Special Issue "Nanofluids and Nanofluidics"

A special issue of Nanomaterials (ISSN 2079-4991). This special issue belongs to the section "Nanofabrication and Nanomanufacturing".

Deadline for manuscript submissions: closed (28 February 2021).

Special Issue Editor

Prof. Dr. S. M. Sohel Murshed
E-Mail Website
Guest Editor
Department of Mechanical Engineering, Instituto Superior Tecnico, University of Lisbon, 1049-001 Lisbon, Portugal
Interests: nanofluids; nanomaterials; microfluidics; nanofluidics; cooling and energy technologies; thermophysical properties and thermal transport
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Special Issue Information

Dear Colleagues,

Both nanofluids and nanofluidics are popular research fields that have attracted huge research interest in recent years. This is mainly due to their great potential applications in many important fields ranging from energy and electronics to biomedical. While nanofluids are suspensions of any kind of solid nanoparticles in any conventional or new heat transfer liquids, nanofluidics is the study and manipulation of fluids confined within nano-sized structures or devices. It is known that the current technological trend towards being smaller and faster raises a lot of technical challenges. For instance, small and high performance devices also generate very high power (heat) densities, and conventional cooling techniques are increasingly falling short of meeting these high and fast cooling needs. Here nanofluids and nanofluidics can play a major role in overcoming such challenges (e.g., cooling) of high-tech small devices and systems. In addition to the huge potential markets, there are also numerous other technological challenges facing many other fields (like drag-delivery in biomedical) where either nanomaterials, nanofluids or nanofluidics can be a game changer in the future.

Due to this importance and the potential applications, it is timely to cover some major research and application areas of these two popular fields in this Special Issue on “Nanofluids and Nanofluidics” in Nanomaterials which is a high-impact (IF:3.504) journal in nanoscience and nanotechnology.

Prof. Dr. S. M. Sohel Murshed
Guest Editor

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Keywords

  • Nanofluids
  • Energy and cooling applications of nanofluids
  • Thermal transport of nanofluids
  • Nanofluidics
  • Applications of nanofluidics, Lab-on- a-chip
  • Fabrication of nanofluidic devices
  • Nanofluidics for new nanomaterials

Published Papers (9 papers)

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Research

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Article
Carbon Nanotori Structures for Thermal Transport Applications on Lubricants
Nanomaterials 2021, 11(5), 1158; https://doi.org/10.3390/nano11051158 - 29 Apr 2021
Viewed by 589
Abstract
Carbon nanostructures have been recently applied to improve industrial manufacturing processes and other materials; such is the case for lubricants used in the metal-mechanic industry. Nanotori are toroidal carbon nanostructures, obtained from chemical treatment of multi-wall carbon nanotubes (MWCNTs). This material has been [...] Read more.
Carbon nanostructures have been recently applied to improve industrial manufacturing processes and other materials; such is the case for lubricants used in the metal-mechanic industry. Nanotori are toroidal carbon nanostructures, obtained from chemical treatment of multi-wall carbon nanotubes (MWCNTs). This material has been shown to have superb anti-wear and friction reduction performance, having the ability to homogeneously disperse within water in concentrations between 1–2 wt.%. Obtained results of these novel nanostructures under water mixtures and novel additives were a set point to our studies in different industrial lubricants. In the present work, nanotori structures have been applied in various filler fractions as reinforcement to evaluate the behavior in thermal transport of water-based (WB) and oil-based (OB) lubricants. Temperature-dependent experiments to evaluate the thermal conductivity were performed using a thermal water bath ranging from room temperature up to 323 K. The obtained results showed a highly effective and favorable improvement in the heat transport of both lubricants; oil-based results were better than water-based results, with nanotori structures increasing the lubricants’ thermal transport properties by 70%, compared to pure lubricant. Full article
(This article belongs to the Special Issue Nanofluids and Nanofluidics)
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Article
Pool Boiling of Nanofluids on Biphilic Surfaces: An Experimental and Numerical Study
Nanomaterials 2021, 11(1), 125; https://doi.org/10.3390/nano11010125 - 07 Jan 2021
Cited by 2 | Viewed by 1013
Abstract
This study addresses the combination of customized surface modification with the use of nanofluids, to infer on its potential to enhance pool-boiling heat transfer. Hydrophilic surfaces patterned with superhydrophobic regions were developed and used as surface interfaces with different nanofluids (water with gold, [...] Read more.
This study addresses the combination of customized surface modification with the use of nanofluids, to infer on its potential to enhance pool-boiling heat transfer. Hydrophilic surfaces patterned with superhydrophobic regions were developed and used as surface interfaces with different nanofluids (water with gold, silver, aluminum and alumina nanoparticles), in order to evaluate the effect of the nature and concentration of the nanoparticles in bubble dynamics and consequently in heat transfer processes. The main qualitative and quantitative analysis was based on extensive post-processing of synchronized high-speed and thermographic images. To study the nucleation of a single bubble in pool boiling condition, a numerical model was also implemented. The results show an evident benefit of using biphilic patterns with well-established distances between the superhydrophobic regions. This can be observed in the resulting plot of the dissipated heat flux for a biphilic pattern with seven superhydrophobic spots, δ = 1/d and an imposed heat flux of 2132 w/m2. In this case, the dissipated heat flux is almost constant (except in the instant t* ≈ 0.9 when it reaches a peak of 2400 W/m2), whilst when using only a single superhydrophobic spot, where the heat flux dissipation reaches the maximum shortly after the detachment of the bubble, dropping continuously until a new necking phase starts. The biphilic patterns also allow a controlled bubble coalescence, which promotes fluid convection at the hydrophilic spacing between the superhydrophobic regions, which clearly contributes to cool down the surface. This effect is noticeable in the case of employing the Ag 1 wt% nanofluid, with an imposed heat flux of 2132 W/m2, where the coalescence of the drops promotes a surface cooling, identified by a temperature drop of 0.7 °C in the hydrophilic areas. Those areas have an average temperature of 101.8 °C, whilst the average temperature of the superhydrophobic spots at coalescence time is of 102.9 °C. For low concentrations as the ones used in this work, the effect of the nanofluids was observed to play a minor role. This can be observed on the slight discrepancy of the heat dissipation decay that occurred in the necking stage of the bubbles for nanofluids with the same kind of nanoparticles and different concentration. For the Au 0.1 wt% nanofluid, a heat dissipation decay of 350 W/m2 was reported, whilst for the Au 0.5 wt% nanofluid, the same decay was only of 280 W/m2. The results of the numerical model concerning velocity fields indicated a sudden acceleration at the bubble detachment, as can be qualitatively analyzed in the thermographic images obtained in this work. Additionally, the temperature fields of the analyzed region present the same tendency as the experimental results. Full article
(This article belongs to the Special Issue Nanofluids and Nanofluidics)
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Article
Nanofluids for Performance Improvement of Heavy Machinery Journal Bearings: A Simulation Study
Nanomaterials 2020, 10(11), 2120; https://doi.org/10.3390/nano10112120 - 25 Oct 2020
Cited by 3 | Viewed by 722
Abstract
Nanofluids have extensive applications in hydrodynamic journal bearings used in heavy industry machinery. Inorganic fullerene-like tungsten disulfide nanoparticles (IF-WS2 NPs) are the most common additive for lubrication purpose due to their excellent mechanical characteristics along with their effect on reducing friction and [...] Read more.
Nanofluids have extensive applications in hydrodynamic journal bearings used in heavy industry machinery. Inorganic fullerene-like tungsten disulfide nanoparticles (IF-WS2 NPs) are the most common additive for lubrication purpose due to their excellent mechanical characteristics along with their effect on reducing friction and wear. In this work, a computational simulation approach with discrete phase modeling (DPM) of suspended nanoparticles was used to evaluate the application of the IF-WS2 nanofluid lubricant on load carrying capacity of high-load journal bearings where the normal loads are high, considering the bearing dimensions. For accurate simulation, nanofluid viscosity was calculated considering the aggregation effect of NPs by using scanning electron microscopy (SEM) imaging of the nanofluids. A benchmark study was first performed to assess the model accuracy. Hydrodynamic lubrication was simulated under different nanofluid weigh fractions. The simulated pressure distribution was then employed to determine the load capacity of the bearing. The results show an approximately 20% improvement of load carrying capacity at 5% weight fraction of WS2-oil nanofluid. Full article
(This article belongs to the Special Issue Nanofluids and Nanofluidics)
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Article
Two-Dimensional Tungsten Disulfide-Based Ethylene Glycol Nanofluids: Stability, Thermal Conductivity, and Rheological Properties
Nanomaterials 2020, 10(7), 1340; https://doi.org/10.3390/nano10071340 - 09 Jul 2020
Cited by 2 | Viewed by 1089
Abstract
Developing stable nanofluids and improving their thermo-physical properties are highly important in heat transfer applications. In the present work, the stability, thermal conductivity, and rheological properties of tungsten disulphide (WS2) nanoparticles (NPs) with ethylene glycol (EG) were profoundly examined using a [...] Read more.
Developing stable nanofluids and improving their thermo-physical properties are highly important in heat transfer applications. In the present work, the stability, thermal conductivity, and rheological properties of tungsten disulphide (WS2) nanoparticles (NPs) with ethylene glycol (EG) were profoundly examined using a particle size analyzer, zeta-sizer, thermal property analyzer, rheometer, and pH measuring system. WS2 NPs were characterized by various techniques, such as XRD (X-Ray Diffraction), FTIR (Fourier Transform Infrared Spectroscopy), FESEM (Field emission scanning electron microscopy), and high-resolution transmission electron microscopy (HRTEM). The nanofluids were obtained with the two-step method by employing three volume concentrations (0.005%, 0.01%, and 0.02%) of WS2. The influence of different surfactants (Sodium dodecyl sulphate (SDS), Sodium dodecylbenzenesulfonate (SDBS), Cetyltrimethylammonium bromide (CTAB)) with various volume concentrations (0.05–2%) on the measured properties has also been evaluated. Pristine WS2/EG nanofluids exhibit low zeta potential values, i.e., −7.9 mV, −9.3 mV, and −5 mV, corresponding to 0.005%, 0.01%, and 0.02% nanofluid, respectively. However, the zeta potential surpassed the threshold (±30 mV) and the maximum values reached of −52 mV, −45 mV, and 42 mV for SDS, SDBS, and CTAB-containing nanofluids. This showed the successful adsorption of surfactants onto WS2, which was also observed through the increased agglomerate size of up to 1720 nm. Concurrently, particularly for 0.05% SDS with 0.005% WS2, thermal conductivity was enhanced by up to 4.5%, with a corresponding decrease in viscosity of up to 10.5% in a temperature range of (25–70 °C), as compared to EG. Conversely, the viscoelastic analysis has indicated considerable yield stress due to the presence of surfactants, while the pristine nanofluids exhibited enhanced fluidity over the entire tested deformation range. The shear flow behavior showed a transition from a non-Newtonian to a Newtonian fluid at a low shear rate of 10 s−1. Besides this, the temperature sweep analysis has shown a viscosity reduction in a range of temperatures (25–70 °C), with an indication of a critical temperature limit. However, owing to an anomalous reduction in the dynamic viscosity of up to 10.5% and an enhancement in the thermal conductivity of up to 6.9%, WS2/EG nanofluids could be considered as a potential candidate for heat transfer applications. Full article
(This article belongs to the Special Issue Nanofluids and Nanofluidics)
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Article
Electrical Conductivity of New Nanoparticle Enhanced Fluids: An Experimental Study
Nanomaterials 2019, 9(9), 1228; https://doi.org/10.3390/nano9091228 - 29 Aug 2019
Cited by 13 | Viewed by 1224
Abstract
In this research, the electrical conductivity of simple and hybrid nanofluids containing Al2O3, TiO2 and SiO2 nanoparticles and water as the base fluid was experimentally studied at ambient temperature and with temperature variation in the range of [...] Read more.
In this research, the electrical conductivity of simple and hybrid nanofluids containing Al2O3, TiO2 and SiO2 nanoparticles and water as the base fluid was experimentally studied at ambient temperature and with temperature variation in the range of 20–60 °C. A comparison of the experimental data with existing theoretical models demonstrated that the theoretical models under-predict the experimental data. Consequently, several correlations were developed for nanofluid electrical conductivity estimation in relation to temperature and volume concentration. The electrical conductivity of both simple and hybrid nanofluids increased linearly with both volume concentration and temperature upsurge. More precisely, by adding nanoparticles to water, the electrical conductivity increased from 11 times up to 58 times for both simple and hybrid nanofluids, with the maximum values being attained for the 3% volume concentration. Plus, a three-dimensional regression analysis was performed to correlate the electrical conductivity with temperature and volume fraction of the titania and silica nanofluids. The thermo-electrical conductivity ratio has been calculated based on electrical conductivity experimental results and previously determined thermal conductivity. Very low figures were noticed. Concluding, one may affirm that further experimental work is needed to completely elucidate the behavior of nanofluids in terms of electrical conductivity. Full article
(This article belongs to the Special Issue Nanofluids and Nanofluidics)
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Article
Effect of Carbon Nanoparticles on the Crystallization of Calcium Carbonate in Aqueous Solution
Nanomaterials 2019, 9(2), 179; https://doi.org/10.3390/nano9020179 - 01 Feb 2019
Cited by 8 | Viewed by 1458
Abstract
Nanofluids have great application prospects in industrial heat exchange systems because they can significantly improve the heat and mass transfer efficiency. However, the presence of nanoparticles in the fluid might also affect the formation and attachment of inorganic scales, such as calcium carbonate, [...] Read more.
Nanofluids have great application prospects in industrial heat exchange systems because they can significantly improve the heat and mass transfer efficiency. However, the presence of nanoparticles in the fluid might also affect the formation and attachment of inorganic scales, such as calcium carbonate, on the heat exchange surface. The effects of carbon nanoparticles on the crystallization of calcium carbonate in aqueous solution were studied by the scale inhibition test, solution analysis, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). The results showed that carbon nanoparticles had an excellent surface scale inhibition performance for calcium carbonate, which could effectively prevent the adhesion of scale on the heat exchange surface. The carbon nanoparticles did not affect the solubility of calcium carbonate in water, but changed the crystal form of the precipitated calcium carbonate, making it difficult to adsorb on the heat exchange surface and achieving a surface scale inhibition effect. Carbon nanofluids effectively inhibit the adhesion of calcium carbonate to heat exchange surfaces. Full article
(This article belongs to the Special Issue Nanofluids and Nanofluidics)
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Article
Influence of Six Carbon-Based Nanomaterials on the Rheological Properties of Nanofluids
Nanomaterials 2019, 9(2), 146; https://doi.org/10.3390/nano9020146 - 24 Jan 2019
Cited by 24 | Viewed by 1470
Abstract
Nanofluids, dispersions of nanosized solid particles in liquids, have been conceived as thermally-improved heat transfer fluids from their conception. More recently, they have also been considered as alternative working fluids to improve the performance of direct absorption solar thermal collectors, even at low [...] Read more.
Nanofluids, dispersions of nanosized solid particles in liquids, have been conceived as thermally-improved heat transfer fluids from their conception. More recently, they have also been considered as alternative working fluids to improve the performance of direct absorption solar thermal collectors, even at low nanoadditive concentrations. Carbon-based nanomaterials have been breaking ground in both applications as nanoadditives during the last decade due to their high thermal conductivities and the huge transformation of optical properties that their addition involves. In any application field, rheological behavior became a central concern because of its implications in the pumping power consumption. In this work, the rheological behavior of four different loaded dispersions (0.25, 0.50, 1.0, and 2.0 wt%) of six carbon-based nanomaterials (carbon black, two different phase content nanodiamonds, two different purity graphite/diamond mixtures, and sulfonic acid-functionalized graphene nanoplatelets) in ethylene glycol:water mixture 50:50 vol% have been analysed. For this purpose, a rotational rheometer with double cone geometry was employed, which included a special cover to avoid mass losses due to evaporation at elevated temperatures. The flow curves of the twenty-four nanofluids and the base fluid were obtained by varying the shear rate between 1 and 1000 s−1 for seven different temperatures in the range from 283.15 to 353.15 K. The shear-thinning behaviors identified, as well as their dependences on carbon-based nanomaterial, concentration, and temperature, were analyzed. In addition, oscillatory tests were performed for samples with the clearest Non-Newtonian response, varying the deformation from 0.1 to 1000% with constant frequency and temperature. The dependence of the behaviors identified on the employed carbon-based nanomaterial was described. Full article
(This article belongs to the Special Issue Nanofluids and Nanofluidics)
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Article
Evaluation of the Stability of Dielectric Nanofluids for Use in Transformers under Real Operating Conditions
Nanomaterials 2019, 9(2), 143; https://doi.org/10.3390/nano9020143 - 23 Jan 2019
Cited by 12 | Viewed by 1340
Abstract
The application of nanotechnology to the electrical insulation of transformers has become a topic of interest in the last few years. Most authors propose the use of dielectric nanofluids, which are obtained by dispersing low concentrations of nanoparticles in conventional insulating liquids. Although [...] Read more.
The application of nanotechnology to the electrical insulation of transformers has become a topic of interest in the last few years. Most authors propose the use of dielectric nanofluids, which are obtained by dispersing low concentrations of nanoparticles in conventional insulating liquids. Although a good number of works have demonstrated that dielectric nanofluids may exhibit superior dielectric properties than the base fluids, there is a key issue that still needs to be addressed, which is the long-term stability of those liquids. The studies about the stability of dielectric nanofluids fluids that have been published so far analyze the performance of the fluids under laboratory conditions which are far from the real working conditions the liquids would be subjected to when working inside a transformer. In this paper, an experimental study is presented that evaluates the stability of several dielectric nanofluids under realistic transformer operating conditions. As the study demonstrates, the stability of dielectric nanofluids depends strongly on the working temperature, on the materials applied to obtain the fluid, and on the manufacturing procedure, while other aspects, such as the interaction with other materials, are less relevant. Additional topics, such as the methods applied for evaluation of the stability and the physical properties of the dielectric nanofluids under test, are discussed in the paper as well. Full article
(This article belongs to the Special Issue Nanofluids and Nanofluidics)
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Review

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Review
Experimental Research and Development on the Natural Convection of Suspensions of Nanoparticles—A Comprehensive Review
Nanomaterials 2020, 10(9), 1855; https://doi.org/10.3390/nano10091855 - 16 Sep 2020
Cited by 4 | Viewed by 1032
Abstract
Suspensions of nanoparticles, widely known as nanofluids, are considered as advanced heat transfer media for thermal management and conversion systems. Research on their convective thermal transport is of paramount importance for their applications in such systems such as heat exchangers and solar collectors. [...] Read more.
Suspensions of nanoparticles, widely known as nanofluids, are considered as advanced heat transfer media for thermal management and conversion systems. Research on their convective thermal transport is of paramount importance for their applications in such systems such as heat exchangers and solar collectors. This paper presents experimental research on the natural convection heat transfer performances of nanofluids in different geometries from thermal management and conversion perspectives. Experimental results and available experiment-derived correlations for the natural thermal convection of nanofluids are critically analyzed. Other features such as nanofluid preparation, stability evaluation and thermophysical properties of nanofluids that are important for this thermal transfer feature are also briefly reviewed and discussed. Additionally, techniques (active and passive) employed for enhancing the thermo-convection of nanofluids in different geometries are highlighted and discussed. Hybrid nanofluids are featured in this work as the newest class of nanofluids, with particular focuses on the thermophysical properties and natural convection heat transfer performance in enclosures. It is demonstrated that there has been a lack of accurate stability evaluation given the inconsistencies of available results on these properties and features of nanofluids. Although nanofluids exhibit enhanced thermophysical properties such as viscosity and thermal conductivity, convective heat transfer coefficients were observed to deteriorate in some cases when nanofluids were used, especially for nanoparticle concentrations of more than 0.1 vol.%. However, there are inconsistencies in the literature results, and the underlying mechanisms are also not yet well-understood despite their great importance for practical applications. Full article
(This article belongs to the Special Issue Nanofluids and Nanofluidics)
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