SiO2 Nanofluids Research Articles

Characterization of Thermal Conductivity and Viscosity of Nanofluids with Aqueous Base Fluids

Two different nanofluids (SiO2 – EG/DW and SiO2 – DW) with various volume fractions are prepared by dispersing SiO2 nanoparticles (< 20 nm) into two different types of base fluid: distilled water and ethylene glycol/distilled water mixture. The effective thermal conductivity and viscosity of nanofluids are characterized and compared over a temperature range of 25oC - 50oC. It is found that the effective thermal conductivity and viscosity of nanofluid are influenced by the nanoparticle volume fraction and the operating temperature. The thermal conductivity of the SiO2 nanofluids with different volume concentrations increases as temperature increases while the viscosity decreases with the increasing temperature. The base fluid alters the characteristics of both the thermal conductivity and viscosity of nanofluid. Over the same range of operating temperature, the effective thermal conductivity and viscosity of SiO2 – EG/DW nanofluid manifest stronger dependency on the nanoparticle concentration compared to those of water-base-fluid nanofluid.

Efficacy of SiO2 nanofluids in a miniature plate heat exchanger with undulated surface

In a variety of applications, there is a clear need for an efficient and reliable heat management of high heat flux densities. In this study a miniature Plate Heat Exchanger (PHE) with modulated surface along with nanofluids used as working liquids is proposed aiming for a more compact and efficient cooling equipment for low-temperature applications. The suggested working fluid is a nanofluid, i.e. a 1% v/v aqueous dispersion of SiO2 nanoparticles, which we have proved that can enhance heat transfer rate up to 35% compared to water. Relevant CFD simulations, also conducted during this study, have shown that for a given operating temperature less cooling liquid and consequently less pumping power is needed when this nanofluid is used instead of water. As the SiO2 nanoparticles are relatively inexpensive and their nanofluids are easy to prepare, their use appears to be an attractive solution for mini-scale devices or low-power applications.

An experimental study on the thermal and hydraulic performances of nanofluids flow in a miniature circular pin fin heat sink

This study presents the experimental thermal and hydraulic performance of heat sink with miniature circular pin fin structure using two different types of nanofluid as coolant. ZnO and SiO2 nanoparticles dispersed in DI water with particle volume fraction of 0.2, 0.4 and 0.6 vol.% are tested and compared with the data for water. A heat sink with inline arrangement of circular pins is designed and made from aluminum material. The height, diameter, pitch, and number of pins are 1.2, 1.2, 2.4mm and 143, respectively. Uniform heat flux at the bottom of the heat sink is performed. The present work is conducted at fluid temperature of 15°C. The mass flow rate ranged from 0.65 to 3.32kg/min and the heat flux ranged between 20 and 48kW/m2. The effects of particle type, particle concentration, and mass flow rate on the thermal and hydraulic performances are reported. The measured data show that the heat transfer performance of the nanofluid-cooled heat sink is higher than that of the water-cooled heat sink. Comparison between ZnO and SiO2 nanofluids, higher heat transfer performance for ZnO–water nanofluids is observed by about 3–9%. For hydraulic performance, the results show that the addition of nanoparticles in the base fluid have a small effect on the pumping power. Finally, new heat transfer and pressure drop correlations are proposed to predict the Nusselt number and pressure drop of nanofluids flow in heat sinks with pin fin configuration.

Experimental study of nanofluid flow and heat transfer over microscale backward- and forward-facing steps

This paper investigates experimentally the effects of laminar nanofluid flow over the microscale backward-facing step (MBFS) and forward-facing step (MFFS) on the heat transfer characteristics. The experiments were implemented on MBFS and MFFS with a step height of 600μm. Both MBFS and MFFS have the upstream and downstream lengths of 0.1m and 0.15m respectively. The Reynolds number ranged of 280–480. The concentrations of SiO2 nanoparticle valued at 0.005 and 0.01 with a diameter of 30nm were immersed in a distilled water. The experimental results revealed that the concentration of 0.01 water–SiO2 nanofluid recorded the highest Nusselt number. The comparison between MBFS and MFFS revealed that the highest Nusselt number is obtained through the use of the MFFS, which is approximately twice that of MBFS. However, the friction factor recorded a higher value for MFFS. The experimental results were in a good agreement with the numerical published results.

Absorption and solubility measurement of CO2 in water-based ZnO and SiO2 nanofluids

The experiments of the absorption of carbon dioxide in the water-based nanofluids of spherical silica (SiO2) and zinc oxide (ZnO) nanoparticles are carried out in an isothermal stirred high pressure cell using quasi-static method through gas pressure measurement. The SiO2 and ZnO nanoparticle compounds were purchased and synthesized, respectively; and characterized through X-ray diffraction (XRD) pattern and scanning electron microscopy (SEM) images. Moreover, the zeta potential is measured to show the stability of these nanoparticles in water. The experiments are performed at 2, 5 and 8°C and a range 1bar up to gas hydrate equilibrium pressure; and in 15, 25 and 40°C at 1–36bar. The CO2 solubility measurement in pure water and the 0.1wt% of the two nanofluids show that the amount of the absorbed CO2 enhances in presence of nanoparticles so that the ZnO nanofluids are more effective than SiO2 nanofluids at the all experimental conditions. In addition, the solubility of CO2 is measured in the 0.05, 0.1, 0.5 and 1wt% of ZnO nanofluid at 5°C and pressure range of 1–22bar so that the amount of absorption was enhanced by increasing the ZnO mass loading at the all measurements. The mechanism of CO2 absorption in the nanofluids are fully discussed and compared with those gas solubility results in pure water.

Comparative Studies on Thermal Performance of Conic Cut Twist Tape Inserts with SiO2 and TiO2 Nanofluids

This paper presents a comparison study on thermal performance conic cut twist tape inserts in laminar flow of nanofluids through a constant heat fluxed tube. Three tape configurations, namely, quadrant cut twisted tape (QCT), parabolic half cut twisted tape (PCT), and triangular cut twisted (VCT) of twist ratio y = 2.93 and cut depth de = 0.5 cm were used with 1% and 2% volume concentration of SiO2/water and TiO2/water nanofluids. Typical twist tape with twist ratio of y = 2.93 was used for comparison. The results show that the heat transfer was enhanced by increasing of Reynolds number and nanoparticles concentration of nanofluid. The results have also revealed that the use of twist tape enhanced the heat transfer coefficient significantly and maximum heat transfer enhancement was achieved by the presence of triangular cut twist tape insert with 2% volume concentration of SiO2 nanofluid. Over the range investigated, the maximum thermal performance factor of 5.13 is found with the simultaneous use of the SiO2 nanofluid at 2% volume concentration VCT at Reynolds number of 220. Furthermore, new empirical correlations for Nusselt number, friction factor, and thermal performance factor are developed and reported.

Enhance heat transfer in the channel with V-shaped wavy lower plate using liquid nanofluids

The heat transfer and flow characteristics in corrugated with V-shape lower plate using nanofluids are numerically studied. The computations are performed on uniform heat flux over a range of Reynolds number (Re) 8000–20,000. The governing equations are numerically solved in the domain by a finite volume method (FVM) using the k–ε standard turbulent model. Studies are carried out for different types of nanoparticles Al2O3,CuO, SiO2 and ZnO with different volume fractions in the range of 0–4%. Three different types of base fluid (water, glycerin, ethylene glycol) are also examined. Results indicated that the average Nusselt number for nanofluids is greater than that of the base liquid. The SiO2 nanofluid yields the best heat transfer enhancement among all other type of nanofluids. Heat transfer enhancement increase with increases the volumetric concentration, but it is accompanied by increasing pressure drop values. Moreover, the average Nusselt number increases with an increase in Reynolds number and volume concentration. The SiO2–glycerin nanofluid has the highest Nusselt number compared with other base fluids. The present study shows that these V-shaped wavy channels have advantages by using nanofluids and thus serve as promising candidates for incorporation into efficient heat transfer devices.

Energy, economic, and environmental analysis of a flat-plate solar collector operated with SiO2 nanofluid

To overcome the environmental impact and declining source of fossil fuels, renewable energy sources need to meet the increasing demand of energy. Solar thermal energy is clean and infinite, suitable to be a good replacement for fossil fuel. However, the current solar technology is still expensive and low in efficiency. One of the effective ways of increasing the efficiency of solar collector is to utilize high thermal conductivity fluid known as nanofluid. This research analyzes the impact on the performance, fluid flow, heat transfer, economic, and environment of a flat-plate solar thermal collector by using silicon dioxide nanofluid as absorbing medium. The analysis is based on different volume flow rates and varying nanoparticles volume fractions. The study has indicated that nanofluids containing small amount of nanoparticles have higher heat transfer coefficient and also higher energy and exergy efficiency than base fluids. The measured viscosity of nanofluids is higher than water but it gives negligible effect on pressure drop and pumping power. Using SiO2 nanofluid in solar collector could also save 280 MJ more embodied energy, offsetting 170 kg less CO2 emissions and having a faster payback period of 0.12 years compared to conventional water-based solar collectors.

Heat transfer and friction factor of water based TiO2 and SiO2 nanofluids under turbulent flow in a tube

The heat transfer coefficient and friction factor of TiO2 and SiO2 water based nanofluids flowing in a circular tube under turbulent flow are investigated experimentally under constant heat flux boundary condition. TiO2 and SiO2 nanofluids with an average particle size of 50nm and 22nm respectively are used in the working fluid for volume concentrations up to 3.0%. Experiments are conducted at a bulk temperature of 30°C in the turbulent Reynolds number range of 5000 to 25,000. The enhancements in viscosity and thermal conductivity of TiO2 are greater than SiO2 nanofluid. However, a maximum enhancement of 26% in heat transfer coefficients is obtained with TiO2 nanofluid at 1.0% concentration, while SiO2 nanofluid gave 33% enhancement at 3.0% concentration. The heat transfer coefficients are lower at all other concentrations. The particle concentration at which the nanofluids give maximum heat transfer has been determined and validated with property enhancement ratio. It is observed that the pressure drop is directly proportional to the density of the nanoparticle.

Impact of Metal Oxide Nanoparticles on Enhanced Oil Recovery from Limestone Media at Several Temperatures

Recently, researchers have proved the application of nanoparticles (NPs) for enhanced oil recovery (EOR) in ambient temperature. However, to our knowledge no attempt has been undertaken experimentally to investigate the influence of NPs on EOR at higher temperatures. In this study, aluminum oxide (Al2O3), titanium dioxide (TiO2), and silicon dioxide (SiO2) were selected for EOR purposes from an intermediate-wet limestone sample at 26, 40, 50, and 60 °C. These metal NPs were dispersed in deionized water at concentration of 0.005 wt %. First, transportation of the NPs through limestone was evaluated. It was found that Al2O3 (8.2%) had the lowest and TiO2 (27.8%) and SiO2 (43.4%) had the highest adsorption on the limestone. Consequently, wettability of the limestone was changed into water-wet through NPs adsorption. The contact angle in the presence of Al2O3, TiO2, and SiO2 nanofluids was measured as 71° ± 2°, 57° ± 2°, and 26° ± 2°, respectively. Interfacial tension was also noticeably reduced with these na...

Experimental and numerical study of nanofluid flow and heat transfer over microscale forward-facing step

Experimental and numerical investigations are presented to illustrate the nanofluid flow and heat transfer characteristics over microscale forward-facing step (MFFS). The duct inlet and the step height were 400μm and 600μm respectively. All the walls are considered adiabatic except the downstream wall was exposed to a uniform heat flux boundary condition. The distilled water was utilized as a base fluid with two types of nanoparticles Al2O3 and SiO2 suspended in the base fluid. The nanoparticle volume fraction range was from 0 to 0.01 with an average nanoparticle diameter of 30nm. The experiments were conducted at a Reynolds number range from 280 to 480. The experimental and numerical results revealed that the water–SiO2 nanofluid has the highest Nusselt number, and the Nusselt number increases with the increase of volume fraction. The average friction factor of water–Al2O3 was less than of water–SiO2 mixture and pure water. The experimental results showed 30.6% enhancement in the average Nusselt number using water–SiO2 nanofluid at 1% volume fraction. The numerical results were in a good agreement with the experimental results.

Numerical validation of experimental heat transfer coefficient with SiO2 nanofluid flowing in a tube with twisted tape inserts

A numerical model has been developed for turbulent flow of nanofluids in a tube with twisted tape inserts. The model is based on the assumption that van Driest eddy diffusivity equation can be applied by considering the coefficient and the Prandtl index in momentum and heat respectively as a variable. The results from the numerical analysis are compared with experiments undertaken with SiO2/water nanofluid for a wide range of Reynolds number, Re. Generalized equation for the estimation of nanofluid friction factor and Nusselt number is proposed with the experimental data for twisted tapes. The coefficient and the Prandtl index in the eddy diffusivity equation of momentum and heat is obtained from the numerical values as a function of Reynolds number, concentration and twist ratio. An enhancement of 94.1% in heat transfer coefficient and 160% higher friction factor at Re = 19,046 is observed at a twist ratio of five with 3.0% volumetric concentration when compared to flow of water in a tube. A good agreement with the limited experimental data of other investigators is observed with Al2O3 and Fe3O4 nanofluids indicating the validity of the numerical model for use with twisted tape inserts.

Superior Performance of Nanofluids in an Automotive Radiator

Abstract This study compares the performance of three different nanofluids containing aluminum oxide, copper oxide, and silicon dioxide nanoparticles dispersed in the same base fluid, 60:40 ethylene glycol and water by mass, as coolant in automobile radiators. The computational scheme adopted here is the effectiveness-number of transfer unit (ε − NTU) method encoded in matlab. Appropriate correlations of thermophysical properties for these nanofluids developed from measurements are summarized in this paper. The computational scheme has been validated by comparing the results of pumping power, convective heat transfer coefficients on the air and coolant side, overall heat transfer coefficient, effectiveness and NTU, reported by other researchers. Then the scheme was adopted to compute the performance of nanofluids. Results show that a dilute 1% volumetric concentration of nanoparticles performs better than higher concentration. It is proven that at optimal conditions of operation of the radiator, under the same heat transfer basis, a reduction of 35.3% in pumping power or 7.4% of the surface area can be achieved by using the Al2O3 nanofluid. The CuO nanofluid showed slightly lower magnitudes than the Al2O3 nanofluid, with 33.1% and 7.2% reduction for pumping power or surface area respectively. The SiO2 nanofluid showed the least performance gain of the three nanofluids, but still could reduce the pumping power or area by 26.2% or 5.2%. The analysis presented in this paper was used for an automotive radiator but can be extended to any liquid to gas heat exchanger.

Mixed Convection Over a Backward-Facing Step in a Vertical Duct Using Nanofluids—Buoyancy Opposing Case

Predictions are reported for buoyancy-opposing laminar mixed convection using nanofluids over a backward-facing step in a vertical duct, in which the upstream wall and the step simulated are adiabatic surfaces, while the downstream wall from the step is heated to a uniform temperature that is higher than the inlet fluid temperature. The straight wall that forms the other side of the duct was maintained at constant temperature equivalent to the inlet fluid temperature. The conservation equations are solved using the finite volume method. Eight different types of nanoparticles, Au, Ag, Al2O3, Cu, CuO, diamond, SiO2, and TiO2, with 5% volume fraction are used. Results presented in this paper are for a step height of 4.9 mm and an expansion ratio of 1.942, while the total length in the downstream of the step is 0.5 m. The Reynolds number is in the range of 33� 3 ≤ Re ≤ 100. The downstream wall was fixed at uniform wall temperature in the range of 0 ≤ �T ≤ 30 � C which is higher than the inlet flow temperature. Results reveal that the recirculation region that develops behind the backward-facing step in the case of forced convection and low buoyancyopposing level disappears when the buoyancy-opposing increases. An upward opposing flow is developed at the heated downstream wall from the exit to the step wall at high Reynolds number and high temperature difference, while at low Reynolds number and high temperature difference; the upward opposing flow is passed over the step wall and a shallow recirculation region is formed on the adiabatic upstream wall. It is found that SiO2 nanofluid has the highest Nusselt number at the highest buoyancy level. The skin friction coefficient decreases as Reynolds number and Prandtl number increase.

Aggregation based model for heat conduction mechanism in nanofluids

A new mathematic model for heat conduction of nanofluid is developed based on the experimental findings. Effective medium theory, nanolayer of liquid molecule around solid particle, aggregation, nano-convection due to the Brownian motion of nanoparticle, and interfacial thermal resistance are included to elucidate the heat conduction mechanism in nanofluids. The analytical result fits well with the experimental data and the maximum deviation is obtained to be 1.52% for SiO2 nanofluid. The effects of aggregate shape (i.e., ellipsoid, sphere and fiber) and its size are investigated to evaluate the thermal conductivity of the nanofluids. The prediction shows that nano-convection induced by the movement of aggregates, is leading the main contribution for thermal conductivity enhancement at a low concentration of ∼0.1vol%. Thermal conductivity of aggregate becomes crucial to affect the static contribution for the enhancement. In addition, it is found that the interfacial thermal resistance and nanolayer have little effect on the thermal conductivity enhancement of nanofluids at a very low concentration of nanoparticles.

Combined convection nanofluid flow and heat transfer over microscale forward-facing step

The laminar mixed convection flow of nanofluids over a 3D horizontal microscale forward-facing step (MFFS) was numerically investigated using a finite volume method. Various nanoparticle materials, such as SiO2, Al2O3, CuO, and ZnO, were dispersed in ethylene glycol as a base fluid with volume fractions in the range of 0 and 0.04. The duct has a step height of 650 μm. The downstream wall was heated with a uniform heat flux of 12 Watt, and the straight wall of the duct was kept at a constant temperature of 323 K. The Reynolds number value was maintained at 35. The results revealed that the SiO2 nanofluid had the highest Nusselt number, which increased with decreasing nanoparticle material density, increasing volume fraction and decreasing nanoparticles diameter. The static pressure and the wall shear stress increased with increasing particle volume fraction and decreasing particle diameter. Moreover, the nanoparticle volume faction, material and diameters had small effect on the skin friction coefficient.

Study of forced convection nanofluid heat transfer in the automotive cooling system

The heat transfer enhancement for many industrial applications by adding solid nanoparticles to liquids is significant topics in the last 10 years. This article included the friction factor and forced convection heat transfer of SiO2 nanoparticle dispersed in water as a base fluid conducted in a car radiator experimentally and numerically. Four different concentrations of nanofluids in the range of 1–2.5vol% have been used. The flowrate changed in the range of 2–8 LPM to have Reynolds number with the range 500–1750. The results showed that the friction factor decreases with an increase in flowrate and increase with increasing in volume concentration. Furthermore, the inlet temperature to the radiator has insignificantly affected to the friction factor. On the other side, Nusselt number increases with increasing in flowrate, nanofluid volume concentration and inlet temperature. Meanwhile, application of SiO2 nanofluid with low concentrations can enhance heat transfer rate up to 50% as a comparison with pure water. The simulation results compared with experimental data, and there is a good agreement. Likewise, these results compared to other investigators to be validated.

Influence of New SiO<sub>2</sub> Nanofluids on Surface Wettability and Interfacial Tension Behaviour between Oil-Water Interface in EOR Processes

Fine SiO2 nanosphericals (2-5nm) and new various stable nanofluids including Tween 80, Span 80, Lauric alcohol-3EO, CTAB, SDS and K-Laurate surfactants in water or paraffin based solution were used as new SiO2 nanoproducts in oil recovery. These nanofluids can strongly change oil-wet carbonate reservoir rock to complete water-wet wettability and showed an excellent trend of surface tension (S.T) and IFT (interfacial tension) reduction in comparison with pure water and reference solutions. The CaCO3 plates reservoir was then aged for 2, 5 and 8 days into the 1, 3 and 8% of different concentrations of synthesized SiO2 nanofluids (effect of various concentrations via different aging time). Air/water and n-decane/water contact angles on oil-wet and clean carbonate rock aged in designed SiO2 nanofluids were measured and the pH value as a significant factor estimated. The interesting influence of microwave irradiation on surface tension and IFT including various SiO2 nanofluids was investigated after 12 min which some of the especial nanofluid concentrations showed successful reduction. Our findings indicated the important effect of temperature over decreasing of surface tension and IFT between oil and water interface including SiO2 nanofluids after annealing at 70°C. Therefore, this phenomenon can be significantly capable and valuable in applying of new technology in the fabrication of novel nanofluids in EOR processes and saving source of energy regarding to conventional production.

An Experimental Study on Nanofluids Convective Heat Transfer Through a Straight Tube under Constant Heat Flux

In this work, the laminar convective heat transfer performance and the pressure drop of water-based nanofluids containing Al2O3, TiO2 and SiO2 nanoparticles flowing through a straight circular tube were experimentally investigated. The experimental results showed that addition of small amounts of nano-sized Al2O3 and TiO2 particles to de-ionized water increased heat transfer coefficients considerably, while the SiO2 nanofluids showed the opposite behavior attracting the authors' interests. An average of 16% and 8.2% increase in heat transfer coefficient were observed with the average of 28% and 15% penalty in pressure drop for Al2O3 and TiO2 nanofluids.

Preparation and Thermophysical Properties of SiO<sub>2</sub> Nanofluids

Aqueous nanofluids composed of SiO2 nanoparticles with different sizes (15 nm, 30 nm, 50 nm) at a low volume concentration were prepared by a two-step method. The suspension and dispersion characteristics were experimentally examined by the zeta potential, average size and absorption spectrum. The thermophysical properties, such as viscosity, thermal conductivity, surface tension and latent heat of vaporization were experimentally measured. A lot of thermophysical data of SiO2 nanofluids were obtained. The influences of the particle size, particle volume concentration and temperature on thermophysical properties were discussed briefly.