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排序方式: 共有303条查询结果,搜索用时 672 毫秒
31.
Jrme O. Cosandey Axel Günther Philipp Rudolf von Rohr 《Experimental Thermal and Fluid Science》2003,27(8):877-889
The entrainment of soluble (KI, CsI) and non-soluble (Al2O3) substances through droplets, which are produced by disintegrating steam bubbles at the surface of a boiling water pool, is determined in a pilot-scale facility. Integral measurements are conducted at steady-state conditions in an atmosphere of either pure steam or an air–steam mixture. The ratio of the entrained liquid mass flow and the gas mass flow through the pool, the entrainment factor, is determined for air–steam ratios between 0 and 0.47 kg/kg in the gas atmosphere and at constant total pressures between 2 and 6 bar. The influence of the vertical temperature profile in the gas atmosphere on the convective velocity field is demonstrated by phase Doppler anemometry and particle image velocimetry measurements at a location 2.1 m above the pool surface. The influences of nucleation and natural convection are demonstrated during slow de-pressurization of the facility at rates below 420 Pa/s. 相似文献
32.
Highly concentrated oil-in-water (o/w) emulsion stabilised by means of gluten and soya protein isolate (SPI) at low pH have
been characterized by means of linear dynamic viscoelasticity and droplet size distribution analysis (DSD). The microstructure
of these emulsions has been characterized at a colloidal level by using confocal laser scanning microscopy (CLSM) and light
microscopy (LM). These emulsions always exhibited a behaviour characteristic of highly flocculated emulsions with a mechanical
spectrum showing a well-developed plateau region. DSD results generally showed log normal bimodal profiles. Microstructure
images revealed occurrence of a close packing of droplets with a broad distribution of sizes participating in the formation
of a three dimensional flocculated network. The Mason model of elasticity of compressed emulsions has been used to correlate
viscoelastic and microstructural parameters giving adequate fitting but underestimating the elastic properties obtained for
the highest concentration of gluten. These deviations may be explained in terms of an enhancement of the elastic network formed
in the aqueous phase in which the glutenin fraction must play an important role.
Paper presented at the Annual European Rheology Conference (AERC) 2005, April 21-23, Grenoble, France. 相似文献
33.
Alexander?Y.?MalkinEmail author Irina?Masalova Paul?Slatter Keith?Wilson 《Rheologica Acta》2004,43(6):584-591
Rheological properties of highly concentrated emulsions of the water-in-oil type were studied. Water phase (concentration approximately 91%) consists of a supersaturated aqueous solution of nitrate salts; water comprises less than 20% by mass. The average size of droplets, D, in the emulsions was varied. It was found that the emulsions are non-Newtonian liquids and flow curves measured in a sweep regime of shearing have clear low-shear-rate Newtonian domain. The complete flow curves are fitted by the Cross equation. The elastic modulus is practically constant in a very wide frequency range. Hence the viscoelastic relaxation processes might be expected at times >>100 s and in the short-term side of the curve at approximately 0.01 s. The elastic modulus (measured in oscillating testing and in elastic recovery as well) is proportional to D-2 while the Newtonian viscosity is proportional to D–1.The time effects were observed: it was found that the emulsions behave as rheopectic materials because prolonged shearing results in an increase of viscosity in the low shear rate domain of several orders of magnitude.Presented in part at the First Annual European Rheological Conference, Guimarães, Portugal, 11–13 September 2003 相似文献
34.
One of the key design parameters in liquid/liquid extraction is the mass transfer coefficient. A complex list of parameters including fluid dynamics, drop size distribution, chemical properties of the involved species, local interfacial instabilities (Marangoni convection) is required in order to determine the transient evolution of the mass transfer coefficient. The influence of Marangoni convection on single drop mass transfer cannot yet be described in an analytical manner, and empirical correlations available in literature fail to predict the mass transfer process. In the present study, experimental investigations on deformable single droplets in the toluene/acetone/water system are presented which shows strong interfacial instabilities. Parameters varied are the drop diameter, the initial solute concentration and the mass transfer direction. Experimental results are compared with the well-known models by Kronig and Brink and Handlos and Baron. The Kronig and Brink model cannot describe Marangoni dominated systems, but comparisons reveal the influence of deformation on the mass transfer enhancement. In contrary, with a slight modification to the Handlos and Baron model, the mean droplet concentration of the transferred component was successfully modelled as a function of Fourier number. 相似文献
35.
Improved numerical methods and physical models have been applied to droplet collision modeling. Numerically, an adaptive collision mesh method is developed to calculate collision rate. This method produces a collision mesh that is independent of the gas phase mesh and adaptively refined according to local parcel number density. An existing model describing the satellite droplet formation during the collision process is improved to reflect the experimental findings that the satellite droplets are much smaller than the parent droplets. The adaptive collision mesh and the improved satellite model have been used to simulate three impinging spray experiments. The model was able to qualitatively predict the occurrence of small satellite drops and bi-modal post-collision drop size distributions. The effect of the collision mesh and the satellite droplet model on a high-speed non-evaporating diesel spray is also assessed. 相似文献
36.
Osamu Moriue Masato Mikami Naoya Kojima Christian Eigenbrod 《Proceedings of the Combustion Institute》2005,30(2):1973-1980
Spontaneous ignition of single n-heptane droplets in a constant volume filled with air is numerically simulated with the spherical symmetry. The volume is closed against mass, species, and energy transfer. The numerical model is fully transient. It continues calculation even after the droplet has completely vaporized, and therefore can predict pre-vaporized ignition. Initial pressure and initial air temperature are fixed at 3 MPa and 773 K, respectively. The droplet is initially at room temperature, and its diameter is between 1 and 100 μm. When the overall equivalence ratio is fixed to be sufficiently large, there exists no ignition limit in terms of initial droplet diameter d0, and the ignition delay takes a minimum value at certain d0. In such a case, transition from the heterogeneous ignition to the homogeneous ignition with decreasing d0 is observed. When d0 is fixed to be so small that the ignition would not occur in an infinite volume of air, the ignition delay takes a minimum value at certain , which is less than unity. Two-stage ignition behavior is investigated with this model. Ignition delay of a cool flame has the dependence on d0 that is similar to that of ignition delay of a hot flame when is unity. When is almost zero, the ignition limit for cool flame in terms of d0 is not identified unlike that for hot flame. 相似文献
37.
Á. Nemcsics L. Tóth L. Dobos Ch. Heyn A. Stemmann A. Schramm H. Welsch W. Hansen 《Superlattices and Microstructures》2010
Self-assembled strain-free quantum dot (QD) structures were grown on AlGaAs surface by the droplet epitaxal method. The QDs were developed from pure Ga droplets under As pressure. The QDs were investigated by atomic force microscopy (AFM) and transmission electron microscopy (TEM). Both techniques show that the QDs are very uniform in size and their distribution on the surface is also homogeneous. The high resolution cross-sectional TEM investigation shows perfect lattice matching between the QD and the substrate, and also the faceting of the side walls of QD can be identified exactly by lattice planes. Analytical TEM (elemental mapping by EELS) unambiguously identifies the presence of Al in the QD. 相似文献
38.
Using lattice Boltzmann approach, a phase-field model is proposed for simulating droplet motion with soluble surfactants. The model can recover the Langmuir and Frumkin adsorption isotherms in equilibrium. From the equilibrium equation of state, we can determine the interfacial tension lowering scale according to the interface surfactant concentration. The model is able to capture short-time and long-time adsorption dynamics of surfactants. We apply the model to examine the effect of soluble surfactants on droplet deformation, breakup and coalescence. The increase of surfactant concentration and attractive lateral interaction can enhance droplet deformation, promote droplet breakup, and inhibit droplet coalescence. We also demonstrate that the Marangoni stresses can reduce the interface mobility and slow down the film drainage process, thus acting as an additional repulsive force to prevent the droplet coalescence. 相似文献
39.
Magnetic digital microfluidics uses magnetic force to manipulate droplets on a Teflon‐coated substrate through the added magnetic particles. To achieve a wide range of droplet manipulation, hydrophilic patterns, known as surface energy traps, are introduced onto the Teflon‐coated hydrophobic substrate. However, the Teflon‐coated substrate is difficult to modify because it is nonwettable, and existing techniques for patterning surface energy traps have many limitations. Inspired by the mussel adhesion mechanism, we use polydopamine, a bioinspired substance that adheres strongly to almost any materials, to pattern surface energy traps on the Teflon‐coated substrate with a great ease. We have optimized the polydopamine coating protocol and characterized the surface properties of the polydopamine surface energy traps. Droplet operations including particle extraction, liquid dispensing, liquid shaping, and cross‐platform transfer have been demonstrated on the polydopamine surface energy trap‐enabled magnetic digital microfluidic platform in both single‐plate and two‐plate configurations. Furthermore, the detection of hepatitis B surface antigen using ELISA has been demonstrated on the new magnetic dgitial microfluidic platform. This new bioinspired magnetic digital microfluidic platform is easy to fabricate and operate, showing a great potential for point‐of‐care applications. 相似文献
40.
A novel microfluidic droplet generator is proposed, which can control the droplet size through turning an integrated micrometer head with ease, and the size of the produced micro-droplet can be automatically and real-time monitored by an open-sourced software and off-the-shelf hardware. 相似文献