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Nanofluids are complex fluids, mainly proposed to improve the efficiency of thermal systems. However, their poor stability, caused by the agglomeration and sedimentation of ...nanoparticles over time, has limited their practical application. A common technique to increase the stability of nanofluids is to add surfactants, which produce electrostatic or steric repulsion between nanoparticles, thus avoiding their agglomeration. This work evaluated the effects of surfactants and their concentration on the zeta potential and hydrodynamic diameter at different pH values as an indicator of nanofluids stability. Commercial alumina nanoparticles (0.1 wt.%) were dispersed in deionized water using two surfactants (cetyltrimethylammonium bromide, CTAB and sodium dodecylbenzenesulfonate, SDBS) at different concentrations, and the pH values were varied (2–12) by adding hydrochloric acid and sodium hydroxide. The results show the importance of the critical micelle concentration value in the nanofluids stabilization by electrostatic repulsion between nanoparticles and indicate that SDBS at a concentration of 0.064 wt.% (critical micelle concentration) offers the best dispersion conditions according with their zeta potential values, allowing high stability regardless of the pH value of the suspension.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This work investigates the stability of dispersions of zirconium oxide nanoparticles, synthesized by the sol-gel method, with zirconium isopropoxide precursors. Nanofluids at concentrations of ...0.1 wt% were prepared by dispersing the synthesized nanoparticles in deionized water. Anionic sodium dodecylbenzene sulfonate (SDBS), cationic cetyltrimethylammonium bromide (CTAB), and non-ionic polyvinyl pyrrolidone (PVP) at concentrations of 0.01 wt%, 0.03 wt%, and 0.05 wt% were used for nanoparticle dispersion. Stability was analyzed by means of dynamic light scattering (DLS), zeta potential, pH, visual inspection, and UV–vis. Transmission electron microcopy (TEM) images revealed particles with a size of 59.9 ± 13.5 nm, and x-ray diffraction (XRD) showed crystalline materials. The results of sedimentation, hydrodynamic radius, and absorbance indicate that the presence of surfactants reduces agglomeration and improves the stability of nanofluids over time. The non-ionic surfactant, PVP, produced a better effect on the hydrodynamic radius than its ionic counterparts (SDBS and CTAB). In addition, the type of surfactant was found to have a significant effect on the pH, zeta potential, and isoelectric point of the ZrO2 nanoparticles. Finally, the stability analysis revealed that stable nanofluids with a final concentration of 0.01 wt% of particles can be obtained after 20 days, demonstrating the potential of such nanofluids for heat transfer applications.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The effect of oxygen enriched air was tested for a diesel-biogas dual fuel engine. The operation and performance characteristics, such as thermal efficiency, pollutant emissions and combustion ...parameters were determined. Experiments have been carried out with a stationary compression ignition (CI) engine coupled with a generator in dual mode using a typical biogas composition of 60 vol. %CH4 and 40% vol. %CO2. For every engine load evaluated, the oxygen concentration in the intake air engine was varied from 21% to 27% O2 v/v. Ignition delay time and methane emissions were decreased when using oxygen enriched air with respect to normal air (21%O2), whereas the thermal efficiency was increased.
► Ignition delay time and methane emissions were decreased. ► Thermal efficiency was increased 28% at 40% load and 27% O2 in the air. ► Additions of O2 to intake combustion air improve combustion stability.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
In this study, the effects of pristine carbon nanotubes (CNTs), sodium dodecylbenzene sulfonate (SDBS), and diesel blends on the ignition delay and burning rate are examined experimentally. For this ...purpose, single-droplet combustion tests were conducted in a combustion system for 21 days using CNTs at concentrations of 50 ppm and 100 ppm, which were dispersed in Colombian commercial diesel and stabilized by SDBS. Videos of the diesel droplet burning were obtained using a high-speed camera, and the Shadowgraph optical technique was used to observe the development of the droplet size during combustion. Thus, records of the process were collected, and the treatment was carried out using a MATLAB algorithm. The measurements and processing were carried out along with a stability study, which included measurements of dynamic light scattering (DLS), pH, potential Zeta, and properties such as thermal conductivity and surface tension. The results demonstrated that the temporal stability has a direct impact on the single-droplet combustion tests because a concentration of CNTs of 100 ppm showed a higher stability than those achieved by 50 ppm. Consequently, improvements were found with a concentration of 100 ppm—for instance, the thermal conductivity increased by about 20%, the ignition delay time increased by 16.2%, and the burning rate increased by 30.5%.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The textile sector, an important economic driving force in Antioquia, Colombia, uses great quantities of thermal energy mainly produced by coal combustion, which holds enormous potential for ...recovery. One of the most common processes in a textile plant is heat setting, which uses a significant amount of thermal energy to adjust the properties of fabrics, such as shrinking, stiffness, pull strength, width, and stretching. In this study, we calculate the mass and energy balances of a stenter and propose a system to recover the energy available in its exhaust gases. The energy recovery potential in this heat setting process is 800.97 kW, which represents 87.2% of the total input energy. Additionally, we evaluate different heat exchangers to recover the available heat and present criteria to select them. Finally, thermosyphons, whose thermal efficiency was theoretically determined here, offer a promising alternative for heat recovery from actual stenters.
•Attaching amide functional groups to CNT increased its stability in diesel.•PM emissions decreased with functionalized CTN in diesel by up to 39.8 %.•Functionalized CTN in diesel lowered NO engine ...emissions by up to 29.4 %.•Thermal efficiency increased by up to 18.7 % using functionalized CNT in biodiesel.•CO emissions decreased by up to 20.1 % using functionalized CNT in biodiesel.
Nanomaterials used as additives to diesel, biodiesel, and its blends have shown promising results in improving thermal efficiency and reducing pollutant emissions in compression ignition engines. However, the stability of dispersions has been noted in the literature as a primary challenge to the effective use of nanomaterials as fuel additives. Between nanomaterials used as additives to fuels are carbon nanotubes (CNTs). These carbonaceous materials have shown positive and negative results concerning engine performance and emissions, and the differences could be associated with the dispersion stability of the nanomaterials in the fuel. Therefore, there is still much uncertainty regarding the relationship between the stability of nanomaterial dispersion and the impact of nanofuels on engine performance. Specifically, the current literature lacks sufficient information regarding the impact of incorporating amide-functionalized carbon nanotubes (CNT) on the stability of diesel-biodiesel blends and their influence on particulate matter emissions in ICE. In this study CNT and amide-functionalized CNT were dispersed in Colombian commercial diesel (10 % vol. of palm oil biodiesel) and palm oil biodiesel, and its stability was evaluated. The most stable blends were used in a stationary Ignition Compression Engine (ICE) to evaluate the impact of the nanomaterials on thermal efficiency and pollutant emissions. Results show that it was not possible to disperse CNT in Colombian commercial diesel (10 % vol. of palm oil biodiesel and 90 % vol. of petroleum diesel) due to its high rate of agglomeration and sedimentation. In contrast, the opposite behavior was shown using biodiesel as a base fuel. An amide functionalization of the CNT process was carried out to generate a repulsion of CNT and improve its stability in commercial diesel fuel. Amide-functionalized carbon nanotubes (CNTF) were obtained using pristine CNT and Oleylamine as nitrogen functional group precursors. X-ray Photoelectron Spectroscopy confirmed the amide functional groups on the CNT surface, and a loss weight of 14 % was identified in the temperature range of 150–550 °C, indicating a high grade of functionalization. Functionalized and non-functionalized CNT were dispersed in Colombian commercial diesel and palm oil biodiesel using a concentration of 100 mg/L to evaluate the dispersion's colloidal stability. This stability was examined for three days by visual inspection and variation of the hydrodynamic diameter using dynamic light scattering. The most stable dispersions were prepared at two concentrations (50 and 100 mg/L) and used as fuels in a stationary compression ignition engine. Colloidal stability was enhanced when CNTF were dispersed in diesel compared to the unstable, pristine CNT dispersion. However, in biodiesel, the dispersion behavior of the CNT and CNTF was similar. Compared to diesel, the diesel-CNTF dispersion did not considerably improve the engine´s thermal performance at 6 kW, and only a minor gain was observed at 12 kW at a concentration of 100 mg/L. However, at 6 kW, they reduced particulate matter emissions by up to 39.8 %. In the case of biodiesel, utilizing both functionalized and non-functionalized carbon nanotubes as additives, the thermal efficiency was increased, and CO emissions decreased.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This paper presents an experimental study carried out in an industrial furnace for frits production using different configurations of burners based on different combustion techniques such as enriched ...air combustion, flat-flame oxy-combustion and preheater air combustion. The residence time of combustion gases inside the furnace also was modified. Several combustion configurations were tested and its effects on productivity and thermal energy specific consumption and efficiency were determined. The results show that higher residence time of the combustion gases can decrease significantly the specific consumption of fuel, while the change of the burners and combustion techniques did not show significant effects on decreasing the energy consumption. However, it is highlighted that the oxy-combustion flat-flame burners produced the lowest specific consumption of fuel. Even though the experiments were conducted in a furnace for frit production, the corresponding results can also be applied to guide or improve other industrial high temperature processes.
La adición de nanomateriales a los lubricantes convencionales se ha presentado como una alternativa para modificar sus propiedades termofísicas y tribológicas, buscando incrementar su rendimiento. ...Este estudio presenta los resultados de la evaluación experimental de estabilidad, conductividad térmica y viscosidad dinámica de los nanolubricantes PEG400-CuO, PEG400-Grafeno y PEG400-CuO/Grafeno. Los nanolubricantes se prepararon por el método de dos pasos y se utilizaron dos concentraciones 0.1 y 0.5 % p/p de cada tipo de nanomaterial. Los resultados experimentales mostraron que las dispersiones con menor aglomeración y sedimentación durante el tiempo de evaluación fueron las preparadas con 0.1 % p/p de grafeno. La conductividad térmica de la dispersión PEG400-CuO no presentó diferencias significativas con respecto a la conductividad del PEG400. Sin embargo, la conductividad para las dispersiones PEG400-Grafeno y PEG400-CuO/Grafeno (0.5 % p/p), incrementó hasta un 13.5 % y 5.2 %, respectivamente. La viscosidad dinámica de las dispersiones con una concentración de 0.1 % p/p no presentó cambios significativos con respecto al PEG400, mientras que la viscosidad de la dispersión G-PEG para la concentración de 0.5 % p/p fue superior que la del PEG400 para todas las temperaturas evaluadas.
The reinforcing effect of boehmite nanoparticles (BNP) in epoxy resins for fiber composite lightweight construction is related to the formation of a soft but bound interphase between filler and ...polymer. The interphase is able to dissipate crack propagation energy and consequently increases the fracture toughness of the epoxy resin. Usually, the nanoparticles are dispersed in the resin and then mixed with the hardener to form an applicable mixture to impregnate the fibers. If one wishes to locally increase the fracture toughness at particularly stressed positions of the fiber-reinforced polymer composites (FRPC), this could be done by spraying nanoparticles from a suspension. However, this would entail high costs for removing the nanoparticles from the ambient air. We propose that a fiber fleece containing bound nanoparticles be inserted at exposed locations. For the present proof-of-concept study, an electrospun polycarbonate nonwoven and taurine modified BNP are proposed. After fabrication of suitable PC/EP/BNP composites, the thermomechanical properties were tested by dynamic mechanical analysis (DMA). Comparatively, the local nanomechanical properties such as stiffness and elastic modulus were determined by atomic force microscopy (AFM). An additional investigation of the distribution of the nanoparticles in the epoxy matrix, which is a prerequisite for an effective nanocomposite, is carried out by scanning electron microscopy in transmission mode (TSEM). From the results it can be concluded that the concept of carrier fibers for nanoparticles is viable.
This study evaluates the effect of using alumina (Al.sub.2O.sub.3)-water nanofluids stabilized by sodium dodecylbenzene sulfonate (SDBS) on the thermal performance and capillary limit of a screen ...mesh heat pipe. Nanofluids were prepared using three Al.sub.2O.sub.3 concentrations (0.1 mass/%, 0.5 mass/%, and 1.0 mass/%) and two SDBS concentrations (0.064 mass/% and 0.32 mass/%). The stability of the nanofluids was studied by means of UV-absorbance measurements prior to the experimental test. The results show that the thermal resistance of the heat pipe decreased by up to 50% with Al.sub.2O.sub.3 and SDBS at concentrations of 0.5 mass/% and 0.32 mass/%, respectively. Nevertheless, the capillary limit was reduced between 25 and 45 W compared to the operation with water. Finally, the capillary limit was improved by 5 W (compared to water) using an Al.sub.2O.sub.3 concentration of 0.1 mass/% and no surfactant.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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