Mass Fraction Of Nanoparticles Research Articles

Effect of concentration on R134a/Al2O3 nanolubricant mixture boiling on a reentrant cavity surface

This paper quantifies the influence of Al2O3 nanoparticles on the pool boiling performance of R134a/polyolester mixtures on a Turbo-BII-HP boiling surface. Nanolubricants with 10 nm diameter Al2O3 nanoparticles of various volume fractions (1.6%, 2.3%, and 5.1%) in the base polyolester lubricant were mixed with R134a at two different mass fractions (0.5% and 1%). The study showed that nanolubricants can improve R134a boiling on a reentrant cavity surface as long as the nanoparticles remain well dispersed in the lubricant and are at sufficiently large concentration. For example, three of the refrigerant/nanolubricant mixtures with the smallest nanoparticle mass fraction exhibited average enhancements over the entire heat flux range of approximately 10%. However, when the nanoparticle mass fraction was increased to a point that likely encouraged agglomeration, an average heat transfer degradation of approximately 14% resulted. An existing model was used to predict the boiling heat transfer.

Integrating sphere study of the optical properties of aluminum nanoparticles in tetranitropentaerytrite

The dependences of the transmission coefficients and the sum of the transmission and absorption coefficients for light with a wavelength of 643 nm in compressed pentaerythritol tetranitrate (PETN) samples containing aluminum nanoinclusions (average radius of 50 nm) on the pellet thickness and the mass fraction of aluminum nanoparticles in it are studied with an integrating sphere. The light absorption and scattering in this system is simulated using the Mie theory and a radiative transfer equation. The depth profile of absorbed energy in a sample is shown to approximately obey the Bouguer-Beer law. The effective cross section of radiation absorption by aluminum nanoparticles, which takes into account both light absorption and scattering by an ensemble of nanoparticles, exceeds the geometrical cross section.

Effect of silica nanoparticles on polyurethane foaming process and foam properties

Flexible polyurethane foams (FPUF) are commonly used as cushioning material in upholstered products made on several industrial sectors: furniture, automotive seating, bedding, etc. Polyurethane is a high molecular weight polymer based on the reaction between a hydroxyl group (polyol) and isocyanate. The density, flowability, compressive, tensile or shearing strength, the thermal and dimensional stability, combustibility, and other properties can be adjusted by the addition of several additives. Nanomaterials offer a wide range of possibilities to obtain nanocomposites with specific properties. The combination of FPUF with silica nanoparticles could develop nanocomposite materials with unique properties: improved mechanical and thermal properties, gas permeability, and fire retardancy. However, as silica particles are at least partially surface-terminated with Si-OH groups, it was suspected that the silica could interfere in the reaction of poyurethane formation.The objective of this study was to investigate the enhancement of thermal and mechanical properties of FPUF by the incorporation of different types of silica and determining the influence thereof during the foaming process. Flexible polyurethane foams with different loading mass fraction of silica nanoparticles (0-1% wt) and different types of silica (non treated and modified silica) were synthesized. PU/SiO2 nanocomposites were characterized by FTIR spectroscopy, TGA, and measurements of apparent density, resilience and determination of compression set. Addition of silica nanoparticles influences negatively in the density and compression set of the foams. However, resilience and thermal stability of the foams are improved. Silica nanoparticles do not affect to the chemical structure of the foams although they interfere in the blowing reaction.

Turbulent forced convection effectiveness of alumina–water nanofluid in a circular tube with elevated inlet fluid temperatures: An experimental study

The present study aims to explore experimentally the influence of elevated inlet fluid temperature on the turbulent forced convective heat transfer effectiveness of using alumina–water nanofluid over pure water in an iso-flux heated horizontal circular tube at a fixed heating power. A copper circular pipe of inner diameter 3.4mm was used in the forced convection experiments undertaken for the pertinent parameters in the following ranges: the inlet fluid temperature, Tin=25°C, 37°C and 50°C; the Reynolds number, Rebf=3000–13,000; the mass fraction of the alumina nanoparticles in the water-based nanofluid formulated, ωnp=0, 2, 5, and 10wt.%; and the heating flux, qo″=57.8–63.1kW/m2. The experimental results clearly indicate that the turbulent forced convection heat transfer effectiveness of the alumina–water nanofluid over that of the pure water can be further uplifted by elevating its inlet temperature entering the circular tube well above the ambient, thereby manifesting its potential as an effective warm functional coolant. Specifically, an increase in the averaged heat transfer enhancement of more than 44% arises for the nanofluid of ωnp=2wt.% as the inlet fluid temperature is increased from 25°C to 50°C.

Experimental investigation of flow boiling heat transfer of R-600a/oil/CuO in a plain horizontal tube

The aim of this paper is to experimentally investigate the effect of CuO nanoparticles on flow boiling of R-600a/Polyester mixture (99/1) inside a horizontal smooth tube. The experimental conditions of this study include mass velocities from 50 to 400kg/m2s, inlet vapor qualities from 0 to 0.9, heat fluxes from 3 to 8kW/m2and mass fractions of CuO nanoparticles from 0 to 1.5wt%. The well instrumented experimental apparatus including pump, flow meter, preheater, test evaporator, by-pass and condenser was designed, fabricated and installed in order to measure the experimental data on flow boiling heat transfer of refrigerant, refrigerant oil and refrigerant nanooil. Ultrasonic instrument was used to approach to the well dispersed nanooil and then the nanooil was injected with a syringe into the pure refrigerant through the cycle. The solutions were mixed by running them through the system at a high velocity for approximately 3h. The results show that, nanoparticles cause a maximum heat transfer enhancement up to 63% relative to heat transfer coefficient of R-600a/oil without nanoparticles.

Interfacial Tension of the n-Hexane–Water System under the Influence of Magnetite Nanoparticles and Sodium Dodecyl Sulfate Assembly at Different Temperatures

The influence of sodium dodecyl sulfate (SDS) and magnetite nanoparticles (NPs), individually and simultaneously, on the interfacial tension of n-hexane–water was studied over the temperature range from (288.2 to 308.2) K. Results show that SDS in the range from (0 to 2.00·10–4) mol·dm–3 is adsorbed positively; while, NPs in the mass fraction range from (0 to 5.00·10–4) are adsorbed negatively and cause interfacial tension to rise. Interestingly, with the presence of both SDS and NPs, interfacial tension is reduced more than with SDS only, because the repulsive interactions between SDS molecules are weakened in the presence of positively charged NPs. An almost linear decrease in interfacial tension with temperature is also relevant in all cases. The experimental data, below the critical micelle concentration of SDS, were nicely reproduced by the Szyszkowski adsorption isotherm. Accordingly, obtained SDS saturated interface excess is reduced with NPs mass fraction, and on the other hand, adsorption tendency increases with temperature and NPs mass fraction.

Experimental investigation of the forced convective boiling heat transfer of R-600a/oil/nanoparticle

In this paper an experimental study of convective boiling heat transfer of R-600a/oil/nanoparticle mixtures is investigated. The experimental setup was prepared with a smooth horizontal tube as a test section with the length and diameter of 9.5 and 103mm, respectively, and pure R-600a was applied for evaluating the heat transfer enhancement. Six mixtures containing 1% weight fraction of R-600a/oil with different concentrations of CuO nanoparticles including 0.0, 0.5, 1.0, 1.5, 2.0 and 5.0% weight fraction of R-600a/oil/nanoparticle were used in our study.The mass velocity per cross area was considered at the range of 50–700kg/m2s for low vapor quality (ϕ<0.25). The results showed that the convective boiling heat transfer coefficient will be increased by increasing the mass fraction of nanoparticles up to 2%, while by increasing the mass fraction of nanoparticles up to 5% the heat transfer coefficient will be reduced.

Methodological features in research of pool boiling processes of nanofluid isopropanol/Al2O3

Promising direction of heat-transfer intensification is modification of the liquids used as coolants or working bodies for various kinds of equipment. Within this framework the usage of nanofluids (suspensions of nano-size particles (up to 100 nm) in a base fluid) is proposed.The results obtained have shown that the additive of Al2O3 nanoparticles to isopropanol increases the heat transfer coefficient during pool boiling up to 10–26 %. However, such effect was found only at the low heat flux densities. At the high heat flux densities the presence of the nanoparticles in isopropanol leads to decreasing the heat-transfer coefficient. According to the authors, this is the result of nanofluid destabilization. It is shown that the complex nature of nanoparticles Al2O3 effect on the changes in heat-transfer coefficient is related to a combined contribution of different factors: interaction of nanoparticles with heating surfaces, changing in thermal properties of nanofluids compared to the base fluid, hydrodynamic radius of nanoparticles and their concentration in isopropanol.According to the authors, the possible reason of nanofluid destabilization during pool boiling may be the destruction of heterogeneous micelles on the heater surface. Therefore, the study of nanofluids pool boiling and correct interpretation of the collected data should consider the stability, concentration changes of nanofluid and heating surface properties. The study on hydrodynamic radius of nanoparticles was carried out using experimental setup wherein DLS method has been realized. The results has shown increasing in hydrodynamic radius from 53 to 86 nm with an increasing in the mass fraction of nanoparticles from 0.036 to 4.2 wt. %.The experiments to determine the stability of nanofluid has shown that the system remains stable throughout the period of the experiment (100 hours), temperatures interval (20–70 °C) and the mass fraction of nanoparticles (0.036–4.2 wt.%). In addition, in this paper, the dependence of the mass fraction of Al2O3 nanoparticles in isopropanol on the value of the transmitted light through the nanofluid was obtained. The magnitude of the transmitted through the nanofluid light is proportional to the mass fraction of nanoparticles.

Experimental investigation of the latent heat of vaporization in aqueous nanofluids

This paper reports an experimental investigation of the latent heat of vaporization (hfg) in nanofluids. Two different types of nanoparticles, graphite and silver, suspended in deionized water were exposed to a continuous laser beam (130 mW, 532 nm) to generate boiling. The latent heat of vaporization in the nanofluids was determined by the measured vapor mass generation and the heat input. To ensure that the measured hfg values are independent of heating method, the experiments were repeated with an electrically heated hot wire as a primary heat input. These experiments show considerable variation in the hfg of nanofluids. That is, graphite nanofluid exhibits an increased hfg and silver nanofluid shows a decrease in hfg compared to the value for pure water. As such, these results indicate that relatively low mass fractions of nanoparticles can apparently create large changes in hfg.

Experimental Investigation on Photothermal Properties of MWCNT-H&lt;sub&gt;2&lt;/sub&gt;O Nanofluids for Direct Absorption Solar Collectors

Optical and photothermal properties of MWCNT-H2O nanofluids were investigated in the present work. The transmittance of nanofluids over solar spectrum (250 to 2500nm) was measured by the UV-Vis-NIR spectrophotometer based on integrating sphere principle. The photothermal properties of nanofluids were studied expose to the solar radiation. The experimental results show that the transmittance of MWCNT-H2O nanofluids is much less than that of deionized water, and decreases with increasing nanoparticle mass fraction. The highest temperature and heat gain of MWCNT-H2O nanofluids (0.02wt%) can increased up to 31.87% and 54.14% compared with deionized water, respectively. From the results it can be concluded that MWCNT-H2O nanofluids is suitable for direct absorption solar thermal energy systems.

Femtosecond laser deposition of TiO2 nanoparticle-assembled films with embedded CdS nanoparticles

Based on the normal pulsed laser ablation method, femtosecond pulsed laser deposition (fs-PLD) is adopted in vacuum for the production of TiO2 nanoparticle-assembled films. We study the morphology and electronic characteristics of TiO2 nanoparticle-assembled films deposited at different oxygen background gas pressures from high vacuum (∼10−4 Pa) to 100 Pa and different deposition time. Our results show that TiO2 nanoparticle-assembled films obtained in high vacuum present both a mixture with rutile phase and anatase phase and a pure rutile phase. At the same time, there are more mesoporous structures in the film after annealing, which is beneficial for the enhancement of photocatalytic activity. In water splitting experiment, part of the TiO2 nanoparticle-assembled films embedded with a small mass fraction of CdS nanoparticles (∼5%) present an interesting photocurrent enhancement with a maximum value of ∼0.2 mA/cm2 under a solar simulator.

Experimental Investigation on Radiation Characteristic of Nanofluids for Direct Absorption Solar Collectors

In this article, Cu-H2O, Co-H2O, MWCNT-H2O nanofluids were prepared through two-step method. The transmittance of nanofluids over solar spectrum (250 to 2500nm) was measured by the UV-Vis-NIR spectrophotometer based on integrating sphere principle. The factors of various particle size, mass fraction and optical path influencing transmittance of nanofluids were investigated. The experimental results show that the transmittance of the three nanofluids is much less than that of deionized water. The transmittance decreased with the nanoparticle size and mass fraction increasing, but increased with the optical path length reducing. With the same mass fraction, the transmittance of MWCNT-H2O nanofluids is the minimum. The transmittance of Co-H2O nanofluids is higher than that of Cu-H2O nanofluids within 250~775nm wavelength range, while inverse in 775~1370nm wavelength range. It indicates that different particle has diverse light absorption properties in different wavelength range.

Structural, electrical, and rheological properties of palladium/silver bimetallic nanoparticles prepared by conventional and ultrasonic-assisted reduction methods

Polyvinylpyrrolidone stabilized Pd/Ag bimetallic nanoparticles (NPs) with average particle sizes of 9 and 6nm were synthesized by simultaneous reduction in the presence and absence of ultrasound waves, respectively. The prepared NPs were characterized by six methods including X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution-TEM (HRTEM), UV–vis spectroscopy, scanning tunneling microscopy (STM), and energy dispersive X-ray (EDX) analysis. The rheological properties of Pd/Ag NPs in ethylene glycol as a base fluid with various mass fractions of NPs from 2% to 5% at different temperatures were studied experimentally and theoretically. The experimental results showed that viscosity of Pd/Ag NPs in ethylene glycol increases with increasing particle mass fraction and decreases with increasing temperature. A maximum of 31.58% increase in viscosity of ethylene glycol at 20°C was observed when 5% Pd/Ag NPs was added. Measurement of the electrical conductivity of nanofluids of Pd/Ag bimetallic NPs in distilled water at different mass fractions and temperatures was performed. A 3841% increase in electrical conductivity of distilled water at 25°C was observed when 1% Pd/Ag NPs was added. Both the rheological and electrical properties of Pd/Ag bimetallic NPs were measured in ethylene glycol and distilled water, respectively for the first time.

Experimental and Numerical Investigation on Natural Convection Heat Transfer of TiO2–Water Nanofluids in a Square Enclosure

An experimental and numerical investigation on natural convection heat transfer of TiO2–water nanofluids in a square enclosure was carried out for the present work. TiO2–water nanofluids with different nanoparticle mass fractions were prepared for the experiment and physical properties of the nanofluids including thermal conductivity and viscosity were measured. Results show that both thermal conductivity and viscosity increase when increasing the mass fraction of TiO2 nanoparticles. In addition, the thermal conductivity of nanofluids increases, while the viscosity of nanofluids decreases with increasing the temperature. Nusselt numbers under different Rayleigh numbers were obtained from experimental data. Experimental results show that natural convection heat transfer of nanofluids is no better than water and even worse when the Rayleigh number is low. Numerical studies are carried out by a Lattice Boltzmann model (LBM) coupling the density and the temperature distribution functions to simulate the convection heat transfer in the enclosure. The experimental and numerical results are compared with each other finding a good match in this investigation, and the results indicate that natural convection heat transfer of TiO2–water nanofluids is more sensitive to viscosity than to thermal conductivity.

Heat Transfer Enhancement by Using Nanomaterial in Phase Change Material for Latent Heat Thermal Energy Storage System

Latent heat energy storage systems using paraffin wax could have lower heat transfer rates during melting / freezing processes due to its inherent low thermal conductivity. The thermal conductivity of paraffin wax can be enhanced by employing high conductivity materials such as alumina (Al2O3) nanopowder. In this paper the experimental investigation has been carried out to study the performance enhancement of paraffin wax with nanoalumina (Al2O3) particles in mass fraction of 1, 3, and 5% in a Latent Heat Thermal Energy Storage (LHTES) System at constant flow rate and variable temperature of heat transfer fluid (HTF). The effect of alumina nanoparticle on total cyclic time of LHTES for different mass fraction has been studied. Commercially available paraffin wax is used as a phase change material (PCM). The present results illustrate that the suspended nanoparticles substantially increase the heat transfer rate and also the nanofluid heat transfer rate increased with an increased in the nanoparticles mass fraction. The comparative results with and without nanoalumina (Al2O3) enhancement indicate that the charging rate of thermal energy can be greatly enhanced using paraffin wax with alumina as compared with a simple paraffin wax as PCM. The increase of the heat release rate of the nanoparticle-enhanced phase change materials shows its great potential for diverse thermal energy storage application.

Grashof Number Effects on Nanofluids in Natural Convection Heat Transfer

The natural convection of nanofluids in a two-dimensional enclosure is numerically simulated. The effects of nanoparticle concentration and Grashof number (Gr) on heat transfer properties are investigated. The results indicate that for a given initial Gr value, the heat transfer rate of the nanofluid increases remarkably with the increase of nanoparticles mass fraction, and that for low Gr value the heat transfer process is dominant with the heat exchange, while for high Gr value it is dominant with the natural convection. In addition, the intensity of the streamline is increased with the increases of the Gr values.

Jet impingement heat transfer using a Field’s alloy nanoparticle – HFE7100 slurry

An experimental study was performed to investigate jet impingement heat transfer of HFE7100 dielectric liquid with metallic phase change materials (Field’s alloy) in nanometer particulate form (nano PCM). A simple method was used to prevent the precipitation of Field’s alloy nanoparticles in a HFE7100 suspension by surface modification with silane monolayers. The optical transmittance of the nanoparticle suspension was monitored by a portable spectrometer and there was no significant change in optical transmittance over time. The nano PCM particle suspension impinges on a heated surface and absorbs heat by phase change process from solid to liquid phase coupled with the evaporation of HFE7100. The present study shows that the mass fraction of nanoparticles plays an insignificant role in pressure drop but an important role on heat transfer performance. The high-heat-flux removal capability has been demonstrated by repeated closed loop test. Our results show that slurries with 30% particle mass fraction can improve the average heat transfer coefficient by 70% when compared to pure HFE7100 in the temperature range of 62–66°C.

Formation of Particle Coated Fusiform Droplets via Lowering Interface Tension with Polyaluminum Sulfate

It was found that the interface tension between water and alkenyl succinic anhydride (ASA) was significantly reduced by polyaluminum sulfate (PAS), increased considerably though by TiO2 nanoparticle. PAS with basicity of 0.75 (PAS-0.75) reduced the interface tension to a larger extent than PAS with basicity of 0.3 (PAS-0.3). By reducing interface tension with PAS-0.75, ASA-in-water emulsion bearing fusiform geometries was constructed. The emulsion stabilized by PAS-0.3 and TiO2 nanoparticle bore spherical shapes with the exception when mass fraction of TiO2 nanoparticle was low, in which case fused nonspherical drops were formed. Forming nonspherical emulsion crucially depends on ASA-water interface tension, where a critical interface tension was identified to be 0.6–0.7 mN/m. The fusiform geometries were transformed into spherical shapes when interface tension was higher than 0.7 mN/m. Both the lowering mechanism of the interface tension and the formation mechanism of the fusiform emulsion were proposed.

A novel copper/polydimethiylsiloxane nanocomposite for copper‐containing intrauterine contraceptive devices

In this article, a novel composite of copper (Cu) nanoparticles and polydimethiylsiloxane (PDMS) has been prepared and investigated for the potential application in Cu-containing intrauterine device. The Cu/PDMS composite with various mass fraction of Cu nanoparticles was fabricated via the hot vulcanizing process. The chemical structures and surface morphologies of the Cu/PDMS composites were characterized confirming the physical interaction between Cu nanoparticles and PDMS. The surface morphology observation using scanning electron microscope and atomic force microscope showed the agglomeration of Cu nanoparticles in PDMS matrix and the distribution of the agglomerations was more uniform with increased amount of Cu nanoparticles. The cupric ion release behaviors of the Cu/PDMS composites with different amounts of Cu nanoparticles were investigated in simulated uterine fluid at 37°C for 150 days. The corrosion morphologies of the Cu/PDMS composites were also characterized. Both the burst release rate of the cupric ion in the first few days and the steady release rate after 30-day immersion were improved. The cytotoxicity test has been done for the Cu/PDMS composites.

Experimental determination of temperature-dependent thermal conductivity of solid eicosane-based nanostructure-enhanced phase change materials

The effective thermal conductivity of composites of eicosane and copper oxide nanoparticles in the solid state was measured experimentally by using the transient plane source technique. Utilizing a controllable temperature bath, measurements were conducted at various temperatures between 10 and 35°C for the solid samples. In the course of preparation of the solid specimen, liquid samples with eight different mass fractions (0, 1, 2, 3.5, 5, 6.5, 8 and 10wt%) of nanoparticles were poured into small diameter molds and were degassed within a vacuum oven. The molds were then subjected to one of the three solidification procedures, i.e. ambient solidification, ice-water bath solidification or oven solidification method. Measured thermal conductivity data of the composites were found to be nearly independent of the measurement temperature for a given loading of CuO nanoparticles regardless of the solidification procedure. Irrespective of the solidification method, as the melting temperature was approached, thermal conductivity data of the solid disks rose sharply for the three sets of samples. The ice-water bath solidification route for the eicosane–CuO samples consistently exhibited the lowest values of thermal conductivity, whereas the samples of oven solidification scheme exhibited to the highest values. This behavior is assumed to be due to the greater void percentage of ice-water bath samples and/or crystal structure variations due to the adopted phase transition method.