Increase In Size Of Nanoparticles Research Articles

Molecular dynamic modeling and analysis of the sintering behaviors of GDC modified BSCF nanorods for rSOC oxygen electrode

Degradation including segregation and high stress related issues are significant challenges for reversible solid oxide cells (rSOCs), particularly concerning the oxygen electrode. Understanding the sintering preparation is crucial for enhancing the performance and reliability of the oxygen electrode under long-term dual-mode operation. In this study, the sintering process of Ba0.5Sr0.5Co0.8Fe0.2O3-δ nanorods anchored with Gd-doped CeO2 nanoparticles (GDC-BSCF-NR) was predicted by using molecular dynamics method. To optimize the sintering process, the stress distribution, A-site ion migration behavior and thermal properties of the composite electrode materials were analyzed at different sintering temperature, the effects of nanoparticle size were also investigated. Both thermal conductivity and thermal expansion increase with sintering temperature. The particle stress of the composites correlates positively with the diffusion coefficient of ions. The diffusion coefficients of surface and internal Ba/Sr ions increase by 6%–9% from 973 K to 1373 K, while stress increases by 19%–33 %. The diffusion coefficient of BSCF particles decrease by 15.1 % with an increase in GDC nanoparticle size, which is beneficial for suppressing Ba/Sr segregation.

Ozone degradation of tetracycline hydrochloride enhanced by magnetic nanofluid composed of Fe3O4 nanoparticles.

Magnetic Fe3O4 nanoparticles were added into the aqueous phase to form nanofluid systems, in which ozone was used for the oxidation of tetracycline hydrochloride (TC) in the solution. The nanomaterials were characterized using SEM, XRD, EDS, and FT-IR. The effects of nanoparticles size, addition ratio, and number of cycles on the process of ozone oxidation of TC were investigated. The results indicated that the addition ratio of nanoparticles have a certain impact on the performance of ozone oxidation. When the addition ratio increased from 0.02% to 0.4%, the removal rate of TC in the solution was improved significantly. Besides, the particle size of nanoparticles showed a greater impact on ozone oxidation. At the nanoscale, Fe3O4 nanoparticles exhibited significant strengthening properties, which is attributed to the construction of nanofluid systems. The removal rate of TC in solution decreased obviously with the increase of nanoparticles size. The Fe3O4 nanoparticles with particle size of 20 nm showed the most significant effect on TC degradation. The recycling experiment showed that magnetic Fe3O4 nanoparticles had stable regeneration performance. For three times of recycling treatment, with a Fe3O4 addition ratio of 0.4%, the removal rate of TC reached 98.7%, 97.21%, and 96%, respectively. Based on the characterization results, the strengthening mechanism was analyzed. The experimental results indicated that construction of nanofluids systems could improve the utilization rate of ozone, and Fe3O4 nanoparticles were reusable and easily recyclable.

Effect of gravity settling on the onset of thermal convection in a nanofluid-saturated porous medium layer

The onset of convection in a horizontal porous medium layer saturated with a nanofluid and heated from below is investigated via linear stability analysis and numerical simulation. The Darcy–Buongiorno model is used to describe the convective transport behaviour of the nanofluid and the settling effect of nanoparticles due to gravity is considered in addition to thermophoresis and Brownian diffusion. The linear stability analysis shows that the gravity settling is a substantial stabilizing mechanism restraining the destabilizing factors such as thermal buoyancy and thermophoresis. The stability threshold is determined by the relative strength of thermophoresis to gravity settling. It is found that the system is destabilized when the thermophoretic mobility prevails. As the nanoparticle size increases, the gravity settling effect is promoted and makes the system more stable. In particular, the onset of instability is dominated by the oscillatory mode once the nanoparticle concentration is in a stably stratified profile across the porous layer. When the Rayleigh–Darcy number $Ra_D$ exceeds the critical value, the spectrum of the growth rates of the unstable modes rises with increasing $Ra_D$ and $Rn$ (i.e. the concentration Rayleigh number), and eventually the unstable modes in the high-wavenumber region exhibit the same instability. The evolution of the convection is further examined by numerical simulation. The results verify the stability characteristics predicted by linear stability analysis. Moreover, the pattern of fingering convection of the nanofluid concentration is observed once the nanofluid concentration is unstably stratified and the density difference across the porous layer is large enough.

Surface modified single-step nanofluid for improved CO2 absorption and storage Prospects at pore-scale in micromodels: CO2 utilization for saline porous media

The utilization (absorption and areal sweep) of injected carbon dioxide (CO2) can be enhanced if a viscous and agglomeration free nanofluid is used as most of the nanoparticles (NPs) prefer to stay in bulk phase rather than adsorbing on CO2 surface. NP adsorption can be improved if non-participating NPs are surface modified with a suitable surface modifying agent e.g., triethoxy (vinyl)silane (TVS). Thus, in this study, single-step approach was used to synthesize agglomeration free TiO2 nanofluid whose surface modification was carried out in varying proportion of TVS (1–5% v/v) followed by the discussion on comparative CO2 absorption and storage performance by different tools such as DLS, IFT, Rheology, Contact-angle, and Micromodel flow. The basic nanofluid (To) showed greater CO2 absorption after surface modification as demonstrated by molality results. However, surface modification also decreased dispersion stability of surface modified nanofluids (T1, T2, and T3) and T2 was regarded as the most stable nanofluid with −64.4 mV (ζ-potential) and 153 nm (NP size). After surface modification, increase in NP size and settlement was higher for surface modified nanofluids than To, which exhibited dispersion stability of 84 d with −53.4 mV and 15 nm. Contact angle results also showed that surface modified nanofluids possess greater affinity for CO2 absorption than basic nanofluid (To). Rheological analysis was also consistent with other tests where viscosity was found dependent on both storage period and temperature, and NP settlement was found to be the most influential parameter on flow properties of nanofluid. Finally, pore scale analysis was performed to understand areal sweep of injected CO2 in micromodel with and without nanofluid, where nanofluid imparted greater CO2 storage by diverting it in un-swept pore networks of micromodel which were untapped by CO2 without nanofluid.

Effect of aspect ratio on the x-ray attenuation of nanoparticles: A theoretical study

PurposeThere has been a significant focus on the potential applications of nanoparticle suspensions in the past few decades particularly as targeted contrast agents for specific pathological conditions. However, the question of optimal size and shape of nanoparticles for contrast enhancement is inadequately addressed. MethodsWe present a comprehensive and conclusive theoretical analysis using first principles by considering the attenuating property of a single nanoparticle of any arbitrary shape. As a special case, ellipsoidal nanoparticles and nanorods are considered, for two independent directions of incidence of x-rays. These results are extended for a suspension of nanoparticles in a liquid. ResultsIt is seen that for a nanoparticle with dimensions much less than 1/μ(E), where μ(E) is the attenuation coefficient of the material, the attenuation by the nanoparticle is independent of its shape and size; and attenuation per unit mass reduces as the nanoparticle size increases. ConclusionsTo achieve maximum attenuation, the nanoparticle sizes should be as small as possible, immaterial of the shape, as long as the dimensions are smaller than 150 nm.

Multifarious Uses of UV-VIS Spectroscopy for Green Synthesis of Silver Nanoparticles for Antibacterial Textiles

Green synthesis is an easy and economical method of synthesizing silver nanoparticles (AgNPs). However, many variables, including the ideal temperature, the volume and concentration of silver nitrate, the amount of plant extract, etc., affect the green synthesis. This article aims to determine the ideal temperature and plant extract amount using the UV-VIS spectrum. It was found above 40 °C was required for both Calendula arvensis (field marigold) leave extract and silver nitrate to synthesize AgNPs. The optimum temperatures were 55 °C and 60 °C for AgNO3 and plant extract, respectively and it was determined using Taguchi orthogonal array based on the UV-VIS spectrum. Silver nanoparticles (AgNPs) can be incorporated into textiles by padding and in-situ methods, but they need accurate plant extract amounts for good antibacterial efficiency. Two equations were proposed for determining the optimum plant extract amount for padding and in-situ methods. Several AgNPs loaded samples were prepared following the derived equations. For evaluating the efficiency of the equations C.reticulata (orange) peel extract was used besides C.arvensis plant extract. The samples were also characterized by antibacterial tests, Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS), and X-ray diffraction (XRD). It showed when plant extract was taken according to the equations, around 45 nm nanoparticle size and 100% antibacterial activity were obtained. However, taking 1 ml more plant extract than that of the calculated amount of plant extract increased nanoparticle size to 107 nm and reduced antibacterial activity to 90%.

The relationship between cellular microstructure and the mechanical properties of styrene/methyl methacrylate copolymer‐silica nanocomposite foams prepared by a supercritical CO2 blowing agent

AbstractStyrene/methyl methacrylate (St/MMA) copolymer‐silica nanocomposite foams were prepared using supercritical CO2 as blowing agent, and the relationships between their cellular microstructure and mechanical properties were investigated. The effects of nanosilica content, size, and surface chemistry on the foam's microstructure and properties were examined. Dispersion and distribution of silica nanoparticles with different surface chemistry in St/MMA copolymer nanocomposites were discussed. To determine the most suitable copolymer composition for incorporating silica nanoparticles, some operating conditions such as temperature and pressure were primarily examined to study their effects on the microstructure of resulting foams. In compressive mechanical properties of final foams, a considerably high value was obtained for the compressive strength of the foams of up to 9.5 MPa. The prepared low‐density (below 0.2 g/cm3) St/MMA copolymer microcellular foams can be used in green lost foam iron casting processes.Highlights Styrene/methyl methacrylate copolymer‐silica nanocomposite foams were prepared via supercritical CO2. Foams' cell size was changed by changing silica nanoparticle surface chemistry and size. The uniform cellular microstructure was achieved by nanosilica size increment. Increasing nanoparticle size improved the foam's mechanical properties. Low‐density foams were achieved for potential application in lost foam casting.

Protein Binding Leads to Reduced Stability and Solvated Disorder in the Polystyrene Nanoparticle Corona.

Understanding the conformation of proteins in the nanoparticle corona has important implications in how organisms respond to nanoparticle-based drugs. These proteins coat the nanoparticle surface, and their properties will influence the nanoparticle's interaction with cell targets and the immune system. While some coronas are thought to be disordered, two key unanswered questions are the degree of disorder and solvent accessibility. Here, a model is developed for protein corona disorder in polystyrene nanoparticles of varying size. For two different proteins, it is found that binding affinity decreases as nanoparticle size increases. The stoichiometry of binding, along with changes in the hydrodynamic size, supports a highly solvated, disordered protein corona anchored at a small number of attachment sites. The scaling of the stoichiometry versus nanoparticle size is consistent with disordered polymer dimensions. Moreover, it is found that proteins are destabilized less in the presence of larger nanoparticles, and hydrophobic exposure decreases at lower curvatures. The observations hold for proteins on flat polystyrene surfaces, which have the lowest hydrophobic exposure. The model provides an explanation for previous observations of increased amyloid fibrillation rates in the presence of larger nanoparticles, and it may rationalize how cell receptors can recognize protein disorder in therapeutic nanoparticles.

The influence of the polyol solvents on the continuous growth of water-dispersible iron oxide nanoparticles

Magnetic nanoparticles have continued to gain significant attention due to their unique magnetic properties and potential applications. However, it is still challenging to directly synthesize water-dispersible magnetic nanoparticles with controlled size for biomedical applications. This study investigates the influence of solvents on the continuous growth of magnetic nanoparticles, aiming to achieve controlled size and excellent water dispersibility via thermal decomposition in polyol solvents. The size of the nanoparticles gradually increases with longer polyol chain solvents. The increase in nanoparticles size is more significant under a higher reaction temperature (220 °C) compared to a lower temperature (190 °C). These monodispersed nanoparticles exhibit strong superparamagnetic properties, improving with longer solvent chain lengths at the same size. Magnetic resonance imaging (MRI) studies reveal higher relaxivities for magnetic nanoparticles synthesized in longer-chain polyols. This research offers valuable insights for synthesizing magnetic nanoparticles with precise sizes, magnetic properties, and biomedical applications.Graphical abstract

Enhancement of the ORR Activity and Durability of Pt/C by the Modification with Melamine and N-Containing Aromatic Compounds

The ORR activity and durability of Pt catalysts have to be enhanced for the wider spread of PEFCs. We pay special attention to possibility that surface modification of a Pt catalyst increases its ORR activity. On the Pt surface, Pt-OH species is stabilized too much by network structure of water molecules adsorbed there [1]. The overstabilization of Pt-OH impedes the ORR because this species is an intermediate of ORR. Then, we try to enhance the ORR activity by destabilizing Pt-OH. The perturbation of the water network would destabilize Pt-OH. We try to perturbate the water network by adding an external organic compound to enhance the ORR activity.We tested a wide variety of compounds as an enhancer of ORR of Pt. Although most of compounds tested exhibit no influence of inhibitory effects on the ORR, we found that certain kind of N-containing aromatic compounds -melamine (and tetraazaporphyrin)- enhance the ORR activity of Pt catalysts significantly [2-4]. With the addition of melamine, ORR activity at 0.9 V vs. RHE is increased by 1.6 times although the ECSA decreased (Fig. 1). The enhancement of the ORR activity is reasonably ascribed to the destabilization of Pt-OH, judging from the change of cyclic voltammograms of Pt/C after the addition of melamine.This melamine modification method is also applied for another highly active catalyst (Pt/Pd/C core-shell catalyst) to obtain a further activated catalyst. The mass activity of Pt/Pd/C core-shell catalyst increases by 2.4 times after melamine modification and reaches 3600 AgPt -1 at 0.9 V vs. RHE [5].Melamine also enhances the durability considerably. Under an accelerated durability test (ADT) (80 °C, 0.6 V (3s) - 1.0 V (3s), square wave, 10000 cycles), Pt/C undergoes severe degradation; the ECSA significantly decreases because of the increase in the size of Pt nanoparticles (Fig. 1). However, after the ADT in the presence of melamine, the decrease in ECSA is significantly suppressed [6]. This beneficial effect is due to the suppression of the increase in size of Pt nanoparticles. A melamine polymer (poly-melamine sulfonate)-modified Pt/C also exhibits higher durability than unmodified Pt/C [7]. The suppression of Pt-OH by melamine participates in the enhancement of the durability.In this talk, we introduce discovery of melamine as an ORR enhancer, effect of melamine on the ORR activity/durability of Pt/C, and mechanisms of functions of melamine.This paper is based on the results obtained from projects, JPNP20003, commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

How Nanoparticle Size and Bubble Merging Is Governed by Short‐Range Spatially Controlled Double‐Beam Laser Ablation in Liquids

AbstractPulsed laser ablation in liquid (LAL) is a method for synthesizing nanoparticles with controlled composition and high purity. However, current research predominantly examines isolated cavitation bubbles, overlooking real‐world LAL scenarios where numerous bubbles interact simultaneously. This study addresses this gap by investigating the effects of short‐range micrometric spatially controlled double‐pulse laser ablation in liquids on nanoparticle size distribution. Gold and YAG are used as model materials, and a dimensionless parameter, H*, is introduced to quantify the ratio between double bubble spatial separation and their maximum height. This parameter correlates with cavitation bubble merging time, bubble volume change rate, and subsequent nanoparticle size increase. Shadowgraphs provide valuable insights into bubble contact and fusion dynamics, showcasing phase separation by a thin water film and subsequent merging into a single bubble. Notably, a twofold increase in nanoparticle size is observed for both Au and YAG at H* = 0.25. The research indicates a strong association between nanoparticle size trends and cavitation bubble volume rate change, particularly emphasized at H* = 0.25. Understanding the dynamics of neighboring bubbles during LAL emphasizes the relevance of lateral pulse distances in dual‐beam LAL, impacting particle size distribution in a distance‐dependent manner.

Role of Lorentz force and nanoparticles morphology on the dynamics of ternary hybrid nanofluid flow subject to porous disks and gyrotactic microorganisms

This article explains the significance of Lorentz force and nanoparticle morphology on the dynamics of ternary hybrid nanofluid through porous disks. The gyrotactic microorganisms are investigated to avoid possible sedimentation of solid particles and maintain fluid stability. A 3-dimensional flow problem in the presence of two different types of tri-hybrids nanofluid nanomaterials (Metallic and Nonmetallic Oxides) is used here. By eliminating the pressure term, the governing partial differential equations are transformed into a high-order nonlinear system of differential equations. This system is subsequently utilized to construct the boundary layer model, and these equations are solved numerically using a shooting technique based on the Runge–Kutta method, with the assistance of MATLAB software. The comparison and validation results are in good agreement through a numerical approach. Different-shaped nanoparticles have a significant influence on motile microorganisms. Shear stress near porous surfaces was significantly reduced due to an increase in nanoparticle size. The addition of all types of nanoparticles improved the thermal performance. Many desirable results for engineering purposes are observed under suitable conditions of simultaneous effect of magnetohydrodynamics (MHD) with microorganisms.

Nanoparticle Size Influences the Self-Assembly of Gold Nanorods Using Flexible Streptavidin-Biotin Linkages.

The self-assembly of colloidal nanocrystals remains of robust interest due to its potential in creating hierarchical nanomaterials that have advanced function. For gold nanocrystals, junctions between nanoparticles yield large enhancements in local electric fields under resonant illumination, which is suitable for surface-enhanced spectroscopies for molecular sensors. Gold nanorods can provide such plasmonic fields at near-infrared wavelengths of light for longitudinal excitation. Through the use of careful concentration and stoichiometric control, a method is reported herein for selective biotinylation of the ends of gold nanorods for simple, consistent, and high-yielding self-assembly upon addition of the biotin-binding protein streptavidin. This method was applied to four different sized nanorods of similar aspect ratio and analyzed through UV-vis spectroscopy for qualitative confirmation of self-assembly and transmission electron microscopy to determine the degree of self-assembly in end-linked nanorods. The yield of end-linked assemblies approaches 90% for the largest nanorods and approaches 0% for the smallest nanorods. The number of nanorods linked in one chain also increases with an increased nanoparticle size. The results support the notion that the lower ligand density at the ends of the larger nanorods yields preferential substitution reactions at those ends and hence preferential end-to-end assembly, while the smallest nanorods have a relatively uniform ligand density across their surfaces, leading to spatially random substitution reactions.

Analysis of the mechanism of enhanced heat transfer by nanofluids.

Industrial production and humans cannot exist without energy, but the low efficiency of the heat transfer in the excessive use of energy is the most significant aspect of energy saving and emission reduction. Molecular dynamics simulation methods are devoted to simulate the heat transfer efficiency of a nanofluid system with different particle sizes, and the heat transfer enhancement mechanism of the nanofluid is simulated and studied from a microscopic perspective. The analysis showed that as nanoparticle size increases, the thermal conductivity of the Al-Ar nanofluid tends to decrease, but all of them are still higher than the thermal conductivity of the liquid argon system. According to the findings of the density and radial distribution function analyses, it can be seen that the microstructure of the system changes after putting solid nanoparticles to the original fluid. This alteration in the system's microstructure is the primary component responsible for the increased heat transfer efficiency of nanofluids. In this paper, based on the theory of molecular dynamics, the simulation calculations were mainly performed using LAMMPS software, which is a commonly used open source computational program in the field of MD simulation research. VMD is used for visualization and analysis. The Lennard-Jones potential function was used in the simulation to accurately describe the forces acting between the atoms.

X-ray photoelectron spectroscopy and tunable photoluminescence study of gold nanoparticles embedded in PVA films.

This article reports the systematic photoluminescence study of the various contents of gold nanocomposites in polyvinyl alcohol (PVA) films. The variations in the gold content in PVA film were 0.2, 0.5, 1.0, and 1.5wt%. All the samples were excited at two selected wavelengths; those are at 400 nm and 532 nm. On exciting the gold-PVA nanocomposite films at 400 nm the photoluminescence was observed in the region of 430-500 nm in comparison to pure PVA films that show an emission at 400 nm. However, on exciting the gold-PVA nanocomposites at 532 nm, the emission was observed at 560-650 nm with a long tail till 700 nm that is unlike the pure PVA films that do not show any emission peak in this region. This suggests that emission between 430 and 500 nm regions is due to the coordination of PVA with gold nanoparticles because PVA has an emission at 400 nm. However, the emission peak between 560 and 650 nm is entirely due to the gold nanocomposite particle. The peak also shows a smaller red-shift that is usually with the increasing nanoparticles size with the increasing content in the PVA films. The formation of gold nanoparticles was justified by X-ray diffraction (XRD) analysis which is further supported by X-ray photoelectron spectroscopy (XPS) analysis.

Numerical investigation of nanoparticle deposition in the olfactory region among pediatric nasal airways with adenoid hypertrophy

To understand inhaled nanoparticle transport and deposition characteristics in pediatric nasal airways with adenoid hypertrophy (AH), with a specific emphasis on the olfactory region, virtual nanoparticle inhalation studies were conducted on anatomically accurate child nasal airway models. The computational fluid-particle dynamics (CFPD) method was employed, and numerical simulations were performed to compare the airflow and nanoparticle deposition patterns between nasal airways with nasopharyngeal obstruction before adenoidectomy and healthy nasal airways after virtual adenoidectomy. The influence of different inhalation rates and exhalation phase on olfactory regional nanoparticle deposition features was systematically analyzed. We found that nasopharyngeal obstruction resulted in significant uneven airflow distribution in the nasal cavity. The deposited nanoparticles were concentrated in the middle meatus, septum, inferior meatus and nasal vestibule. The deposition efficiency (DE) in the olfactory region decreases with increasing nanoparticle size (1–10 nm) during inhalation. After adenoidectomy, the pediatric olfactory region DE increased significantly while nasopharynx DE dramatically decreased. When the inhalation rate decreased, the deposition pattern in the olfactory region significantly altered, exhibiting an initial rise followed by a subsequent decline, reaching peak deposition at 2 nm. During exhalation, the pediatric olfactory region DE was substantially lower than during inhalation, and the olfactory region DE in the pre-operative models were found to be significantly higher than that of the post-operative models. In conclusions, ventilation and particle deposition in the olfactory region were significantly improved in post-operative models. Inhalation rate and exhalation process can significantly affect nanoparticle deposition in the olfactory region.

Sensible heat thermal energy storage performance of mono and blended nanofluids in a free convective-radiation inclined system

The photothermal conversion performance (PCP) of a nanofluid-based solar energy system is investigated numerically and experimentally. The impacts of particle size, volume concentration, nanoparticle type, base fluid type and collector inclination angle on the PCP are investigated. It is observed that using nanoparticles improves the ability to absorb solar energy. Temperature gain is 2.2, 3.2, 3.8, 4.2, and 9 times better than pure water for water-based Al, Al2O3, Au, Cu, and Graphite mono nanofluids, respectively. Interestingly, blended nanofluids containing the same nanoparticles significantly argument the optical properties, with useful heat enhancement ranging from 62.8 (mono) to 194 kJ/kg (hybrid). However, the collector's inclination angle, which ranges from 0 to 60°, has a negative impact on the PCP by reducing the solar radiation absorption of the nanofluids due to a decrease in the radiation penetrating the collector. Furthermore, as nanoparticle size increases, so does the thermal performance of the nanofluid. An experimental investigation is carried out for pure water and nanofluid at various wind speeds and solar irradiation levels ranging from 1 to 4 m/s and 200–1000 W/m2, respectively, to validate the numerical results.

Superlattice Surface Lattice Resonances in Plasmonic Nanoparticle Arrays with Patterned Dielectrics.

This paper describes how two-dimensional plasmonic nanoparticle lattices covered with microscale arrays of dielectric patches can show superlattice surface lattice resonances (SLRs). These optical resonances originate from multiscale diffractive coupling that can be controlled by the periodicity and size of the patterned dielectrics. The features in the optical dispersion diagram are similar to those of index-matched microscale arrays of metal nanoparticle lattices, having the same lateral dimensions as the dielectric patches. With an increase in nanoparticle size, superlattice SLRs can also support quadrupole excitations with distinct dispersion diagrams. The tunable optical band structure enabled by patterned dielectrics on plasmonic nanoparticle arrays offers prospects for enhanced nonlinear optics, nanoscale lasing, and engineered parity-time symmetries.

Model for particle capture by the solid-liquid interface during solidification of metal matrix nanocomposites

A sharp-interface model for solidification of nanocomposites with nanoparticle-interface interaction is presented. The main novelty of the work is that the engulfment or non-engulfment of nanoparticles is modelled as a function of the local interface velocity and a particle size-based critical velocity. This is incorporated through a variable partitioning coefficient while solving the nanoparticle conservation equation which is modelled similar to an alloying constituent. The movement of nanoparticles is governed by nanoparticle-interface interaction and by diffusion due to Brownian motion. The model couples a sharp-interface solidification model, species transport model and nanoparticle transport model. Thus, the engulfment and the resultant distribution of nanoparticles in the solidified region can be predicted for different combinations of initial undercooling and nanoparticle size. The effect of accumulated nanoparticles on the solute transport and solidification rate is also included in the model. Results show that the engulfment of smaller nanoparticles is very low resulting in high accumulation near the interface. This results in a high restriction to solute diffusion and solidification. Combined variation of initial undercooling and particle size shows that the average engulfment values for initial undercooling of 0.3, 0.5, and 0.7 are 2.75 %, 7.75 % and 21.50 % for r* = 0.1, 15.5 %, 53.5 %, and 82.5 % for r* = 0.5, and 38.0 %, 77.75 %, and 93.25 % for r* = 0.9. Thus, the engulfment of nanoparticles into the solid improves with increase in nanoparticle size and with the increase in solidification rate.

Conditions of enhanced evaporation for nanofluids droplet and inhibition of coffee-ring effect under buoyancy and Marangoni convection

Evaporation of nanofluid droplets whose size is larger than capillary length is common in industrial processes, but there is currently a lack of research on the evaporation kinetics and more complex deposition patterns under the combined effects of buoyancy and Marangoni convection of large evaporating droplet. Experimental investigations on evaporation of Al2O3H2O nanofluid sessile droplet with initial contact line diameter of 4 mm on heating PTFE coating substrate are reported. The variation in contact angle, contact radius, and droplet volume over time under different conditions were obtained through experiments. The average evaporation rate is calculated. Internal flow characteristics are inferred through the surface temperature distribution detected by the top view infrared camera. The constant contact radius mode takes place at the beginning of evaporation. Then mixed evaporation mode and stick slip mode may occur for different substrate temperature, nanoparticle mass concentration and nanoparticle size. Increasing nanoparticle size causes a decrease in average evaporation rate. Whether the use of nanofluids can improve evaporation rate and heat transfer or not depends on multiple factors. Convection cells exist, and three kinds of deposition patterns are formed due to the underlying coupled transport phenomena. Under the combined effect of buoyancy and Marangoni convection in this article, the most common coffee-ring pattern does not appear. The deposition patterns are directly affected by the pinning stability, which decrease at higher temperature.