Increase In Diameter Of Nanoparticles Research Articles

Assisted and Opposed Mixed Convective Nanofluids Flow Over Vertical Backward Facing Step Having a Baffle

Laminar mixed convection flow using nanofluids over backward facing step in a heated rectangular duct having a baffle mounted on its wall are numerically simulated. The continuity, momentum and energy equations are solved using finite volume method (FVM) and the SIMPLE algorithm scheme is applied to examine the effects of the baffle on heat transfer characteristics. In this study, several parameters such as different types of nanoparticles (Al2O3, CuO, SiO2 and ZnO), different volume fractions in the range of 1% to 4%, different nanoparticles diameter in the range of 25 to 80 nm, and wall flux in the range of 10 = qw = 70 W/m2 were used. The effects of the baffle height Hb, baffle thickness Wb, and distance between the backward-facing step and baffle D on Nusselt number variation are numerically investigated. The numerical results indicate that the nanofluid with SiO2 has the highest Nusselt number compared with other nanofluids types. The Nusselt number increases as the volume fraction of nanoparticles and the Reynolds number increase, while it decreases as the nanoparticles diameter increases. Effects of baffle distances baffle heights and baffle widths on heat transfer characteristics are significant, while, effects of wall flux are slightly insignificant.

Numerical Study of Turbulent Mixed Convection of Nanofluids in Three-Dimensional Horizontal Concentric Annuli

Three-dimensional turbulent mixed convection flow using nanofluids in horizontal concentric annuli is numerically simulated. The continuity, Navier-Stokes and energy equations are solved using finite volume method (FVM) and the SIMPLE algorithm scheme is applied to examine the effects of turbulent flow on heat transfer characteristics. In this study, several parameters such as different types of nanoparticles (Al2O3, CuO, SiO2 and ZnO), different volume fractions in the range of 1% to 4%, different nanoparticles diameter in the range of 20 to 80 nm were used. Reynolds numbers are considered in the turbulent range of 6000 =Re = 18000. Different nanoparticle shapes (i.e., blades, platelets, cylindrical, bricks, and spherical), and effects of inner cylinder and outer cylinder heat fluxes were analyzed. Hydraulic diameter ratio was also examined. The numerical results indicate that the nanofluid with SiO2 has the highest Nusselt number and pressure drop compared with other nanofluids types. Heat transfer characteristic increases as the volume fraction of nanoparticles increases while it decreases as the nanoparticles diameter increases. Effects of hydraulic diameter ratio, nanoparticle shapes and location of applying heat flux on heat transfer characteristics are significant.

Study of heat transfer due through rib-groove channel to turbulent How of nanofluids

Nanofluids for improve characteristics flow in a rib-groove channel are investigate. The continuity, momentum and energy equations were solved by FLUENT program. The bottom wall of channel is heated while the upper wall is symmetry, the left side velocity inlet, and the right side is outlet (pressure out). Four different rib-groove shapes are used. Four different types of nanoparticles, Al2O3, CuO, SiO2, and ZnO with different volumes fractions in the range of 1% to 4% and different nanoparticle diameter in the range of 25 nm to 70 nm, are dispersed in the base fluid water are used. In this paper, several parameters such as different Reynolds numbers in the range of 10000 < Re < 40000 are investigated. The numerical results indicate that the trapezoidal with increasing height in the flow direction rib- trapezoidal groove has the best heat transfer and high Nusselt number; the nanofluids with SiO2 have the best behavior. The Nusselt number increases as the volume fraction increases and it decreases as the nanoparticle diameter increases.

Heat transfer enhancement of turbulent nanofluid flow over various types of internally corrugated channels

A numerical study is carried out to investigate the effects of different geometrical parameters and various nanofluids on the thermal performance of rib–grooved channels under uniform heat flux. The continuity, momentum and energy equations are solved by using the finite volume method (FVM). Three different rib–groove shapes are studied (rectangular, semi-circular and trapezoidal). Four different types of nanoparticles, Al2O3, CuO, SiO2 and ZnO with different volume fractions in the range of 1% to 4% and different nanoparticle diameters in the range of 20nm to 60nm, are dispersed in the base fluids such as water, glycerin and ethylene glycol. The Reynolds number varies from 5000 to 25,000. To optimize the shape of rib–groove channels different rib–groove heights from 0.1Dh (4mm) to 0.2Dh (8mm) and rib–groove pitch from 5e (20mm) to 7e (56mm) are examined. Simulation results reveal that the semi-circular rib–groove with height of 0.2Dh (8mm) and pitch equals to 6e (48mm) has the highest Nusselt number. The nanofluid containing SiO2 has the highest Nusselt number compared with other types. The Nusselt number rises as volume fraction increases, and it declines as the nanoparticle diameter increases. The glycerin–SiO2 nanofluid has the best heat transfer compared to other base fluids. It is also observed that in the case of using nanofluid by changing parameters such as nanoparticle diameter, volume fraction and base fluids the skin friction factor has no significant changes.

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.

Farbrication and Characterization of Flexible, Transparent and Self-standing Sb Doped SnO2 Electrospun Nanofiber Films†

Flexible,transparent and self-standing Sb doped SnO2(ATO) nanofiber films were successfully fabricated by means of a low-cost and scalable electrospinning process,with tin tetrachloride and antimony trichloride as precursors. The as-prepared ATO nanofiber films are typical interconnected nanofiber networks and show a single SnO2 rutile crystal structures. With increasing the calcination temperature from 520 ℃ to 700℃,the average diameter of ATO nanofibers decrease from 200 nm to 150 nm,but accompanied by an increase in the average diameter of ATO nanoparticles. Meanwhile,the transmittance of the ATO nanofiber film increases from 72% to 80%,while their resistance decreases from 5. 23 Ω·cm to 2. 20 Ω·cm. Importantly,after500 cycles of bending,the self-standing ATO nanofibers show no obvious electrical degradation. The ATO nanofiber films show promise for application in many fields,such as flexible liquid crystal displays,solar cells and flexible and transparent functional electronics.

Enhancement heat transfer characteristics in the channel with Trapezoidal rib–groove using nanofluids

Numerical study of heat transfer due to turbulent flow of nanofluids through rib–groove channel have been investigated. The continuity, momentum and energy equations are solved by the finite volume method (FVM). Four different rib–groove shapes have been examined. Four different types of nanoparticles, Al2O3, CuO, SiO2, and ZnO with different volumes fractions in the range of 1–4% and different nanoparticle diameter in the range of 25–70nm, have been also studied. The computations are performed under constant temperature over a range of Reynolds number (Re) 10,000–40,000. Results indicate that the Trapezoidal with increasing height in the flow direction rib–trapezoidal groove has the best heat transfer rate and high Nusselt number. It is also found that the SiO2 – nanofluid has the highest value of Nusselt number in comparison with the other type of nanofluids. The Nusselt number increases as the volume fraction increases and it decreases as the nanoparticle diameter increases. The present study shows that these Trapezoidal rib–groove using nanofluids have the potential to dramatically increase heat transfer characteristics and thus can be good candidates for the development of efficient heat exchanger device.

Mixed convective nanofluid flow in a channel having backward-facing step with a baffle

Two-dimensional laminar and turbulent mixed convection flows using nanofluids over backward facing step in a heated rectangular duct having a baffle mounted on its wall are numerically simulated. The continuity, momentum and energy equations are solved using Finite Volume Method (FVM) and the SIMPLE algorithm scheme is applied to examine the effects of the baffle on flow and heat transfer characteristics. The bottom wall of the duct is being heated with a constant heat flux, while other walls are being thermally insulated. In this study, several parameters such as different types of the nanoparticles (Al2O3, CuO, SiO2 and ZnO), different volume fractions in the range of 1% to 4%, and different nanoparticle diameters in the range of 25 to 80nm were used. The Reynolds number of laminar flow was in the range of 100≤Re≤400, while for turbulent flow it was in the range of 7500≤Re≤15,000. The effects of baffle distances in the range of ∞≤D≤4, baffle widths in the range of 0.01≤wb≤0.04, and baffle heights in the range of 0.005≤hb≤0.015 were studied. Baffle locations at the top wall and at bottom wall of the duct, and the number of baffles from 1 to 3 were also examined. The numerical results indicate that the nanofluid with SiO2 has the highest Nusselt number compared with other nanofluid types. The Nusselt number increases as the volume fraction of the nanoparticles and the Reynolds number increase, while it decreases as the nanoparticle diameter increases. The effects of baffle distance heights, and baffle locations on fluid flow and heat transfer characteristics are significant, while the effects of baffle widths and baffle numbers are slightly insignificant.

Assisting and Opposing Combined Convective Heat Transfer and Nanofluids Flows Over a Vertical Forward Facing Step

Numerical simulations of two-dimensional (2D) laminar mixed convection heat transfer and nanofluids flows over forward facing step (FFS) in a vertical channel are numerically carried out. The continuity, momentum, and energy equations were solved by means of a finite volume method (FVM). The wall downstream of the step was maintained at a uniform wall heat flux, while the straight wall that forms the other side of the channel was maintained at constant temperature equivalent to the inlet fluid temperature. The upstream walls for the FFS were considered as adiabatic surfaces. The buoyancy assisting and buoyancy opposing flow conditions are investigated. Four different types of nanoparticles, Al2O3, CuO, SiO2, and ZnO with different volumes' fractions in the range of 1–4% and different nanoparticle diameters in the range of 25–80 nm, are dispersed in the base fluid (water) are used. In this study, several parameters, such as different Reynolds numbers in the range of 100 &lt; Re &lt; 900, and different heat fluxes in the range of 500 ≤ qw ≤ 4500 W/m2, and different step heights in the range of 3 ≤ S ≤ 5.8 mm, are investigated to identify their effects on the heat transfer and fluid flow characteristics. The numerical results indicate that the nanofluid with SiO2 has the highest Nusselt number compared with other nanofluids. The recirculation region and the Nusselt number increase as the step height, Reynolds number, and the volume fraction increase, and it decreases as the nanoparticle diameter increases. This study has revealed that the assisting flow has higher Nusselt number than opposing flow.

A Particle-Based Model for Effective Properties in Infiltrated Solid Oxide Fuel Cell Electrodes

A modeling framework for the numerical reconstruction of the microstructure of infiltrated electrodes is presented in this study. A particle-based sedimentation algorithm is used to generate the backbone, while a novel packing algorithm is used to randomly infiltrate nanoparticles on the surface of backbone particles. The effective properties, such as the connected triple-phase boundary length, the effective conductivity, the effective diffusivity, are evaluated on the reconstructed electrodes by using geometric analysis, finite volume and random-walk methods, and reported in dimensionless form to provide generality to the results. A parametric study on the effect of the main model and operating parameters is performed. Simulations show that the critical loading (i.e., the percolation threshold) increases as the backbone porosity decreases and the nanoparticle diameter increases. Large triple-phase boundary length, specific surface area and good effective conductivity can be reached by infiltration, without detrimental effects on the effective transport properties in gas phase. Simulations reveal a significant sensitivity to the size and contact angle of infiltrated particles, suggesting that the preparation process of infiltrated electrodes should be properly tailored in order to obtain the optimized structures predicted by the model.

EFFECT OF NANOFLUID VARIABLE PROPERTIES ON MIXED CONVECTION FLOW AND HEAT TRANSFER IN AN INCLINED TWO-SIDED LID-DRIVEN CAVITY WITH SINUSOIDAL HEATING ON SIDEWALLS

In this study, mixed convection fl uid fl ow and heat transfer in an inclined two-sided lid-driven cavity subjected to Al2O3–water nanofl uid (with diff erent particle diameters from 15 to 99 nm) has been investigated numerically. The geometry is a double lid-driven square cavity with sinusoidal temperature distribution on the left sidewall, while the right wall is kept at Tc. The top and bott om walls of the cavity, which move in opposite directions, are assumed to be insulated. The eff ects of inclination angle, Richardson number, nanoparticle volume fraction, temperature, and nanoparticle diameter based on recent variable property formulations are studied. The eff ects of an increase in Richardson number while the solid volume fraction is constant and eff ects of an increase in solid volume fraction when the Richardson number is kept constant are investigated. Also, the obtained results show that an increase in nanoparticle diameter infl uences the fl ow patt ern and isotherm contours inside the cavity relatively when the Richardson number is kept constant and the diameter is varied from 15 to 99 nm. As the mean nanoparticle diameter increases, the corresponding fl ow velocity decreases, and hence the heat transfer enhancement is reduced. The results indicate that as Richardson number increases, the average Nusselt number rapidly increases for diff erent values of dp. Moreover, the results have clearly indicated that the addition of Al2O3 nanoparticles has produced a remarkable enhancement on heat transfer with respect to that of the pure fl uid.

Combined Convection Heat Transfer of Nanofluids Flow over Forward Facing Step in a Channel Having a Blockage

Numerical simulations of two dimensional laminar combined convection flows using nanofluids over forward facing step with a blockage are analyzed. The continuity, momentum and energy equations are solved using finite volume method (FVM) and the SIMPLE algorithm scheme is applied to examine the effect of the blockage on the heat transfer characteristics. In this project, several parameters such as different types of nanofluids (Al2O3, SiO2, CuO and ZnO), different volume fraction in the range of 1% - 4%, different nanoparticles diameter in the range of 25nm-80nm were used. Effects of different shapes of blockage (Circular, Square and Triangular) were studied. The numerical results indicated that SiO2nanofluid has the highest Nusselt number. The Nusselt number increased as the volume fraction and Reynolds number increase, while it decreases as the nanoparticles diameter increases. Circular blockage produced higher results compared to triangular and square one.

Effect of nanoparticles size on thermal performance of nanofluid in a trapezoidal microchannel-heat-sink

This paper deals with spherical nanoparticles size effects on thermal performance and pressure drop of a nanofluid in a trapezoidal microchannel-heat-sink (MCHS). Eulerian–Eulerian two-phase numerical approach is utilized for forced convection laminar, incompressible and steady three dimensional flow of copper-oxide nanoparticles with water as base fluid at 100 to 200nm diameter and 1% to 4% volume concentration range. Continuity, momentum, energy and volume conservation equations are solved at whole of the computational domain via finite volume method. Obtained results signify that pressure drop increases 15% at Re=500 and 1% volume concentration while nanoparticles diameter increases from 100 to 200nm. By increasing volume concentration, nanoparticles size effect becomes more prominent and it is observed that increment rate of pressure drop is intensified for above 150nm particles diameter. Unlike the pressure drop, heat transfer decreases with an increase in nanoparticles diameter. Also, it is observed that with an increase in nanoparticles diameter, average Nusselt number of base fluid decreases more than that of the nanoparticles and this signifies that base fluid has more efficacy on thermal performance of copper-oxide nanofluid.

Plasmon properties of silver spherical nanoparticles and films

The effects of the geometrical shape of silver nanoparticles and the electronic configurations of Ag atom in the ground and excited states on the plasmon characteristics of nanoparticles are considered. A relationship between the static polarizability of silver and gold atoms and the plasmon energies of nanoparticles is found. The ΔE excitation energy of a silver atom that corresponds to the 4d105s(2S1/2) → 4d105p(2P1/2 and 2P3/2) transition is shown to determine the plasmon energy of thin silver films. In the case of spherical silver nanoparticles in aqueous solution, the size effect—namely, the correlation between λpl wavelengths of plasmon transitions and d diameters of nanoparticles—is discovered. With the increase in the diameter of nanoparticles, the plasmon transition peaks are red shifted. In the range of d = 9–120 nm, λpl values are shown to change from 370 to 440 nm. The resonance splitting of plasmon bands determined by the mixed valence states of silver atoms is predicted.

Size Variation of Gold Nanoparticles Synthesized Using Tannic Acid in Response to Higher Chloroauric Acid Concentrations

The size evolution of gold nanoparticles synthesized using tannic acid with initial gold chloride concentrations ranging from 0.2 - 2 mM at various tannic acid to chloroauric acid molar ratios (ranging from 2:1 to 12:1) has been analysed. Dynamic light scattering spectroscopic and tramission electron microscopic analyses were performed to assess the size of formed gold nanoparticles. Two different patterns of nanoparticle size evolution were obtained; the size evolution trend below 1 mM chloroauric acid concentration was found to be different from the one obtained at gold chloride concentrations higher than or equal to 1 mM. In case of sizes obtained for less than 1 mM gold chloride concentration, a general decrease in particle size was observed with increase in gold salt concentration. On the contrary, for the particles synthesised using chloroauric acid concentrations higher than or equal to 1 mM, with increase in gold salt concentration, a general increase in nanoparticle diameter was seen. For the molarities 0.2 and 0.5 mM, with increase in tannic acid/ chloroauric acid ratios, first the size decreases and then increases and finally reaches saturation. Particles formed at molarities greater than equal to 1 mM do not exhibit plateaux in their size rather initially decrease and then increase in response to increasing tannic acid/chloroauric acid ratios except for 2 mM concentration at which a small saturation is observed. The findings enumerate that higher gold chloride concentrations leave a significant impact on the sizes of gold nanaparticles obtained using tannic acid as a reducing agent of chloroauric acid solution.

Effects of controlled surface treatment on titanium dioxide electrode nanostructure for dye-sensitized solar cells

A stable surface treatment for the nanoporous TiO2 electrode of dye-sensitized solar cells (DSCs) has been developed via sol-gel processing of titanium(IV) isopropoxide (TiP), enabling controllable performance improvements, which has been hitherto unachievable. A systematic study of the electrode chemistry and morphology was performed to examine the mechanisms by which the treatment contributes to enhancement in DSC performance. The electrode exhibited a linear increase in mass with TiP concentration and a corresponding reduction in porosity. The increase in nanoparticle diameter resulted in the increase in surface area without altering the surface chemistry, leading to an increase in dye loading. Current–voltage characteristics and incident photon-to-electron conversion efficiencies (IPCE) were analyzed. A linear increase in the short-circuit photocurrent was measured with TiP concentration, increasing by 30 % for a 4 mM TiP treatment, which resulted in a corresponding efficiency gain of 23 %. This was found to primarily result from a controllable increase in the charge collection efficiency, via a 30 % faster electron transport time and a 19 % increase in the electron lifetime. The results elucidate the underlying physical mechanisms for improvement in DSC performance by surface treatment.

When Nanoparticle Size and Molecular Geometry Matter: Analyzing the Degree of Surface Functionalization of Gold Nanoparticles with Sulfur Heterocyclic Compounds

The degree of surface functionalization of colloidal dispersions of Au nanoparticles (AuNPs) by sulfur heterocyclic compounds is determined using localized surface plasmon resonance spectroscopy (LSPRS), morphological characterization, and electrodynamic modeling. We demonstrate that AuNP surface coverage is the result of the interplay between the molecular geometry of ligands and the Au nanoparticle diameter. For the same ligand, it is found that the surface density of molecules (σ) is almost constant or slightly decreases as the Au nanoparticle diameter increases, while for the same NP size the degree of surface coverage increases as the length of the molecule increases. The chemical interaction between the ligand molecules and the AuNP surface is demonstrated using surface enhanced Raman scattering (SERS) and 1H NMR. For the same average AuNP size, the full width at half maximum (fwhm) of the LSPR is significantly greater for derivatized AuNPs, a feature that shows the important role played by chemical interface damping in NP surface functionalization. The strong chemical stability of the modified AuNPs is further probed against KCN etching, indicating that there is a close correspondence between σ and the slow kinetics of the decay of the LSPR peak.

Thermal stability of gold-PS nanocomposites thin films

Low-temperature transmission electron microscopy (TEM) studies were performed on polystyrene (PS, M w = 234 K) — Au nanoparticle composite thin films that were annealed up to 350°C under reduced pressure conditions. The composite thin films were prepared by wet chemical approach and the samples were then subsequently spin-coated on a carbon-coated copper grid for TEM measurements. TEM measurements were performed at liquid nitrogen temperatures to reduce the electron-beam-induced radiation damage. The results showed a marginal increase in Au nanoparticle diameter (2.3 nm–3.6 nm) and more importantly, an improved thermal stability of the polystyrene (PS) composite film much above its glass transition temperature.

One parameter control of the size of iron oxide nanoparticles synthesized in reverse micelles

Iron oxide nanoparticles were synthesized via reverse micelle methods. The initial iron concentration was varied, while maintaining all other parameters constant, in order to investigate the effect of the iron concentration on the resultant iron oxide nanoparticle size. Increasing the iron concentration from 0.125M to 0.5M yielded an increase in average nanoparticle diameter from 4.71 to 7.95 nm, as measured by transmission electron microscopy. Three other concentrations between 0.125M and 0.5M showed corresponding size variations, all with statistical significance. Magnetic characterization by vibrating sample magnetometry and powder x-ray diffraction was performed to verify proper phase and material. Further insight into the reverse micelle method was acquired along with the ability to tune the nanoparticle size.

Phase Diagrams of Self-Assembled Mono-Tethered Nanospheres from Molecular Simulation and Comparison to Surfactants

We perform Brownian dynamics simulations on model 3-D systems of mono-tethered nanospheres (TNS) to study the equilibrium morphologies formed by their self-assembly in a selective solvent. We predict that in contrast to flexible amphiphiles the nanospheres are locally ordered and there is an increase in the local order with an increase in concentration or relative nanoparticle diameter. We present the temperature vs concentration phase diagram for a system of TNS and propose a dimensionless scaling factor F(v) (headgroup volume/tether volume) that allows a comparison between the morphologies formed from TNS and traditional surfactants.