Increase In Diameter Of Nanoparticles Research Articles

Electron transfer dynamics and electrocatalytic oxygen evolution activities of the Co3O4 nanoparticles attached to indium tin oxide by self-assembled monolayers.

The Co3O4 nanoparticle-modified indium tin oxide-coated glass slide (ITO) electrodes are successfully prepared using dicarboxylic acid as the self-assembled monolayer through a surface esterification reaction. The ITO-SAM-Co3O4 (SAM = dicarboxylic acid) are active to electrochemically catalyze oxygen evolution reaction (OER) in acid. The most active assembly, with Co loading at 3.31 × 10−8 mol cm−2, exhibits 374 mV onset overpotential and 497 mV overpotential to reach 1 mA cm−2 OER current in 0.1 M HClO4. The electron transfer rate constant (k) is acquired using Laviron’s approach, and the results show that k is not affected by the carbon chain lengths of the SAM (up to 18 -CH2 groups) and that an increase in the average diameter of Co3O4 nanoparticles enhances the k. In addition, shorter carbon chains and smaller Co3O4 nanoparticles can increase the turn-over frequency (TOF) of Co sites toward OER. The Co3O4 nanoparticles tethered to the ITO surface show both a higher number of electrochemically active Co sites and a higher TOF of OER than the Co3O4 nanoparticles bound to ITO using Nafion.

Explaining the structure sensitivity of Pt and Rh for aqueous-phase hydrogenation of phenol.

Phenol is an important model compound to understand the thermocatalytic (TCH) and electrocatalytic hydrogenation (ECH) of biomass to biofuels. Although Pt and Rh are among the most studied catalysts for aqueous-phase phenol hydrogenation, the reason why certain facets are active for ECH and TCH is not fully understood. Herein, we identify the active facet of Pt and Rh catalysts for aqueous-phase hydrogenation of phenol and explain the origin of the size-dependent activity trends of Pt and Rh nanoparticles. Phenol adsorption energies extracted on the active sites of Pt and Rh nanoparticles on carbon by fitting kinetic data show that the active sites adsorb phenol weakly. We predict that the turnover frequencies (TOFs) for the hydrogenation of phenol to cyclohexanone on Pt(111) and Rh(111) terraces are higher than those on (221) stepped facets based on density functional theory modeling and mean-field microkinetic simulations. The higher activities of the (111) terraces are due to lower activation energies and weaker phenol adsorption, preventing high coverages of phenol from inhibiting hydrogen adsorption. We measure that the TOF for ECH of phenol increases as the Rh nanoparticle diameter increases from 2 to 10nm at 298K and -0.1V vs the reversible hydrogen electrode, qualitatively matching prior reports for Pt nanoparticles. The increase in experimental TOFs as Pt and Rh nanoparticle diameters increase is due to a larger fraction of terraces on larger particles. These findings clarify the structure sensitivity and active site of Pt and Rh for the hydrogenation of phenol and will inform the catalyst design for the hydrogenation of bio-oils.

Brownian motion and thermophoretic effects of flow in channels using nanofluid: A two-phase model

Nanofluid is a new class of fluid that aims to enhance heat transfer. Nanoparticles sedimentation may play a role in the heat extractions from a hot surface. Brownian and thermophoretic effects may help in understanding the sedimentation effects. In the present paper, we attempted to investigate these phenomena (Brownian motion and thermophoretic effects) in three-rectangular channel configurations heated from below. The working fluids we considered are three different mixtures with 1%vol Al 2 O 3 nanoparticles in various base fluids such as water, ethylene glycol, and a mix of 50% water and 50% ethylene glycol. Different flow rates were implemented in the model using the finite element technique. Results revealed that 1%vol Al 2 O 3 /water is the best mixture for heat removal based on thermal efficiency criteria. The presence of solid-blocks in the channel further enhanced the performance of the 1%vol Al 2 O 3 /water nanofluid; when the height/base of the blocks increases. As the nanoparticles diameter increases, the average Nusselt number and the thermal efficiency of nanofluid also increases. It appears that between 31 to100 nm particle diameter, the increase in heat extraction is minimal. For a Reynolds number below 600, as the nanoparticles diameter increase above 31 nm, the sedimentation increases accordingly. However, regardless of the nanoparticle's diameter, for a Reynolds number in the range of 840, uniform nanoparticles distribution is observed.

Synthesis and Electrophoretic Concentration of Ag–Cu Nanoparticles of the Core–Shell Type in an AOT Microemulsion in n-Decane

Stable organosols of silver and copper bimetallic nanoparticles were obtained in sodium bis(2-ethylhexyl) sulfosuccinate (AOT) reverse micelles in the emulsion and microemulsion variants and characterized by physicochemical methods. The adsorption layer of nanoparticles in AOT solutions in n-decane was found to have a complex multilayer structure; an increase in the mole fraction of copper led to an increase in the hydrodynamic diameter of nanoparticles from 14 to 23 nm and a decrease in the electrokinetic potential from 18 to 7 mV. The surface charge of nanoparticles can be increased by diluting the sols with chloroform, and electrophoretic concentration can be performed with concentration factors of 30–50 depending on the composition. Based on the XRD data for solid composites in AOT, it was concluded that the structure of nanoparticles is most likely of the “core–shell” type with a silver metal core and a surface layer of X-ray amorphous copper.

Resistive Pulse Sensing as a High‐Resolution Nanoparticle Sizing Method: A Comparative Study

AbstractOne of the main challenges of sizing methods for nanoparticle (NP) suspensions is to distinguish between particles and particle populations with very small size differences. This would be especially important to follow various surface functionalization processes of nanoparticles resulting in small alterations of their size. In this respect, methods involving the detection of single particles, such as resistive pulse sensing (RPS) or nanoparticle tracking analysis, are generally considered superior to ensemble measuring methods such as dynamic light scattering. However, to compare the exact capabilities of these methodologies require systematic investigations in optimized conditions for each method. Here, such a study is presented for a narrow size range of spherical latex nanoparticles (60–200 nm). It is concluded that the RPS methodology based on quartz nanopipets as single nanopore counters, is the only sizing method among those studied capable to fully resolve a ternary mixture of 70, 110, and 140 nm average diameter NPs. The practical usefulness of this size resolution is demonstrated by following the increase in diameter of latex nanoparticles after their surface modification with antibodies.

Natural convection of power-law nanofluid in a square enclosure with a circular cylinder: An immersed boundary-lattice Boltzmann study

In this paper, natural convection of power-law Al2O3-water nanofluids with temperature-dependent properties in a square enclosure with a circular cylinder is studied. The governing equations of the flow and temperature fields are solved by the lattice Boltzmann method (LBM), and the curved velocity and thermal boundary conditions are treated by immersed boundary method (IBM). The effects of Rayleigh number, power-law index, nanoparticle volume fractions, radius of circular cylinder, nanoparticle diameter and temperature difference on flow and heat transfer characteristics are discussed in detail. The results indicate that the heat transfer rate is increased with the increases of Rayleigh number, radius of circular cylinder and temperature difference, while it generally decreases with an increase in power-law index and nanoparticle diameter. Additionally, it is observed that there is an optimal volume fraction at which the maximum heat transfer enhancement is obtained, and the value of it is found to increase slightly with decreasing the nanoparticle diameter, and to increase remarkably with increasing the temperature difference.

Heat transfer around copper nanoparticle with high superheat in water pool: A molecular dynamics simulation

Rapid boiling of a liquid occurs when it is highly superheated near the thermodynamic critical temperature that is much higher than the saturation temperature. Many experimental investigation have been conducted to observe the rapid ejection phenomenon near the heated surface. However, these study were limited by either length or time scale because of the limitation of classical macroscopic theory. In this work, a molecular dynamics simulation of heat transfer from a nanoparticle to its surrounding liquid pool was carried out to study the effect of nanoparticle diameter on the heat transfer of water around it. The interactions among copper atoms were described by the Embedded Atom Method (EAM) potentials, and the TIP4P water model was used to model the water atoms. The results show that the temperature of water increases more quickly for nanoparticle with larger diameter, the heat flux increases apparently when the nanoparticle diameter increases, and the interfacial thermal resistance is relatively larger for bigger nanoparticle due to the vibrational mismatch present at the interface.

Turbulence Combined Convective Heat Transfer and Nanofluids Flows over Double Forward Facing Steps

Predictions are reported for mixed convection using various types of nanofluids over forward-facing double steps in a duct. The continuity, momentum and energy equations are discretized and the simple algorithm is applied to link the pressure and flow fields inside the domain. Different types of nanoparticles Al2O3, CuO, SiO2 and ZnO, with different volume fractions in range of 1-4% are investigated to identify their effects on the heat transfer and fluid characteristics. Numerical investigations are conducted using finite volume method. The results indicate that SiO2 -water has the highest Nusselt number followed by Al2O3-water, CuO -water and ZnO-water. The Nusselt number increases as the volume fraction increases but decreases as the nanoparticles diameter increases.

Numerical study of flow and heat transfer of water-Al2O3 nanofluid inside a channel with an inner cylinder using Eulerian–Lagrangian approach

The present paper is a numerical study on heat transfer and pressure drop of a nanofluid including water as base fluid with Al2O3 nanoparticles inside a square channel having an inner cylinder, with and without fin under constant heat flux condition using two-phase Euler–Lagrange approach. Numerical investigation has been carried out for various combinations of base fluid, nanoparticle size and concentration through a straight cylinder. Simulation has been performed in a laminar flow regime using finite volume method. Besides, the thermal boundary condition of constant uniform heat flux on the channel wall was applied. The results show that the increase in Reynolds number and nanoparticle volume concentration have considerable effects on heat transfer coefficient enhancement. The heat transfer coefficient decreases when nanoparticles diameter increases. The passive way used in this study, leads to higher pressure drops. For all fluids under consideration, pressure drop escalates with Reynolds number. Adding nanoparticles to the base fluid leads to rise in pressure drop, and this effect is more intensive for higher concentrations.

Room temperature sintering of printer silver nanoparticle conductive ink

Future electronics devices are not only smaller and thinner, but are also flexible, bendable and even wearable. This evolution in technology requires direct printing of patterns onto any substrate using conductive inks made of a dispersion of metallic nanoparticles. In this study, Cl- ions was used to induce spontaneous sintering of silver nanoparticles (Ag NPs). Ag NPs with an average diameter of 56 nm were synthesized by polyol method using silver nitrate (AgNO3) and ethylene glycol (EG) as precursor and solvent, respectively. Poly(vinyl pyrrolidone) was used as the capping agent. Water-based inks were formulated containing different Ag NP loading (10–25 wt %). Using 50 mM NaCl aqueous solution as the dispersing medium, an ink with 15 wt % Ag exhibited a sheet resistance of about 2.85 Ω/sq. This very low sheet resistance was attributed to sintering of Ag NPs, which was accompanied by an increase in average diameter of nanoparticles from 56 to 569 nm.

Laminar Mixed Convective Nanofluid Flow in a Channel with Double Forward Facing Steps: A Numerical Simulation Study

Predictions are reported for mixed convection using various types of nanofluids overforward-facing double steps in a duct. The continuity, momentum and energy equations arediscretized and the simple algorithm is applied to link the pressure and flow fields inside the domain. Different types of nanoparticles Al2O3, CuO, SiO2 and ZnO, with different volume fractions in range of 1-4% and different nanoparticles diameter in the range of 20 – 80nm in base fluid (water) were used. Numerical investigations are conducted using finite volume method. In this study, different parameters such as the geometrical specifications (different steps heights in the range of h1= 0.01m-0.04m and h2 = 0.03m-0.06m for FFS) are used. Different Reynolds numbers in the range of 50-2000 (laminar flow) are investigated to identify their effects on the heat transfer and fluid characteristics. The results indicate that SiO2-water has the highest Nusselt number followed by -water, -water and ZnO-water. The Nusselt number increases as the volume fraction increases but it decreases as the nanoparticles diameter increases. The velocity magnitude increases as the density of nanofluids decreases. The recirculation region and the Nusselt number increase as the step height, Reynolds number, and the volume fraction increase.

Application of three-level general factorial design approach for thermal conductivity of MgO/water nanofluids

In this study, a three-level general factorial design was employed to evaluate the effect of parameters of temperature, volume fraction and nanoparticle diameter on thermal conductivity coefficient of MgO/water nanofluids. The reason of investigating MgO/water nanofluid is because of there is no certain defined relationship between thermal conductivity of MgO/Water nanofluid and temperature, volume fraction and particle size parameters. The factors under investigation were selected based on previous experiences and also the restrictions existing in the process. Also, the range of each variable was selected in a way that the effect of each one on the response of process is noticeable as much as possible. The nanofluid thermal conductivity coefficient was evaluated in different volume fractions ranging from 0.01 to 0.03. Regression analysis indicated good fit of the experimental data to the third-order polynomial model with coefficient of determination (R2) value of 0.9994 and F-value of 2570.57. The results revealed that all three parameters of temperature, nanoparticle volume fraction, and nanoparticle size and the interaction between them affect the nanofluid thermal conductivity coefficient. The optimum value of temperature, nanoparticle size and volume fractions for thermal conductivity of MgO/water nanofluid were 25°C, 40nm and 0.03, respectively. Also, the results show that the effect of an increase in nanoparticle diameter on thermal conductivity coefficient is low and it has a decreasing influence.

Nanofluid flow in micro-annular tubes at constant wall temperature considering the non-uniform distribution of nanoparticles

In this paper, the modified two-component non-homogeneous mixture model of Buongiorno is developed for the case of forced convection of alumina–water non-homogeneous nanofluid flow in concentric micro-annular tubes at constant wall temperature (CWT). Two different thermal boundary conditions have been considered such that for Case A the inner wall is adiabatic and the outer wall is kept at a constant temperature while for Case B the inner wall temperature remains constant and the outer wall is thermally isolated. Assuming a hydrodynamically and thermally fully developed flow, the governing equations of nanofluids in a concentric annulus are reduced to a nonlinear system of ordinary differential equations and solved using an appropriate reciprocal numerical algorithm via Runge–Kutta–Fehlberg method. The effects of NBT (from 0.7 to 10), ϕB (from 0.01 to 0.03), λ (from 0.05 to 0.2) and ζ (0.4, 0.5 and 0.6) on the non-dimensional volume fraction of nanoparticles, velocity, and temperature profiles have been investigated for both cases. It is indicated that the anomalous heat transfer enhancement depends on the thermal boundary condition as well as the ratio of thermophoresis and Brownian motion. Furthermore, for Case B, there is an optimum nanoparticle diameter around 0.5<NBT<1 that the thermal performance reaches its peak. However, for Case A, the thermal performance increases as the nanoparticle diameter increases. For both cases, the thermal performance decreases with an increase in the nanoparticle concentration.

Laminar Mixed Convective Nanofluid Flow in a Channel with Double Forward-Facing Steps: A Numerical Simulation Study

Predictions are reported for mixed convection using various types of nanofluids over forward-facing double steps in a duct. The continuity, momentum and energy equations are discretized and the simple algorithm is applied to link the pressure and flow fields inside the domain. Different types of nanoparticles Al2O3, CuO, SiO2 and ZnO, with different volume fractions in range of 1-4% and different nanoparticles diameter in the range of 20 – 80nm in base fluid (water) were used. Numerical investigations are conducted using finite volume method. In this study, different parameters such as the geometrical specifications (different steps heights in the range of h1= 0.01m-0.04m and h2 = 0.03m-0.06m for FFS) are used. Different Reynolds numbers in the range of 50-2000 (laminar flow) are investigated to identify their effects on the heat transfer and fluid characteristics. The results indicate that SiO2-water has the highest Nusselt number followed by Al2O3-water,Cuo-water and ZnO-water. The Nusselt number increases as the volume fraction increases but it decreases as the nanoparticles diameter increases. The velocity magnitude increases as the density of nanofluids decreases. The recirculation region and the Nusselt number increase as the step height, Reynolds number, and the volume fraction increase.

Turbulent heat transfer and nanofluid flow in a protruded ribbed square passage

In this article, turbulent heat transfer of nanofluid flow in square passage with protruded rib shape is numerically and experimentally studied over Reynolds number ranges of 4000–18000. Different nanoparticles (Al2O3, CuO, and ZnO), with different concentration (φ) range of 1–4% and different nanoparticle diameter (dnp) range of 30–45nm are disperse in water (base fluid). Several parameters such as stream wise distance (Xs/dp) range of 1.4–2.6, span wise distance (Ys/dp) range of 1.4–2.6, ratio of protruded height to print diameter (ep/dp) range of 0.83–1.67 also studied to find the consequence on thermal and hydrodynamic characteristics. Simulations were carried out to obtain heat and fluid flow behaviour of smooth and ribbed square channel using commercial CFD software, ANSYS 15.0 (Fluent). Renormalization k-ε model was employed to assess the influence of protruded ribs on turbulent flow and velocity field. The outcome indicates that Al2O3 nanofluid has the highest value of average Nusselt number as compare to other nanofluids. The average Nusselt number increases as the concentration increases and it decreases as nanoparticle diameter increases. The thermal hydrodynamic performance parameter based on equal pumping power, average Nusselt number and average friction factor were found to be highest for Al2O3, φ=0.04, dnp=30nm, Xs/dp=1.8, Ys/dp=1.8 and ep/dp=1.0. The numerical data are compared with the corresponding experimental data. Comparison between CFD and experimental analysis results showed that good agreement as the data fell within ±7.0% error band.

Natural convection investigation in square cavity filled with nanofluid using dispersion model

A cooling achieved with compact and efficient device is one of the major challenges encountered in the promising technique of fuel cell stacks. The safe and reliable use of such a system is highly dependent on the efficiency of the assured heat transfer and consequently on the quality of the coolant used. To test the possible improvement of the coolant performances, laminar natural convection in square cavity filled with copper-water nanofluid is numerically carried out taking into account the thermal dispersion effect on the heat transfer intensity. The finite element method is used to solve the governing equations. The hydrodynamic structure of the flow and its thermal behavior are studied for a wide range of Rayleigh numbers. The obtained results showed an enhancement of heat transfer with an increase in nanoparticle volume fraction for all examined Rayleigh numbers. However, it is found that an increase in nanoparticle diameter enhances heat transfer only when thermal dispersion is significant. Correlation with 99.94% confidence coefficient is proposed to quantify the heat transfer intensity according to the Rayleigh number and particle diameter and concentration.

Numerical Investigation of Heat Transfer Characteristics in Triangular Channel in Light Water Nuclear Reactor by using CuO-Water based Nanofluids

Nanofluid plays a very crucial role in nuclear power plant for improving heat transfer. It opens a new portal for improving heat transfer for reducing thermal hydraulics problems in nuclear reactor. The aim of this study to represent the numerically investigated result of CuO/Water based nanofluid heat transfer in light water nuclear reactor. In this investigation the 1/6th part of hexagonal geometry of nuclear fuel rod assembly has been taken for simulation. For focusing the effect of nanoparticle concentration and flow rate on heat transfer fluid flow in triangular channel two phase model is used. For improving the thermal properties of conventional fluid CuO/water nanofluid is used. A uniform heat flux is applied at the inner wall. Profiles of heat transfer coefficient and wall adjacent temperature are shown and these are the function of flow rate of nanofluid and concentration of nanoparticles. For getting better result accuracy, k-ω SST turbulence model and mesh quality of fuel rod bundle in triangular array are studied. Results are compared with analytical equations of heat transfer. The results show that prediction of nanofluid heat transfer is very well by using two phase model in place of using single phase model. Results indicates that heat transfer coefficient is increasing by adding the nanoparticles which is in low concentration and heat transfer coefficient is also increasing with increase in Reynold Number. It also indicates that wall adjacent temperature is decreasing by adding the nanoparticles and heat transfer coefficient is also decreasing with increase in diameter of nanoparticles.

Differential effects of P25 TiO2 nanoparticles on freshwater green microalgae: Chlorella and Scenedesmus species

P25 TiO2 nanoparticles majorly used in cosmetic products have well known detrimental effects towards the aquatic environment. In a freshwater ecosystem, Chlorella and Scenedesmus are among the most commonly found algal species frequently used to study the effects of metal oxide nanoparticles. A comparative study has been conducted herein to investigate differences in the toxic effects caused by these nanoparticles towards the two algae species. The three different concentrations of P25 TiO2 NPs (0.01, 0.1 & 1μg/mL, i.e., 0.12, 1.25 and 12.52μM) were selected to correlate surface water concentrations of the nanoparticles, and filtered and sterilized fresh water medium was used throughout this study. There was significant increase (p<0.001) in hydrodynamic diameter of nanoparticles with respect to both, time (0, 24, 48 and 72h) as well as concentration under all the exposure conditions. Although, significant dose-dependent morphological (surface area & biovolume) interspecies variations were not observed, it was evident at the highest concentration of exposure within individuals. At 1μg/mL exposure concentration, a significant difference in toxicity was noted between Chlorella and Scenedesmus under only visible light (p<0.001) and UVA (p<0.01) irradiation conditions. The viability data were well supported by the results obtained for oxidative stress induced by NPs on the cells. At the highest exposure concentration, superoxide dismutase and reduced glutathione activities were assessed for both the algae under all the irradiation conditions. Increased catalase activity and LPO release complemented the cytotoxic effects observed. Significant interspecies variations were noted for these parameters under UVA and visible light exposed cells of Chlorella and Scenedesmus species, which could easily be correlated with the uptake of the NPs.

Natural convection of Al2O3–water nanofluid in an inclined enclosure with the effects of slip velocity mechanisms: Brownian motion and thermophoresis phenomenon

Effects of inclination angle on natural convective heat transfer and fluid flow in an enclosure filled with Al2O3–water nanofluid are studied numerically. The left and right walls of enclosure are kept in hot and cold constant temperature while the other two walls are assumed to be adiabatic. Considering Brownian motion and thermophoresis effect (two important slip velocity mechanisms) the two-phase mixture model has been employed to investigate the flow and thermal behaviors of the nanofluid. The study was performed for various inclination angles of enclosure ranging from γ = 0° to γ = 60°, volume fraction from 0% to 3%, and Rayleigh numbers varying from 105 to 107. The governing equations are solved numerically using the finite volume approach. The results are presented in the form of streamlines, isotherms, distribution of volume fraction of nanoparticles and Nusselt numbers. They demonstrated that the slip velocity mechanisms have caused the decreasing Nusselt number with increasing volume fraction of nanoparticles. They also indicate important differences between single-phase and two-phase models. In addition, the highest value for Nusselt number is reached at γ = 30°. Increase in nanoparticle diameter leads to decrease and increase in Nusselt number and non-uniformity, respectively. The investigation of inclination angle effects on natural convection of nanofluid in an enclosure has been carried out for the first time by two-phase mixture model including slip velocity mechanisms (Brownian motion and thermophoresis phenomenon) effects.

Laminar filmwise condensation of nanofluids over a vertical plate considering nanoparticles migration

This is an investigation on developing the transport phenomenon of the nanofluids falling condensate film, taking into account the effects of nanoparticle migration. The intensity and direction of nanoparticle migration are able to manage the thermophysical properties of nanofluids, as well as the control of flow, heat transfer, and mass transfer, in order to improve the cooling performance. Thus, Brownian motion and thermophoretic diffusivity have been considered by using the modified Buongiorno model to observe the effects of nanoparticle slip velocity relative to the base fluid. Our outcomes have been obtained for different parameters, including the ratio of Brownian motion to thermophoretic diffusivity NBT, saturation nanoparticle volume fraction ϕsat, and normal temperature difference γ=(Tsat−Tw)/Tw. It is revealed that increasing ϕsat and decreasing γ enhance the heat transfer rate and the nanoparticle volume fraction inside the condensate film. In addition, as the nanoparticle diameter increases, its migration grows in the film, which intensifies the nanoparticle volume fraction on the cold wall. Further, inclusion of alumina nanoparticles signifies a better cooling performance than titania.