Search Results (7)

Diffusiophoresis of a weakly charged dielectric droplet in a cylindrical pore is investigated theoretically in this study. The governing fundamental electrokinetic equations are solved with a patched pseudo-spectral method based on Chebyshev polynomials, coupled with a geometric mapping scheme to take care of the irregular solution domain. The impact of the boundary confinement effect upon the droplet motion is explored in detail, which is most profound in narrow channels. We found, among other things, that the droplet moving direction may reverse with varying channel widths. Enhanced motion-inducing double-layer polarization due to the presence of a nearby channel wall is found to be responsible for it. In particular, an interesting and seemingly peculiar phenomenon referred to as the “solidification phenomenon” is observed here at some specific critical droplet sizes or electrolyte strengths in narrow channels, under which all the droplets move at identical speeds regardless of their viscosities. They move like a rigid particle without the surface spinning motions and the induced interior recirculating vortex flows. As the corresponding shear rate is zero at this point, the droplet is resilient to undesirable exterior shear stresses tending to damage the droplet in motion. This provides a helpful guideline in the fabrication of liposomes in drug delivery in terms of the optimal liposome size, as well as in the microfluidic and nanofluidic manipulations of cells, among other potential practical applications. The effects of other parameters of electrokinetic interest are also examined. Full article

The surface morphology of X80 steel with hydrophilic underwater oleophobic characteristic is described greater comprehensively and quantitatively in this work by combining fractal dimension and multifractal. X80 steel with hydrophilic underwater oleophobic surface characteristics was constructed using a chemical etching method. Then, with the aid of three wettability parameters—contact angle, rolling angle, and adhesion work—this study investigated the relationship between the surface fractal dimension of X80 and the stability of the water ring in the core annular flow. The results showed that: (1) the fractal dimension of X80 steel specimens increased first and then decreased with the increase of reaction time. Besides that, the value of it was greater than 2, indicating that the surface had obvious fractal characteristics. The spectral difference, Δf(α), and the spectral width, Δα, supplemented the description of the X80 steel surface morphology, which was consistent with the scanning electron microscope results. (2) When the maximum fractal dimension was 2.0808, the minimum contact angle of distilled water on its surface was 50.2°, and the maximum contact angle of underwater oil droplets was 166.4°. The larger the fractal dimension of X80 steel with hydrophilic underwater oleophobic properties, the more hydrophilic and underwater oleophobic it is. This illustrated that there was a strong binding force between the water and the X80 steel pipe wall, and hence the quality and efficiency of the core annular flow was improved, which was more conducive to the promotion of this technology in the field of heavy oil transportation. Full article

Relative dispersion (ɛ) is a key expression used to parameterize various cloud processes in global circulation models (GCMs) and meteorological mesoscale models. Aerosols, updraft velocity (w), and different growth stages of warm clouds are known to affect relative dispersion. A two-dimensional detailed bin microphysical cloud model is used to investigate the combined impacts of aerosol number concentration (N_a) and updraft velocity on relative dispersion in the collision–coalescence stage. In addition, the causes potentially controlling the changes in ɛ with updraft velocity are explored. There are three main influence regimes: the updraft velocity main influence regime, the aerosol main influence regime, and the joint influence regime. The cause of the variations in ɛ with updraft velocity is found to be different in the three main influence regimes. In the updraft velocity main influence regime, vigorous collision–coalescence due to stronger w results in a shift in the cloud droplet number concentration spectrum toward larger droplets, and the average cloud droplet radius increases, but the spectral width is less variable, so ε decreases. In the joint influence regime, stronger cloud droplet evaporation due to the stronger dragging effect of large cloud droplets widens the spectrum, mainly by reducing the cloud droplet number concentration (N_c) of 4–30 μm, and ε increases with the reduction in w. In the aerosol main influence regime, the strongest dragging effect reduces N_c at all radii with decreasing w, and the cloud droplet number concentration spectrum (CDNCS) narrows, which becomes the formation mechanism of the positive correlation between ε and w. Evaporation mainly causes a negative correlation between ε and N_c, but weak evaporation causes the correlation to become positive under the background of high aerosol concentration. At low aerosol concentrations, a strong collision–coalescence effect leads to a negative correlation between N_c and ε, but at high aerosol concentrations, the correlation is the opposite due to a weak collision–coalescence effect. Full article

The aerial atomizer is the most essential component of the plant protection UAV (unmanned aerial vehicle). However, the structural optimization of existing aerial atomizers lacks comprehensive consideration of spray parameters and structural parameters, and there is a shortage of available atomizer spray models, resulting in the unstable effect of UAV application. In our previous work, an aerial dual-atomization centrifugal atomizer was developed. In order to obtain an aerial atomizer with good atomization effect and its atomization model, structural optimization at different rotation speeds and flow rates of the atomizer, and its atomization performance, are studied in this paper. Firstly, with the droplet volume median diameter (VMD) and spectral width (SRW) as the evaluation index, through the single-factor, Plackett–Burman and Box–Behnken tests, the influence of rotation speed, flow rate, tooth number and tooth shape were studied. The regression models of the droplet VMD and SRW were established using multiple quadratic regression fitting of the test data. Secondly, in order to achieve the lowest droplet VMD and SRW, the response surface method and post-hoc multiple comparison method were used to obtain the optimized structure of the atomizer’s rotation ring at different rotation speeds (600–7000 r/min) and flow rates (500–1000 mL/min). Lastly, with the effective swath width (ESW) of the optimized atomizer as the evaluation index, through the Box–Behnken test, the influence of rotation speed, flow rate and spray height were studied. The multiple quadratic regression model of ESW was established with the test data. The test results indicated that rotation speed, flow rate and tooth number had a significant effect on droplet VMD and SRW; tooth shape had no significant effect on the droplet VMD and SRW, however, the square tooth shape had the best atomization effect; and rotation speed, flow rate and spray height had a significant effect on ESW. The optimized structural parameters were tooth shape: square, and tooth number: 20. The determination coefficient $R^2$ of the regression model of VMD, SRW and ESW were 0.9976, 0.9770 and 0.9974, respectively, which indicates that the model was accurate, and can evaluate and predict the spray effect. This paper provides an optimized dual-atomization centrifugal atomizer, and its regression models of VMD, SRW and ESW for UAV applications can provide a reference for efficient UAV spraying. Full article

This study explores the drift potential characteristics of a flat fan nozzle. The atomization and drift characteristics of fan-shaped pressure nozzles were studied at a spraying height of 0.6 m and a lateral wind speed of 0–6 m/s through a combination of computational fluid dynamics (CFD) analyses and wind tunnel experiments. The nozzle Lu 120-03 had a spraying pressure of 0.3 MPa. The results show that as the wind speed varies from 0 m/s to 6 m/s, the spray droplet spectrum also changes, and the droplet volume medium diameter increases. The cumulative droplet ratio and droplet spectral width of M oscillate within certain ranges. The amount of spray drift increases at higher wind speeds. The concentration of droplet deposition on the bottom of the wind tunnel gradually spreads downward in the wind direction. The determination coefficient R² of the straight-line fitting of the drift characteristics is 0.982, which is highly consistent with the CFD simulation results. A CFD simulation-assisted wind tunnel test method, which is more convenient and repeatable than traditional field tests, is proposed to analyze the droplet spectrum and drift of Lechler series nozzles. The program can accurately simulate the actual drift and provide theoretical and data support for the optimization of atomization and drift characteristics of several types of flat fan nozzles under different spraying pressures and crosswinds in practical applications. Full article

Single phase β-Si₃N₄ with microcrystals was synthesized via carbothermal reduction-nitridation (CRN) of quartz and carbon coke powder as starting materials. The effects of reaction parameters, i.e., heating temperature, holding time, C/SiO₂ ratio, Fe₂O₃ additive and β-Si₃N₄ seeds on the phase transformation and morphology of products were investigated and discussed. Rather than receiving a mixture of both α- and β- phases of Si₃N₄ in the products, we synthesized powders of β-Si₃N₄ single polymorph in this work. The mechanism for the CRN synthesis of β-Si₃N₄ from quartz and the formation mechanism of Fe₃Si droplets were discussed. We also firstly reported the formation of Fe₃Si Archimedean solids from a CRN process where Fe₂O₃ was introduced as additive. Comparing to the gear-like short columnar morphology observed in samples without β-Si₃N₄ seeding, the addition of β-Si₃N₄ seeds led to an elongated morphology of final products and much finer widths. In addition, the β-Si₃N₄ microcrystals exhibited a violet‒blue spectral emission range, which could be highly valuable for their future potential optoelectronic applications. Full article

Cloud droplet size distribution (CDSD) is a critical characteristic for a number of processes related to clouds, considering that cloud droplets are formed in different sizes above the cloud-base. This paper analyzes the in-situ aircraft measurements of CDSDs and aerosol concentration ( $N_a$ ) performed in stratiform clouds in Hebei, China, in 2015 to reveal the characteristics of cloud spectral width, commonly known as relative dispersion ( $\epsilon$ , ratio of standard deviation (σ) to mean radius (r) of the CDSD). A new algorithm is developed to calculate the contributions of droplets of different sizes to $\epsilon$ . It is found that small droplets with the size range of 1 to 5.5 μm and medium droplets with the size range of 5.5 to 10 μm are the major contributors to ε, and the medium droplets generally dominate the change of ε. The variation of $\epsilon$ with $N_a$ can be well explained by comparing the normalized changes of $\sigma$ and $r$ ( $k_{\sigma }/\sigma$ and $k_r/r$ ), rather than $k_{\sigma }$ and $k_r$ only ( $k_{\sigma }$ is Δσ/Δ $N_a$ and $k_r$ is Δr/Δ $N_a$ ). From the perspective of external factors affecting $\epsilon$ change, the effects of $N_a$ and condensation are examined. It is found that $\epsilon$ increases initially and decreases afterward as $N_a$ increases, and “condensational broadening” occurs up to 1 km above cloud-base, potentially providing observational evidence for recent numerical simulations in the literature. Full article