共查询到20条相似文献,搜索用时 46 毫秒
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The work presents calculation of Ag2 dimers emission from the substrate into the vapor medium in case of joint deposition of silver and water vapors on ideal substrate formally modeling the crystal of water ice in terms of energy properties. It is assumed that the dimers are formed on the condensation surface as a result of random collisions of atoms at their surface migration, and the dimers emission is conditioned by thermal fluctuations of crystal lattice of water ice. The calculations based on the modified Langmuir adsorption model allowed concluding that emission of silver and water dimers takes place in the entire range of the studied water vapor pressure, binding energy of silver-water, and crystal temperature. Dynamics of emission from the beginning of deposition and dependence of dimers emission on micro-roughness of the condensate surface have been investigated. Statistical processing of results has shown that the probability of dimers emission from the condensate surface is determined not only by the value of the binding energy between the dimer and condensate but by configuration of the nearest dimer environment on the condensation surface. It has been found that there is a certain value of micro-roughness of condensation surface providing the maximal intensity of dimer emission. Dimers emission from the surfaces bordering on the flows of vapor mixtures contaminates the flows with unsuspected admixtures. The latter one makes investigation of this phenomenon important for aeromechanics of vapor and gas mixtures. 相似文献
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Heat transfer with vapor condensation inside a longitudinally finned tube is numerically studied. The proposed model considers vapor condensation on two initial flow areas, namely, annular and rivulet. The model allows prediction of pressure difference along the tube length, vapor velocity profiles in the central channel and an interfin groove, and also a velocity profile in the condensate rivulet at the bottom of the interfin channel, local heat transfer coefficients at different fin points, and average heat transfer coefficients over tube section and length. The calculations showed that in the case of vapor condensation in longitudinally finned tubes of a small diameter it is of fundamental importance to divide the flow tube section into a central channel and interfin channels. The governing vapor velocities in these channels may differ by more than an order of magnitude. The reduced vapor velocity, used in engineering calculations, does not reflect the character of dynamic vapor impact on a condensate film on the most part of the heat transfer surface. For tubes with relatively large fins the proposed model describes vapor condensation almost completely,meanwhile, the mass vapor quality by the time of filling of the grooves reaches 0.01–0.05. The highest heat transfer intensification was obtained for “sharp fins” with a high value of the fin head curvature. Comparison of results of calculation by the model with results of the known experiments on water vapor condensation yields a good qualitative and quantitative agreement for low vapor velocities at the channel inlet (under 30 m/s). The wall thermal conductivity coefficient value affects significantly the condensation efficiency. 相似文献
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G. V. Benemanskaya A. I. Besyul’kin M. S. Dunaevskii A. K. Kryzhanovskii N. M. Shmidt 《Physics of the Solid State》2003,45(6):1026-1029
Thermal stability of GaN epilayers grown through metal-organic compound vapor deposition on a (0001) sapphire substrate was studied using atomic-force spectroscopy. Samples differing in quality were thermally annealed in ultrahigh vacuum in the range 700–950°C. Mosaic spread in the epitaxial layers is shown to strongly affect their thermal stability. Epilayers with a well-ordered mosaic structure exhibit surface degradation at a temperature of ~950°C. The surface morphology of layers with a large mosaic spread starts to change at lower temperatures, ~780°C. 相似文献
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V. V. Poplavsky A. V. Dorozhko V. G. Matys 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2016,10(5):981-988
Layers formed by the ion-beam-assisted deposition of cadmium, zinc, and aluminum onto the surface of carbon and stainless steels to protect aluminum and its alloys from corrosion in the case of their contact with steel parts are investigated. The protective layers are created via ion-beam-assisted deposition, in which metal deposition and mixing of the deposited layer with the substrate surface (this process is implemented by accelerated (U = 5 kV) ions of the same metal) occurs, respectively, from a neutral vapor fraction and the vacuum arc plasma of a pulsed electric-arc ion source. The morphology and composition of the generated surface layers are studied by means of scanning electron microscopy, electron-probe microanalysis, and Rutherford backscattering spectrometry. The layer composition is revealed to include atoms of the deposited metal, the substrate material, oxygen, and carbon. The layer thickness varies from ~50 to 80 nm, and the deposited metal content of the layers is ~(1.0–3.5) × 1017 atom/cm2. Corrosion tests of the aluminum and its alloy in contact with the materials under study confirm the efficiency of the ion-beam modification of steel surfaces. 相似文献
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A. V. Sobolev 《Thermophysics and Aeromechanics》2012,19(2):267-277
The calculation procedure of the ejector with water-vapor condensation in primary nozzle and in converging chamber is presented. Calculations are performed in a wide range of temperatures of primary and secondary gases. The differences are identified in the properties of gas- and vapor-driven ejectors. Limiting mass rates ratios of gas ejectors are reached by primary temperature increase, but the highest performance of vapor-driven ejectors is realized with the use of saturated vapor. 相似文献
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膜蒸馏过程中的膜内冷凝现象是该技术在实际应用中不可忽视的一个重要问题。本文以疏水化改性处理的纤维膜作为研究对象,采用实验现象观察和理论分析并用的方法,研究了纤维膜在膜蒸馏过程发生膜内毛细管冷凝的影响因素包括膜蒸馏模块结构、蒸馏膜参数、热力学参数,探讨了毛细冷凝对膜蒸馏的影响。实验表明毛细冷凝可以在膜蒸馏过程中发生,但并不终止膜蒸馏过程,而是减小了传质系数。毛细冷凝容易发生在蒸馏膜厚度小、热料液温度高、冷却液温度低或气隙小的情况下。实验结果和理论分析表明,传质系数实验值的降低可作为膜孔内发生毛细冷凝的判定依据。通过简化蒸气在疏水多孔介质的传递过程,建立了膜蒸馏过程发生毛细冷凝时的传质平衡模型。 相似文献
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S. V. Shevkunov 《Journal of Experimental and Theoretical Physics》2008,107(6):965-983
Monte Carlo simulations of water vapor nucleation on a perfect crystal surface and on a surface with defects are performed. Mass exchange with the vapor phase is modeled by using an open ensemble. Cluster-substrate interaction is described in terms of conventional atom-atom potentials. The Hamiltonian of the system includes expressions for electrostatic, polarization, exchange, and dispersion interactions. The Gibbs free energy and work of adsorption are calculated by Monte Carlo simulation in the bicano?nical ensemble. The microscopic structure of nuclei is analyzed in terms of pair correlation functions. Periodic boundary conditions are used to simulate an infinite substrate surface. Molecule-substrate and molecule-molecule long-range electrostatic interactions are calculated by summing the Fourier harmonics of the electrostatic potential. Dispersion interactions are calculated by direct summation over layers of unit cells. Nucleation on a surface with matching structure follows a layer-by-layer mechanism. The work of adsorption per molecule of a monolayer on the substrate surface has a maximum as a function of nucleus size. The steady rate of nucleation of islands of supercritical size is evaluated. The work of adsorption per molecule for layer-by-layer film growth is an oscillating function of cluster size. As a function of layer number, it has a minimum depending on the vapor pressure. The electric field generated by a microscopic surface protrusion destroys the layered structure of the condensate and eliminates free-energy nucleation barriers. However, point lattice defects do not stimulate explosive nucleation. 相似文献
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Ultra-thin and near-fully relaxed SiCe substrate is fabricated using a modified Ce condensation technique, and then a 25-nm-thiek biaxially tensile strained-Si with a low rms roughness is epitaxially deposited on a SiGe- on-Insulator (SGOI) substrate by ultra high vacuum chemical vapor deposition (UHVCVD). High-Resolution cross-sectional transmission electron microscope (HR-XTEM) observations reveal that the strained-Si/SiGe layer is dislocation-free and the atoms at the interface are well aligned. Furthermore, secondary ion mass spectrometry (SIMS) results show a sharp interface between layers and a uniform distribution of Ge in the SiCe layer. One percent in-plane tensile strain in the strained-Si layer is confirmed by ultraviolet (UV) Raman spectra, and the stress maintained even after a 30-s rapid thermal annealing (RTA) process at 1000℃. According to those results, devices based on strained-Si are expected to have a better performance than the conventional ones. 相似文献
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Thin films of the perylene derivative N,N′-dimethylperylene-3,4,9,10-bis-dicarboximide (MePTCDI) incorporated in SiO2 matrix at various concentrations are obtained by condensation of host and dye in high vacuum. Photoluminescence spectroscopy is applied to study the spectral properties of the layers. Significant alterations in luminescence spectra in dependence on dye quantity are explained as a consequence of dye aggregation and resonant energy transfer. We demonstrate that the deposition geometry and preparation conditions offer an effective way to reduce the possibilities for non-radiative transitions, thus increasing the photoluminescence quantum efficiency. 相似文献
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Haleh Kangarlou Arash Abdollahi Maryam Motallebi Aghgonbad 《Optics and Spectroscopy》2012,113(3):321-326
Zinc sulfide nano layers were deposited on glass substrates at 300 K by physical vapor deposition method, under high vacuum conditions and different deposition angles. Thickness of the layers were measured 73 nm, by quartz crystal method. Optical reflectance and transmittance of the layers were measured in the wave length of 300?C1100 nm. Optical constants were calculated by Kramers-Kronig relations. The influence of deposition angle in optical properties of ZnS nano layers are investigated. By using Generalized Gradient Approximations in context of plane wave pseudo-potentials (norm conserving and Ultrasoft) and full-potential linearized augmented plane wave methods, Band structure calculated and compared with experimental results. Possible energy transitions are also reported. 相似文献
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N. Yu. Bykov 《Thermophysics and Aeromechanics》2009,16(2):177-187
The mathematical model of water vapor condensation was developed for the direct simulation Monte Carlo method. This model
describes a chain of reactions providing formation and decay of water clusters with consideration of accompanying energy transfer
processes. One-dimensional expansion of water vapor into vacuum from an evaporating spherical surface was studied numerically
within the range of parameters, corresponding to the flows transitional by the Knudsen number. The influence of condensation
on the gas-dynamic pattern of the flow, including the parameters of the Knudsen layer, is discussed.
The work was financially supported by the Russian Foundation for Basic Research (Grant No. 07-01-00354-a). 相似文献
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Titanium layers with different thicknesses of 21, 83.7, and 133 nm and same other deposition conditions were deposited on glass substrates at 300 K, by physical vapor deposition method under high vacuum conditions. The optical reflectance of the layers was measured in the wave length range of 400–800 nm. The optical properties were calculated by using Kramers-Kronig relations. Relation between the optical properties and nanostructure of the layers was investigated. By using Generalized Gradient Approximations in context of plane wave pseudopotentials (norm conserving and ultrasoft) method, band structure calculated and compared with experimental results. 相似文献
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A. A. Velichko V. A. Ilyushin N. I. Filimonova A. V. Katsyuba 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2013,7(3):488-492
The influence of the surface microroughness of Si(001) substrates on the morphology of CaF2 epitaxial layers is investigated in the high-temperature growth mode. The atomic-force microscopy method is used to demonstrate that the silicon surface relief substantially affects the nucleation, growth, and formation of the morphology of CaF2 layers. 相似文献