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 the dispersions of graphene nanoplatelets (GnPs) or MgO nanoparticles in a stearate PCM. The new proposed materials were synthesized using a two-step method, and acetic acid was selected as a surfactant to improve the stability of the dispersions. An extensive characterization of the constitutive materials and the developed dispersions using different spectroscopy techniques is reported. Also, the GnP nanopowder was explored by using the XPS technique with the aim to characterize the used carbon nanomaterial. The obtained spectra were investigated in terms of the chemical bonds related to the observed 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. This discussion focuses on the differentiated and distinguished effects of the dispersed GnPs and MgO on the properties of the NePCMs. A comprehensive analysis of the measurements to elucidate the mechanism that promoted higher improvements using GnPs instead of MgO was performed.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
•Review of experimental heat transfer studies comparing hybrid and mono nanofluids.•Analysis of hybrid and mono nanofluids for single-phase and two-phase convection.•Laminar single-phase convection: ...mono nanofluids better than hybrids (mixtures).•Laminar flow: thermal conductivity is straight related to convective heat transfer.•Turbulent single-phase convection and two-phase convection: few and divergent data.
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.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•PCMEs with 2–10 wt% of paraffin and droplet sizes of ∼90–150 nm were designed.•Samples were stable over time, throughout freeze–thaw cycles and under stirring.•Enhancements in energy storage ...capacity may reach 26%.•Tested nucleating agents slightly reduced sub-cooling of PCMEs.•k and ρ decreased with PCM concentration up to 9% and 3%, respectively.
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.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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 C2mimCH3SO3 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.
•Ionic liquid-water mixtures were prepared.•pH of developed new fluids is measured and good stability is noticed.•Al2O3 NEIL density is experimentally examined and good agreement with existing equations was noticed.•Al2O3 NEIL thermal conductivity is experimentally examined and an enhancement was noted.•Al2O3 NEIL thermal conductivity correlations are proposed.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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.
Display omitted
•MgO/n-C14 nanofluids are designed for cold thermal energy storage applications•The experimental thermophysical profile of the novel stable nanofluids is reported•A new relationship on transport properties of nanofluids is proposed and analysed•A further understanding on the enhancing mechanism of nanofluids is approached
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The lack of a standard experimental procedure to determine thermal conductivity of fluids is noticeable in heat transfer processes from practical and fundamental perspectives. Since a wide variety of ...techniques have been used, reported literature data have huge discrepancies. A common practice is using manufactured thermal conductivity meters for nanofluids, which can standardize the measurements but are also somewhat inaccurate. In this study, a new methodology to perform reliable measurements with a recent commercial transient hot-wire device is introduced. Accordingly, some extensively studied fluids in the literature (water, ethylene glycol, ethylene glycol:water mixture 50:50 vol%, propylene glycol, and n-tetradecane) covering the range 0.100 to 0.700 W m−1 K−1 were used to check the device in the temperature range 283.15 to 333.15 K. Deviations between the collected data and the theoretical model, and repeatabilities and deviations between reported and literature values, were analyzed. Systematic deviations in raw data were found, and a correction factor depending on the mean thermal conductivity was proposed to operate with nanofluids. Considering all tested effects, the expanded (k = 2) uncertainty of the device was set as 5%. This proposed methodology was also checked with n-hexadecane and magnesium-oxide-based n-tetradecane nanofluids.
Temperature and loading dependences on the rheological behavior and isobaric specific heat capacity of several suspensions of alumina nanoparticles in a binary mixture of C2mimCH3SO3 ionic liquid and ...water were experimentally determined to assess its potential condition of enhanced heat transfer fluids. Rheological tests show a clear Newtonian behavior for the base fluid and the NEILs with lower Al2O3 concentrations while higher amounts of alumina nanoparticles entail non-Newtonian fluids and increase in viscosity up to 78%. The heating-cooling viscosity tests reveal that no significant viscosity hysteresis occur and VFT equation adequately describe the temperature dependence. Isobaric specific heat capacities decrease (<10%) with nanoparticle mass fraction and increase (<10%) with temperature. The goodness of the Raud et al. correlation for predicting the isobaric specific heat capacity of nanoparticles enhanced fluids is discussed.
•New NEILs based on C2mimCH3SO3 ionic liquid + water and Al2O3 are proposed.•NEILs viscosity increases as 39–78% by dispersing nanoparticles.•Heating-cooling cycles dependence on the prepared samples viscosity.•VFT model describes viscosity values for the NEILs with deviations less than 1.3%.•Cp(T) curves entails an increase up to 10% for the selected IL + W as base fluid.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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 temperature of the variation with oxidation of the studied properties, including the FOMs, was almost null, except for ATF A; therefore, FOMs should be used to compare the cooling performance of ATFs for electric drivetrains instead of a single property, such as thermal conductivity.
The drying processing of agglomerated instant coffee can change the quality of the product due to the production of volatile compounds associated with the undesirable cereal aroma. Using fractional ...factorial planning, this study aimed to understand how the processing parameters (burner temperature, BT; steam pressure, SP; process air flow, AF; and fluidized hot bed section, LT) influenced the volatile profiles. The BT, AF, and the interaction of these variables (BT*AF) have significant influence (p < 0.10) on cereal aroma intensity. Results from the principal component analysis showed that 4,5-dimethylthiazole, 2-ethyl-3-methylpyrazine, and 4-ethyl-2-methoxyphenol are related to the undesirable cereal aroma.
The agglomeration process of coffee affects the volatile compounds
Burner temperature and process air flow significantly interfere in the cereal aroma of coffee
The usage of intermediate parameters in the agglomeration process reduces the cereal aroma
Full text
Available for:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Assessing the effectiveness of protected areas for sustaining species and identifying priority sites for their conservation is vital for decision making, particularly for freshwater fishes in South ...America, the global centre of freshwater fish diversity. Several conservation planning studies have used threatened freshwater fishes or species that are vulnerable to climate change as conservation targets, but none has included both in priority‐setting analysis.
The objectives of this study were to identify gaps in the coverage of the existing protected areas in representing the endemic freshwater fishes of the Tropical Andes region, and to identify conservation priority areas that adequately cover threatened species and species vulnerable to climate change.
Data on 648 freshwater fishes from the Tropical Andes were used to identify gaps in the protected area coverage, and to identify conservation priority sites under three scenarios: (i) prioritize threatened species; (ii) prioritize species that are vulnerable to climate change; and (iii) prioritize both threatened species and species vulnerable to climate change.
A total of 571 species (88% of all species) were not covered by any protected areas; most of them are restricted to ≤10 catchments. To represent both threatened species and species vulnerable to climate change in the third scenario, 635 catchments were identified as priority areas, representing 26.5% of the study area. The number of irreplaceable catchments for this scenario is 475, corresponding to 22.5% of the total area.
The results of this study could be crucial for designing strategies for the effective protection of native fish populations in the Tropical Andes, and for planning proactive climate adaptation. It is hoped that the identification of priority areas, particularly irreplaceable catchments, will help to guide conservation and management decisions in the Andean region.
Full text
Available for:
FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
PDF
