Papers by Keyword: Evaporation

Abstract: This paper presents the results of mathematical modelling of three–dimensional heat transfer in a closed two-phase thermosyphon taking into account phase transitions. Three-dimensional conduction equation was solved by means of the finite difference method (FDM). Locally one-dimensional scheme of Samarskiy was used to approximate the differential equations. The effect of the thermosyphon height and temperature of its bottom lid on the temperature difference in the vapor section was shown.

Abstract: Because of the different melting point, it is difficult to doped Ag element in ZnO film. Ag dopant can adjust the properties of ZnO materials. In this paper, we deposited Ag doped ZnO film using two step vapour evaporation method on c-plane sapphire substrate. The SEM image shows that the doped film was composed of small grain which compact in order and the Ag microwires was dispersed on the surface. The EDX graph proves that the Ag was indeed in the film. The XRD pattern reveals that the doped film has prefer orientation along the c-axis with wurtzite structure and the dopants have not effect the crystal quality.

Abstract: High-temperature heat shock is caused by pouring a liquid alloy (cast iron in this case) into cavity of a wet sand mould. In the mould material, thermal-chemical-physical phenomena of very high intensity occur. These phenomena are important in metal alloys casting only insofar as they influence quality of a casting (dynamics od solidification and casting’s structure, gas and shrinkage defects). This quality can be forecasted using simulation codes dedicated for the foundry branch. The most important phenomena are subject of hard and/or soft modeling. Heat transfer from a casting to a mould is related to simultaneous mass transfer. This coupling of phenomena is differently interpreted by creators of simulation codes and introduced to algorithms solved numerically. The paper presents an example of simplified modeling of phenomena of thermal influence of a wet mould sand on solidification of a test cast iron casting, with use of selected foundry simulation codes.

Abstract: In the influence of the atmosphere,the soil of the subgrade would frequently in continuous humidification and dehumidifying situation, and it will result in large variation of the engineering properties of the subgrade. So, it is important to study the water migration in subgrade under the influence of the climate. In this paper, based on moisture and heat coupling thermal, non isothermal equation of unsaturated soil are introduced, the subgrade evaporation model are established. The theoretical analysis and numerical calculation of the subgrade moisture changes and its influence factors under the effect of the atmosphere are studied. The study results show that: solar intensity are the most important factors to the subgade moisture, the solar radiation makes the temperature of the pavement rising, the evaporation of the pavement would be speed up. In the wet and dry cycle process, as the rainfall intensity is small, it has little effect to the subgrade moisture, in the same rainfall duration conditions, although the evaporation duration is the same, the subgrade moisture still changes with the rainfall intensity, the larger the rainfall, the more changes of the subgrade moisture. Little intensity and long duration rainfall pattern affect the subgrade moisture more intensity than that of large intensity and short duration rainfall pattern.

Abstract: The problem presented in the paper concerns physical properties of porous multi-component mould material, into which a liquid metal is poured. The aim of the study was to determine the distribution of moisture in an intensively heated porous sand mould. In the past, several measuring methods have been developed, consisting in water evaporation out of a test sample (at a given time moment , the selected position coordinates of a sample), to determine the accumulated amount of water in the sample, which is a percentage of moisture content. The study described in the paper includes experiments of heating a green sand sample. Moisture distribution in a moisture transfer zone of the sample (temperature of the molding sand is approx. 100°C) was determined. In order to determine the moisture distribution, an original method was used. This method allows interfere in various layers of material of predetermined thickness, parallel to the surface of the mould in contact with a heat source. The classical measurement method (gravimetric method) was used for determining the moisture content of each layer.

Abstract: Determination of the surface temperature in order to evaluate the risk of mould growth is currently already a common task. Good knowledge of boundary conditions is necessary for precise evaluation of this risk. Standardized requirements are suitable for a preliminary design and a general comparison of various assembly details, as they help us understand how these details will work (in defined boundary conditions). But the real user behaviour varies greatly and is not always in agreement with the standardized requirements. Air humidity is one of the parameters which significantly influence the mould growth. It varies depending on the use of the building and especially on the number of moisture (humidity) sources. To determine the production of moisture by different sources we built an vaporization climatic chamber, where we monitor the production of moisture in dependence on relative air humidity and air temperature.

Abstract: Nanostructure TiO₂ films were prepared by electron beam evaporation with glancing angle deposition technique at room temperature. The morphology, crystal structure and optical properties at various substrate rotation speeds (0-10 rpm) were investigated by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and UV-vis spectrophotometer. The cross-section FE-SEM images illustrate that the nanostructures consist of different morphology: slanted columnar, spiral and vertical align nanorods at 0, 0.01 and 10 rpm-rotation speed, respectively. In particular, the rotation speed-controlled incoming vapor flux was found to play crucial role in the growth of nanostructure TiO₂ films.

Abstract: Indium doped tin oxide (ITO) thin films were deposited on silicon wafer (100) and glass slide by ion assisted electron beam evaporation deposition. After deposition, the ITO thin films were annealed in vacuum (100-300°C) and their structural, optical and electrical properties were systematically investigated. X-ray diffraction,atomic force microscopy, ultraviolet–visible (UV–vis) spectrophotometer and hall-effect measurement were employed to obtain information on the crystallization, transmission and resistivity the films.It was found that the rapid thermal annealing can improve the resistivity of ITO thin films which specializes for the transparent conductive layers.

Abstract: The influence of the laser-beam radial distribution of the energy flux density is theoretically studied for the Gaussian distribution (mode TEM₀₀), and doughnut distribution of TEM_01* mode for the values of the Peclet number from 0 to 3. The model of linear thermal conduction in the target indicates that profile TEM₀₀ is the best for thermo-activated treatment processes that can be accomplished in a wide temperature range and profile TEM_01* can be advantageous for a narrow range of the permissible processing temperature. If the phase transitions of melting/solidification and evaporation are included into the model, the estimate of the width of the laser-treated band is reduced but the tendencies predicted by the linear model are not changed.

Abstract: Reducing the carbon concentration in Czochralski (CZ) silicon crystals is crucial in order to improve the properties of high-power devices, such as on-resistance and carrier lifetime. To achieve carbon concentration reduction, it is necessary to reduce carbon monoxide (CO) contamination from the CZ furnace graphite components and to remove the carbon impurities originating from the starting material. In this study, suppressing the chemical reaction between silicon monoxide (SiO) and the graphite heater effectively reduced the CO contamination rate. Furthermore, we attempted to promote CO evaporation during the CZ process in order to remove carbon impurities from the melt. Increasing the Ar gas flow velocity above the melt surface was found to be effective in increasing the CO evaporation rate during both the melting and growth processes. The CO evaporation rate during the melting process of 8-inch CZ silicon was calculated as being of the order of 10^-2 μg/s. Owing to the effects of the CO evaporation, 8-inch CZ silicon crystals with carbon concentrations lower than 2.0 × 10¹⁴ atoms/cm³ at a solidified fraction of 0.85 were grown.