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1.
Due to the high surface tension and high conductivity, water is unsuitable for electrohydrodynamic (EHD) atomization using a DC electric field in air. The high local electric field, that is required to atomize water, is likely to generate corona discharge and consequently destabilize the atomization process. This study describes a novel low voltage EHD spray nozzle that can be used to atomize water and weak saline solutions in the stable cone jet mode. The properties of the atomization have been investigated together with the generated droplet size distribution. The nozzle operates at very low flow rates (0.5–4.0 μl/min). Due to the high dielectric constant of water and the low flow rate, the atomization takes place outside the applicability range of the scaling laws. The experimental results show that the droplet size is approximately constant when the flow rate is increased from 0.5 to 4.0 μl/min. The atomization of water was numerically simulated using computational fluid dynamics (CFD). The simulation results agree reasonably well with the experimental results with respect to the liquid cone shape and droplet size.  相似文献   

2.
An electrohydrodynamic (EHD) atomization from a point-to-plate system, with a wet porous point as a corona electrode, has been studied. And the atomized water droplets from the wet porous point, as well as the water droplet traces, the water droplet charge-to-mass ratios, and the water droplet number concentrations, were investigated. It was observed that the wet porous point can atomize abundant amounts of water droplet, 2.8, 2.6 and 2.2 mg/min for negative, AC and positive corona, respectively. The migrated water droplet traces were observed. The positive wet porous point atomized very fine water droplets than those obtained with the negative wet porous point. Moreover, the water droplets atomized from the AC corona showed granular-like larger traces. A weak corona discharge can atomize water droplets very effectively. On the other hand, an intensive corona discharge can eject more water droplets. As a result with the wet porous point, the maximum corona-current-based and corona-power-based water droplet atomization yields of YC = 3.34, 3.32 and 3.25 μg/μAs and YP = 0.35, 0.40 and 0.27 mg/Ws have been obtained for the negative, AC and positive corona discharges.  相似文献   

3.
《Ultrasonics sonochemistry》2014,21(6):2032-2036
Aqueous suspensions containing silica or polystyrene latex were ultrasonically atomized for separating particles of a specific size. With the help of a fog involving fine liquid droplets with a narrow size distribution, submicron particles in a limited size-range were successfully separated from suspensions. Performance of the separation was characterized by analyzing the size and the concentration of collected particles with a high resolution method. Irradiation of 2.4 MHz ultrasound to sample suspensions allowed the separation of particles of specific size from 90 to 320 nm without regarding the type of material. Addition of a small amount of nonionic surfactant, PONPE20 to SiO2 suspensions enhanced the collection of finer particles, and achieved a remarkable increase in the number of collected particles. Degassing of the sample suspension resulted in eliminating the separation performance. Dissolved air in suspensions plays an important role in this separation.  相似文献   

4.
Ultrasonication may be a cost-effective emulsion formation technique, but its impact on emulsion final structure and droplet size needs to be further investigated. Olive oil emulsions (20 wt%) were formulated (pH  7) using whey protein (3 wt%), three kinds of hydrocolloids (0.1–0.5 wt%) and two different emulsification energy inputs (single- and two-stage, methods A and B, respectively). Formula and energy input effects on emulsion performance are discussed. Emulsions stability was evaluated over a 10-day storage period at 5 °C recording the turbidity profiles of the emulsions. Optical micrographs, droplet size and viscosity values were also obtained. A differential scanning calorimetric (DSC) multiple cool–heat cyclic method (40 to ?40 °C) was performed to examine stability via crystallization phenomena of the dispersed phase.Ultrasonication energy input duplication from 11 kJ to 25 kJ (method B) resulted in stable emulsions production (reduction of back scattering values, dBS  1% after 10 days of storage) at 0.5 wt% concentration of any of the stabilizers used. At lower gum amount samples became unstable due to depletion flocculation phenomena, regardless of emulsification energy input used. High energy input during ultrasonic emulsification also resulted in sub-micron oil-droplets emulsions (D50 = 0.615 μm compared to D50 = 1.3 μm using method A) with narrower particle size distribution and in viscosity reduction.DSC experiments revealed no presence of bulk oil formation, suggesting stability for XG 0.5 wt% emulsions prepared by both methods. Reduced enthalpy values found when method B was applied suggesting structural modifications produced by extensive ultrasonication. Change of ultrasonication conditions results in significant changes of oil droplet size and stability of the produced emulsions.  相似文献   

5.
A laboratory electrostatic precipitator (ESP) together with a bipolar pre-charger has been designed for studying charge-induced agglomeration and fine particle collection. In terms of particle numbers, the ESP collection efficiency drops to its minimum of near 90% for particles with diameters of near 0.2 μm and 3 μm. For other particles, its value is around 94%–95%. By using the bipolar pre-charger, the grade efficiency can be significantly increased for all particle sizes due to the charge-induced particle agglomeration. The grade collection efficiency rises to about 95%–98% for all size particles.  相似文献   

6.
The use of emulsifying methods is frequently required before spray drying food ingredients, where using high concentration of solids increases the drying process yield. In this work, we used ultrasound to obtain kinetically stable palm oil-in-water emulsions with 30 g solids/100 g of emulsion. Sodium caseinate, maltodextrin and dried glucose syrup were used as stabilizing agents. Sonication time of 3, 7 and 11 min were evaluated at power of 72, 105 and 148 W (which represents 50%, 75% and 100% of power amplitude in relation to the nominal power of the equipment). Energy density required for each assay was calculated. Emulsions were characterized for droplets mean diameter and size distribution, optical microscopy, confocal microscopy, ζ-potential, creaming index (CI) and rheological behavior. Emulsions presented bimodal size distribution, with D[3,2] ranging from 0.7 to 1.4 μm and CI between 5% and 12%, being these parameters inversely proportional to sonication time and power, but with a visual kinetically stabilization after the treatment at 148 W at 7 min sonication. D[3,2] showed to depend of energy density as a power function. Sonication presented as an effective method to be integrated to spray drying when emulsification is needed before the drying process.  相似文献   

7.
In this work, the effect of PZT particle size on the properties of PZT–PC composites was investigated. PZT of various median particle sizes (3.8–620 μm) were used at 50% by volume to produce the composites. The results showed that the dielectric properties of the composites increased marginally with PZT particle size where εr = 176 and 167 for composites with 620 μm and 3.8 μm PZT particle size, respectively. A noticeable increase in d33 values was also found when the particle size was increased where the composite with 620 μm PZT particles size was found to have d33 value of 26 pC/N compared to 17 pC/N for the composite with 3.8 μm PZT particle size. The enhancement in the dielectric and piezoelectric properties was contributed to lesser contacting surfaces between the cement matrix and the PZT particles.  相似文献   

8.
Polycrystalline MgB2 films of different thickness have been prepared by employing spray pyrolysis technique on MgO (1 0 0) substrate. The MgB2 and other phases have been confirmed using X-ray diffraction technique and no trace of impurities phases have been found. The resistivity behavior shows that the superconducting transition temperature lies in the range of 37–39 K with narrow transition width. The transport critical current density vary with films thickness and achieved highest value ~1.2 × 106 A/cm2 at 20 K for 2.0 μm thick film and its values increase as thickness increases.  相似文献   

9.
Synthesis of scorodite (FeAsO4·2H2O) using dynamic action agglomeration and the oxidation effect from ultrasound irradiation was investigated. The effect of different reaction temperatures (90, 70, 50, and 30 °C) on the size and morphology of scorodite particles synthesized under O2 gas flow and ultrasound irradiation was explored because the generation of fine bubbles depends on the solution temperature. At 90 °C, the size of scorodite particles was non-homogeneous (from fine particles (<1 μm) to large particles (>10 μm)). The oxidation–reduction potential (ORP) and yield at 90 °C showed lower values than those at 70 °C. The scorodite particles, including fine and non-homogeneous particles, were generated by a decrease in the oxidation of Fe(II) to Fe(III) and promotion of dissolution caused by the generation of radicals and jet flow from ultrasound irradiation. Using ultrasound irradiation in the synthesis of scorodite at low temperature (30 °C) resulted in the appearance of scorodite peaks in the X-ray diffraction (XRD) pattern after a reaction time of 3 h. The peaks became more intense with a reaction temperature of 50 °C and crystalline scorodite was obtained. Therefore, ultrasound irradiation can enable the synthesis of scorodite at 30 °C as well as the synthesis of large particles (>10 μm) at higher temperature. Oxide radicals and jet flow generated by ultrasound irradiation contributed significantly to the synthesis and crystal growth of scorodite.  相似文献   

10.
Lead zirconate titanate (PZT) nano-powder was prepared by a triol sol–gel process. X-ray diffraction and transmission electron microscopy results showed that as-synthesized amorphous powder started to crystallize at the calcination temperature above 500 °C. The crystalline powder was formed into pellets and sintered at temperatures between 900 and 1300 °C. Co-existence of tetragonal and rhombohedral phase was observed in all ceramics. Microstructural investigation of PZT ceramics showed that uniform grain size distribution with average grain size of ∼0.8–2.5 μm were received with sintering temperature up to 1200 °C. Further increasing the temperature caused abnormal grain growth with the grain as large as 13.5 μm. An attempt to optimize densification with uniform grain size distribution was also performed by varying heating rate and holding time during sintering. It was found that dense (∼97%) sol–gel derived PZT ceramic with uniform microstructure was achieved at 1100 °C with a heating rate of 5 °C min−1 and 6 h dwell time.  相似文献   

11.
《Optik》2013,124(16):2373-2375
We demonstrate a new device concept for wavelength division demultiplexing based on planar photonic crystal waveguides. The filtering of wavelength channels is realized by shifting the cutoff frequency of the fundamental photonic bandgap mode in consecutive sections of the waveguide. The shift is realized by modifying the size of the border holes.The proposed demultiplexer has an area equal to (16.5 μm × 6.5 μm) and thus it is verified that this structure is very small and can be integrated easily into optical integrated circuits with nanophotonic technologies. The output wavelengths of designed structure can be tuned for communication applications, around 1550 nm. The wavelengths of demultiplexer channels are λ1 = 1.590 μm, λ2 = 1.566 μm, λ3 = 1.525 μm, λ4 = 1.510 μm, λ5 = 1.484 μm, λ6 = 1.450 μm, λ7 = 1.400 μm respectively. Designs offering improvement of number of the separate wavelengths (seven), miniaturization of the structure (107.25 μm2) is our aim in this work.In our structure, we consider that the 2D triangular lattice photonic crystal is composed of air holes surrounded by dielectric. Its parameters are: radius of holes (r = 0.130 μm), lattice constant (a = 0.380 μm), and index of membrane (n = 3.181:InP). The numerical model used to simulate the structure of the demultiplexer is based on the finite difference time domain (FDTD).  相似文献   

12.
The polymorphic forms of lactose in alcoholic suspensions have been determined by 13C CP-MAS NMR spectroscopy, employing hand-made glass inserts. Suspensions of alpha lactose monohydrate (Lα·H2O) with particle size between 2 and 200 μm were prepared by 24 h reflux or by storage for 28 d in anhydrous ethanol without agitation. These suspensions were compared to an ethanolic sub-micron lactose suspension provided by a 3 M Health Care (Loughborough). The 13C CP-MAS NMR spectra indicated that Lα·H2O dehydrated to stable anhydrous alpha lactose polymorph (LαS) whilst suspended in ethanol. In addition, strong ethanol 13C resonances were observed for some samples, indicating a liquid–solid interaction between the ethanol and lactose surface. Replacement of ethanol with anhydrous methanol, n-butanol and 3-methylbutan-2-ol implied that the solvent mediated dehydration of Lα·H2O to LαS occurs as a result of sterically controlled interactions.  相似文献   

13.
Efficiency as high as 26% is obtained for generation of mid-infrared radiation at 6.04 μm by frequency doubling of ammonia laser emission at 12.08 μm in a 15 mm long type-I cut AgGaSe2 crystal. The NH3 laser used for this work is optically pumped by a commercial TEA CO2 laser operating on 9.22 μm and produces pulsed output of ∼210 mJ with a duration of ∼200 ns at 12.08 μm. The generated radiation at 6.04 μm is separated out from the residual radiation at 12.08 μm by exploiting the principle of polarization dependent diffraction of reflection grating.  相似文献   

14.
Pubic concerns related to particulate matter emissions from animal housing operations are increasing. The goal of this study was to custom develop a simple and low cost electrostatic precipitator (ESP) for poultry dust control. The performance of the improved electrostatic precipitator (iESP) to remove a test aerosol was evaluated under a series of operating voltages between ?60 kV and 60 kV. The mass and size distributions of the particles were measured by a cascade impactor. The overall dust removal efficiency ranged from 37% to 79% with the maximum efficiency obtained at ?30 kV. The iESP shows high removal efficiencies for particles less than 2.1 μm.  相似文献   

15.
We have previously reported on the morphological control of calcium carbonate by changing synthetic conditions such as temperature, pH and degree of supersaturation in liquid reaction. The present study reports the effect of amplitude and frequency of ultrasonic irradiation on the particle size of calcium carbonate using a horn type ultrasonic apparatus at two different frequencies. The calcium carbonate precipitated by mechanical stirring had a particle size of about 20 μm. By contrast, the particle size of vaterite formed under ultrasonic irradiation was about 2 μm, with a specific surface area of 25–30 m2/g. The major polymorph of calcium carbonate formed by ultrasonic irradiation was vaterite with some calcite present. For 40 kHz ultrasonic irradiation, the specific surface area of the calcium carbonate increased with increasing amplitude. The particle size of vaterite formed at this frequency was about 2 μm, and its distribution was sharper than that obtained at 20 kHz. The mode diameter of the synthesized vaterite was found to decrease with increasing amplitude at 40 kHz.  相似文献   

16.
A 3C-silicon carbide (SiC) thin film grown on a Si(1 0 0) surface using an ethylene (C2H4) molecular beam has been studied by atomic force microscopy. At the center of the irradiation area of the ethylene beam, the shape of the SiC islands was rectangular, the average length of which was 74.5 nm and the average height was 13.1 nm. Each SiC island consists of the SiC particles with the average diameter of 17 nm. Just inside of the boundary region of the beam irradiation, the average size and height of the islands decreased to 50.1 and 8.2 nm, respectively. Just outside of the boundary region, the average size and height decreased to 17.7 and 5.1 nm, respectively. The average reaction probabilities at the above three points were estimated to be 0.14, 0.27 and 2.7%, respectively. New growth mode of the crystal growth is proposed (particles gathering island mode).  相似文献   

17.
Zirconia (ZrO2) nanostructures of various sizes have been synthesized using sol–gel method followed by calcination of the samples from 500 to 700 °C. The calcined ZrO2 powder samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infra-red spectroscopy (FT-IR), UV–visible spectroscopy (UV–vis.), Raman spectroscopy (RS) and thermogravimetric analysis (TGA). The phase transformation from tetragonal (t) to monoclinic (m) was observed. The average diameter of the ZrO2 nanostructures calcined at 500, 600 and 700 °C was calculated to be 8, 17 and 10 nm, respectively. The ZrO2 sample calcined at 500 °C with tetragonal phase shows a direct optical band gap of 5.1 eV. The value of optical band gap is decreased to 4.3 eV for the ZrO2 calcined at 600 °C, which contains both tetragonal (73%) and monoclinic (27%) phases. On further calcination at 700 °C, where the ZrO2 nanostructures have 36% tetragonal and 64% monoclinic phases, the optical band gap is calculated to be 4.8 eV. The enhancement in optical band gap for ZrO2 calcined at 700 °C may be due to the rod like shape of ZrO2 nanostructures. The tetragonal to monoclinic phase transformation was also confirmed by analyzing Raman spectroscopic data. The TG analysis revealed that the ZrO2 nanostructure with dominance of monoclinic phase is found to be more stable over the tetragonal phase. In order to confirm the phase stability of the two phases of ZrO2, single point energy is calculated corresponding to its monoclinic and tetragonal structures using density functional theory (DFT) calculations. The results obtained by theoretical calculations are in good agreement with the experimental findings.  相似文献   

18.
MMoO4 (M=Ca, Ba) particles were synthesized by a metathetic reaction in ethylene glycol assisted by cyclic microwave irradiation followed by further heat-treatment. The MMoO4 (M=Ca, Ba) particles were well crystallized after heat-treatment at 400–600 °C for 3 h. The microstructures exhibited fine morphologies with sizes of 0.5–1 μm and 1.5–2 μm for the CaMoO4 and BaMoO4 particles, respectively. The synthesized MMoO4 (M=Ca, Ba) particles were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. The optical properties were examined by photoluminescence emission and Raman spectroscopy.  相似文献   

19.
The luminescent properties of phosphors are sensitive to the size of phosphor particles. The commercial Y2SiO5:Tb3+ phosphors usually show relatively larger particle size (5–10 μm) due to the irregular morphology of rare earth oxide precursor and thus degrade the luminescent properties. In this paper, we report the Y2SiO5:Tb3+ phosphors synthesized from the uniform Tb-doped Y2O3 precursor by a homogeneous precipitation method. Compared with the commercial phosphors, the obtained Y2SiO5:Tb3+ phosphors manifest the uniform morphology with much smaller particles distributing from 0.8 μm to 1.9 μm. Consequently, the cathodoluminescent intensity under low excitation voltage (1–5 kV) was increased, demonstrating a strong green emission with a dominant wavelength of 545 nm. Our results indicate an effective way to develop the high-quality phosphors for field emission display.  相似文献   

20.
The motion of a single water droplet in oil under ultrasonic irradiation is investigated with high-speed photography in this paper. First, we described the trajectory of water droplet in oil under ultrasonic irradiation. Results indicate that in acoustic field the motion of water droplet subjected to intermittent positive and negative ultrasonic pressure shows obvious quasi-sinusoidal oscillation. Afterwards, the influence of major parameters on the motion characteristics of water droplet was studied, such as acoustic intensity, ultrasonic frequency, continuous phase viscosity, interfacial tension, and droplet diameter, etc. It is found that when the acoustic intensity and frequency are 4.89 W cm−2 and 20 kHz respectively, which are the critical conditions, the droplet varying from 250 to 300 μm in lower viscous oil has the largest oscillation amplitude and highest oscillation frequency.  相似文献   

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