Dispersion Stability Of Nanofluids Research Articles

Stability and sedimentation characteristics of water based Al2O3 and TiO2 nanofluids

Nanofluids are regarded as promising heat transfer fluid due to their ultrafast cooling capability. However, stability analysis of nanofluids is very critical before its application in heat transfer .The present paper reports about an investigation on the stability of water-based Al2O3 and TiO2 nanofluids at ambient temperature. Nanoparticles, namely Al2O3 and TiO2 at different concentrations of 1, 0.5, 0.1, 0.05, and 0.01 wt.% respectively were directly dispersed in water without adding any dispersant and placed in a static container to observe gravitation settling. Change of sedimentation height with respect to time was measured using the sedimentation photograph capturing method. DLS (Dynamic Light Scattering) and zeta potential analysis were also executed to examine the stability of nanofluids. The results show that the visualization method, DLS and zeta potential analysis are in good correspondence to each other. Sedimentation velocity increases with an increase in nanoparticle concentration and aging. Brownian motion of nanoparticles resist the sedimentation in nanofluids. It is observed that TiO2nanofluid is more stable as compared to Al2O3 nanofluid due to its smaller particle size. Finally authors recommend smaller particle size, optimized sonication time, low nanoparticle concentration and use of surfactant to obtain better dispersion stability of nanofluids

Experimental investigation on photothermal conversion properties of lampblack ink nanofluids

Solar energy is an appropriate alternative to replace fossil fuel. Making high efficient use of solar energy is a critical issue. As a kind of solar collecting medium, nanofluid shows excellent optical and photothermal conversion properties. In this work, lampblack ink, a type of traditional Chinese ink, was used as heat collecting medium for photothermal conversion. Two-step method was taken to prepared water-based lampblack ink nanofluids at mass fraction of 0.01%, 0.02%, 0.05%, 0.1% and 0.2% respectively. The thermal conductivity of lampblack ink nanofluid was mearsured. The transmission spectrum of lampblack ink nanofluid was tested by uv–vis-nir spectrophotometer. Extinction coefficient and solar weighted absorption fraction were also calculated. Dispersion stability of nanofluid was also considered. Photothermal conversion experiments were taken under solar simulator and natural sunlight. The results showed that lampblack ink nanofluids have better photothermal conversion performance than DI water. With increasing of mass fraction, photothermal conversion performance of lampblack ink nanofluid increased and then decreased. The maximum photothermal conversion efficiency could reach 76.7% under solar simulator, which was 26.4% higher than that of DI water. This work could provide new insights on the application of photothermal such as solar collectors for an effective and low-cost way to address the critical energy shortages challenges.

Dispersion stability and rheology study of canola oil containing TiO2nanoadditives for tribological applications: An experimental approach

Recently, the biodegradable lubricants developed from vegetable oils are gaining popularity concerning biodegradability and sustainability. Moreover, the stabilized suspension of nanoparticles in the base lubricant is a crucial requirement of any nanolubricant for the long term. To evaluate the aggregation behaviour of nanoparticles in base lubricant and rheological properties of nanolubricants are important as other properties. Keeping in view of these, the aim of the present study has been categorized into two parts. Firstly, the dispersion stability of nanofluids in terms of the aggregation behaviour of nanoadditives with the standing time has been investigated under three non-ionic surfactants and one anionic surfactant with several TiO2- to-surfactant mass ratios utilizing dynamic light scattering (DLS) technique. The outcomes demonstrated that the TiO2- to-Triton X-100 mass ratio of 1:3 has long term stability. Secondly, the rheological behaviour of canola oil containing a varying range of nanoadditives has been conducted for various temperatures and shear rates. The results indicated that all the nanofluids exhibit Newtonian behaviour and the viscosity of canola oil increases as nanoadditives concentration increases. The experimental results are also compared and validated with the existing viscosity models, and a new regression model has been suggested.

Impact of anionic surfactant on stability, viscoelastic moduli, and oil recovery of silica nanofluid in saline environment

Controlling nanofluid stability in saline environment has been a long-standing challenge as salt ions screen-out the surface charge of the nanoparticles (NPs), rendering them unstable. This study thus reports the use of an anionic surfactant (sodium dodecylsulfate, SDS), as co-stabilizer, that not only controls the effect of salt, but also dramatically improves nanofluid stability by controlling the agglomeration rate. Silica NPs of 0.5 wt%, SDS with concentration ≥ critical micelles concentration (CMC), and polymer polyacrylamide (PAM) of 1000 ppm were used while the concentration of NaCl was explored up to 5 wt%. The dispersion stability of nanofluid without salt (NaCl) was found to be ~4 weeks which further increased to ~7 weeks with increasing SDS concentration. With increasing SDS (>CMC), a reduction in NP agglomeration was observed that delayed the NP settlement. The effect of salinity was also investigated for flow properties of nanofluids and, an unstable rheological response (transition from viscoelastic to viscous) was observed with increasing NaCl concentration. However, SDS (>CMC) made nanofluid rheologically stable up to saline environment of 3 wt%, an optimum salinity was identified. SDS role on nanofluid stabilization in saline environment is also generalized for enhanced oil recovery (EOR) applications in a porous media enriched with varying salinity. With increasing salinity, the cumulative oil recovery from sand-pack reduced and reached to minimum level of 48% original oil in place (OOIP) at 3 wt% NaCl which was 58% OOIP without salinity. Oil recovery re-established to 55% OOIP in presence of increasing SDS concentration, which is remarkable for nanofluid applicability in saline environment where conventional methods typically show challenges. Even in the presence of 4 wt% NaCl, the synergy between surfactant and nanofluid enabled an improvement in oil recovery and subdued surfactant adsorption in both unconsolidated and consolidated porous media, paving future way for field implementation.

Heat transfer and mechanical friction reduction properties of graphene oxide nanofluids

A large amount of energy consumption has been caused by friction and inefficient heat transfer in the industry. Current research suggests a promising future for graphene nanofluids. In this paper, graphene oxide-deionized water (GO-DI) nanofluids with both friction reduction and high efficiency heat transfer properties was prepared by a two-step method in this paper. The graphene oxide was characterized using FTIR spectroscopy, Raman spectroscopy, XPS and SEM. The dispersion stability of nanofluids was analyzed by dynamic light scattering. An experimental system for measuring the convective heat transfer coefficient of nanofluids was established. The convection heat transfer and friction properties of GO-DI nanofluid were tested. The experimental results show that the addition of GO nanoparticles to the base fluid increases the convective heat transfer coefficient. The proportion of Nunf/Nuf of nanofluids increases from 1.02 to 1.18 as volume fraction rises. For GO-DI nanofluids, the friction coefficient decreased 71% compared to deionized water, when 0.1 vol% of GO and 3 N normal load were applied. The abrasion loss in 0.05 vol% GO-DI nanofluids was 18.5% less than that in deionized water. The association equation for calculating the convective heat transfer coefficient was proposed and the friction reduction mechanism of GO-DI nanofluids was elucidated.

The effect of foam system containing surfactant and silica nanoparticles on oil recovery of carbonate rocks

ABSTRACTIt is of significance to improve the oil recovery of carbonate reservoirs which are rich in oil resources. Most carbonate rocks are oil-wet or neutral-wet, and the heterogeneity is strong, which makes it difficult to improve crude oil recovery. This paper discussed the effect of foam systems containing surfactant and silica nanoparticles on oil recovery. The influence of surfactant concentration and nanoparticle concentration on the dispersion stability of nanofluid was tested. The effects of nanoparticles on foam performance and wettability were investigated. The results showed that when the surfactant concentration was 0.2 wt%, increasing the nanoparticle concentration appropriately enhanced foam stability and wettability alteration. Core flooding experiments also proved that the addition of nanoparticles significantly improved the oil displacement efficiency of surfactant flooding and foam flooding in fractured carbonated rock cores due to the synergistic effect.

High efficiency heat transfer and antifriction characteristics of SMWCNTs nanofluids

In this paper, the thermal conductivity and tribological properties of ethylene glycol/water-based nanofluids with hydroxylated short multi-walled carbon nanotubes (SMWCNTs(OH)) were investigated. Long-term stable ethylene glycol/water-based nanofluids were prepared by a two-step method. The morphology and surface functional group characteristics of SMWCNTs(OH) were characterized by field emission scanning electron microscopy and Fourier transform infrared spectroscopy. The kinematic viscosity of the base fluid and nanofluids at different temperatures was measured using a rotary rheometer. The dispersion stability of nanofluids was analyzed by dynamic light scattering. Thermal conductivity test was performed using the transient hot wire method. The reciprocating friction test was carried out by UMT5 test machine, and the appearances of wear scars were analyzed by white light morphology. Results show that a significant enhancement of thermal conductivity could be achieved by increasing the temperature of the nanofluids and adjusting the concentration of the carbon nanotubes compared with the corresponding base. At 60 °C, the thermal conductivity of the nanofluids increases significantly and reaches 6.0%at the volume fraction of 25% for ethylene glycol/water. It is shown that the SMWCNTs(OH) have good self-lubrication antifriction effect in the water base nanofluids for the GCr15 friction pair. Meanwhile, the wear loss of the wear scar is greatly reduced, and the friction coefficient is reduced by 15.4% compared with the pure water, which shows a good application prospect of nanofluids in pump drive fluid loops.

Stable SiO2–TiO2 composite-based nanofluid of improved rheological behaviour for high-temperature oilfield applications

ABSTRACTNanofluid synthesis in pure water is associated with premature settlement resulting in least dispersion stability. Therefore, in this study, polyacrylamide (PAM) is used as viscosity enhancer to improve dispersion stability of nanofluid stabilized by composites of silica and titania. Different techniques such as dynamic light scattering measurements, electrical conductivity, scanning electron microscopy, and rheological studies are used to support the analysis. The use of silica and titania nanoparticles together with PAM has additional advantage over particle agglomeration, and thus, the dispersion stability improved. Further, nanofluid stabilized by composites of silica and titania was tested for rheological measurements at 90°C to find nanotechnology applicability in high-temperature applications. The shear-thinning behaviour of nanofluids at high temperature (90°C) was least affected by shear deformation and reduced to 0.48 mPa.s at higher shear rate (4200 s−1), while shear thinning of PAM solution seriously varied with increasing shear deformation and takes the edge of 0.0005 mPa.s at higher shear rate (4200 s−1). In addition, the thermal stability of nanofluids was better due to slight decrease in viscosity with increasing temperature, which makes them suitable to be utilized at high-temperature applications in widespread industrial areas including oilfield where the temperature becomes a major factor.

Dynamic stability, sedimentation, and time-dependent heat transfer characteristics of TiO2 and CNT nanofluids

Nowadays, the stability and heat transfer properties of nanofluids have been extensively studied. However, for the practical application, the dynamic stability, sedimentation, and fouling characteristics are also important issues. Whether nanofluids can maintain stable heat transfer characteristics during intermittent operation in the system is also a worthwhile issue. In this paper, the dynamic stability, sedimentation, and fouling characteristics as well as the time-dependent heat transfer characteristics of TiO2 and CNT nanofluids are investigated sequentially. The results show that compared with static condition, the dispersion stability of nanofluids is much better, and the sedimentation and fouling on solid surface are much less in dynamic condition. For the nanofluids in this paper, the sedimentation and fouling on solid surface are loose and can easily washed out after slight flushing. Rough surfaces are easier to adsorb the nanoparticles sedimentation and form fouling, but it can be greatly removed using ultrasonication. Long-term shutdown reduces the convective heat transfer enhancement of nanofluids, but it can be well restored after the action of ultrasonication.

Stability of nanofluids: Molecular dynamic approach and experimental study

Nanofluids as volumetric absorbent in solar energy conversion devices or as working fluid in different heat exchangers have been proposed by various researchers. However, dispersion stability of nanofluids is an important issue that must be well addressed before any industrial applications. Conditions such as severe temperature gradient, high temperature of heat transfer fluid, nanoparticle mean diameters and types of nanoparticles and base fluid are among the most effective parameters on the stability of nanofluid. A molecular dynamic approach, considering kinetic energy of nanoparticles and DLVO potential energy between nanoparticles, is adopted to study the nanofluid stability for different nanofluids at different working conditions. Different forces such as Brownian, thermophoresis, drag and DLVO are considered to introduce the stability diagrams. The latter presents the conditions for which a nanofluid can be stable. In addition an experimental investigation is carried out to find a stable nanofluid and to show the validity of the theoretical approach. There is a good agreement between the experimental and theoretical results that confirms the validity of our theoretical approach.

Effect of Oleic Acid Surface Modification on Dispersion Stability and Breakdown Strength of Vegetable Oil-Based Fe3O4 Nanofluids

Well-dispersed Fe3O4 nanoparticles were prepared and modified by oleic acid at the temperature of 70°C for different reaction times. The surface modification of oleic acid could improve dispersion stability of Fe3O4 nanoparticles in vegetable oil by forming an effective chemisorbed modification layer on the surface of nanoparticles. The interaction between coordination pattern and mass faction of chemisorbed oleic acid on nanoparticles and dispersion stability of nanofluid was discussed. The optimal dispersion stability of vegetable-oil based Fe3O4 nanofluids was obtained to the nanoparticles modified for 8 hours, which has the highest AC breakdown strength of 67.78 kV.

CO2 Capture/Separation Control by SiO2 Nanoparticles and Surfactants

In this study, the performance enhancement of CO2 capture and separation by the SiO2 nanoparticles and surfactants is evaluated. The main objectives are to test the dispersion stability of nanofluids (DI water with nanoparticles and surfactants), to quantify the effect of the nanoparticles and surfactants on the CO2 capture and separation performance, and to find the optimum conditions of the nanoparticles and surfactants. It is found that the CO2 capture and separation performances are enhanced up to 13.1% and 7.8% at the nanoparticle concentration of 0.01 vol%, respectively. It is concluded that nanoparticles enhance both CO2 capture and separation rates, while the surfactants enhance the CO2 capture rate but they interrupt the CO2 separation rate.

Experimental Study on Dispersion Stability of Rutile TiO<sub>2</sub> Nano-Particles Suspension of Ammonia-Water Solution

In order to apply nanofluids to ammonia-water absorption refrigeration, several groups of nanofluids mixing with rutile TiO2(r-TiO2) and ammonia-water were perpared by an optimizing method. Observation tests were carried out to investigate the effects of the kind and mass fraction of dispersant, mass fraction of ammonia-water basefluid and durations of supersonic vibration on the dispersion stability of nanofluids. The results show that, all three factors have influences on the dispersion. The optimal dispersing condition of 0.1wt% r-TiO2 nanofluids was 0.1% of PAA in 25% ammonia water basefluid with 10 minutes of ultrasonic vibration.

Stability of TiO2 and Al2O3 Nanofluids

Aiming at the dispersion stability of nanofluids, we investigate the absorbency and the zeta potential of TiO2 and Al2O3 nanofluids under different pH values and different dispersant concentrations. The results show that in the mass fraction 0.05% alumina and 0.01% titanium dioxide nanosuspensions, the absolute value of the zeta potential and the absorbency of the two nanofluids with sodium dodecyl sulfate (SDS) dispersant are the highest at an optimal pH (pHAl2O3 ≈ 6.0, pHTiO2 ≈ 9.5) and that there is a good correlation between absorbency and zeta potential: the higher the absolute value of the zeta potential is, the greater the absorbency is, and the better the stability of the system is. The optimizing concentrations for SDS are 0.10% and 0.14%, respectively, at which the two nanofluids have the best dispersion results. The calculated DLVO interparticle interaction potentials verify the experimental results of the pH effect on the stability behavior.

Thermal conductivity measurement and characterization of binary nanofluids

Binary nanofluids, nanoparticle suspensions in binary mixture, are developed to enhance the heat and mass transfer performance of absorption refrigeration cycles. To stabilize the nanoparticles in a strong electrolyte, polymer is used as a steric stabilizer. The effective thermal conductivities of the binary nanofluids with the concentrations of nanoparticle up to 0.1 vol% are measured using the transient hot wire method. Comparing the thermal conductivity change with time, it is found that the dispersion stability of nanofluids is a dominant factor for enhancing the thermal conductivity of binary nanofluids. It is also found that the thermal conductivity of the binary nanofluids (H 2O/LiBr binary mixture with Al 2O 3 nanoparticles) increases with the particle volume concentration and enhances by 2.2% at 0.1 vol% concentration condition. Also a modified dimensionless group is proposed to find the maximum radius of nanoparticles to maintain stable nanofluids. In this study, it was estimated ∼1.3 μm.