Browsing by Author "Prado, Jose I."

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    A 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, Luis
    The 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.
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    Development of paraffinic phase change material nanoemulsions for thermal energy storage and transport in low–temperature applications
    (Applied Thermal Engineering, 2019-05-27) Cabaleiro, David; Agresti, Filippo; Barison, Simona; Marcos, Marco A.; Prado, Jose I.; Rossi, Steffano; Bobbo, Sergio; Fedele, Laura
    In this study, new phase change material nanoemulsions (PCMEs) were designed and characterized as possible storage and heat transfer media for low–temperature thermal uses. Water–and (ethylene glycol+water)–based emulsions with fine droplets of n–heptadecane and RT21HC commercial paraffin were produced by a solvent–assisted emulsification method. No phase separation or significant growth in PCM drops were observed for the prepared emulsions through storage, after freeze–thaw cycles and under mechanical shear. Phase change transitions were characterized and a significant sub–cooling was observed, with solidification temperatures up to 13 K below the melting point. One pure alkane and two commercial paraffin waxes with higher melting points were considered as nucleating agents to reduce sub–cooling effect. Although the emulsions exhibited diminutions in thermal conductivity up to 9% with respect to the carrier fluids used as base fluid, enhancements in energy storage capacity (considering an operational temperature interval equal to the sub–cooling) reached 26% in the case of RT21HC nanoemulsion based on the (ethylene glycol+water) mixture that contained 10% in mass of paraffin. In addition, the thermal reliability of the nanoemulsions was verified analyzing the changes in latent heat after storage and throughout 1000 thermal cycles.
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    Enhancing 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, Luis
    The 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.
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    Experimental 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, Luis
    In 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.
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    Hybrid 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, Luis
    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 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.