Special Issue "The Potential of Nano Additives in Lubricants and Heat Transfer Fluids"

A special issue of Nanomaterials (ISSN 2079-4991).

Deadline for manuscript submissions: 25 March 2021.

Special Issue Editors

Prof. Dr. Josefa Fernández
Website
Guest Editor
University of Santiago de Compostela, Galicia, Spain
Interests: Nanolubricants, nanoparticles; lubrication; additives; friction; wear; nanofluids, ionic liquids, tribology, transport properties, high pressures
Dr. Luis Lugo
Website
Guest Editor
Department of Applied Physics, University of Vigo, 36310 Vigo, Spain
Interests: nanofluids; heat transfer fluids; lubricants; thermophysical properties; rheology
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Special Issue Information

Dear Colleagues,

In the last two decades we are witnessing a deep evolution of lubricants and heat transfer fluids due to the dispersion of different nanoadditives. These dispersions have received increasing attention because of their potential in energy systems. This field is multidisciplinary and includes many complex phenomena and processes that are really encouraging and stimulating to investigate. To date, the foremost challenge for developing a new nanolubricant or nanofluid is to achieve stable suspensions in the currently used base fluids or lubricant base oils. In order to solve this issue, the studies about the use of classical nanoparticles as metals and metal oxides have evolved to more complex nanoparticles and one and two dimensional nanomaterials with coated surfaces among other structural changes for both applications. Nano additive synthesis as well as nanodispersion preparation and the thermophysical, tribological, optical and rheological characterization of both nanomaterials as proposed new materials are necessary studies to suggest next-generation applications of nanomaterials with outstanding performances in industrial applications, renewable energies and automotive engines in particular.

This Special Issue is aimed at providing significant contributions on advances in dispersions including the manufacture and characterization of nanolubricants as well as nanofluids for heat transfer and storage of thermal energy focusing on potential industrial applications and renewable energies in particular. New studies about advances nanoadditives as coated nanoparticles, hybrid nanoparticles, two-dimensional and one-dimensional nano additives, are also welcomed. Synergies studies with other nanoadditives used in the current formulations are expected. Original high-quality research papers dealing with complete experimental analysis, molecular simulations or theoretical advances covering the most recent advances as well as comprehensive reviews addressing state-of-the-art topics in the field will be considered for publication.

Prof. Dr. Josefa Fernández
Dr. Luis Lugo
Guest Editors

Manuscript Submission Information

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Keywords

  • Nanolubricants
  • Synergies with other additives
  • Nanofluids
  • Nano additives
  • Phase change-based heat transfer
  • Storage of thermal energy
  • Industrial applications

Published Papers (9 papers)

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Research

Open AccessArticle
Optical Limiting of Carbon Nanohorn-Based Aqueous Nanofluids: A Systematic Study
Nanomaterials 2020, 10(11), 2160; https://doi.org/10.3390/nano10112160 - 29 Oct 2020
Cited by 1
Abstract
Nowadays, the use of lasers has become commonplace in everyday life, and laser protection has become an important field of scientific investigation, as well as a security issue. In this context, optical limiters are receiving increasing attention. This work focuses on the identification [...] Read more.
Nowadays, the use of lasers has become commonplace in everyday life, and laser protection has become an important field of scientific investigation, as well as a security issue. In this context, optical limiters are receiving increasing attention. This work focuses on the identification of the significant parameters affecting optical limiting properties of aqueous suspensions of pristine single-wall carbon nanohorns. The study is carried out on the spectral range, spanning from ultraviolet to near-infrared (355, 532 and 1064 nm). Optical nonlinear properties are systematically investigated as a function of nanohorn morphology, concentration, dimensions of aggregates, sample preparation procedure, nanostructure oxidation and the presence and concentration of surfactants to identify the role of each parameter in the nonlinear optical behavior of colloids. The size and morphology of individual nanoparticles were identified to primarily determine optical limiting. A cluster size effect was also demonstrated, showing more effective optical limiting in larger aggregates. Most importantly, we describe an original approach to identify the dominant nonlinear mechanism. This method requires simple transmittance measurements and a fitting procedure. In our suspensions, nonlinearity was identified to be of electronic origin at a 532 nm wavelength, while at 355 nm, it was found in the generation of bubbles. Full article
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Open AccessArticle
On Aqua-Based Silica (SiO2–Water) Nanocoolant: Convective Thermal Potential and Experimental Precision Evaluation in Aluminum Tube Radiator
Nanomaterials 2020, 10(9), 1736; https://doi.org/10.3390/nano10091736 - 01 Sep 2020
Abstract
Although the research on potential use of nanofluids in automotive vehicles is in its embryonic stage, a number of studies have suggested the strong prospect of nanofluids for the efficient thermal management of automotive vehicles. Nevertheless, the pinnacle of nanofluid-based systems awaits stable [...] Read more.
Although the research on potential use of nanofluids in automotive vehicles is in its embryonic stage, a number of studies have suggested the strong prospect of nanofluids for the efficient thermal management of automotive vehicles. Nevertheless, the pinnacle of nanofluid-based systems awaits stable nanoparticle suspension. The present work studies the heat transfer performance of an aluminum tube automotive radiator with 31 flattened tubes and louvered fins using water and different concentrations (0.04, 0.08, and 0.12 vol.%)-based SiO2/water nanofluids as the engine coolant. Inlet temperature and flowrate of the fluid were varied from 60 to 70 °C and 12 to 18 LPM, respectively. The topmost increment in heat transfer rate of 36.92% and Nusselt number of 45.53% were observed in the upper range of tested operational parameters, however, the relative heat transfer increment percentage dropped from 5% (between 0.04 and 0.08 vol.%) to 3.5% (between 0.08 and 0.12 vol.%) due to agglomeration and cluster formation caused by the presence of a greater number of nanoparticles. Precise evaluation of the experimental results was also carried out by reperforming the tests after three days of initial experimentations. A mere deviation of less than 1% was observed between the initial and repeated tests, however, the decline was caused due to the synergistic effects of clustering and fouling. Full article
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Open AccessArticle
The Indirect Tribological Role of Carbon Nanotubes Stimulating Zinc Dithiophosphate Anti-Wear Film Formation
Nanomaterials 2020, 10(7), 1330; https://doi.org/10.3390/nano10071330 - 08 Jul 2020
Abstract
Experimental studies reveal that the simultaneous addition of zinc dialkyl dithiophosphates (ZDDPs) and multi-wall carbon nanotubes (MWCNTs) to a poly-alpha-olefin base oil strongly reduces wear. In this paper, it is shown that MWCNTs promote the formation of an anti-wear (AW) layer on the [...] Read more.
Experimental studies reveal that the simultaneous addition of zinc dialkyl dithiophosphates (ZDDPs) and multi-wall carbon nanotubes (MWCNTs) to a poly-alpha-olefin base oil strongly reduces wear. In this paper, it is shown that MWCNTs promote the formation of an anti-wear (AW) layer on the metal surface that is much thicker than what ZDDPs can create as a sole additive. More importantly, the nanotubes’ action is indirect, i.e., MWCNTs neither mechanically nor structurally strengthen the AW film. A new mechanism for this effect is also proposed, which is supported by detailed tribometer results, friction track 3D-topography measurements, electron diffraction spectroscopy (EDS), and Raman spectroscopy. In this mechanism, MWCNTs mediate the transfer of both thermal and electric energy released on the metal surface in the friction process. As a result, this energy penetrates more deeply into the oil volume, thus extending the spatial range of tribochemical reactions involving ZDDPs. Full article
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Open AccessArticle
Nanofluid Development Using Silver Nanoparticles and Organic-Luminescent Molecules for Solar-Thermal and Hybrid Photovoltaic-Thermal Applications
Nanomaterials 2020, 10(6), 1201; https://doi.org/10.3390/nano10061201 - 19 Jun 2020
Cited by 1
Abstract
Exploiting solar energy using photo-thermal (PT) and/or hybridised photovoltaic/thermal (PVT) systems can represent a viable alternative to the growing demand for renewable energy. For large-scale implementation, such systems require thermal fluids able to enhance the combined conversion efficiency achievable by controlling the ‘thermal’ [...] Read more.
Exploiting solar energy using photo-thermal (PT) and/or hybridised photovoltaic/thermal (PVT) systems can represent a viable alternative to the growing demand for renewable energy. For large-scale implementation, such systems require thermal fluids able to enhance the combined conversion efficiency achievable by controlling the ‘thermal’ and ‘electrical’ components of the solar spectrum. Nanofluids are typically employed for these purposes and they should exhibit high heat-transfer capabilities and optical properties tuned towards the peak performance spectral window of the photovoltaic (PV) component. In this work, novel nanofluids, composed of highly luminescent organic molecules and Ag nanoparticles dispersed within a base fluid, were tested for PT and PVT applications. These nanofluids were designed to mimic the behaviour of luminescent down-shifting molecules while offering enhanced thermo-physical characteristics over the host base fluid. The nanofluids’ conversion efficiency was evaluated under a standard AM1.5G weighted solar spectrum. The results revealed that the Ag nanoparticles’ inclusion in the composite fluid has the potential to improve the total solar energy conversion. The nanoparticles’ presence minimizes the losses in the electrical power component of the PVT systems as the thermal conversion increases. The enhanced performances recorded suggest that these nanofluids could represent suitable candidates for solar energy conversion applications. Full article
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Open AccessArticle
Thermal Conductivity Performance of 2D h-BN/MoS2/-Hybrid Nanostructures Used on Natural and Synthetic Esters
Nanomaterials 2020, 10(6), 1160; https://doi.org/10.3390/nano10061160 - 12 Jun 2020
Cited by 1
Abstract
In this paper, the thermal conductivity behavior of synthetic and natural esters reinforced with 2D nanostructures—single hexagonal boron nitride (h-BN), single molybdenum disulfide (MoS2), and hybrid h-BN/MOS2—were studied and compared to each other. As a basis for the synthesis [...] Read more.
In this paper, the thermal conductivity behavior of synthetic and natural esters reinforced with 2D nanostructures—single hexagonal boron nitride (h-BN), single molybdenum disulfide (MoS2), and hybrid h-BN/MOS2—were studied and compared to each other. As a basis for the synthesis of nanofluids, three biodegradable insulating lubricants were used: FR3TM and VG-100 were used as natural esters and MIDEL 7131 as a synthetic ester. Two-dimensional nanosheets of h-BN, MoS2, and their hybrid nanofillers (50/50 ratio percent) were incorporated into matrix lubricants without surfactants or additives. Nanofluids were prepared at 0.01, 0.05, 0.10, 0.15, and 0.25 weight percent of filler fraction. The experimental results revealed improvements in thermal conductivity in the range of 20–32% at 323 K with the addition of 2D nanostructures, and a synergistic behavior was observed for the hybrid h-BN/MoS2 nanostructures. Full article
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Open AccessArticle
Tribological Behavior of Nanolubricants Based on Coated Magnetic Nanoparticles and Trimethylolpropane Trioleate Base Oil
Nanomaterials 2020, 10(4), 683; https://doi.org/10.3390/nano10040683 - 05 Apr 2020
Cited by 3
Abstract
The main task of this work is to study the tribological performance of nanolubricants formed by trimethylolpropane trioleate (TMPTO) base oil with magnetic nanoparticles coated with oleic acid: Fe3O4 of two sizes 6.3 nm and 10 nm, and Nd alloy [...] Read more.
The main task of this work is to study the tribological performance of nanolubricants formed by trimethylolpropane trioleate (TMPTO) base oil with magnetic nanoparticles coated with oleic acid: Fe3O4 of two sizes 6.3 nm and 10 nm, and Nd alloy compound of 19 nm. Coated nanoparticles (NPs) were synthesized via chemical co-precipitation or thermal decomposition by adsorption with oleic acid in the same step. Three nanodispersions of TMPTO of 0.015 wt% of each NP were prepared, which were stable for at least 11 months. Two different types of tribological tests were carried out: pure sliding conditions and rolling conditions (5% slide to roll ratio). With the aim of analyzing the wear by means of the wear scar diameter (WSD), the wear track depth and the volume of the wear track produced after the first type of the tribological tests, a 3D optical profiler was used. The best tribological performance was found for the Nd alloy compound nanodispersion, with reductions of 29% and 67% in friction and WSD, respectively, in comparison with TMPTO. On the other hand, rolling conditions tests were utilized to study friction and film thickness of nanolubricants, determining that Fe3O4 (6.3 nm) nanolubricant reduces friction in comparison to TMPTO. Full article
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Open AccessArticle
Graphene-Ionic Liquid Thin Film Nanolubricant
Nanomaterials 2020, 10(3), 535; https://doi.org/10.3390/nano10030535 - 17 Mar 2020
Cited by 2
Abstract
Graphene (0.5 wt.%) was dispersed in the hydrophobic room-temperature ionic liquid 1-octyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide (IL) to obtain a new non-Newtonian (IL + G) nanolubricant. Thin layers of IL and (IL + G) lubricants were deposited on stainless steel disks by spin coating. The [...] Read more.
Graphene (0.5 wt.%) was dispersed in the hydrophobic room-temperature ionic liquid 1-octyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide (IL) to obtain a new non-Newtonian (IL + G) nanolubricant. Thin layers of IL and (IL + G) lubricants were deposited on stainless steel disks by spin coating. The tribological performance of the new thin layers was compared with those of full fluid lubricants. Friction coefficients for neat IL were independent of lubricant film thickness. In contrast, for (IL + G) the reduction of film thickness not only afforded 40% reduction of the friction coefficient, but also prevented wear and surface damage. Results of surface profilometry, scanning and transmission electron microscopy (SEM and TEM), energy dispersive analysis (EDX), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were discussed. Full article
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Open AccessArticle
NePCM Based on Silver Dispersions in Poly(Ethylene Glycol) as a Stable Solution for Thermal Storage
Nanomaterials 2020, 10(1), 19; https://doi.org/10.3390/nano10010019 - 19 Dec 2019
Cited by 6
Abstract
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 [...] Read more.
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. Full article
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Open AccessArticle
Evaporation Rate of Colloidal Droplets of Jet Fuel and Carbon-Based Nanoparticles: Effect of Thermal Conductivity
Nanomaterials 2019, 9(9), 1297; https://doi.org/10.3390/nano9091297 - 11 Sep 2019
Cited by 2
Abstract
Adding nanoparticles to liquid fuel is known to promote its combustion characteristics through improving several thermo-physical properties. This study investigates the effects of adding carbon nanoparticles on thermal conductivity and evaporation rate of liquid jet fuel. Multi-walled carbon nanotubes, activated carbon nanoparticles, and [...] Read more.
Adding nanoparticles to liquid fuel is known to promote its combustion characteristics through improving several thermo-physical properties. This study investigates the effects of adding carbon nanoparticles on thermal conductivity and evaporation rate of liquid jet fuel. Multi-walled carbon nanotubes, activated carbon nanoparticles, and graphene nanoplatelets were added to jet fuel at different concentrations to prepare colloidal suspensions. Thermal conductivity is determined by passing known amounts of heat through a very thin layer of fuel and measuring temperature difference across its thickness. A fiber-supported droplet technique is also used to evaluate evaporation rate due to force convection of a hot inert gas. It is observed that both thermal conductivity and evaporation rate increase as a result of nanoparticle addition. Since there is no radiation heat transfer mechanism, the increase in evaporation rate is concluded to be only due to enhanced thermal conductivity. Full article
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