Browsing by Author "Lugo, Luis"
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- ItemA new relationship on transport properties of nanofluids. Evidence with novel magnesium oxide based n-tetradecane nanodispersions(Powder Technology, 397 (2022) 117082, 2022-02-03) Prado, Jose I.; Vallejo, Javier P.; Lugo, LuisThe worldwide increasing of thermal energy consumption fosters new technological solutions based on nanomaterials. The use of nanofluids enhances energy efficiency leading to eco-friendlier devices. Thus, researchers are encouraged to understand how modified thermophysical properties improve heat transfer capability. Magnesium oxide based n-tetradecane nanofluids are designed in terms of stability for cold storage application. Thermal conductivity, viscosity, density, and isobaric heat capacity were determined by transient hot wire, rotational rheometry, mechanical oscillation U-tube, and differential scanning calorimetry. Furthermore, a useful relationship on thermal conductivity and viscosity of nanofluids is proposed based on Andrade, Osida and Mohanty theories. Its reliability is checked with the here reported results and literature data of different nanofluids: titanium oxide within water, silver within poly(ethylene glycol), and aluminium oxide within (1-ethyl-3-methylimidazolium methanesulfonate + water). Similar trends have been found for all nanofluids excepting titanium oxide aqueous nanofluids, this differentiated behaviour being expected by the proposed relationship.
- ItemAnalysis of Heat Transfer Characteristics of a GnP Aqueous Nanofluid through a Double-Tube Heat Exchanger(Nanomaterials 2021, 11(4), 844, 2021) Calviño, Uxía; Vallejo, Javier P.; Buschmann, Matthias H.; Fernández-Seara, José; Lugo, LuisThe 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 are obtained using the thermal resistances method, reaching enhancements for the nanofluid of up to 13%. The reported improvements are achieved without clear enhancements in the nanofluid thermal conductivity. Finally, dimensionless analyses are carried out by employing the Nusselt and Péclet numbers and Darcy friction factor.
- ItemEnhancing the Thermal Performance of a Stearate Phase Change Material with Graphene Nanoplatelets and MgO Nanoparticles(ACS Applied Materials & Interfaces, 2020-08-17) Prado, Jose I.; Lugo, LuisThe effectiveness of dispersed nanomaterials to improve the thermal performance of phase change materials (PCMs) is well-proven in the literature. The proposal of new engineered nanoenhanced phase change materials (NePCMs) with customized characteristics may lead to more efficient thermal energy storage (TES) systems. This work is focused on the development of new NePCMs based on dispersions of graphene nanoplatelets (GnPs) or MgO nanoparticles in a stearate PCM. The new proposed materials were developed using the two-step method and acetic acid was selected as surfactant to improve the stability of the dispersions. An extensive characterization of the constitutive materials and the developed dispersions through different spectroscopy techniques is reported. Also, the GnPs nanopowder was explored by using the XPS technique with the aim to characterized the used carbon nanomaterial. The obtained spectra were discussed in terms of the chemical bonds related to the found peaks. The thermophysical profile (density, thermal conductivity, isobaric heat capacity and thermal diffusivity) was experimentally determined once the main components of the NePCMs were characterized and dispersions were designed and developed. The differentiated and distinguished effect of the dispersed GnPs and MgO in the properties of the NePCMs have focused the discussion. A comprehensive analysis of the measurements to elucidate the mechanism that promoted higher improvements using GnPs instead of MgO was performed.
- ItemExperimental study on thermophysical properties of alumina nanoparticle enhanced ionic liquids(Journal of Molecular Liquids, 2019-07-07) Cherecheş, Elena Ionela; Prado, Jose I.; Cherecheş, Marius; Adriana Minea, Alina; Lugo, LuisIn this experimental study, several alumina Nanoparticle Enhanced Ionic Liquids were prepared and studied in regard to their stability, pH, density and thermal conductivity. These new fluids were manufactured by dispersing aluminium oxide nanoparticles in different mixtures based on water and 1-ethyl-3-methylimidazolium methanesulfonate ionic liquid. Furthermore, thermophysical properties (density, thermal conductivity) of pure and binary mixtures with water and 1-ethyl-3-methylimidazolium methanesulfonate were studied in order to select and propose base fluids to design new advanced heat transfer fluids. The pH of the dispersions was determined as around 8.0 - 8.5. In regard to density, the overall [C2mim][CH3SO3] density is higher by 25% than that of water and the influence of ionic liquid density over the mixtures was found to be much higher than that of water, while for the alumina Nanoparticle Enhanced Ionic Liquids the density respects classical equations. Evaluation of thermal conductivity revealed an increase of up to 13% in thermal conductivity when nanoparticles are added to the base fluids and new correlations based on mass fraction and temperature were proposed.
- ItemHybrid or mono nanofluids for convective heat transfer applications. A critical review of experimental research(Applied Thermal Engineering 23, 25 february, 117926, 2021) Vallejo, Javier P.; Prado, Jose I.; Lugo, LuisResearch 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 two-phase 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.
- ItemInfluence of crystal structure on the thermophysical properties and figures-of-merit of propylene glycol: water-based SiC nanofluids(Powder Technology, 2024) Vallejo, Javier P.; Febrero-Garrido, Lara; Cacabelos, Antón; González-Gil, Arturo; Lugo, LuisSilicon carbide is a material with a promising thermal conductivity. However, no literature has been found on SiC nanofluids based on propylene glycol:water mixtures (widely used in renewable installations). Likewise, the contribution of α-SiC and β-SiC to the thermophysical properties of nanofluids has scarcely been explored. In this work, dispersions of α-SiC and β-SiC on propylene glycol:water 30:70 wt% at 1 and 2% wt% concentration are designed. Densities, thermal conductivities, dynamic viscosities, and isobaric heat capacities from 293.15 to 313.15 K are obtained by vibrating tube densimetry, transient-hot-wire technique, rotational rheometry and differential scanning calorimetry, respectively. Convective heat transfer performance is also assessed using figures-of-merit. Thermal conductivity and viscosity show a greater dependence on the crystal structure. The β-SiC nanofluids present the highest increases of thermal conductivity (12%) and dynamic viscosity (17%). The least complex crystal structure (β-SiC) exhibits better prospects for convection applications both for laminar and turbulent flow.
- ItemThermophysical, rheological and electrical properties of mono and hybrid TiB2/B4C nanofluids based on a propylene glycol:water mixture(Powder Technology 395 (2022) 391-399, 2021) Vallejo, Javier P.; Zyla, Gawel; Ansia, Lucas; Fal, Jacek; Traciak, Julian; Lugo, LuisHybrid nanofluids aim to further improve the characteristics of mono nanofluids. However, experimental studies that jointly explore the physical properties of hybrids and the corresponding mono nanofluids are missing. In this work, mono B4C and TiB2 and hybrid TiB2:B4C nanoadditives are used for the first time to design nanofluids based on propylene glycol:water 20:80 wt%. The density, isobaric heat capacity, and thermal conductivity of the nanofluids are determined by the oscillating U-tube, differential scanning calorimetry, and transient hot wire methods, respectively. The rheological behaviour is investigated through rotational rheometry. Additionally, surface tension and electrical conductivity are investigated. The B4C mono nanofluid shows the highest improvements of thermal conductivity (6.0%) and electrical conductivity (70 times higher), but also the highest viscosity increases (51–54%). The hybrid nanofluid presents intermediate values between those of the mono nanofluids for all the properties except dynamic viscosity. Interactions between spherical and sheet-like nanoparticles explain this behaviour.
- ItemTuning the thermal properties of aqueous nanofluids by taking advantage of size-customized clusters of iron oxide nanoparticles(Journal of Molecular Liquids 344 (2021) 117727, 2021) Elsaidy, Amir; Vallejo, Javier P.; Salgueiriño, Verónica; Lugo, LuisIn this study, the thermal conductivity of aqueous nanofluids containing clusters of iron oxide (Fe3O4/γ-Fe2O3) nanoparticles has been investigated experimentally for the first time, with the aim of assessing the role of a controlled aggregation of nanoparticles in these final nanofluids. For that, clusters of iron oxide nanoparticles of different cluster size (46–240 nm diameter range) were synthesized by a solvothermal method and fully characterized by transmission electron microscopy, X-ray diffraction and Raman spectroscopy. The rheological behavior of the optimal nanofluids was also studied by rotational rheometry. The nanofluids were obtained by dispersing the clusters of iron oxide nanoparticles in water taking into account different solid volume fractions (from 0.50 to 1.5 wt%) and the experiments were conducted in the temperature range from 293.15 K to 313.15 K. The study reveals and quantifies enhancements in the thermal conductivity of nanofluid with increase of cluster size and temperature. Furthermore, a 0.50 wt% concentration of clusters of iron oxide nanoparticles within the whole range of proposed nanofluids offers great stability and improved thermal conductivity for heat transfer applications with an small dynamic viscosity increase. In addition, the larger the size of the clusters of iron oxide nanoparticles, the greater the increase in thermal conductivity for the designed Fe3O4/γ-Fe2O3 cluster-based nanofluids, with thermal conductivity values following a constant upward trend and reaching a maximum increase of 4.4% for the largest synthesized clusters (average size of 240 nm). These results open the door for the development of iron oxide-based nanofluids on which taking advantage of an optimized aggregation of nanoparticles by using size-customized clusters.