Surface Tension Of Nanofluids Research Articles

Wetting behavior of multi-walled carbon nanotube nanofluids

Nanofluids—engineered colloidal suspensions in base liquids—have captivated the interest of researchers over the last two decades for various existing as well as emerging technological applications. The main impetus for the synthesis of such novel nanocomposite liquids is the potential to alter properties of the base liquid, such as its viscosity, thermal conductivity, and surface tension, and to introduce specific optical and magnetic properties. Numerous studies suggest trends and explanations for the effects associated with the addition of nanoparticles, and that deviation from the base liquid properties are dependent on nanoparticle concentration. However, there remains a certain ambiguity in the available literature. The wetting behavior and surface tension of nanofluids are particular examples where highly conflicting results exist. In this study, we used multi-walled carbon nanotubes (MWCNTs) functionalized by plasma treatment and dispersed in reverse osmosis water and 99% anhydrous ethanol. Our observations reveal that the surface tension and wetting behavior of the stable aqueous and ethanol-based nanofluids containing plasma functionalized MWCNTs are unaffected by the MWCNT loading up to 120 (0.012) and ∼210 (0.021) ppm (vol%), respectively. The ethanol-based MWCNT nanofluids allowed us to extend the study to higher loadings, and a linear increase of the surface tension past ∼200 ppm was observed. Conversely, nanofluids containing non-functionalized or surfactant-stabilized MWCNTs show drastically different contact angle values when compared to the base liquids even at very low concentrations (less than 100 ppm). We demonstrate that the stability of nanofluid and method of stabilization are crucial parameters in determining the wetting behavior of nanofluids.

Experimental Study on the Surface Tension of Al<sub>2</sub>O<sub>3</sub>-H<sub>2</sub>O Nanofluid

Due to the good performance of thermal conductivity, nanofluids are regarded as a new type of heat transfer working medium, which have huge potential value. The addition of nanoparticles makes nanofluids exhibit different thermal properties from the base fluids. In this experiment, the maximum bubble pressure method was adopted to measure the surface tension of Al2O3-H2O nanofluids whose nanoparticle sizes are 10 nm and 20 nm with four different volume fractions (1%, 1.5%, 2% and 1.5%), and 50 nm and 100 nm with the volume fraction of 2.5%. The temperatures of nanofluids are within the scope of 18 °C to 30 °C. The surface tension ratio (the ratio of surface tension value of nanofluids to its base fluids) is also calculated at different temperature points. Results show that the surface tension of nanofluids decreases with the elevation of temperature and decreases with the increase of volume fraction. For different temperatures and particle sizes of nanofluids, there exists a corresponding critical concentration value. Only reaching the value, the addition of nanoparticles can reduce the surface tension of the base fluids.

Microwave irradiation based non-chemical method to manipulate surface tension of nanofluids

Manipulation of the surface tension is one of the key pathways to enhance heat and mass transfer performances of nanofluids in thermal systems. Current practices and existing literature on the surface tension reduction indicate that surfactant is usually employed as a chemical-additive to manipulate surface tension. This study, on the other hand, aims to explore a physical method to manipulate the surface tension of nanofluids based on microwave irradiation. This paper, therefore, is the first publication to report surface tension behaviors of nanofluids during and after microwave irradiation. Experimental results show that after microwave treatment, lower surface tensions were observed for both TiO2 and Fe2O3 based nanofluids for an extended period of time, even though the temperature has returned to its initial condition. These preliminary findings suggest that microwave irradiation treatment has the potential to be a non-chemical method to manipulate surface tension of nanofluids.

Experimental and theoretical investigation on Nano-fluid surface tension

Effect of γ-Al2O3 and MgO nanoparticle on surface tension of Tri Ethylene Glycol (TEG) was studied for different nanoparticle concentrations. Furthermore, the effect of nanoparticle size on the Nano-fluid surface tension was investigated. Results showed that surface tension increases for some particle concentrations and decreases for some others; in other words, a certain particle concentration could not be determined as the boundary for the increase or decrease of surface tension. Moreover, Sorbitan oleate was added to TEG solution to investigate the changes in surface tension that may occur due to the addition of surfactants. It is shown that by increasing surfactant concentration, Nano-fluid surface tension would decrease. The effect of nanoparticle size on surface tension was analyzed as well. Using experimental data, five empirical and thermodynamic-based models; i.e., Redlich–Kister (RK), Malanovsky-Marsh (MM), Jufu et al. (JBZ), Chunxi et al. (CWZ) and Santos et al. (SFF) were evaluated for surface tension estimation, and it was found that SFF method is the best method to correlate nano fluid surface tension in this study.

Effect of surface tension on SiO2 -methanol nanofluids

Surface tension, the cohesive energy of an interface dominated the transportation behaviour of the liquids play an important role in the heat transfer performance. A new class of heat transfer fluid denoting “Nanofluids” with impressive thermo-physical properties, proved its promising potentiality in the heat transfer performance. However, very few numbers of studies observed for the effect of nanoparticles on the surface tension of liquids, also noted controversial results. In the present study, SiO2 nanoparticles dispersed in methanol solution to investigate the effect of surface tension with the change of concentration and their sizes. The most common Du-Nouy ring method was used to measure the surface tension of methanol based nanofluids by an automatic surface tensiometer.The results denote that the surface tension of the nanofluids increases with increase in concentration. On the other hand, the results indicate that the surface tension decreases with the increase in temperatures. Besides, the surface tension of SiO2-methanol nanofluids enhances compared to pure methanol. All in all, the enhancement observed 1.7% to 8.9% of the variation of volume fractions (0.05 Vol % to 0.25 Vol %) and the temperature change of 25 °C to 50 °C.

Measurements of the surface tension of nanofluids and development of a new correlation

Surface tension measurements were performed on four nanofluids containing aluminum oxide (Al2O3), zinc oxide (ZnO), titanium dioxide (TiO2) and silicon dioxide (SiO2) nanoparticles suspended in a base fluid of 60% propylene glycol and 40% water by mass (60:40 PG/W). First, benchmark tests for the surface tension of water were performed, for which accurate data are available in the published literature. Measured data agreed well with the published data confirming the accuracy of the apparatus, as well as the experimental procedure. Following the benchmark tests, measurements were performed on nanofluids over a temperature range of 30 °C to 70 °C for particle volumetric concentrations ranging from 0 to 6 % and particle sizes in the range of 15–50 nm. From the experimental data, it was observed that the surface tension of nanofluids decreased with an increase in temperature. At a constant temperature, an increase in the particle volumetric concentration of a nanofluid caused a decrease in the surface tension. For nanofluids at fixed volumetric concentration and temperature, the surface tension was found to be lower for smaller particle sizes except the ZnO nanofluid. A statistical analysis performed on the experimental data yielded a single correlation valid for all the nanofluids tested. This surface tension correlation is a function of temperature, volumetric concentration and the size of the nanoparticles, which predicts results successfully with an average deviation of 2.6% from the measured values.

Thermal conductivity, viscosity and surface tension of nanofluids based on FeC nanoparticles

The main goal of the present study was to prepare and also to investigate the effects of both temperature and weight concentration on the thermo-physical properties of FeC/water nanofluids. The FeC nanoparticles were obtained by the laser pyrolysis technique. The TEM, XRD, EDX Raman and FT-IR spectroscopy techniques were used to characterize structure, purity and size of the nanoparticles. Thermal conductivity, viscosity and surface tension of FeC/water nanofluids were investigated within the range of the temperature of 10°C to 70°C, for three weight concentrations (0.1, 0.5 and 1.0wt%). The experimental results show that the thermal conductivity of FeC/water nanofluids increases with the increase of both weight concentration of the nanoparticles and temperature, in all cases studied. The data also indicate that the influence of weight concentration of the nanoparticles on viscosity becomes less significant for temperatures above 55°C. The surface tension of FeC/water nanofluids increases with the increase of the weight concentrations of the nanoparticles. In the cases of low concentrations of nanoparticles (0.1% and 0.5%), the surface tension of nanofluids was lower than the surface tension of the water. For a concentration of the nanoparticles of 1.0%, the surface tension of the nanofluids within the range of 10°C to 40°C was close to the surface tension of the water.

Experimental investigation on surface tension of metal oxide–water nanofluids

“Nanofluids”, smart fluids with advanced thermal properties, have proved their promising potential in enhancing the heat transfer performance of a thermal system as well as mitigating the energy crisis of the universe. Besides all other's thermo–physical properties, surface tension governs the transport of the liquid and plays a crucial role in the heat transfer. However, the studies on the effect of surface tension on the performance of nanofluids are quite a few and demonstrated debatable results. Therefore, the present experimental study attempts to determine the surface tension of the nanofluids by dispersing Al2O3, TiO2, and SiO2 nanoparticles in Distilled Water (DW). The experiment was conducted by using the most common Du-Noüy ring method in DCAT 11EC automatic surface tensiometer. In this study, the authors analyzed all the possible effects on surface tension of nanofluids with the change in concentrations (from 0.05 to 0.25vol.%) and temperatures (from 30°C to 50°C), as well as the impact of various nanoparticles along with their sizes. The results indicate that the surface tension of the nanofluids increases with concentration, whereas decreases with the increase in temperature. Besides, the smaller nanoparticles exhibit lower surface tension than the larger ones. All in all, the surface tension of the nanofluids augments from 3.1% to 7.8% in compared with the base fluid for concentrations of 0.05vol.% to 0.25vol.% and temperatures of 30°C to 50°C, in all cases.

Effect of Nanoparticles Concentration and Their Sizes on Surface Tension of Nanofluids

“Nanofluids”, a colloidal mixture consisting of nano-sized particles dispersed in a fluid medium with amended thermo-physical properties play a critical role in the heat transfer performance of a thermal system. Surface tension is the surface energy per unit area or the force per unit length dominates the transportation of the liquid and shows a significant role in heat transfer. However, a few numbers of studies demonstrated about the effect of surface tension of nanofluids. Thus, the present experimental study investigates the effect of nanoparticles concentration as well as the influence of variation of nanoparticles along with their sizes. The nanofluids are prepared by dispersing Al2O3(13nm and 50nm),TiO2 (21nm) and SiO2 (5∼15nm and 10∼20nm) nanoparticles in Distilled Water (DW).The traditional Du-Noüy ring method was used to measure the value of the surface tension of nanofluids by an automatic surface tensiometer (DCAT 11EC). The results show that the surface tension of the nanofluids increases with increase in concentration and nanoparticle sizes. Besides,TiO2-DW nanofluids exhibit higher surface tension than Al2O3-DW and SiO2-DW nanofluids respectively. All in all, the results indicate surface tension of the nanofluids enhances from 2.62% to 4.82% in comparison with the base fluids for concentration variation of 0.05 Vol % to 0.25 Vol % at 25°C.

Experimental Investigation on Surface Tension of Water-Based Graphene Oxide Nanofluids

The water-based graphene oxide nanofluids were prepared. The surface tension of nanofluids with different mass fraction, temperature and different nanoparticle size was researched. The surface tension value was measured through ringmethod. The experimental results show that the surface tension of nanofluids is increased with increasing the mass faction of nanoparticles. But the surface tension of nanofluids with maximum concentration (0.1 wt %) is only increased up to 2.9% compared with deionized water. The surface tension of nanofluids decreases with increasing temperature and decreasing nanoparticle size. The results of this paper may provide reference for the research of absorption liquid for absorption refrigeration cycle.

Surface tension, viscosity, and rheology of water-based nanofluids: a microscopic interpretation on the molecular level

Nanofluids are suspensions of nanometer-sized particles which significantly modify the properties of the base fluids. Nanofluids exhibit attractive properties, such as high thermal conductivity, tunable surface tension, viscosity, and rheology. Various attempts have been made to understand the mechanisms for these property modifications caused by adding nanoparticles; however, due to the lack of direct nanoscale evidence, these explanations are still controversial. This work calculated the surface tension, viscosity, and rheology of gold–water nanofluids using molecular dynamics simulations which provide a microscopic interpretation for the modified properties on the molecular level. The gold–water interaction potential parameters were changed to mimic various nanoparticle types. The results show that the nanoparticle wettability is responsible for the modified surface tension. Hydrophobic nanoparticles always tend to stay on the free surface so they behave like a surfactant to reduce the surface tension. Hydrophilic nanoparticles immersed into the bulk fluid impose strong attractive forces on the water molecules at the free surface which reduces the free surface thickness and increases the surface tension of the nanofluid. Solid-like absorbed water layers were observed around the nanoparticles which increase the equivalent nanoparticle radius and reduce the mobility of the nanoparticles within the base fluid which increases the nanofluid viscosity. The results show the water molecule solidification between two or many nanoparticles at high nanoparticle loadings, but the solidification effect is suppressed for shear rates greater than a critical shear rate; thus Newtonian nanofluids can present shear-thinning non-Newtonian behavior.

Effect of particle concentration, temperature and surfactant on surface tension of nanofluids

Heat transfer performance with nanofluids depends on the thermo physical properties of the suspension. Surface tension is an important property for heat transfer calculation. In this paper, various parameters that effect on the surface tension of nanofluids such as nanofluid preparation method, effect of volume fraction, temperature, and surfactants on nanofluids have been studied. Additionally, precise assessments on the theoretical correlations related to the surface tension of nanofluids have also been included. Based on the existing experimental results, surface tension augments respectively with volume fraction intensification. Surface tension of nanofluids decreases accordingly with the increase of temperature and surfactant concentration. Nevertheless, there have been some contradictory results on the effect of volume fraction and surfactant on surface tension of nanofluids.

Surface tension of evaporating nanofluid droplets

Measurements of nanofluid surface tension were made using the pendant droplet method. Three different types of nanoparticles were used – laponite, silver and Fe 2O 3 – with de-ionized water (DW) as the base fluid. The reported results focus on the following categories: (1) because some nanoparticles require surfactants to form stable colloids, the individual effects of the surfactant and the particles were investigated; (2) due to evaporation of the pendant droplet, the particle concentration increases, affecting the apparent surface tension; (3) because of the evaporation process, a hysteresis was found where the evaporating droplet can only achieve lower values of surface tension than that of nanofluids at the same prepared concentrations; and (4) the Stefan equation relating the apparent surface tension and heat of evaporation was found to be inapplicable for nanofluids investigated. Comparisons with findings for sessile droplets are also discussed, pointing to additional effects of nanoparticles other than the non-equilibrium evaporation process.

Effect of surface tension on nanotube nanofluids

This letter presents heat transfer results that single-walled carbon nanotube (CNT) suspensions in a boiling environment can extend the saturated boiling regime and postpone catastrophic failure of the material even further than previously reported if the surface tension of the nanofluid is carefully controlled. The maximum enhancement in the critical heat flux is nearly four times for a surfactant to CNT concentration ratio of 1:5. The experimental results show that the material burnout is a strong function of the relaxation of the nanofluid surface tension with the base fluid.

Vapour-liquid equilibria and surface tensions for the nitrogen-argon-methane system at 90·67° K

Effect of γ-Al2O3 and MgO nanoparticle on surface tension of Tri Ethylene Glycol (TEG) was studied for different nanoparticle concentrations. Furthermore, the effect of nanoparticle size on the Nano-fluid surface tension was investigated. Results showed that surface tension increases for some particle concentrations and decreases for some others; in other words, a certain particle concentration could not be determined as the boundary for the increase or decrease of surface tension. Moreover, Sorbitan oleate was added to TEG solution to investigate the changes in surface tension that may occur due to the addition of surfactants. It is shown that by increasing surfactant concentration, Nano-fluid surface tension would decrease. The effect of nanoparticle size on surface tension was analyzed as well. Using experimental data, five empirical and thermodynamic-based models; i.e., Redlich–Kister (RK), Malanovsky-Marsh (MM), Jufu et al. (JBZ), Chunxi et al. (CWZ) and Santos et al. (SFF) were evaluated for surface tension estimation, and it was found that SFF method is the best method to correlate nano fluid surface tension in this study.