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International audience; The evolution in nanofluid technology in the last few decades has proved the prodigious potential in several applications, especially thermal management and lubrication. An extensive investigation of nanofluid's rheological profile is vital to characterize the fluid flow behavior. This study signifies the rheological aspects of graphene and its hybrid nano-dispersions in thermal oil. The experimental investigation involves three sets of nanofluids containing graphene, graphene-carbon nanotubes, and graphene-carbon nanofiber hybrid nanofluid dispersions in thermal oil with varying loadings (0–2 mass%). The flow behaviors of all sets of nanofluids are measured at a wide shear range of 1–2000 s−1 and five different temperatures from 298 K to 338 K. The morphology and stability are validated by performing several characterizations for nanomaterials and nanofluids. Non-Newtonian fluid behavior is observed in all nanofluids. This study reveals a few interesting outcomes where the fluid behaving as a Power Law model is shifted to the Herschel-Bulkley model at high loadings of nanomaterials. A comparative analysis illustrates that both hybrid additives act as viscosity reducers for graphene-based nanofluids, where graphene-carbon nanofibers hybrid nanofluids exhibit noticeable reduction. A parametric analysis is performed on the viscous behavior involving the impact of shear rate, temperature, nanomaterial loading, and surfactant concentration. The increment in viscosity shoots up to 180 % for graphene-nanofluid at the 2000 s−1 shear rate and 338 K temperature, but still exhibits shear thinning phenomena. A correlation is also proposed for the nanofluid viscosity in terms of nanomaterial loading and temperature, indicating a good agreement at varying shear rates.

International audience; The objective of this research is to examine how ultrasonication time affects agglomeration, stability, thermal conductivity, and viscosity of CuO nanofluid. Using different reaction conditions, distinct shaped CuO nanoparticles are synthesised and dispersed in an EG: DW (70:30) ratio with 0.3 vol%. Microscopic and TEM images are used to analyze colloidal solutions with varying sizes and shapes of nanoparticles. After 30 days of preparation, the zeta potential is measured to ensure that the suspension is stable. The Bridgman equation is used to compute thermal conductivity using sound velocity values. Viscosity of colloidal suspension is measured by viscometer. All of the studies are performed at 30° ± 2 °C room temperature for ultrasonication times ranging from 30–120 min. At an optimal sonication time of 80 min, there is less agglomeration and more stable particle dispersion. In comparison to other morphological suspensions, CuO spherical shape suspended nanofluid has the lowest viscosity and maximum thermal conductivity, as well as the most stable fluid. At the optimal sonication period, measured results demonstrate thermal increase and decreased viscosity, which could have implications for heat transfer applications.

International audience; Nanofluids have emerged as powerful instruments in heat transfer applications due to their improved thermophysical properties. Additionally, many heat transfer equipments are started to be operated within the range of transitional flow regions in the advances in thermal management enhancement techniques. However, up to date, the friction factor and heat transfer coefficient features of nanofluids within the transitional flow regions and the effect of nanoparticle addition into the base fluid on the laminar-to-turbulent transition characteristics are still not understood clearly with contradictory published results. At this point, this paper comprehensively reviews the studies dealing with the nanofluid flow within the transitional flow regions for internal flow applications. After the presentation of applications of nanofluid flow in the transitional flow regions, the nanofluid properties such as nanoparticle type and concentration and base fluid type in the reviewed studies are given in detail. The pressure drop and heat transfer features of nanofluid flow within the transitional flow regions are distinctly identified and discussed for internal flows. The effect of the nanoparticle addition into the liquid on the transition onset is discussed with results from different research groups. A complete evaluation, challenges and further studies are proposed based on available results in the literature.

International audience; While numerical modelling of different types of nanofluids in various microchannel heat sink geometry under different flow conditions are many, few involved utilizations of experimental data. Reports so far have indicated the potential cooling capability of nanofluids in general, yet none have investigated the effects of the surfactant alone on the fluid flow, in particular the thermofluid flow pattern. This paper reports the results of a numerical simulation with CFD on the fluid flow of Triton TX-100 surfactant with boron nitride nanotubes (BNN) in distilled water (base fluid) at 30 and 50 °C. The nanofluid (BNNT) operated at high temperature provided a lower thermal resistance. A higher pumping power was found for BNNTs and TX-100 at 30 ℃ compared to distilled water at both temperatures. The outcomes of the present study provide a better understanding of flow characteristic and flow visualization along a microchannel heat sink so that better design decision can be made for improvement of this application for different needs.

International audience; A hybrid solar photovoltaic-thermal collector is the combination of a solar thermal unit and a photovoltaic panel for the simultaneous generation of heat and electricity. In these systems, a fluid is used to cool photovoltaic panels and, thus, prevent their reduction of electrical efficiency. The hot fluid leaving the system can also be used in various kinds of engineering applications, from agriculture to heating, ventilation and air conditioning units, and process heat in utilities. Coolants used in photovoltaic-thermal units include air, water and nanofluids, among which air is less efficient than water and nanofluids due to its low specific heat capacity. Although extensive research has been done on the exergy performance of photovoltaic-thermal units, the number of published review articles in this field is very limited. This paper presents a critical review with some recommendations for future research on the topic of exergy examination of water-based and nanofluid-based photovoltaic-thermal units. As a first step, the concept and mathematical exergy relations are introduced. Then, water-based and nanofluid-based photovoltaic-thermal units are exergetically discussed in detail, followed by the description of novel units. At the end of each section, some suggestions are presented for future exergy examination of those types of photovoltaic-thermal units.

A computational analysis has been performed in this study to solve three-dimensional thermo-solutal natural convection in a differentially heated cubical enclosure filled with micropolar CNT/water nanofluid stabilized by two types of surfactants lignin and sodium polycarboxylate. The work is carried out for different pertinent parameters as Rayleigh number (104 $$\le$$ Ra $$\le$$ 106), micropolar parameter (0 $$\le$$ K $$\le$$ 10), buoyancy ratio (−1 $$\le$$ N $$\le$$ 0) and nanoparticles’s volume fraction (0.0055% $$\le \varphi \le$$ 0.557%). It is observed that the heat and mass transfer rates are lower for a micropolar nanofluid model when compared to the pure nanofluid model. In fact, the enhancement of micropolar parameter results a decrease in average Nusselt and Sherwood numbers. The use of lignin as a surfactant ameliorates heat and mass transfer rate and nanofluid flow better than the use of sodium polycarboxylate as a surfactant. The nanoparticles volume fraction can be used as a control element for heat rate and fluid flow. Thus, for a nanoparticles volume concentration less than the critical value, the flow intensity is ameliorated and is deteriorated when it exceeds this value.

International audience; A parametric numerical investigation has been performed of three-dimensional combined thermal-solutal capillary and buoyancy convection performances of micropolar multi-walled carbon nanotubes-water nanofluid. The governing equations are given based on vorticity-vector potential formulation and numerically resolved with finite volume method. The effects of Rayleigh number (10(4)

International audience; Nanofluids are considered as a new generation of heat transfer fluids since they exhibit thermophysical properties improvements compared with conventional heat transfer fluids. The high thermal conductivity of nanofluids and even the isobaric specific heat enhancements over conventional liquids make these colloidal suspensions very attractive in many research areas, including solar energy. In this work, nanofluids based on tungsten disulphide (WS2) nanosheets have been prepared from the thermal oil currently used as heat transfer fluid in Concentrating Solar Power (CSP) plants. The high aspect ratio of WS2 bidimensional nanostructures provides high long-term colloidal stability to the nanofluids and facilitates heat transport. Cetyltrimethylammonium bromide and polyethylene glycol have been used as surfactants to improve the exfoliation process and enhance the colloidal stability of the nanomaterial dispersions. Some properties such as density and viscosity of the base fluid have not been significantly altered by the presence of WS2 nanosheets in the base fluid. However, studies on the thermal properties of nanofluids have shown promising results with increases in thermal conductivity of up to 33% and heat transfer coefficient by 21% over the base fluid. Furthermore, it has been estimated that the overall efficiency of the CSP system could be improved by 31% by replacing the conventional thermal fluid with 2D-WS2-based nanofluids.

International audience; In this study, the combined impact of carbon nanotube volume fractions and the electric field on the enhancement of dielectric oil heat transfer is investigated. The geometry studied is an annular layer filled with the dielectric oil and bounded by two eccentric or concentric cylinders. A temperature gradient and an electrical potential difference are applied between the two cylindrical walls. The goal is to analyse the flow behaviour and the heat transfer improvement using a double enhancement technique by combining an active (electric field) and passive (nanoparticles) approach. An in-house numerical simulation code using the finite volume method was developed to solve the set of coupled equations describing the conservation laws of the electro-thermo-hydrodynamic flow associated with the oil. A parametric study, outlining the influence of different relevant variables has been performed. The parameters investigated are the thermal Rayleigh number , the electrical Rayleigh number , the radius ratio , the eccentricity , the nanotubes volume fraction and the injection level respectively. The effect of these variables on the heat transfer intensification is examined in detail. According to the adopted configuration, heat transfer intensifications between 3% and 77% have been recorded essentially when an electric field was applied. Also, the addition of a 0.5% volume fraction of carbon nanotubes provides a heat transfer improvement of around 27%. Furthermore, for a first time a multiparameter correlation has been developed. This correlation can be useful to better understand the impact of various physical parameters on the heat transfer in annular spaces and also to predict exact values of the Nusselt number.

International audience; This editorial note is dedicated to the Virtual Special Issue about the “Advances in Rheological Behavior of Nanofluids and Ionanofluids”. After a brief presentation of the objectives of this VSI, the contributions published in the Journal of Molecular Liquids are introduced.

International audience; The main aim of the present study is to evaluate the influence of multi-walled carbon nanotubes (MWCNTs) and TiO2 nanoparticles (NPs) on lubricant and fluid flow within natural gas turbine meters. In light of this purpose, disparate concentration of TiO2 NPs (0.1, 0.2, and 0.3 wt%), various volume flow rates 0.14, 0.35, and 0.12 were employed for experimental analyses. In the facet of simulation, Gambit software version 2. 4. 6 to mesh oil pathway and Fluent software version for solving the equations were utilized. It was revealed that the pressure drop in the presence of nanoparticles was increased. Moreover, there was an increase in pressure drop value with raising the NPs concentration; for instance, the pressure drop value of MWCNTs-containing nanofluids at the volume flow rate of 0.35 cm enhanced from 92.72 Pa to 94.64 Pa as the NPs concentration raised from 0.1 to 0.3. Furthermore, modeling outcomes corroborated the uptrend in pressure drop value by increasing the volume flow rate and reported the maximum pressure drop value of 0.12 . On the other hand, the numerical results revealed that the friction coefficient is directly and inversely proportional to NPs concentration and the volume flow rates, sequentially. Additionally, with increasing the volume flow rate, the entrance length increased, and reaching the developed state was delayed. It is worth noting as the final finding of this study that increasing the NPs concentration resulted in decreasing the entrance length and the fast reaching of the developed state.

This paper presents the preparation and thermal/physical characterization of phase change materials (PCMs) based on poly(ethylene glycol) 400 g&middot, mol&minus, 1 and nano-enhanced by either carbon black (CB), a raw graphite/diamond nanomixture (G/D-r), a purified graphite/diamond nanomixture (G/D-p) or nano-Diamond nanopowders with purity grades of 87% or 97% (nD87 and nD97, respectively). Differential scanning calorimetry and oscillatory rheology experiments were used to provide an insight into the thermal and mechanical changes taking place during solid-liquid phase transitions of the carbon-based suspensions. PEG400-based samples loaded with 1.0 wt.% of raw graphite/diamond nanomixture (G/D-r) exhibited the lowest sub-cooling effect (with a reduction of ~2 K regarding neat PEG400). The influences that the type of carbon-based nanoadditive and nanoparticle loading (0.50 and 1.0 wt.%) have on dynamic viscosity, thermal conductivity, density and surface tension were also investigated in the temperature range from 288 to 318 K. Non-linear rheological experiments showed that all dispersions exhibited a non-Newtonian pseudo-plastic behavior, which was more noticeable in the case of carbon black nanofluids at low shear rates. The highest enhancements in thermal conductivity were observed for graphite/diamond nanomixtures (3.3&ndash, 3.6%), while nano-diamond suspensions showed the largest modifications in density (0.64&ndash, 0.66%). Reductions in surface tension were measured for the two nano-diamond nanopowders (nD87 and nD97), while slight increases (within experimental uncertainties) were observed for dispersions prepared using the other three carbon-based nanopowders. Finally, a good agreement was observed between the experimental surface tension measurements performed using a Du No&uuml, y ring tensiometer and a drop-shape analyzer.

International audience; Nanofluids which consist of nanoparticles added to conventional fluids (or base fluids) are considered as promising heat transfer fluids. Compared to metal, metal oxide nanoparticles and carbon nanotubes, graphene with its extremely high intrinsic thermal conductivity became the best candidate to design nanofluids. Such nanofluids have the potential to be highly-efficient heat transfer fluid by reducing loss of heat and increasing cooling rates. Over the last ten years, graphene-based nanofluids have shown significant thermal conductivity enhancements, however due to the numerous and interlinked parameters to consider, optimisation of their efficiency is still challenging. The present review article analyses and discusses the reported thermal conductivity in term of performance with respect to the amount of the used graphene to develop the prepared nanofluids. The enhancement of thermal conductivity must meet the minimal graphene amount due to its production cost and because graphene nanoparticles induces high viscosity in the nanofluid leading to higher energy consumption for the heat transfer systems. Unprecedented in the literature, this work proposes a simple approach to quantitatively compare the enhancement of the thermal conductivity of the nanofluids. The thermal conductivity performance parameter introduced could be applied to all nanofluid families and may become a reference tool in the nanofluid community. Such tool will help to determine the optimal preparation conditions without compromising the superior thermal performances.

This paper reports the influence of surfactant Triton X-100 on boron nitride nanotubes (BNNTs) nanofluid in non-optimized and optimized microchannel heat sink (MCHS) at 30 °C and 50 °C. The MCHS performance was evaluated in terms of thermal resistance and pressure drop, utilizing experimental thermophysical properties of distilled water, a mixture of distilled water and surfactant Triton X-100 as base fluid, and nanofluid BNNTs at weight concentration of 0.001% into MCHS models which was further optimized with the Multiple Objective Particle Swarm Optimization (MOPSO) technique. It is found that the surfactant at 30 °C improves the MCHS thermal capabilities without nanotubes by 0.8% even after optimizing the MCHS according to the fluid properties. Conversely, surfactant Triton X-100 reduces pressure drop greatly with any change in thermal resistance at 50 °C and paired cooperatively with BNNTs nanofluid 0.001wt.% - mitigating pressure drop increment caused by the nanofluid resulting an overall performance improvement by 1.25% and 1.97% for thermal resistance and pressure drop respectively in MCHS systems and reduced to 1.3% and 3.2% after optimization. Optimized MCHS dimensions given by MOPSO could be manufactured and additionally gave wider solutions for large reduction of pressure drop up to 80% for economic MCHS with a drawback of higher thermal resistance.

We theoretically investigate the thermoelectric properties of semiconducting (gapped) materials by varying the degrees of polynomials in their energy dispersion relations, in which either the valence or conduction energy dispersion depends on the wave vector raised to the power of two, four, and six. The thermoelectric transport coefficients such as the Seebeck coefficient, electrical conductivity, and thermal conductivity are calculated within the linearized Boltzmann transport theory combined with the relaxation time approximation. We consider various effects such as band gaps, dimensionalities, and dispersion powers to understand the conditions that can give the optimal thermoelectric efficiency or figure of merit ($ZT$). Our calculations show that the so-called pudding-mold band structure produces larger electrical and thermal conductivities than the parabolic band, but no significant difference is found in the Seebeck coefficients of the pudding-mold and parabolic bands. Furthermore, we find that a high $ZT$ can be obtained by tuning the band gap of the material to an optimum value simultaneously with breaking the band symmetry. The largest $ZT$ is found in a combination of two-contrasting polynomial powers in the dispersion relations of valence and conduction bands. This band asymmetry also shifts the charge neutrality away from the undoped level and allows optimal $ZT$ to be located at a smaller chemical potential. With some reasonable values of thermal conductivity parameters, the maximum $ZT$ for the bulk systems can be larger than 1, while for one-dimensional systems it can even reach almost 4. We expect this work to trigger high-throughput calculations for screening of potential thermoelectric materials combining various polynomial powers in the energy dispersion relations of semiconductors., Comment: 12 pages, 11 figures

International audience; This work investigates the convective heat transfer enhancement of water-based nanofluids in pipe heat exchanger used for the ethanol condensation process. The nanofluids were produced with different nature of nanoparticles, Cu, Fe3O4, MWCNT, and graphene, in the volume concentration 0.01–0.1%, using different surfactants. These nanoparticles are characterized by X-ray powder diffraction (XRD), Scanning electron microscopy (SEM), specific surface area (BET), and Dynamic light scattering (DLS). Density, thermal conductivity, and viscosity of base fluids and nanofluids were experimentally determined at a relevant temperature of 20 °C. Convective heat transfer enhancement under laminar regime was evaluated from a well-designed experimental setup. As the main results, the thermal conductivity of nanofluids increases up to 3–5% and the viscosity can increase or decrease with nanoparticle concentration, showing a lubricating effect of nanoparticles coupled with respective surfactant. It was shown that the heat transfer properties, heat transfer coefficient, and Nusselt number, are increased with nanofluids compared to water and base-fluids, up to 20%, in the range of Pe 2000–10000. Experimental heat transfer properties are shown to be greater than theoretical ones. Finally, copper nanofluid at low concentration appear to be the best candidate for the application and pipe flow geometry considered.

International audience; : Concerns over the exponential increase in the heat produced per unit area in electronic chips have driven advanced research into the nanofluid capability as a coolant. Generally reported for its improved thermal conductivity in particular at higher concentrations, different types of surfactant normally added used to stabilize the nanofluid have reported different thermal resistance to heat flow. This paper reports an analysis of the thermal performance of a nanofuid-cooled microchannel heat sink (MCHS) with 0.1% volume fraction of CNT nanofluid utilizing two different surfactants; Lignin (N2) and sodium polycarboxylate (N3) as stabilizers. Multi-objective particle swarm optimization (MOPSO) algorithm was utilized to simultaneously minimize the thermal resistance and pumping power by optimizing the design parameters; the wall width and channel aspect ratios. Optimization outcomes showed that the thermal resistance of CNT nanofluids is lower than water by 1% at 20°C. Nanofluid with N3 has a significantly higher pressure drop than water, up to 47%. CNT nanofluid with N3 performed poorly due to the high viscosity which consequently results both in higher thermal resistance and pressure drop. Since a surfactant alters the properties of nanofluid, it could improve or deteriorate the performance of a MCHS overall and must not be taken lightly as a MCHS is expected to operate for a long time.

International audience; In this research, two different diesel oil-based nanofluids were prepared and the influence of temperature and nanoparticle content were examined on viscosity, tribological, and physicochemical features of diesel oil. The kinematic viscosity of samples was experimentally evaluated based on standard ASTM D445. The greatest viscosity increment was diagnosed at 0.7 wt% and 100 °C for both of the prepared nanofluids. The anti-friction behavior of the nanofluids was studied utilizing a pin-on-disc tribometer. The acquired outcomes revealed that ZnO and MoS2 nanoparticles (NPs) could promote the tribological characteristics of pure diesel oil. By analyzing the friction coefficient values and line roughness of the wear surface (Ra), an optimal concentration of ZnO and MoS2 nanoparticles (NPs) were found to be around 0.4 wt% and 0.7 wt%, respectively. The friction factor and pumping power were also measured at diverse content of nanoparticles and flow rates showing that the pumping power was enhanced by the incorporation of nanoparticles.

International audience; Recent advancements in thermo-fluid technology assisted with highly thermal conductive nanomaterials have shown assuring outcomes. It is also proven that thermal conductivity alone cannot define the overall heat transfer characteristics, and the viscous properties are equally significant towards thermal management. Therefore, this research involves investigating the rheological behavior of hybrid nanosuspensions containing high thermally conductive diamond and graphene nanoplatelets (1:1). These nanomaterials are dispersed in mineral oil using a two-step technique. Hybrid nanofluids' stability is achieved using a non-ionic stabilizer Span85, exhibiting no sedimentation for a minimum of five months. Nanomaterial characterizations are performed to study morphology, purity, and chemical analysis. The flow behavior of hybrid nanosuspensions is investigated at varying nanomaterial mass concentrations (0–2%), temperatures (298.15–338.15 K), and shear rates (1–2000 s−1). Hybrid nanofluids exhibit shear-thinning behavior, which is also correlated with the Ostwald-de-Waele model. The temperature-viscosity relationship is well predicted using the Vogel-Fulcher-Tammann model. Hybrid nanofluids show a maximum enhancement of 35% viscosity at 2% concentration. A generalized two-variable correlation is used to express viscosity as a function of temperature and nanofluid concentration with an excellent agreement. Three different machine learning methods, i.e., Artificial Neural Network (ANN), Gradient Boosting Machine (GBM), and Random Forest (RF) algorithms are also introduced to predict the viscosity of hybrid nanofluids based on the three input parameters (temperature, concentration, and shear rate). The parity plots conclude that all algorithms can predict big-data viscous behavior with high precision. © 2021 Elsevier B.V.

International audience; This experimental study aims to energetically and exergetically compare the performance of a PVT system with sheet-and-plain serpentine tube collector (base PVT system) with two cases of modified PVT systems. The modified PVT systems are the replacements of plain serpentine tube with rifled serpentine tube with 3 ribs (3-start rifled PVT system) and 6 ribs (6-start rifled PVT system). The electrical parameter of the PV module without cooling is compared with the three cases of the PVT system with cooling. The cooling fluid is water/magnetite nanofluid. The effect of nanofluid flow rates (20–80 kg/h) and nanoadditive volume concentrations (0–2%) over the three cases of the PVT system is investigated to propose a suitable combination of flow rate and NA concentration offering the best energetic and exergetic performances. Thus, the 6-start rifled PVT system achieved a maximum of 22.5% and 3.8% higher overall energy efficiency, and 5.9%, and 1.9% higher overall exergy efficiency than the base and 3-start rifled PVT systems at flow rate and concentration of 80 kg/h and 2%. Finally, the electrical power generated by the base, 3-start rifled, and 6-start rifled PVT systems achieved maximum enhancement of 27.5%, 29.5%, and 31.5% compared to the PV module without cooling.

International audience; Thermosyphons are heat transfer devices characterized 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 characterized 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 sulfate 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.

International audience; Concentrating solar power (CSP) technology can become a very valuable contributor to the transformation and decarbonization of our energy landscape, but for this technology to overcome the barrier toward market deployment, significant enhancements in the solar-to-thermal-to-electric energy conversion efficiency are needed. Here, an in-depth experimental analysis of the optical and transport properties of Pd-containing aromatic oil-based nanofluids is presented, with promising results for their prospective use as volumetric absorbers and heat transfer fluids in next-generation parabolic-trough CSP plants. A 0.030 wt % concentration of Pd nanoplates increases sunlight extinction by 90% after 20 mm propagation length and thermal conductivity by 23.5% at 373 K, which is enough to increase the overall system efficiency up to 45.3% and to reduce pumping requirements by 20%, with minimum increases in the collector length. In addition to that, molecular dynamics simulations are used to gain atomistic-level insights about the heat and momentum transfer in these nanofluids, with a focus on the role played by the solid–liquid interface in these phenomena. Molecules chemisorbed at the interface behave as a shelter-like boundary that hinders heat conduction, as a high thermal resistance path, and minimizes the impact of the solid on dynamic viscosity, as it weakens the interactions between the nanoplate and the surrounding nonadsorbed fluid molecules.

International audience; Nowadays, different types of strategies are proposed and tested to find the best scenario for upgrading the productivity of heat transfer fluids, especially nanofluids. Some optimum empirical conditions demonstrated that the best size, shape, and nature of nanoparticles and their dispersion have positive influences on nanofluid thermal conductivity improvements. Therefore, the specific physicochemical properties of the base fluid can be taken into account as one of the decisive factors in heat transfer operations. Deep eutectic solvents (DESs) are nominated as valuable materials to meet the demands for sustainable ecological processes and open opportunities for overcoming the limitations of conventional fluids. The purpose of this study is to briefly introduce the DESs for evaluating their thermal potential applicability and their use to produce nanofluids. DES-based nanofluids represent a new and creative type of heat transfer fluids that possess high potential in different target applications and are not harmful to the environment. This type of nanofluid has higher thermal properties than the base DESs. Increasing the temperature and the volume fraction of nanoparticles lead to further increment in their thermal properties. In this study, the chemical structure and preparation method have been addressed for the DES and DES-based nanofluids. Also, the theoretical approaches have been considered formodeling and predicting their behavior. A discussion was extended to investigate the usage of DES as host fluid for producing nanofluids, and its advantages and drawbacks are also presented. It is deduced that the DES-based nanofluids are one of the smart choices for the progression of nanofluids and give the most promising results for application in heat transport fluids. The contents may shed light on a detailed awareness of the heat transfer potential of the DESs.

International audience; This study reports the synthesis and the characterization of ethylene glycol silver-based nanofluids produced from the polyol process. This synthesis process is based on the reduction of silver nitrate (AgNO3) with the presence of the aqueous emulsion of latex copolymer, used here for the first time along with ethylene glycol. The influence of latex copolymer content for a fixed amount of AgNO3 for the production of silver-based nanofluids is investigated. The efficiency of the synthesis process is demonstrated from UV-Vis spectrometry, TEM and EDS characterization of the nanofluids. In addition, the dynamic viscosity of both the base fluids and nanofluids is experimentally measured over a wide shear rate and temperature range. While the base fluids behave in a non-Newtonian manner due to the presence of copolymer nanoparticles, it appears that the nanofluids are simply Newtonian without any noticeable viscosity enhancement compared to pure ethylene glycol. The thermal conductivity of the produced ethylene glycol silver-based nanofluids shows an enhancement of about 3% for the higher initial contents in copolymer latex. Such a thermophysical profile of ethylene glycol silver-based nanofluids is promising for their potential applications as circulating heat transfer fluids.

High-quality graphene is an especially promising carbon nanomaterial for developing nanofluids for enhancing heat transfer in fluid circulation systems. We report a complete study on few layer graphene (FLG) based nanofluids, including FLG synthesis, FLG-based nanofluid preparation, and their thermal conductivity. The FLG sample is synthesized by an original mechanical exfoliation method. The morphological and structural characterization are investigated by both scanning and transmission electron microscopy and Raman spectroscopy. The chosen two-step method involves the use of thee nonionic surfactants (Triton X-100, Pluronic&reg, P123, and Gum Arabic), a commercial mixture of water and propylene glycol and a mass content in FLG from 0.05 to 0.5%. The thermal conductivity measurements of the three FLG-based nanofluid series are carried out in the temperature range 283.15&ndash, 323.15 K by the transient hot-wire method. From a modeling analysis of the nanofluid thermal conductivity behavior, it is finally shown that synergetic effects of FLG nanosheet size and thermal resistance at the FLG interface both have significant impact on the evidenced thermal conductivity enhancement.

International audience; This editorial note is dedicated to the 1st International Conference on Nanofluids (ICNf19), which was organized under the auspices of Nanouptake COST Action in June 2019, in Castelló (Spain). After a brief report about the conference issues, the successful selected contributions to this SpecialIssue of Energies about the ICNf19 are introduced.

International audience; In this study, a series of low-concentration carbon nanotubes (CNT) water-based nanofluids (0.0055, 0.055, 0.111 and 0.278 vol%) were used as coolants in a shell and tube cooler of the residue fluid catalytic cracking gasoline product to analyze their effects on heat performance of the heat exchanger. The coolants and gasoline flow in tube side and shell side, respectively. This work was performed through simulating the heat exchanger by ASPEN HTFS+ 7.3 software. The performance of the nanofluids to heat transfer was analyzed in comparison with cooling water. Results illustrated that 0.055% CNT concentration could enhance heat transfer properties of the heat exchanger such as Nusselt number, total heat transfer coefficient and heat transfer rate more than other concentrations. Therefore, the lowest temperature of outlet shell-side fluid was also observed at this concentration. Moreover, increment in mass flow rates of both the tube-side and shell-side fluids caused enhancement of the heat transfer, especially with 0.055 vol% CNT. Although there is an optimum concentration among the studied CNT volume fractions, all nanofluids exhibit better thermal performance of the heat exchanger than cooling water, whereas pressure drop increases with CNT loading.

International audience; Nanofluids are considered as promising alternative in heat exchange processes to the classical fluids, whichusually present poor thermal properties. One interesting application for nanofluids is as heat transfer fluid insolar thermal applications plants. Boron nitride nanotubes present interesting thermophysical properties for usein nanofluids. Therefore, nanofluids based on boron nitride nanotubes were prepared by a two-step method,dispersing this nanomaterial in a heat transfer fluid typically used. Stability, rheological and thermal propertiesof the nanofluids were analysed. To check the stability, ultraviolet–visible spectroscopy and particle size andζ-potential measurements were performed for a month, obtaining that the nanofluids were stable. Furthermore,surface tension was measured and no significant differences were observed with regard to the base fluid. In avariable range of temperature, nanofluids show Newtonian behaviour with a slight increase in viscosity. Besides,the boron nitride nanotubes caused an increase in thermal conductivity of up to 33% with regard to the basefluid. The use of these nanofluids also led to an improvement in the heat transfer coefficient under turbulent flowconditions of up to 18%. Finally, the analysis of the outlet temperature in solar thermal applications shows thatthese nanofluids are a promising alternative in this application.

Nano-colloidal suspensions of nanomaterials in a fluid, nanofluids, are appealing because of their interesting properties related to heat transfer processes. While nanomaterials based on transition metal chalcogenides (TMCs) have been widely studied in catalysis, sensing, and energy storage applications, there are few studies of nanofluids based on TMCs for heat transfer applications. In this study, the preparation and analysis of nanofluids based on 2D-WS

Nano-colloidal suspensions of nanomaterials in a fluid, nanofluids, are appealing because of their interesting properties related to heat transfer processes. While nanomaterials based on transition metal chalcogenides (TMCs) have been widely studied in catalysis, sensing, and energy storage applications, there are few studies of nanofluids based on TMCs for heat transfer applications. In this study, the preparation and analysis of nanofluids based on 2D-WS2 in a typical heat transfer fluid (HTF) used in concentrating solar power (CSP) plants are reported. Nanofluids prepared using an exfoliation process exhibited well-defined nanosheets and were highly stable. The nanofluids were characterized in terms of properties related to their application in CSP. The presence of WS2 nanosheets did not modify significantly the surface tension, the viscosity, or the isobaric specific heat, but the thermal conductivity was improved by up to 30%. The Ur factor, which characterizes the thermal efficiency of the fluid in the solar collector, shows an enhancement of up to 22% in the nanofluid, demonstrating great promise for CSP applications. The Reynolds number and friction factor of the fluid were not significantly modified by the addition of the nanomaterial to the HTF, which is also positive for practical applications in CSP plants. Ab initio molecular dynamics simulations of the nanoparticle/fluid interface showed an irreversible dissociative adsorption of diphenyl oxide molecules on the WS2 edge, with very low kinetic barrier. The resulting "decoration" of the WS2 edge dramatically affects the nature of the interface interactions and is therefore expected to affect significantly the rheological and transport properties of the nanofluids. Ministerio de Ciencia, Innovación y Universidades RTI2018-096393-B-I00, UNCA15-CE-2945 Junta de Andalucía sol-201800107510-tra Engineering and Physical Sciences Research Council EP/L000202

International audience; We report in this study the experimental investigation of the dynamic viscosity of purified multi-walled carbon nanotubes (MWCNT) water and water-propylene glycol-based nanofluids in the temperature range 10-80 degrees C. Four weight concentrations of MWCNTs are considered, between 0.005 and 0.1 wt.%. Triton X-100, a common nonionic surfactant, is used to disperse the nanotubes and stabilize the nanofluids as evidenced by optical characterization. Purified and non-damaged MWCNTs are used for nanofluid preparation by the two-step method. MWCNT characterization is deeply investigated from a set of complementary techniques such as thermogravimetric analysis, transmission electron microscopy, and Raman spectroscopy. The studied nanofluids behave as Newtonian fluids for low nanotube content while a shear-thinning behavior is noticed for higher concentration. Finally, the viscosity enhancement of nanofluids with MWCNT loading is compared to the modified Maron-Pierce model considering the presence of aggregates and their size obtained from optical observations.

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 (&eta, ), isobaric heat capacity (Cp), density (&rho, ), and surface tension (&sigma, ) 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, &rho, and &sigma, 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&ndash, Fulcher&ndash, Tammann equation and a first-order polynomial &eta, ( ϕ v , n p ) correlation, with absolute average deviations of 2.2% and 0.55%, respectively.

This study compares the tribological and thermophysical features of the lubricating oil using MoS2 and ZnO nano-additives. The average size of MoS2 and ZnO nanoparticles were 90 nm and 30 nm, respectively. The nanoparticles were suspended using Triton X-100 in three different concentrations (0.1, 0.4 and 0.7 wt.%) in a commercial diesel oil. Tribological properties such as mass loss of the pins, friction coefficient, and worn surface morphologies and thermophysical properties such as viscosity, viscosity index, flash point and pour point of resulting nano lubricant were evaluated and compared with those of pure diesel oil. The tribological behavior of nano lubricants was evaluated using a pin-on-disc tribometer. The worn surface morphologies were observed by scanning electron microscopy. The overall results of this experiment reveal that the addition of nano-MoS2 reduces the mass loss values of the pins in 93% due to the nano-MoS2 lubricant effect. With 0.7 wt.% in nanoparticles content, the viscosity of MoS2 and ZnO nano lubricants at 100 °C increased by about 9.58% and 10.14%, respectively. Pure oil containing 0.7 wt.% of each nanoparticle increased the flash point because of its small size and surface modifying behavior compared to the pure oil. Moreover, the addition of ZnO nanoparticles with pure oil lubricant is more suitable than MoS2 nanoparticles for improving the thermophysical properties of pure oil.

International audience; Nanofluids are recent nanomaterials with improved thermophysical properties that could enhance the efficiency and reliability of heat transfer systems. Relevant properties for heat transfer calculation, thin film flows, droplet impingements or microfluidic are surface tension and wettability. However, to date, the understanding of those properties in nanofluids field is at the beginning compared to transport properties. At this stage, this review focus on the effect of nanoparticles and base fluid nature, temperature, use of surfactant, nanoparticle concentration, size and shape as well on the surface tension and wettability of nanofluids. After the presentation of heat transfer processes involving the influence of surface tension and wettability, this paper is organized according to the nature of the nanoparticles dealing with oxide, carbon-based and metallic nanofluids as well as unusual or less considered nature of nanoparticles. The factors affecting the surface tension of nanofluids are relatively well identified, but concentration and surfactant effects present some inconsistent outcomes. In any case, the dispersion of nanoparticles have an effect on the surface tension of base fluid significantly lower than that on transport properties. Based on results available in the literature and existing empirical correlations, a comprehensive assessment, challenges and future works are suggested. © 2018 Elsevier Ltd

Wettability is the ability of the liquid to contact with the solid surface at the surrounding fluid and its degree is defined by contact angle (CA), which is calculated with balance between adhesive and cohesive forces on droplet surface. Thermophysical properties of the droplet, the forces acting on the droplet, atmosphere surrounding the droplet and the substrate surface are the main parameters a ecting on CA.With nanofluids (NF), nanoparticle concentration and size and shape can modify the contact angle and thus wettability. This study investigates the validity of single-phase CA correlations for several nanofluids with di erent types of nanoparticles dispersed in water. Geometrical parameters of sessile droplet (height of the droplet, wetting radius and radius of curvature at the apex) are used in the tested correlations, which are based on force balance acting on the droplet surface, energy balance, spherical dome approach and empirical expression, respectively. It is shown that single-phase models can be expressed in terms of Bond number, the non-dimensional droplet volume and two geometrical similarity simplexes. It is demonstrated that they can be used successfully to predict CA of dilute nanofluids’ at ambient conditions. Besides evaluation of CA, droplet shape is also well predicted for all nanofluid samples with 5% error.

International audience; 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.

International audience; A comprehensive review of research and development on rheological characteristics of nanofluids for their advanced heat transfer applications is performed and reported in this paper. It identifies the research anomaly and importance on this topic besides analysing rheology of nanofluids. Various classical and recently developed viscosity models for nanofluids are presented and discussed. Nanofluids are classified as metallic and nonmetallic types and research findings on this key property of available nanofluids are analyzed. Effects of several important factors such as concentration of nanoparticles and temperature on viscosity of each type of nanofluids have been explicitly reviewed. Results from various research groups and predictions from viscosity models are also compared and discussed in detail. Role and importance of the viscosity in connection with other thermal properties and parameters for their thermal management applications are highlighted. Furthermore, the research challenges and needs in this important area of nanofluids are also revealed.

Authors wish to thank Dr. Magdalena Gizowska from Department of Nanotechnology, Institute of Ceramics and Building Materials, Warsaw, Poland for measurements of density of nanopowders. The authors acknowledge also Loïc Joanny from CMEBA, Université Rennes 1 and Mathieu Pasturel from the Institut des Sciences Chimiques de Rennes, Université Rennes 1 for performing respectively SEM and XRD characterization.; International audience; Since the second half of the twentieth century, nanofluids are very promising engineering materials that can find numerous applications in the processes of heat exchange. Scientist and engineers are developing new and more advanced nanosuspensions which may differ from their physical properties, production costs and practical use. The aim of this paper is to study the differences between two nanofluids containing a mixture of graphite and nanodiamonds with various ash content. Here, ethylene glycol was used as a base fluid. Rheological properties, thermal and electrical conductivities at a constant temperature 298.15K were investigated for nanoparticle volume content ranging from 0.004 to 0.023. It was presented that ash content in nanofluids changes significantly rheological properties of nanofluids containing graphite/nanodiamonds mixture nanoparticles. While the variation in ash content does not affect thermal conductivity of nanofluids, a big impact on electrical conductivity is reported.