Surface Tension Of Nanofluids Research Articles

The Role of Dispersed Particles in the Physicochemical Behavior of Nanofluids

Nanodispersions can be used to solve various practical problems, such as increasing the efficiency of heating systems, cooling of electrical equipment, intensifying oil recovery, etc., because dispersing nanoparticles in liquid media provides an inexpensive and convenient way to significantly improve various functional properties of a base fluid. Although the influence of dispersed particles on surface phenomena in systems comprising nanofluids has been studied for more than 30 years, due to a number of factors, the problem of appropriate and self-consistent description of the behavior of nanofluids will apparently remain to be the focus of scientific attention in the coming decades. This paper presents a brief review of recently published results that are of general importance for understanding the behavior of the surface tension of nanofluids, as well as the processes accompanying wetting with nanofluids and their spreading over various surfaces.

Surface-tension change of graphene-based water nanofluid and its effects on heat-transfer process

Nanofluids with high thermal conductivities are gaining attention for heat-exchange applications, particularly in boiling processes. Nanofluid heat-transfer efficiency is significantly influenced by the surface tension (ST) and wettability patterns of the nanofluid. This study investigated graphene-based water nanofluids prepared from three different viscoelastic polymer solutions. The effects of the dispersant, graphene concentration, and temperature on the ST were investigated, and the wetting behavior of nanofluids on stainless steel and polypropylene random surfaces was determined. The results indicated that the ST of the nanofluids exhibited a negative correlation with the dispersant concentration and temperature. Additionally, the inclusion of graphene reduced the ST in xanthan-gum systems but increased it in sodium carboxymethyl cellulose and polyethylene-oxide systems. Overall, the nanofluids exhibited a lower ST than water. The decrease in the nanofluid ST is ascribed to the development of a rigid network resulting from the co-adsorption of graphene nanoparticles and the dispersant at the gas–liquid interface. Furthermore, graphene has been demonstrated to enhance the wettability of the base fluids of various materials. A decrease in ST led to increased frictional resistance; however, this was counteracted by an increase in the contact angle, resulting in an overall reduction in frictional resistance. Moreover, reducing the ST can improve the fluid boiling heat transfer. Therefore, these nanofluids exhibited the dual effect of reduced flow resistance and enhanced heat-transfer efficiency. This study offers valuable insights into the behavior of nanofluids and their potential applications in areas such as energy storage and spacecraft thermal management.

The effect of SiO2 nanoparticles and surfactant on the wetting properties of an enzyme-based nanofluid as a liquid binder in the enzyme granulation process

This study investigated the effect of SiO2 nanoparticles and SDS surfactant on the wetting properties of an enzyme-based liquid binder and granule size distribution in a fluidized bed granulation process. The nanofluids were prepared by adding different SiO2 and SDS concentrations to the alkaline protease enzyme liquor with sodium carboxymethylcellulose as the granulating binder. The surface tension (ST) and contact angle (CA) of nanofluids with powder compact were measured by the pendant and sessile drop methods. A new correlation was also proposed for the ST of nanofluids. Furthermore, the influence of the nanoparticle and surfactant on the enzyme activity of nanofluids was evaluated. The results showed that nanoparticles increased both ST and CA of the base fluid, while the SDS had the opposite effect. The granulation results revealed the granule size was increased by increasing the adhesion tension of the binder, whereas the size distribution became narrower and more uniform.

Experimental investigation of nanofluids for heat pipes used in solar photovoltaic panels

The current study is aimed to measure and analyze the impact of temperature (10°C < T < 90°C) and particle concentration (0.05% < ϕ < 1.5%) on thermo-physical properties of TiO2, ZnO and CuO nanoparticles suspended in Therminol-55. The nanoparticles were characterized by using various techniques, including TEM, XRD, FTIR, TGA/DSC. TEM images reveal that the morphology of TiO2 and ZnO as spherical nanoparticles whereas that of CuO is in the form of flakes. XRD pattern for TiO2, ZnO and CuO nanoparticles possess anatase, heaxagonal and monoclinic phase respectively. TGA results show that that TiO2 losses less mass than the ZnO and CuO nanoparticles at each stage of decomposition. Thereby making it more stable thermally as compared to the other samples. Two-step method has been employed to formulate stable Therminol-55 based nanofluids containing TiO2, ZnO and CuO nanoparticles for varying particle concentrations. Results show that the thermal conductivity of suspensions containing solid conducting particles increase with increasing nanoparticle content and temperature of dispersions in the fluid. The thermal conductivity of TiO2/Therminol-55, ZnO/Therminol-55 and CuO/Therminol-55 nanofluids increases up to 17.62%, 21.55% and 24.32% at particle concentration of 1.5 wt%. Further, the experimental results demonstrate that the density of nanofluids increased significantly with increase in concentration and decreased with temperature. Surface tension of nanofluids shows decrease with increase in particle concentration. This indicates that adding nanoparticles improve thermo-physical properties of nanofluid, making it suitable for use in heat pipe. The measured data for thermal conductivity and density are compared with existing theoretical models of nanofluids to check the effectivity of conventional models. A multi-variable new generalized correlations for thermal conductivity and density of Therminol-55 based nanofluids containing TiO 2, ZnO and CuO nanoparticles are proposed.

Surface Tension of Ethylene Glycol-Based Nanofluids Containing Three Types of Oxides: Zinc Oxide (ZnO), Magnesium Oxide (MgO) and Indium Oxide (In_2O_3)

The paper presents the results of an experimental study of the density and surface tension of ethylene glycol-based nanofluids containing zinc oxide, magnesium oxide and indium oxide. Du Noüy ring method was employed to determine the values of the surface tension of these nanofluids. Samples were prepared in various mass fractions from 0.01 to 0.05 with 0.01 step. Examination was performed in the temperature range from 283.15 K up to 318.15 K. The averaged surface tension values for the studied ZnO14-EG, ZnO25-EG, MgO-EG, In_2O_3-EG nanofluids at 298.15 K are 48.685, 48.471, 48.335, and 48.462 mN·m^{-1}, respectively. It was presented that surface tension value could be consider as constant within the examined mass fraction of the particles, and the explanation of such behaviour was provided.

Effect of nanoparticles saturation on the surface tension of nanofluids

The present work focuses on the surface tension of nanofluids. An empirical model of the surface tension of nanofluids and a mechanism for the influence of nanoparticles on the value of this property are proposed. The paper explains the processes causing an increase as well as a decrease in the surface tension of nanofluids and why the value of the surface tension changes with increasing nanoparticle concentration only within a certain range. A mathematical function is presented to model this behaviour and predict both the maximum value of the surface tension and the nanoparticle concentration at which this value is reached. For the verification of the model, experimental studies of the surface tension of four types of ethylene glycol - based nanofluids indium oxide (In2O3), titanium oxide (TiO2), zinc oxide (ZnO) and multiwalled carbon nanotubes (MWCNT) at a temperature of 298.15 K were carried out. The proposed model agrees well with the obtained surface tension values of the investigated nanofluids.

The effect of boiling in a thermosyphon on surface tension and contact angle of silica and graphene oxide nanofluids

Thermosyphons are heat transfer devices characterised by high efficiency due to simultaneous phase changes occurring in the evaporation-condensation cycle of working fluid. One of the most promising solutions to enhance their heat transfer capacity of the device is the use of nanofluids – suspensions of particles with at least one dimension below 100 nm. It was determined that nanofluid does not influence the work of thermosyphons condenser section and the focus should be put on the boiling process in the evaporator section. During boiling, nanoparticles tend to deposit on the heater’s surface, what alters characteristics of this surface and near surface hydrodynamics. This changes the appearance of nanofluid, but the precise effect on how the deposition of particles affects the properties of nanofluid is unknown. Changes in surface tension and wettability affect boiling regimes (e.g. reduced surface tension reduces the size of departing bubbles and inhibits geysering), and efficiency of heat transfer through the device. Understanding of those parameters is crucial for the development of appropriate models describing heat transfer in thermosyphon working with nanofluids. The main goal of this study is to determine surface tension and contact angle of nanofluids based on silica nanoparticles and nano-sized graphene oxide flakes before and after the experimental boiling cycle in the thermosyphon. Results show that, in comparison with water, silica nanofluid (2 vol%) is characterised by lower surface tension and contact angles on both analysed surfaces. After-use silica nanofluid exhibited noticeably higher averaged surface tension and smaller contact angles in comparison to the fresh working medium. The change was most likely due to the decreased concentration caused by the deposition of nanoparticles during the thermosyphon operation. Still, the differences between before-use and after-use samples were smaller than the measurement uncertainties. Before-use graphene oxide nanofluid already showed surface tension and contact angle similar to water due to low concentration of graphene flakes (0.1 g/L). Consequently, the properties of after-use graphene oxide fluid were also not much different from water. Additional measurements of surface tension for graphene oxide nanofluid with and without addition of sodium dodecyl sulphate surfactant allowed to differentiate the effects caused by graphene flakes and surfactant. The surfactant reduced the surface tension of the nanofluid, but the change was smaller than in case of surfactant addition to pure water.

3D printed measuring device for the determination the surface tension of nanofluids

The paper presents a method for building a low-cost tensiometer to measure the interfacial surface tension between liquid and air. The project is based on common and well-known devices (analytical balance, Arduino micro controller, DC motor) and manufacturing techniques (CAD, 3D printing), mostly available in scientific and industrial laboratories. For the control of proposed devices the user-friendly software with graphical user interface was prepared in an open-source widget toolkit Qt with the use of programming language C++. The source code of the software and CAD models for printing components that allow to the self-build of the described tensiometer, were provided. Finally, the proposed measuring device was used to determine the surface tension of two types of ethylene glycol based nanofluids containing silicon nitrides and multi-walled carbon nanotubes. It was presented that proposed device could be successfully used with complex systems like nanofluids, even in case that commercially available equipment fails.

Ultrasonically tuned surface tension and nano-film formation of aqueous ZnO nanofluids

Nanofluids’ thermophysical properties and heat transfer performance has been investigated for many years, while research on their surface tension (ST) and wetting behavior is very limited. To assess nanofluids potential as industrial products, a complete picture is required to prove their performance in a specific application. Boiling heat transfer, microfluidics and drug development are among the applications where ST is a variable. ST of water-based ZnO nanofluids were measured in the presence and absence of direct ultrasonication. The experiments covered variation of ST with ZnO concentration (0.05–0.4 vol%), ultrasonication amplitude (40% and 100%) and duration. To the best of the authors’ knowledge, this is the first report of ST– ultrasonication process relation for a nanofluid. Results showed that after direct ultrasonication, nanofluids ST is strongly affected by the temperature raise, and in those cases relative ST may provide a clearer picture. A nano-film over individual and agglomerated nanoparticles spotted via TEM imaging was affected from the ultrasonication. Such a nano-film can play a key role in the anomalous thermal transport and wettability of nanofluids. Statistical analyses revealed that changes in ultrasonication amplitude resulted in a statistically significance difference on nanofluid ST and relative ST. Changes in nanoparticle concentration caused a significant difference on the nanofluid ST while the difference in relative ST was insignificant. Variation of ultrasonication duration caused significant variations on the relative ST while the difference in nanofluid ST was not significant. This work highlights that based on specific applications ST and other related features of any nanofluid can be adjusted employing proper ultrasonication conditions.

4S consideration (synthesis, sonication, surfactant, stability) for the thermal conductivity of CeO2 with MWCNT and water based hybrid nanofluid: An experimental assessment

The main objective of the present study is to investigate the impact of nanofluid stabilization techniques (hybrid stabilization approach, i.e., a combination of different mechanical and chemical methods) on the stability and thermal conductivity of CeO2+MWCNT (80:20)/water based hybrid nanofluid. The nanofluid has been prepared by using the two-step method, and a broad range of ultrasonication time (30, 60, 90, 120, 150, and 180 min) has been used. Furthermore, different kinds of charged surfactants, two anionic (sodium dodecyl benzene sulfonate (SDBS), sodium dodecyl sulphate (SDS)), two cationic (cetyltrimethylammonium bromide (CTAB), distearyl dimethylammonium chloride (DDC)), and two polymers (gum Arabic (GA), PVP (polyvinyl pyrrolidone)) have been added to the base fluid with a different nanoparticle to surfactant mixing ratios (5:0, 4:1, 3:2, 2:3 and 1:4). The prepared samples were investigated at different pH values and different preparation days (15th, 30th, 45th,60th, and 90th day) to evaluate which surfactant and mixing ratios are sufficient to achieve a stable nanofluid for more than 90 days. The observed optimum volumetric mixing ratio of surfactant and CeO2+MWCNT nanoparticle, pH level and sonication time are around 3:2, 9.5, and 90 min, respectively, for which hybrid nanofluid yields maximum zeta potential value as an indicator of nanofluids long term stability. The results of zeta potential analysis indicated that CTAB surfactant shows the best impact up to the 30th day from preparation, after the 30th day, the SDBS surfactant shows the highest degree of stability of the hybrid nanofluid applying 3:2 mixing ratio and 90 min sonication. Results clearly showed that the nanofluid hybrid stabilization approach has a strong relation with thermal conductivity. The addition of higher amounts of surfactant (more than 3:2 mixing ratio) caused a small thermal conductivity reduction. Additionally, precise assessments of the surfactant effect on a hybrid nanofluid's surface tension have also been studied. Finally, a correlation to predict the experimental value of thermal conductivity has been proposed from the experimental data, which could be beneficial for various heat transfer applications.

Dominance of cohesion of EG-water molecules over Van der Waals force between SiO2-ZnO nanoparticles in the liquid interface

The effects of loading SiO2-ZnO nanoparticles on EG-water surface tension were examined in this study. Using SITA dynotester, surface tension was measured at 25–50°C. The dispersed nanoparticles reduce the density of liquid molecules at the interface and weaken the cohesion which in turn attenuate the surface tension. On the other hand, the strong force of Van der Waals between nanoparticles strengthens the surface tension. Laboratory results showed that the effects of the reduction in cohesive force could not compensate by the Van der Waals force which consequently the EG-water surface tension reduced up to 13.2%.For the base fluid, the sensitivity of surface tension to the temperature was 0.1233 mN/m°C, while this figure for the nanofluid at 0.1 and 2 vol% was 0.0952 and 0.0566 mN/m°C, respectively. Therefore, it is claimed that the presence of nanoparticles decreased surface tension sensitivity to temperature. Finally, a correlation-based on the regression technique was developed by which the nanofluid surface tension behavior navigated with acceptable accuracy.

Sensitivity of adhesive and cohesive intermolecular forces to the incorporation of MWCNTs into liquid paraffin: Experimental study and modeling of surface tension

In this study, the effect of the presence of MWCNTs on the surface tension of paraffin-based fluid was examined. Surface tension measurements of samples containing MWCNTs (0.005–5 wt%) were performed at temperatures of 25–70°C by SITA dynotester. Surface tension corresponds to the adhesive and cohesive forces resultant. Adding nanoparticles diminishes the cohesive force and simultaneously strengthens the adhesive force. Owing to the presence of MWCNTs, the effect of adhesion on the surface tension was superior to the effect of cohesion which consequently diminishes the surface tension. The loading nanoparticles efficacy on surface tension is weekend as the temperature increases. On the other hand, the presence of particles diminishes the sensitivity of surface tension to the temperature growth. In other words, temperature and mass fraction weaken each other's effects. The highest decrease in surface tension is reported to be 18.6%, which occurs at the lowest temperature as well as the maximum mass fraction. The prediction of MWCNTs/liquid paraffin surface tension behavior was performed by applying nonlinear regression and artificial neural network techniques, and statistical calculations revealed that the R-squared for the first and second techniques was calculated to be 0.99 and 0.998, respectively. Both techniques accurately predict nanofluid surface tension.

Dispersion stability and surface tension of SDS-Stabilized saline nanofluids with graphene nanoplatelets

The dispersions of engineered nanomaterials in fluids have envisioned numerous industrial applications. Despite less experimental data available on the surface tension of nanofluids, it is one of the critical parameters to define thermal configurations and two-phase transport properties. This study focuses on the benchmark experimental investigation of the surface tension behavior in graphene nanoplatelets-based saline nanofluids in ambient air using the pendant drop method. Graphene nanoplatelets are dispersed in saline fluid (30PPT) using optimum anionic SDS stabilizer and ultrasonication, exhibiting excellent stability for minimum 72 h. Different characterizations are performed for nanoplatelets and nanofluid stability such as electron microscopy, FTIR, XRD, DLS and sedimentation analysis. Surface tension measurements are taken at varying concentrations of graphene nanoplatelets range of 0-0.25 wt% and temperature range of 25−65 °C. The obtained results from this research exhibit that the addition of nanoplatelets drops the surface tension of saline fluid by 21 %. However, the increase in concentration from 0.05 wt% to 0.25 wt% does not have a considerable implication on the overall surface tension behavior. It is observed that the surface tension of the saline fluid and the nanofluid decrease with the elevation in temperature.

Effect of Nanoparticle Type and Surfactant on Heat Transfer Enhancement in Spray Cooling

In this study, the heat transfer characteristics of nanofluids used in spray cooling systems were examined. Three nanofluids, i.e., Cu, CuO, and Al2O3, respectively, with volume fractions ranging from 0.1% to 0.5%, as well as different volume fractions of a surfactant Tween 20, were used. In addition, their contact angles were measured to examine the heat-transfer characteristics. Under the same experimental conditions, with the increase in the volume fraction of the Cu nanoparticles from 0.1% to 0.5%, the maximum heat flux qmax increased from 3.36 MW/m2 to 3.48 MW/m2 from the impinging central point to r = 30 mm (r is the distance from the impingement point), and the corresponding temperature of qmax increased from 400°C to 420°C. Results revealed that with increasing Tween 20 concentrations, the contact angle decreased because of the decrease in the surface tension of nanofluids and improvement of the wetting ability, and the corresponding qmax increased from 3.48 MW/m2 to 3.94 MW/m2 at the impact central point.

Surface tension of functionalized MWCNT-based nanofluids in water and commercial propylene-glycol mixture

Nanofluids which consist of the addition of nanoparticles in a base fluid are envisaged for a large domain of applications. For many of them, the surface tension (ST) behavior of the prepared nanofluids is a key parameter to exploit their thermophysical properties. Due to their remarkable properties, carbon nanotubes (CNTs) are commonly used to develop nanofluids. However, the evolution of the ST of CNT-based nanofluids is still far from being understood and predictable. In the present work, two base fluids were used: water and a commercial mixture of propylene-glycol/water (around 40:60 wt%). The impact of the used multi-walled CNT (MWCNT) addition, MWCNT concentration (0.001 and 0.1 wt%) and temperature variation (273.15–333.15 K) on the density and ST evolution for the two kinds of CNT-based nanofluids is studied. The chemically modified MWCNTs are assumed to bear both localized hydrophilic areas due to grafted functional groups and remaining hydrophobic surfaces. The found difference in ST behavior between the two types of nanofluids is explained in light with the involved interfaces in each nanofluid. ST evolution is found to strongly depend on the CNT surface properties.

Surface tension of ethylene glycol-based nanofluids containing various types of nitrides

This paper focuses on an experimental study of the surface tension of nanofluids based on ethylene glycol with various types of nitride nanoparticles. Samples were prepared using a two-step method with mass content between 1 and 5% of particles. Nanofluids contain three types of nitride nanoparticles: aluminum nitride, silicon nitride and titanium nitride with various particle average sizes. Surface tension of nanofluids was investigated at a constant temperature of 298.15 K with two different techniques: du Noüy ring method and pendant drop method. It is presented that experimental values obtained with both methods are in good agreement with each other. Also, results obtained during this study show that the addition of this type of nanoparticles does not have a significant impact on the surface tension of base fluid for the concentrations and diameters of nitride nanoparticles considered.

The relationship between the surface tension and the saturated vapor pressure of model nanofluids

Information on surface tension is necessary for modeling boiling processes in nanofluids. It was shown that the problem of predicting the surface tension of complex thermodynamic systems, such as nanofluids, remains outstanding. It should be noted that the surface tension of liquids and the saturated vapor pressure are due to a specific intermolecular interaction in the region of spatial heterogeneity of the substance (surface layer). Moreover, the compositions of the surface layer of nanofluid and its liquid phase are not equal. The presence of nanoparticles in the base fluid affects the composition of the surface layer of liquids. However, there are no methods for determining the composition of the surface layer of nanofluids and this fact complicates establishing the dependence of the surface tension on the state parameters of nanofluids. It should be mentioned that the number of possible methodological errors in measurements of the saturated vapor pressure of nanofluids is significantly lower than for the surface tension measurements. Therefore, in the development of models for predicting the surface tension, scientific and practical interest has establishing the relationship between the surface tension and the saturated vapor pressure of nanofluids. In the presented work, we consider the nanofluids of isopropanol/Al2O3 nanoparticles and o-xylene/fullerenes C60. Saturated vapor pressure and surface tension of nanofluids of isopropanol/Al2O3 nanoparticles have been studied in the temperature range 293 – 363 K and concentrations of Al2O3 nanoparticles 0-8.71 g/kg. Measurement of saturated vapor pressure and surface tension of nanofluids of o-xylene/fullerenes C60 have been performed in the temperature range 283 – 348 K and the concentration of C60 0-7.5 g/kg. It is shown that additives of Al2O3 nanoparticles and fullerenes C60 lead to a decrease in the surface tension and increase in the saturated vapor pressure. It is shown that there is a universal dependence between the reduced surface tension and saturated vapor pressure for the researched nanofluids.

Analysis of flow and heat transfer characteristics of nanofluids surface tension driven convection in a rectangular cavity

The addition of nanoparticles into base fluid not only can improve thermophysical properties, but also can change its surface tension, so the flow and heat transfer of nanofluids surface tension driven convection can be significantly influenced by nanoparticles. The present paper reports the analysis of flow and heat transfer of nanofluids surface tension driven convection in a rectangular cavity, in which two types of nanofluids of distilled water–Al2O3 and PGW(60% propylene glycol and 40% water by mass)-ZnO are considered, and the two-phase Mixture model is used to simulate the nanofluids flow. The computational results show that, for nanofluid distilled water–Al2O3, the convective intensity and heat transfer performance indicates a nonmonotonic change with nanoparticles volume fraction increasing, however, for nanofluid PGW–ZnO the convective intensity and heat transfer performance decreases monotonously. Moreover, the flow characteristics and entropy generation under different nanoparticles volume fractions are analyzed in detail.

Thermophysical and dielectric profiles of ethylene glycol based titanium nitride (TiN–EG) nanofluids with various size of particles

In this study, thermophysical properties such as thermal conductivity, rheological behavior and surface tension of ethylene glycol (EG) based nanofluids containing titanium nitride (TiN) nanoparticles with volume fraction ranging from 0.0022 to 0.0111 and with various nanoparticle sizes have been experimentally investigated at constant temperature. In addition, dielectric properties of these nanofluids were also measured at same temperature and discussed in detail. It is shown that nanoparticle content increase leads to similar trends for nanofluids properties, while nanoparticle size has different effect following the studied property. Actually, thermal conductivity and surface tension of nanofluids are higher with smaller nanoparticles for same nanoparticle content. Following the nanoparticle content, a transition from Newtonian nature of nanofluids to shear-thinning yield stress material with viscoelastic structure occurs. Lower the nanoparticle size, higher is the viscoelastic structure and the yield stress when they are present. Thixotropy of the nanofluids was also reported and depends both on concentration and size of nanoparticles. Both dielectric properties and electrical conductivity of TiN–EG nanofluids increase with nanoparticle content and are higher for suspensions containing bigger nanoparticles. Moreover, experimental data for thermal and electrical conductivities enhancement were modeled and compared to existing correlations, simple linear relationships were also proposed considering the effect of nanoparticle content and average size.

Surface tension profiles of nanofluid containing surfactant during microwave irradiation

Manipulation of the surface tension is useful in improving heat and mass transfer performances of nanofluids in thermal systems. In our previous study, the effect of microwave irradiation on the reduction of surface tension of nanofluids (Fe2O3) was found even after it was turned off. In this study, a synergistic effect of microwave irradiation and surfactant addition (SDS) was investigated to obtain further surface tension reduction of nanofluid. Experimental results indicate that surfactant addition is effective for wider particle number density in reducing surface tension, and the reduction level strongly depends on the surfactant concentration. On the other hand, effect of the number density on the surface tension reduction is less significant for the same concentration of surfactant. From the obtained data, a combination of microwave irradiation and surfactant addition shows potential to be used as a promising method to manipulate surface tension of nanofluids.