Luis Lugo - Academia.edu (original) (raw)

Papers by Luis Lugo

Applied Sciences

The cooling performance of automatic transmission fluids (ATFs) plays an important role in hybrid... more The cooling performance of automatic transmission fluids (ATFs) plays an important role in hybrid electrical vehicles, in which the electric motor (EM) is placed inside the transmission housing due to their mission of cooling the EM. The cooling performance of the ATFs depends on their thermophysical properties, but these properties change with the oxidation of the ATFs. This work studies the influence of the oxidation of three ATFs (A, B, C) on their thermophysical properties, as well as on some figures-of-merit (FOMs) which are relevant for evaluating the cooling performance. The results indicated that the influence of the molecular structure on thermal conductivity and heat capacity is stronger than on density and viscosity, whereas the molecular structure hardly affects the FOMs of the fresh ATFs; ATFs B and C, formulated with base oils from API Group III, indicated better cooling performance than ATF A which was formulated with base oils from API Group I; the sensitivity to tem...

Gels

The skin of yellowfin tuna is one of the fishery industry solid residues with the greatest potent... more The skin of yellowfin tuna is one of the fishery industry solid residues with the greatest potential to add extra value to its circular economy that remains yet unexploited. Particularly, the high collagen content of fish skin allows generating gelatin by hydrolysis, which is ideal for forming hydrogels due to its biocompatibility and gelling capability. Hydrogels have been used as drug carriers for local administration due to their mechanical properties and drug loading capacity. Herein, novel tuna gelatin hydrogels were designed as drug vehicles with two structurally different antitumoral model compounds such as Doxorubicin and Crocin to be administrated locally in tissues with complex human anatomies after surgical resection. The characterization by gel permeation chromatography (GPC) of purified gelatin confirmed their heterogeneity composition, exhibiting three major bands that correspond to the β and α chains along with high molecular weight species. In addition, the Fourier T...

Nanomaterials, 2021

The thermal properties of graphene have proved to be exceptional and are partly maintained in its... more The thermal properties of graphene have proved to be exceptional and are partly maintained in its multi-layered form, graphene nanoplatelets (GnP). Since these carbon-based nanostructures are hydrophobic, functionalization is needed in order to assess their long-term stability in aqueous suspensions. In this study, the convective heat transfer performance of a polycarboxylate chemically modified GnP dispersion in water at 0.50 wt% is experimentally analyzed. After designing the nanofluid, dynamic viscosity, thermal conductivity, isobaric heat capacity and density are measured using rotational rheometry, the transient hot-wire technique, differential scanning calorimetry and vibrating U-tube methods, respectively, in a wide temperature range. The whole analysis of thermophysical and rheological properties is validated by two laboratories. Afterward, an experimental facility is used to evaluate the heat transfer performance in a turbulent regime. Convective heat transfer coefficients ...

The dispersion and stability of nanofluids obtained by dispersing Al2O3 nanoparticles in ethylene... more The dispersion and stability of nanofluids obtained by dispersing Al2O3 nanoparticles in ethylene glycol have been analyzed at several concentrations up to 25 % in mass fraction. The thermal conductivity and viscosity were experimentally determined at temperatures ranging from 283.15 K to 323.15 K using an apparatus based on the hot-wire method and a rotational viscometer, respectively. It has been found that both thermal conductivity and viscosity increase with the concentration of nanoparticles, whereas when the temperature increases the viscosity diminishes and the thermal conductivity rises. Measured enhancements on thermal conductivity (up to 19%) compare well with literature values when available. New viscosity experimental data yield values more than twice larger than the base fluid. The influence of particle size on viscosity has been also studied, finding large differences that must be taken into account for any practical application. These experimental results were compare...

Applied Thermal Engineering, 2022

Research on nanofluids has increased markedly in the last two decades. Initial attention has focu... more Research on nanofluids has increased markedly in the last two decades. Initial attention has focused on conventional or mono nanofluids, dispersions of one type of solid nano-sized particles in a base fluid. Despite various challenges such as dispersion stability or increased pumping power, nanofluids have become improved working fluids for various energy applications. Among them, convective heat transfer has been the main research topic since the very beginning. Hybrid nanofluids, dispersions of two or more different nanoadditives in mixture or composite form, have received attention more recently. Research on hybrid nanofluids aims to further enhance the individual benefits of each single dispersion through potential synergistic effects between nanomaterials. Multiple experimental studies have been conducted independently analysing the convective heat transfer performance of mono or hybrid nanofluids for single-phase and two-phase convective heat transfer applications. However, there are still no general conclusions about which nanofluids, mono or hybrid, present better prospects. This review summarizes the experimental studies that jointly analyse both hybrid and mono nanofluids for these applications and the results are classified according to the heat transfer device used. Based on this criterion, three large groups of devices were noticed for single-phase convective heat transfer (tubular heat exchangers, plate heat exchangers and minichannel heat exchangers/heat sinks), while one group was identified for twophase convective heat transfer (heat pipes). The main outcomes of these studies are summarized and critically analysed to draw general conclusions from an application point of view.

Fluids, 2021

This study focuses on the preparation, thermophysical and rheological characterization of phase c... more This study focuses on the preparation, thermophysical and rheological characterization of phase change material nanoemulsions as latent functionally thermal fluids. Aqueous dispersions with fine droplets of cetyl alcohol (with a melting temperature at ~321 K) were prepared by means of a solvent-assisted method, combining ultrasonication with non-ionic and anionic emulsifiers. Eicosyl alcohol (melting at ~337 K) and hydrophobic silica nanoparticles were tested as nucleating agents. Droplet size studies through time and after freeze–thaw cycles confirmed the good stability of formulated nanoemulsions. Phase change analyses proved the effectiveness of eicosyl alcohol to reduce subcooling to a few Kelvin. Although phase change material emulsions exhibited thermal conductivities much larger than bulk cetyl alcohol (at least 60% higher when droplets are solid), reductions in this property reached 15% when compared to water. Samples mainly showed desirable Newtonian behavior (or slight she...

In this work, stable homogeneous nanofluids were designed as dispersions of sulfonic acid-functio... more In this work, stable homogeneous nanofluids were designed as dispersions of sulfonic acid-functionalized graphene nanoplatelets in an (ethylene glycol + water) mixture at (10:90)% mass ratio and nanoparticle mass concentrations up to 0.5 wt.%. Nanofluid stability was evaluated by means of Dynamic Light Scattering (DLS) and Zeta Potential measurements. The thermal conductivity and dynamic viscosity of base fluid and nanofluids were experimentally obtained in the temperature range from (283.15 to 343.15) K by using a TPS 2500S Hot Disk and an AR-G2 rotational rheometer, respectively. Thermal conductivity improvements reach up to 5% while the maximum dynamic viscosity increase is 12.6%. Finally, the experimental values of these two transport properties were also utilized to analyze nanoparticle concentration effect on heat transfer performance and pumping power through different figures of merit. NOMENCLATURE INTRODUCTION The exponential growth in energy consumption experimented in the...

One of the most restricting factors in the performance of industrial heat transfer processes is t... more One of the most restricting factors in the performance of industrial heat transfer processes is the low thermal conductivity of the thermal fluids commonly used. Hence, dispersions of nanoparticles with high thermal conductivity in conventional fluids, nanofluids, have received increasingly interest over last decades in order to obtain improvements in heat transfer processes. The thermophysical properties are necessary to their flow behaviour characterization and they are not commonly available in the literature. Therefore, laboratories with wide experience in thermophysical characterization should call attention to this issue. This study aims to determine those properties with a noticeable influence on the heat transfer capability for dispersions of functionalized graphene nanoplatelets in a propylene glycol:water mixture at (30:70) % mass ratio, usually employed in thermal facilities. Initially, nanofluid stabilities were investigated analyzing zeta potential measurements, optimiz...

A new generation of heat transfer fluids, nanofluids, can play a major role in the development of... more A new generation of heat transfer fluids, nanofluids, can play a major role in the development of today’s renewable energies. In the particular case of wind turbines, an undesirable overheating of electrical and mechanical components can provoke a noticeable reduction of overall efficiency due to the temperature is a limiting factor to the electricity generation or even very expensive repair cost because of an unexpected crash of generators, or others turbine components. Dispersions of multiple-layer graphene nanostructures with high thermal conductivity in conventional working fluids are a promising type of new heat transfer fluids due to the excellent performance of nanoadditives in heat transference. Hence, determining the thermophysical properties of these nanomaterials under different conditions is the first step and key issue for analysing and optimizing the dispersions. Although water-based graphene nanoplatelet nanofluids have been investigated and some correlations can be f...

The heat transfer performance of the conventional fluids used in heat exchange processes improves... more The heat transfer performance of the conventional fluids used in heat exchange processes improves by dispersing nanoparticles with high thermal conductivity, as many researches have shown in the last decades. The heat transfer capability of a fluid depends on several physical properties among which the rheological behavior is very relevant, as we have previously pointed out. In this study, different samples of nanofluids have been analyzed by using a DHR-2 rotational rheometer of TA Instruments with concentric cylinder geometry in the temperature range from (278.15 to 323.15) K. The used base fluids were two different binary mixtures of propylene glycol and water at (10:90)% and (30:70)% mass ratios. Two different mass concentrations (viz. 0.25 and 0.5 wt.%) of graphene nanoplatelets functionalized with sulfonic acid (graphenitHW6) were dispersed in these two base fluids. Firstly, with the goal of checking and calibrating the operation of the rheometer, the viscosity-shear stress cu...

Journal of Molecular Liquids, 2021

Journal of Molecular Liquids, 2021

The paper summarized results of experimental studies on thermophysical and electrical properties ... more The paper summarized results of experimental studies on thermophysical and electrical properties of ethylene glycol based nanofluids containing carbon black nanoparticles. Two types of nanoparticles differing in size and specific surface area were used to develop nanofluids. During examination the thermal conductivity, isobaric heat capacity, mass density, nanofluid-air surface tension, dynamic viscosity, refractive index and electrical conductivity were measured in strict controlled temperature 298.15 K. Obtained results indicate that the specific surface area have great influence on these fundamental properties of nanofluids developed with carbon nanoparticles.

Journal of Molecular Liquids, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Energies, 2020

Volumetric properties such as density and isobaric thermal expansivity, and surface tension are o... more Volumetric properties such as density and isobaric thermal expansivity, and surface tension are of paramount importance for nanofluids to evaluate their ability to be used as efficient heat transfer fluids. In this work, the nanofluids are prepared by dispersing few-layer graphene in a commercial heat transfer fluid Tyfocor® LS (40:60 wt.% propylene-glycol/water) with the aid of three different nonionic surfactants: Triton X-100, Pluronic® P-123 and Gum Arabic. The density, isobaric thermal expansivity and surface tension of each of the base fluids and nanofluids are evaluated between 283.15 and 323.15 K. The influence of the mass content in few-layer graphene from 0.05 to 0.5% on these nanofluid properties was studied. The density behavior of the different proposed nanofluids is slightly affected by the presence of graphene, and its evolution is well predicted by the weight-average equation depending on the density of each component of the nanofluids. For all the analyzed samples, ...

Nanomaterials, 2019

The main objective of this study is to design and characterize silver suspensions based on poly(e... 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), dyna...

Applied Sciences, 2020

The application of nanofluids in direct solar absorption, heat transfer or direct solar steam gen... more The application of nanofluids in direct solar absorption, heat transfer or direct solar steam generation entails carrying out a comprehensive study taking into account several physical quantities. Long-term stability, rheological, thermophysical and optical properties of dispersions must be known to assess their potential for envisaged applications. Two low-concentration nanofluids, 0.005 and 0.05 wt%, of sulfonic acid-functionalized and polycarboxylate chemically modified graphene nanoplatelets in water were considered in this work. Elemental analyses of the nanopowders and pH evaluations of the colloids were carried out. The rheological behaviour of dispersions at different temperatures was studied by rotational rheometry. Thermal conductivities were measured by the transient hot wire method and densities by the oscillating U-tube technique. Additionally, a brief report of the optical properties was included to provide a comprehensive physical analysis.

Journal of Molecular Liquids, 2019

Hybrid nanofluids, suspensions of nanocomposites or nanoparticle-decorated complex structures in ... more Hybrid nanofluids, suspensions of nanocomposites or nanoparticle-decorated complex structures in conventional fluids, are focusing the attention of the research in the recent years because of the potential synergistic effects among particles. Nevertheless, deep studies based on systematic experimental investigations are missing. Thus, in this work, a propylene glycol:water 10:90 wt% mixture was proposed as base fluid while various ratios (0:1, 1:4, 1:1, 4:1 and 1:0) between the constituents present in the hybrid nanoadditive (silver/graphene nanoplatelet with different functionalizations) were swept. Eleven nanofluids with three total nanoadditive concentrations of 0.05, 0.1 and 1 wt% were designed. The stability of the samples was assessed by dynamic light scattering measurements over the time. Experimental optical, rheological and thermophysical profiles jointly were analysed with the aim to produce a comprehensive elucidation of the new hybrid nanofluids. Optical properties were investigated through optical spectroscopy, rheological properties through rotational rheometry, thermal conductivity by means of transient hot-wire method, and density through oscillating U-tube technique. The optical transmittance results for all analysed nanofluids confirmed that more than 90% sunlight extinction is achieved for a path length lower or equal to 6 mm. Its spatial distribution in the nanofluid volume can be tailored acting on the concentration of each nanoadditive, allowing the design of customized miniaturized systems. Newtonian behaviour was evidenced for all samples, with viscosity increases lower that 9% for all 0.1 wt% nanofluids, those with optical applications. Thermal conductivity results showed practically no variations with respect the base fluid for all samples with this total concentration.

Nanomaterials, 2019

Graphene is considered a promising substance in applications related to the capture and reduction... more Graphene is considered a promising substance in applications related to the capture and reduction of the environmental impact of fluorinated gases. However, further research is still required to explore all related possibilities. In this work, the potential use in this context of nanofluids (NFs), obtained by dispersing graphene nanosheets in fluorinated ionic liquids (FILs) is investigated. As a starting step, a thermal and structural characterization for this type of IoNanofluids (IoNFs) is presented. The highly nanostructured nature of FILs has been recently demonstrated. The presence of fluorinated moieties is responsible for enhancing the accommodation of solutes such as small gases. The strong tendency to self-assemble forming continuous and supramolecular structures, and the versatility to rearrange in several conformational features allows the stabilization of nano colloidal systems. It is essential to perform a comprehensive study of their structural features to understand ...

Applied Sciences

The cooling performance of automatic transmission fluids (ATFs) plays an important role in hybrid... more The cooling performance of automatic transmission fluids (ATFs) plays an important role in hybrid electrical vehicles, in which the electric motor (EM) is placed inside the transmission housing due to their mission of cooling the EM. The cooling performance of the ATFs depends on their thermophysical properties, but these properties change with the oxidation of the ATFs. This work studies the influence of the oxidation of three ATFs (A, B, C) on their thermophysical properties, as well as on some figures-of-merit (FOMs) which are relevant for evaluating the cooling performance. The results indicated that the influence of the molecular structure on thermal conductivity and heat capacity is stronger than on density and viscosity, whereas the molecular structure hardly affects the FOMs of the fresh ATFs; ATFs B and C, formulated with base oils from API Group III, indicated better cooling performance than ATF A which was formulated with base oils from API Group I; the sensitivity to tem...

Gels

The skin of yellowfin tuna is one of the fishery industry solid residues with the greatest potent... more The skin of yellowfin tuna is one of the fishery industry solid residues with the greatest potential to add extra value to its circular economy that remains yet unexploited. Particularly, the high collagen content of fish skin allows generating gelatin by hydrolysis, which is ideal for forming hydrogels due to its biocompatibility and gelling capability. Hydrogels have been used as drug carriers for local administration due to their mechanical properties and drug loading capacity. Herein, novel tuna gelatin hydrogels were designed as drug vehicles with two structurally different antitumoral model compounds such as Doxorubicin and Crocin to be administrated locally in tissues with complex human anatomies after surgical resection. The characterization by gel permeation chromatography (GPC) of purified gelatin confirmed their heterogeneity composition, exhibiting three major bands that correspond to the β and α chains along with high molecular weight species. In addition, the Fourier T...

Nanomaterials, 2021

The thermal properties of graphene have proved to be exceptional and are partly maintained in its... more The thermal properties of graphene have proved to be exceptional and are partly maintained in its multi-layered form, graphene nanoplatelets (GnP). Since these carbon-based nanostructures are hydrophobic, functionalization is needed in order to assess their long-term stability in aqueous suspensions. In this study, the convective heat transfer performance of a polycarboxylate chemically modified GnP dispersion in water at 0.50 wt% is experimentally analyzed. After designing the nanofluid, dynamic viscosity, thermal conductivity, isobaric heat capacity and density are measured using rotational rheometry, the transient hot-wire technique, differential scanning calorimetry and vibrating U-tube methods, respectively, in a wide temperature range. The whole analysis of thermophysical and rheological properties is validated by two laboratories. Afterward, an experimental facility is used to evaluate the heat transfer performance in a turbulent regime. Convective heat transfer coefficients ...

The dispersion and stability of nanofluids obtained by dispersing Al2O3 nanoparticles in ethylene... more The dispersion and stability of nanofluids obtained by dispersing Al2O3 nanoparticles in ethylene glycol have been analyzed at several concentrations up to 25 % in mass fraction. The thermal conductivity and viscosity were experimentally determined at temperatures ranging from 283.15 K to 323.15 K using an apparatus based on the hot-wire method and a rotational viscometer, respectively. It has been found that both thermal conductivity and viscosity increase with the concentration of nanoparticles, whereas when the temperature increases the viscosity diminishes and the thermal conductivity rises. Measured enhancements on thermal conductivity (up to 19%) compare well with literature values when available. New viscosity experimental data yield values more than twice larger than the base fluid. The influence of particle size on viscosity has been also studied, finding large differences that must be taken into account for any practical application. These experimental results were compare...

Applied Thermal Engineering, 2022

Research on nanofluids has increased markedly in the last two decades. Initial attention has focu... more Research on nanofluids has increased markedly in the last two decades. Initial attention has focused on conventional or mono nanofluids, dispersions of one type of solid nano-sized particles in a base fluid. Despite various challenges such as dispersion stability or increased pumping power, nanofluids have become improved working fluids for various energy applications. Among them, convective heat transfer has been the main research topic since the very beginning. Hybrid nanofluids, dispersions of two or more different nanoadditives in mixture or composite form, have received attention more recently. Research on hybrid nanofluids aims to further enhance the individual benefits of each single dispersion through potential synergistic effects between nanomaterials. Multiple experimental studies have been conducted independently analysing the convective heat transfer performance of mono or hybrid nanofluids for single-phase and two-phase convective heat transfer applications. However, there are still no general conclusions about which nanofluids, mono or hybrid, present better prospects. This review summarizes the experimental studies that jointly analyse both hybrid and mono nanofluids for these applications and the results are classified according to the heat transfer device used. Based on this criterion, three large groups of devices were noticed for single-phase convective heat transfer (tubular heat exchangers, plate heat exchangers and minichannel heat exchangers/heat sinks), while one group was identified for twophase convective heat transfer (heat pipes). The main outcomes of these studies are summarized and critically analysed to draw general conclusions from an application point of view.

Fluids, 2021

This study focuses on the preparation, thermophysical and rheological characterization of phase c... more This study focuses on the preparation, thermophysical and rheological characterization of phase change material nanoemulsions as latent functionally thermal fluids. Aqueous dispersions with fine droplets of cetyl alcohol (with a melting temperature at ~321 K) were prepared by means of a solvent-assisted method, combining ultrasonication with non-ionic and anionic emulsifiers. Eicosyl alcohol (melting at ~337 K) and hydrophobic silica nanoparticles were tested as nucleating agents. Droplet size studies through time and after freeze–thaw cycles confirmed the good stability of formulated nanoemulsions. Phase change analyses proved the effectiveness of eicosyl alcohol to reduce subcooling to a few Kelvin. Although phase change material emulsions exhibited thermal conductivities much larger than bulk cetyl alcohol (at least 60% higher when droplets are solid), reductions in this property reached 15% when compared to water. Samples mainly showed desirable Newtonian behavior (or slight she...

In this work, stable homogeneous nanofluids were designed as dispersions of sulfonic acid-functio... more In this work, stable homogeneous nanofluids were designed as dispersions of sulfonic acid-functionalized graphene nanoplatelets in an (ethylene glycol + water) mixture at (10:90)% mass ratio and nanoparticle mass concentrations up to 0.5 wt.%. Nanofluid stability was evaluated by means of Dynamic Light Scattering (DLS) and Zeta Potential measurements. The thermal conductivity and dynamic viscosity of base fluid and nanofluids were experimentally obtained in the temperature range from (283.15 to 343.15) K by using a TPS 2500S Hot Disk and an AR-G2 rotational rheometer, respectively. Thermal conductivity improvements reach up to 5% while the maximum dynamic viscosity increase is 12.6%. Finally, the experimental values of these two transport properties were also utilized to analyze nanoparticle concentration effect on heat transfer performance and pumping power through different figures of merit. NOMENCLATURE INTRODUCTION The exponential growth in energy consumption experimented in the...

One of the most restricting factors in the performance of industrial heat transfer processes is t... more One of the most restricting factors in the performance of industrial heat transfer processes is the low thermal conductivity of the thermal fluids commonly used. Hence, dispersions of nanoparticles with high thermal conductivity in conventional fluids, nanofluids, have received increasingly interest over last decades in order to obtain improvements in heat transfer processes. The thermophysical properties are necessary to their flow behaviour characterization and they are not commonly available in the literature. Therefore, laboratories with wide experience in thermophysical characterization should call attention to this issue. This study aims to determine those properties with a noticeable influence on the heat transfer capability for dispersions of functionalized graphene nanoplatelets in a propylene glycol:water mixture at (30:70) % mass ratio, usually employed in thermal facilities. Initially, nanofluid stabilities were investigated analyzing zeta potential measurements, optimiz...

A new generation of heat transfer fluids, nanofluids, can play a major role in the development of... more A new generation of heat transfer fluids, nanofluids, can play a major role in the development of today’s renewable energies. In the particular case of wind turbines, an undesirable overheating of electrical and mechanical components can provoke a noticeable reduction of overall efficiency due to the temperature is a limiting factor to the electricity generation or even very expensive repair cost because of an unexpected crash of generators, or others turbine components. Dispersions of multiple-layer graphene nanostructures with high thermal conductivity in conventional working fluids are a promising type of new heat transfer fluids due to the excellent performance of nanoadditives in heat transference. Hence, determining the thermophysical properties of these nanomaterials under different conditions is the first step and key issue for analysing and optimizing the dispersions. Although water-based graphene nanoplatelet nanofluids have been investigated and some correlations can be f...

The heat transfer performance of the conventional fluids used in heat exchange processes improves... more The heat transfer performance of the conventional fluids used in heat exchange processes improves by dispersing nanoparticles with high thermal conductivity, as many researches have shown in the last decades. The heat transfer capability of a fluid depends on several physical properties among which the rheological behavior is very relevant, as we have previously pointed out. In this study, different samples of nanofluids have been analyzed by using a DHR-2 rotational rheometer of TA Instruments with concentric cylinder geometry in the temperature range from (278.15 to 323.15) K. The used base fluids were two different binary mixtures of propylene glycol and water at (10:90)% and (30:70)% mass ratios. Two different mass concentrations (viz. 0.25 and 0.5 wt.%) of graphene nanoplatelets functionalized with sulfonic acid (graphenitHW6) were dispersed in these two base fluids. Firstly, with the goal of checking and calibrating the operation of the rheometer, the viscosity-shear stress cu...

Journal of Molecular Liquids, 2021

Journal of Molecular Liquids, 2021

The paper summarized results of experimental studies on thermophysical and electrical properties ... more The paper summarized results of experimental studies on thermophysical and electrical properties of ethylene glycol based nanofluids containing carbon black nanoparticles. Two types of nanoparticles differing in size and specific surface area were used to develop nanofluids. During examination the thermal conductivity, isobaric heat capacity, mass density, nanofluid-air surface tension, dynamic viscosity, refractive index and electrical conductivity were measured in strict controlled temperature 298.15 K. Obtained results indicate that the specific surface area have great influence on these fundamental properties of nanofluids developed with carbon nanoparticles.

Journal of Molecular Liquids, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Energies, 2020

Volumetric properties such as density and isobaric thermal expansivity, and surface tension are o... more Volumetric properties such as density and isobaric thermal expansivity, and surface tension are of paramount importance for nanofluids to evaluate their ability to be used as efficient heat transfer fluids. In this work, the nanofluids are prepared by dispersing few-layer graphene in a commercial heat transfer fluid Tyfocor® LS (40:60 wt.% propylene-glycol/water) with the aid of three different nonionic surfactants: Triton X-100, Pluronic® P-123 and Gum Arabic. The density, isobaric thermal expansivity and surface tension of each of the base fluids and nanofluids are evaluated between 283.15 and 323.15 K. The influence of the mass content in few-layer graphene from 0.05 to 0.5% on these nanofluid properties was studied. The density behavior of the different proposed nanofluids is slightly affected by the presence of graphene, and its evolution is well predicted by the weight-average equation depending on the density of each component of the nanofluids. For all the analyzed samples, ...

Nanomaterials, 2019

The main objective of this study is to design and characterize silver suspensions based on poly(e... 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), dyna...

Applied Sciences, 2020

The application of nanofluids in direct solar absorption, heat transfer or direct solar steam gen... more The application of nanofluids in direct solar absorption, heat transfer or direct solar steam generation entails carrying out a comprehensive study taking into account several physical quantities. Long-term stability, rheological, thermophysical and optical properties of dispersions must be known to assess their potential for envisaged applications. Two low-concentration nanofluids, 0.005 and 0.05 wt%, of sulfonic acid-functionalized and polycarboxylate chemically modified graphene nanoplatelets in water were considered in this work. Elemental analyses of the nanopowders and pH evaluations of the colloids were carried out. The rheological behaviour of dispersions at different temperatures was studied by rotational rheometry. Thermal conductivities were measured by the transient hot wire method and densities by the oscillating U-tube technique. Additionally, a brief report of the optical properties was included to provide a comprehensive physical analysis.

Journal of Molecular Liquids, 2019

Hybrid nanofluids, suspensions of nanocomposites or nanoparticle-decorated complex structures in ... more Hybrid nanofluids, suspensions of nanocomposites or nanoparticle-decorated complex structures in conventional fluids, are focusing the attention of the research in the recent years because of the potential synergistic effects among particles. Nevertheless, deep studies based on systematic experimental investigations are missing. Thus, in this work, a propylene glycol:water 10:90 wt% mixture was proposed as base fluid while various ratios (0:1, 1:4, 1:1, 4:1 and 1:0) between the constituents present in the hybrid nanoadditive (silver/graphene nanoplatelet with different functionalizations) were swept. Eleven nanofluids with three total nanoadditive concentrations of 0.05, 0.1 and 1 wt% were designed. The stability of the samples was assessed by dynamic light scattering measurements over the time. Experimental optical, rheological and thermophysical profiles jointly were analysed with the aim to produce a comprehensive elucidation of the new hybrid nanofluids. Optical properties were investigated through optical spectroscopy, rheological properties through rotational rheometry, thermal conductivity by means of transient hot-wire method, and density through oscillating U-tube technique. The optical transmittance results for all analysed nanofluids confirmed that more than 90% sunlight extinction is achieved for a path length lower or equal to 6 mm. Its spatial distribution in the nanofluid volume can be tailored acting on the concentration of each nanoadditive, allowing the design of customized miniaturized systems. Newtonian behaviour was evidenced for all samples, with viscosity increases lower that 9% for all 0.1 wt% nanofluids, those with optical applications. Thermal conductivity results showed practically no variations with respect the base fluid for all samples with this total concentration.

Nanomaterials, 2019

Graphene is considered a promising substance in applications related to the capture and reduction... more Graphene is considered a promising substance in applications related to the capture and reduction of the environmental impact of fluorinated gases. However, further research is still required to explore all related possibilities. In this work, the potential use in this context of nanofluids (NFs), obtained by dispersing graphene nanosheets in fluorinated ionic liquids (FILs) is investigated. As a starting step, a thermal and structural characterization for this type of IoNanofluids (IoNFs) is presented. The highly nanostructured nature of FILs has been recently demonstrated. The presence of fluorinated moieties is responsible for enhancing the accommodation of solutes such as small gases. The strong tendency to self-assemble forming continuous and supramolecular structures, and the versatility to rearrange in several conformational features allows the stabilization of nano colloidal systems. It is essential to perform a comprehensive study of their structural features to understand ...