite, whose length-diameter ratio is high and for SiO2 and CNTs, whose hardness values are high, they more easily display shear thinning and shear thickening, and the effect of rheological properties on temperature is obvious.

Stability and rheological properties of nanofluids containing ZnO nanoparticles, poly(propylene glycol) and poly(vinyl pyrrolidone)

In this work, polymer based nanofluids have been prepared by dispersing the ZnO nanoparticles in base fluid of poly(propylene glycol), PPG, aqueous solution of PPG, aqueous solution of poly(vinyl pyrrolidone), PVP, and mixture of these two polymers. Stability and particle size distribution of these nanofluids have been studied by result analysis of UV–vis spectroscopy, zeta potential and dynamic light scattering. Viscosity values of ZnO–PPG and ZnO–PPG–H2O nanofluids have been measured at 293.15, 298.15, 308.15 and 318.15K. The Eyring-NRTL and Eyring-mNRF models have successfully been used for correlating the viscosity values of the nanofluids investigated with temperature dependency considered. The performance of Einstein, Brinkman, Lundgren and Batchelor models in the prediction of viscosity values of ZnO–PPG nanofluid has also been tested. Rheological behavior of investigated nanofluids has been investigated over volumetric solid concentrations (φ1=0, 0.5, 4.5%) and shear rates (γ=0.01–1000s−1) at 298.15K. The nanoparticle suspensions generally exhibited a pseudoplastic flow behavior, indicating an existence of particle aggregations in the liquid medium. Bingham plastic and Herschel–Bulkley models were used to evaluate the shear stress–shear rate dependency. The colloid yield stress was determined from these models.

Electrical conductivity, thermal conductivity, and rheological properties of graphene oxide-based nanofluids

Highly stable graphene oxide (GO)-based nanofluids were simply prepared by dispersing graphite oxide with the average crystallite size of 20 nm, in polar base fluids without using any surfactant. Electrical conductivity, thermal conductivity, and rheological properties of the nanofluids were measured at different mass fractions and various temperatures. An enormous enhancement, 25,678 %, in electrical conductivity of distilled water was observed by loading 0.0006 mass fraction of GO at 25 °C. GO–ethylene glycol nanofluids exhibited a non-Newtonian shear-thinning behavior followed by a shear-independent region. This shear-thinning behavior became more pronounced at higher GO concentrations. The maximum ratio of the viscosity of nanofluid to that of the ethylene glycol as a base fluid was 3.4 for the mass fraction of 0.005 of GO at 20 °C under shear rate of 27.5 s−1. Thermal conductivity enhancement of 30 % was obtained for GO–ethylene glycol nanofluid for mass fraction of 0.07. The measurement of the transport properties of this new kind of nanofluid showed that it could provide an ideal fluid for heat transfer and electronic applications.

Investigation of thermal conductivity and rheological properties of nanofluids containing graphene nanoplatelets

In the present study, stable homogeneous graphene nanoplatelet (GNP) nanofluids were prepared without any surfactant by high-power ultrasonic (probe) dispersion of GNPs in distilled water. The concentrations of nanofluids were maintained at 0.025, 0.05, 0.075, and 0.1 wt.% for three different specific surface areas of 300, 500, and 750 m2/g. Transmission electron microscopy image shows that the suspensions are homogeneous and most of the materials have been well dispersed. The stability of nanofluid was investigated using a UV-visible spectrophotometer in a time span of 600 h, and zeta potential after dispersion had been investigated to elucidate its role on dispersion characteristics. The rheological properties of GNP nanofluids approach Newtonian and non-Newtonian behaviors where viscosity decreases linearly with the rise of temperature. The thermal conductivity results show that the dispersed nanoparticles can always enhance the thermal conductivity of the base fluid, and the highest enhancement was obtained to be 27.64% in the concentration of 0.1 wt.% of GNPs with a specific surface area of 750 m2/g. Electrical conductivity of the GNP nanofluids shows a significant enhancement by dispersion of GNPs in distilled water. This novel type of nanofluids shows outstanding potential for replacements as advanced heat transfer fluids in medium temperature applications including solar collectors and heat exchanger systems.

Design and Evaluation of Carbon Nanotube Based Nanofluids for Heat Transfer Applications

ABSTRACTThe present work investigates the fabrication, thermal conductivity (TC) and rheological properties of water based carbon nanotubes (CNTs) nanofluids (NFs) prepared using a two-step method. As-received (AR) CNTs heated and the effect of heat treatment was studied using X-ray diffraction and thermogravimetric analysis. The AR-CNTs and heat-treated CNTs (HT-CNTs) were dispersed with varying concentration of surface modifiers Gum Arabic (GA) and TritonX-100 (TX) respectively. It was found that heat treatment of CNTs effectively improved the TC and influenced rheological properties of NFs. Scanning electron microscopy analysis revealed TX modified NFs showed better dispersion ability compared to GA. Surface modification of the CNTs was confirmed by Fourier Transformation Infrared (FTIR) analysis. Zeta potential measurement showed the stability region for GA modified NFs in the pH range of 5-11, whereas pH was between 9.5-10 for TX NFs. The concentration of surface modifier plays an extensive role on both TC and rheological behavior of NFs. A maximum TC enhancement of 10% with increases in viscosity around 2% for TX based HT-CNTs NFs was measured. Finally comparison of experimental TC results with the predicted values obtained from a model demonstrated inadequacy of the predictive model for CNT NFs system.

Shear-dependent thermal conductivity of alumina nanofluids

The thermal conductivities (k) of aqueous alumina nanofluids of various particle shapes (rods, bricks, blades) were measured at the dynamic state for the first time. The dynamic k was measured under torsional flows by using a homemade parallel-plate system. The homemade system was validated by numerical simulations and experiments with homogeneous liquids. All the nanofluids tested here showed decreasing k with increasing shear rate. This newly observed phenomenon was named ‘shear-reducing thermal conductivity.’ The dispersion characteristics were characterized by the dynamic light scattering (DLS) and rheological techniques. From the rheological properties of nanofluids it was inferred that the alumina nanofluids should have network structures and these microstructures should be destroyed or deformed by shearing. But not all the networks were destroyed by shearing. The DLS data revealed that some nanoparticles in nanofluids should exist as individual particles. The effective medium theory cannot explain the shear-reducing characteristics of nanofluids at the dynamic state. The rheological data imply that the heat percolation through the network may not be the sole reason for heat transfer enhancement in nanofluids. It is suggested that the Brownian motion of the primary particles cannot be excluded in heat conduction through nanofluids.

Rheological Behaviors of Nanofluids Containing Multi-Walled Carbon Nanotube

Stable nanofluids containing multi-walled carbon nanotubes (MWNTs) treated by concentrated acid and mechanical mill technology have been prepared. Water, ethylene glycol, glycerol, and silicone oil were used as base fluids. The rheological behaviors of the obtained nanofluids with different MWNT volume fractions and at different temperatures were investigated in details. The glycerol based and silicone oil based fluids behave Newtonian manner in all studied MWNT volume fractions and temperatures. The dispersant hexamethyldisiloxane added in silicone oil decreases the silicone oil viscosity but has no effect on the rheological properties of nanofluids. For the water based nanofluids, MWNTs act as lubricative function when the MWNT volume fraction is lower. Furthermore, for the ethylene glycol based and glycerol based fluid, almost no viscosity augmentation appears when the temperature is higher than 55°C.