Extension of the KDO turbulence/transition model to account for roughness

Wall roughness significantly influences both laminar-turbulent transition process and fully developed turbulence. A wall roughness extension for the KDO turbulence/transition model is developed. The roughness effect is introduced via the modification of the k and νt boundary conditions. The wall is considered to be lifted to a higher position. The difference between the original position and the higher position, named as equivalent roughness height, is linked to the actual roughness height. The ratio between the two heights is determined by reasoning. With such a roughness extension, the predictions of the KDO RANS model agree well with the measurements of turbulent boundary layer with a sand grain surface, while the KDO transition model yields accurate cross-flow transition predictions of flow past a 6:1 spheroid.

MODIFICATION OF HEAT-RESISTANT OXIDES AND CHLORIDES OF GRAIN SURFACES OF SYNTHETIC DIAMOND GRINDING POWDERS FOR APPLICATION IN GRINDING TOOLS

Further development of modern technologies of diamond processing is connected with application in the diamond tool of powders with new unique properties, special morphology of grains, with the increased chemical and thermal stability. To increase the heat resistance of diamonds, they are covered with a metal (metallization) or glass-ceramic layer, or introduced into the reaction mixture used in the synthesis of diamonds, alloying additives of certain elements. Recently, other methods of coating to increase the heat resistance of diamonds have been developed, such as: vacuum ion-plasma sputtering, epitaxial synthesis, magnetron sputtering, the method of liquid-phase deposition. The latter method is promising for modifying the grain surface of grinding powders of superhard materials by heat-resistant inorganic non-metallic coatings, as it is the most economically advantageous. Determining the features of the technology of modification by the method of liquid-phase application of heat-resistant inorganic coatings (oxides and chlorides of metals and nonmetals) on the surface of grains of grinding powders of synthetic diamond brand AC6, used for grinding tools in mechanical engineering. Modification was performed by the isothermal method of liquid-phase application of saturated solutions of both heat-resistant oxides (В2О3, Al2O3), chlorides (СаСl2, NaCl, MgCl2, FeCl3), and their mixtures (В2О3+СаСl2, В2О3+NaCl). Based on the analysis of the results of the research, it can be stated that the application of coatings of inorganic substances (some oxides and chlorides) increases the heat resistance of synthetic diamond grinding powders. Modification allows to reduce expenses of diamonds in wheels at grinding. Conditions for modification of heat-resistant oxides and chlorides, as well as their mixtures, grain surface of synthetic diamond grinding powders are determined. Modification of the surface of diamond grains with a combination of B2O3+Al2O3 is guaranteed to double the wear resistance of diamond wheels. It is established that in all cases of modification the roughness of the parameter Ra decreases. It is determined that by changing the surface modifier of diamond grains it is possible to affect the bearing capacity of the rough surface obtained by grinding. The development of effective ways to increase the heat resistance of grinding powders made of superhard materials, primarily abrasive grinding powders made of synthetic diamond powders, helps to improve the quality of the grinding tool.

Assessment of the degradation in mild structural steel using electron backscatter diffraction (EBSD) technique

This paper reports the degradation assessment of mild steel during the plastic tensile process. The electron backscatter diffraction (EBSD) technique was adopted in this study. The orientation maps showed that with the increase of tensile strain, the grain surface become wrinkled, and the deviation level of intragranular orientation also increased. Meanwhile, the parameters based on the image quality of the Kikuchi bands (i.e. BC and MAD) as well as the crystallographic orientation (i.e. LAGBs content, GND density, GOS, and GROD) can be used to evaluate the degradation degree of the mild steel. The results showed that the change of BC and MAD was significant at the end of plastic stage, but was not sufficiently distinctive at the early stage; Meanwhile, the LAGBs content and GND density increased evidently during the plastic tensile. Compared with the former, the GND density exhibited stronger regularity and better evaluation effect; Besides, a general upward trend of GOS and GROD was observed at this tensile process. However, the GROD changed less at the certain plastic stage. Compared with GROD, the GOS exhibited a relatively better evaluation effect; To sum up, the GND density and GOS are the better indicators for evaluating the degradation degree of mild steel.

INVESTIGATION OF THE INFLUENCE OF IMPROVED TECHNOLOGY OF PREPARATION OF WHEAT GRAIN FOR GRINDING ON ITS MICROBIOLOGICAL SAFETY INDICATORS

Качество и безопасность зерна выступает важным и обязательным объектом государственного регулирования и контроля. Рост количества опасных видов сорных растений, вредных насекомых и заболеваний зерновых культур привел к снижению качества зерновой массы, повышению ее микробиальной обсемененности. Важным этапом снижения микробиальной обсемененности зерна является его подготовка к переработке. Для повышения эффективности сепарирования и поверхностной очистки зерна пшеницы и снижения его микробиологической обсемененности учеными Кубанского государственного технологического университета предложена технологическая линия, включающая установку фотоэлектронного сепаратора перед овсюгоотборником для очистки зерновой массы от примесей, отличающихся от зерна пшеницы по цвету, и шлифовального агрегата вместо обоечных машин для очистки поверхности зерна. Цель настоящего исследования – определить эффективность применения предложенной технологии подготовки зерна пшеницы к помолу на примере его микробиологических показателей безопасности. В качестве объектов исследования были образцы зерна пшеницы из партий, поступивших с элеватора в подготовительное отделение мельницы, отобранные на зерноперерабатывающих предприятиях Краснодарского края, работающих как по традиционной, так и по усовершенствованной технологии. Установлено, что в зерновой массе, подготовленной к помолу по разработанной технологии, общее количество бактерий на 65% меньше, а содержание дрожжей и плесеней соответственно в 2 и 3 раза ниже, чем в зерновой массе, подготовленной к переработке по традиционной технологии. Из зерновой массы, подготовленной к переработке по усовершенствованной технологии, были полностью удалены вредные и минеральные примеси, фузариозные зерна и куколь. Результаты исследования показали высокую эффективность применения разработанной технологии подготовки зерна пшеницы к помолу. The quality and safety of grain is an important and mandatory object of state regulation and control. The increase in the number of dangerous species of weeds, harmful insects and diseases of grain crops has led to a decrease in the quality of grain mass, an increase in its microbial contamination. An important step in reducing the microbial contamination of grain is its preparation for processing. To increase the efficiency of separation and surface cleaning of wheat grain and reduce its microbiological contamination, scientists of the Kuban State Technological University have proposed a technological line that includes the installation of a photoelectronic separator in front of the oat collector to clean the grain mass from impurities that differ from wheat grain in color, and a grinding unit instead for cleaning the grain surface. The purpose of this study is to determine the effectiveness of the proposed technology for preparing wheat grain for grinding on the example of its microbiological safety indicators. The objects of the study were samples of wheat grain from batches received from the elevator to the preparatory department of the mill, selected at grain processing enterprises of the Krasnodar region operating both according to traditional and improved technology. It was found that in the grain mass prepared for grinding according to the developed technology, the total number of bacteria is 65% less, and the content of yeast and mold respectively is 2 and 3 times lower than in the grain mass prepared for processing according to traditional technology. Harmful and mineral impurities, fusarium grains and Agrostemma L. were completely removed from the grain mass prepared for processing using improved technology. The results of the study showed the high efficiency of the application of the developed technology for preparing wheat grain for grinding.

Automation of Control of Technological Process of Storage in a Granary with Horizontal Silos

Grain storage and processing is the most important component of the grain market infrastructure. The task of grain storage is to ensure complete safety of quantity and quality with minimal labor and money costs. In the laboratory of the M. Kozybayev North Kazakhstan University, a prototype of an innovative type of grain storage was developed using horizontal silos, designed to reduce the cost of construction and reconstruction of elevators while improving quality, increasing storage times and reducing current storage costs. The design feature makes it possible to automate most of the operations of the technological process of grain storage. This article proposes a method for the automated formation of control actions on grain storage equipment as a result of data analysis from temperature, humidity, carbon dioxide level sensors and 3D measurements of the grain surface. A project of an automated system for monitoring and controlling grain storage facilities with horizontal silos has been developed. A distinctive feature of the proposed automated system is the most complete set of conditions for the correct storage of grain in comparison with other control systems for the technological process of a granary. Automation of work is achieved through the developed method for generating control signals, as well as such computational algorithms as forecasting the completion time of loading based on the conditional filling rate of the grain storage section, forecasting the completion time of unloading based on the conditional grain release rate, calculating the grain volume in the section using 3D measurements. The logic of the functioning of the basic algorithms for an automated monitoring and control system for a granary with horizontal silos is based on the analysis of the parameters of temperature, humidity, carbon dioxide level and 3D measurements of the grain surface in the sections of the granary. In the presented project of an automated system, scientific knowledge and achievements in the field of grain storage and the theory of identification measurements were taken into account, which makes it possible to use the described algorithms in information systems for monitoring grain storage facilities of other types.

Extension of the KDO Turbulence/Transition Model to Account for Roughness

Wall roughness significantly influences both laminar-turbulent transition process and fully developed turbulence. This work has developed a wall roughness extension for the KDO turbulence/transition model. The roughness effect is introduced via the modification of the k and νt boundary conditions, i.e., the wall is considered to be raised at an extra height. The equivalent roughness height is linked to the actual roughness height, and the ratio between them is determined by reasoning. With such a roughness extension, the predictions of the KDO RANS model agree well with the measurements of turbulent boundary layer with a sand grain surface, while the KDO transition model yields accurate cross-flow transition predictions of flow past a 6:1 spheroid.

Heat and mass transfer in the grain under variable conditions

The article describes the drying process in the formulation of the internal problem, the main equations of internal heat and mass transfer of potentials are considered. The process of removing moisture from the surface of the grain, which is determined by the transfer of moisture and the diffusion-convective transfer of heat and moisture through the boundary layer, is studied. The movement of heat in the boundary layer was determined by the molecular thermal conductivity. It is established that the speed of the drying process depends on the rate of removal of water vapor from the surface of the grain. It was found that the change in the quality of the seed material did not depend on the absolute removal of moisture. The first drying period is shown, when the temperature of the grain surface rises from the temperature of the adiabatic air saturation, when the drying agent at the boundary of the grain surface is saturated with water vapor, and the drying speed depends on the speed of their removal from the evaporation surface. At this point, the moisture evaporated, the vapors were removed by the drying agent. At the initial moment, the movement of the evaporation line did not occur, but then it was fixed inside the grain. In the course of research, the process of removing moisture from the seeds is fast, but it has little effect on their quality. The removal of grain moisture reached up to 3 % from the upper layers of the seeds, which did not affect their quality. An analytical expression is considered for calculating the heat transfer coefficient and the drying agent velocity, taking into account the allowed moisture content, as well as the heat flux density. The permissible speed of the drying agent in a dense layer of grain is determined, which depends on the height of the layer, the specific surface of the grain, its temperature and the proportion of heat supplied to heat the material. For drying conditions typical for grain dryers, the drying speed should not exceed 0.6 m/s.

Diversity of supergene gold expressions and implications for gold targeting in an equatorial regolith (AMG’s Couriège exploration prospect, French Guiana)

The Couriège prospect (French Guiana) provides key examples of the diversity of gold distribution related to supergene processes. The nature of gold in two contrasted weathering profiles is examined as a function of the weathering lithofacies. The autochthonous profile hosts weathered Au-bearing quartz veins whereas the pediment profile is enriched in free gold issued from dismantled gold-bearing quartz veins. The gold distribution is controlled by: (i) the preservation of primary gold as free gold in both transported and autochthonous horizons and as electrum inclusions in detrital pyrite, and (ii) the formation of secondary gold through dissolution/precipitation processes, expressed as gold spherulites on free gold grain surface, Ag-depleted rim around transported free gold grains and Ag-depleted gold micro-inclusions hosted by oxidised autochthonous pyrite. Gold enrichment through supergene chemical processes remains limited within the truncated autochthonous profile. A new conceptual model is proposed for the area, defining the role of chemical and physical processes in gold endowment, and accounting for the geomorphological context. The overall evolution includes (i) deep weathering and peneplenation, (ii) dismantlement and transport of lateritic material, and (iii) development of a latosol cover. This study highlights that gold exploration in tropical environments must consider the residual vs transported nature and the inheritance of targeted pedogenic horizons.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5476187