Graphene derivatives are promising nanomaterials for producing nanofluids due to their excellent intrinsic characteristics. Among thermophysical profile, and in addition to thermal properties, relevant property to evaluate the potential of graphene-based nanofluids as efficient and reliable heat transfer fluids is viscosity, and rheological behavior in a wider sense. Therefore, the aim of this review paper is to give a comprehensive overview of the current knowledge and results about the rheological properties of graphene-based nanofluids. After a brief description of the most common methods used for fabricating or extracting graphene derivatives, the main steps of graphenebased nanofluids preparation are introduced. Then, literature results on Newtonian/non-Newtonian behavior as well as variations in apparent dynamic viscosity of suspensions containing graphene derivatives are reviewed, analyzing the effects of shear rate, concentration, base fluids and temperature. Such an analysis is performed distinguishing the different types of graphene derivatives, namely graphene oxide, reduced graphene oxide, pristine graphene, graphene quantum dots, functionalized and doped graphene. Also, the impact of base fluid, temperature, concentration and surfactant on viscosity enhancement of graphene-based nanofluids is graphically and newly presented and discussed. In addition, the current models for viscosity prediction or correlation of those nanofluids are detailed. Finally, challenges and future works are summarized.

Nowadays, the use of nanofluids as alternative to commonly-used industrial heat transfer fluids is a topic of increasing interest. Analysing the improved efficiency of heat transfer processes according to advanced nanomaterials and obtaining stable nanofluids is one of the most interesting challenges. This paper presents a study of nanofluids based on boron nitride nanotubes and using an aqueous solution of Triton X-100 (which acts as a surfactant) as the base fluid. UV-vis spectroscopy, particle size measurements (size between 150-170 nm) and  potential (at about -25 mV) showed that stable nanofluids were obtained. Surface tension measurements were also performed. The surface tension of water was weakly affected by the presence of any amount of nanoparticles and was mainly governed by the presence of surfactant. The rheological properties of the fluids were also analysed, as were their isobaric specific heat and thermal conductivity values. A Newtonian behaviour was observed for the base fluid and the nanofluids, with no significant increase in viscosity. The isobaric specific heat increased by 8% and thermal conductivity by 10 % compared with the base fluid.Thus, the results obtained are interesting because while thermal properties improved with nanoparticle content, rheological behaviour did not change. Consequently, the nanofluids studied in the current paper do not raise the pressure drop and pumping power significantly and may therefore be a good option for thermal system applications. HighlightsStable nanofluids based on boron nitride nanotubes were prepared and analysed Isobaric specific heat increased by 8% and thermal conductivity by 10 % Newtonian behaviour was found for nanofluids with no significant increase in viscosity Surface tension was mainly governed by the presence of Triton X-100 as surfactant Rheological behaviour is not changed with nanoparticle content

The main objective of this study is to design and characterize silver suspensions based on poly(ethylene glycol) PEG400, Ag/PEG400, as energy storage media for low-temperature applications. A polyvinylpyrrolidone (PVP) treatment was applied to ~22 nm silver nanoparticles to ensure good stability in poly(ethylene glycol). An array of different experimental techniques was utilized to analyze the molecular mass and purity of base poly(ethylene glycol), morphology of dry PVP-capped Ag nanoparticles, hydrodynamic average size of dispersed Ag particles, as well as thermal stability of PEG400 and Ag/PEG400 dispersions. Samples exhibited good temporal stabilities with average hydrodynamic diameter around 50 nm according to dynamic light scattering analyses. Melting and solidification transitions were investigated in terms of temperature and enthalpy from differential scanning calorimeter (DSC) thermograms. The thermophysical characterization was completed with thermal conductivity (k), dynamic viscosity (η), isobaric heat capacity (Cp), density (ρ), and surface tension (σ) measurements of designed materials using a Hot Disk thermal conductivimeter, a rotational rheometer, a DSC calorimeter working with a quasi-isothermal modulated method, a U-tube densimeter and a drop shape analyzer, respectively. For a nanoparticle loading of only 1.1% in mass, sub-cooling reduced by 7.1% and thermal conductive improved by 3.9%, with almost no penalization in dynamic viscosity (less than 5.4% of increase). Maximum modifications in Cp, ρ, and σ were 0.9%, 2.2%, and 2.2%, respectively. Experimental results were compared with the values provided by using different theoretical or semi-empirical equations. In particular, good descriptions of dynamic viscosity as functions of temperature and nanoparticle volume concentration were obtained by using the Vogel–Fulcher–Tammann equation and a first-order polynomial η( ϕ v , n p ) correlation, with absolute average deviations of 2.2% and 0.55%, respectively.

To cite this version:Nawal Berrada, Samah Hamze, Alexandre Desforges, Jaafar Ghanbaja, Jérôme Gleize, et al.. Surface tension of functionalized MWCNT-based nanofluids in water and commercial propylene-glycol mixture. Abstract: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 propyleneglycol/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 2 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.

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.