Papers by Keyword: Mass Transfer

Abstract: A lime composition of a dry building mixture for finishing walls of buildings made of aerated concrete is proposed. The composition contains ash aluminosilicate microspheres as a filler. The kinetics of humidification of finishing coatings of building walls is described. For comparison, the work also investigated the processes of mass transfer in cement-sand plaster using quartz sand, as well as in plaster using vermiculite sand. A mathematical model of the process of wetting a composite based on a dry construction mixture is presented. Comparison of calculated and experimental data is carried out, their good agreement is shown. It is shown that a heat-insulating decorative coating based on a composition with ash aluminosilicate microspheres has a higher crack resistance in the process of moistening.

Abstract: Possible causes of mass transfer acceleration of carbon atoms and alloying elements in the surface layers of steels and alloys under extreme heating, under pulsing laser irradiation in particular, are considered. The research shows that the anomaly accelerated mass transfer, including diffusion in particular, in steels and alloys under fast laser heating has a cooperative character and is a result of a simultaneous action of several processes of different physics. It is proved that the carbon atoms mass transfer parameters and alloying elements depend on the scale and the level of emerging tension, relaxation of which goes along with a local plastic deformation, and occurrence of increased number of linear defects in crystal structure.

Abstract: Fireproof coatings at the time of operation of the building structure is a separate and complex task, covering both the stages of the process protection from moisture, and subsequent fire protection formed during the swelling of the coating. They have been proven to create a layer of material on the surface that prevents moisture from penetrating the wood when the destruction of the coating begins. This makes it possible to determine the effect of flame retardants and the properties of the protective compositions on the process of slowing down the rate of water absorption. The process of moisture transfer by flame retardant coating in the presence of a polymeric shell is simulated, the diffusion and mass transfer dependences are obtained, and the diffusion coefficient is determined, which is 7.08·10^-12 m²/s, which allow to obtain a change in the dynamics of moisture upon washing out of the flame retardant. The results of determining the weight loss of the coating sample during exposure to water indicate the ambiguous effect of the nature of the leaching agent. In particular, this implies the availability of data sufficient for qualitatively conducting the process of inhibition of moisture diffusion and detection on its basis of the moment from which the fall of the coating efficiency begins. Features of slowing down the process of moving the moisture to the material that is treated with flame retardant, are in several aspects. Namely, the use of water-insoluble flame retardants and other components, as well as polymer binder, which are characterized by the formation of polymer shell on the surface of the wood.

Abstract: A detailed theoretical analysis of the processes occurring in foam concrete mixtures in the period between their laying in the mold and the phase transition “from viscous to solid” completion moment. The stages of the formation of inter-pore septa in foam concrete mixtures, depending on the material nature and shape of the solid dispersed particles of raw materials, are sequentially considered. It is shown that their shape affects the mass transfer rate and the density of inter-pore septa during the structure formation. The reasons for the fluctuations in the elasticity of foam films during the predominance period of viscous bonds between the components of the raw material are described. The gas inclusions factors of influence on the dispersion parameters and, as a consequence, the aggregative stability of foam mixtures, are ranked. The positive dispersed reinforcement effect on the mass transfer processes in mixtures and the hardened concrete strength is substantiated.

Abstract: The rate of removal of heavy metal Copper ion (Cu ²⁺) from synthetic wastewater was studied using an ion exchange resin and pulsation technique. Variables examined were initial concentration of (Cu ²⁺), ratio of mass of resin to solution liquid volume, frequency, amplitude and geometry of the disc responsible for the pulsation motion. The results were presented mathematically by using the dimensionless analysis and the mass transfer correlation was obtained also Langmuir and Freundlich adsorption isotherms were examined where the date fits Freundlich adsorption isotherms more than Langmuir adsorption isotherms. It is concluded that percentage of (Cu ²⁺) removal decreases as initial concentration of (Cu ²⁺) presented increases and increases with contact time, frequency (rpm), amplitudes and mass of resin per unit volume of solution.

Abstract: The present study is concerned with the removal rate of Copper ions Cu++ from wastewater by cementation of copper from copper sulfate solution on a horizontal steel sheet placed at the bottom of a square stirred tank reactor and fitted with square steel turbulence promoters. The variables studied were solution concentration, rotation speed, impeller geometry, promoter diameter and distance between promoters. The rate of mass transfer was found to increase with the rotational speed and decreased with the increase of distance between promoters. The data were correlated to develop the relationship Sh α Re x

Abstract: The influence of volumetric hydrophobization of cement stone samples on mass transfer processes during hardening has been studied. It was found that the introduction of a hydrophobizing additive at the stage of sample production reduces the amount of water evaporating during drying. With increasing concentration of the hydrophobizer mass transfer processes are slowed down during the hardening of cement concretes, which affects their structural and phase composition, strength characteristics and durability.

Abstract: The studies on cementation focus exclusively on the carbon’s movement. It is described by diffusion equations, often with constant coefficients and without regard to the liaising with temperature. It does not allow to have regard to the further carbon diffusion into the workpiece with the lower temperature range. The most accurate prediction of carbon concentration profiles depending on the parameters of the carburization regime and the chemical composition of steel is possible with the mathematical models using. However, most models show good results for Fe-C austenite without affecting the effect of alloying substitution elements. Taking into account the influence of alloying elements leads to complex empirical dependencies with difficult selected coefficients. It makes their use difficult. The study describes the simulation using the finite element method for the process of austenite’s diffusion saturation Fe-C-Cr system with carbon during cementation. Here is an example of a steel gear 15Cr2 with the temperature influence. The COMSOL Multiphysics program is used to solve the problem numerically. It is found that the model of carbon diffusion in unalloyed austenite for the single-stage cementation regime is in good contact with the experimental data for the Fe-C-Cr austenite of 15Cr2 steel. For a two-stage process, the calculation of the carbon concentration in the surface layer has a slightly greater deviation from the experimental data than it is at a greater depth.

Abstract: The key and most energy-consuming process in obtaining inulin is the extraction process. The effectiveness of technology as a whole depends on this procedure. The present research is devoted to studying statics and kinetics of inulin water extraction from artichoke with the purpose of intensification, optimization and modeling of extraction process. Analysis of technical and patent literature has allowed to reveal the ways of aggregation of inulin extraction, in particular, by influence of ultrasonic oscillations on the object of processing. To study the statics of the extraction process, i.e. equilibrium states of the system of interacting substances with the purpose of determining equilibrium concentrations at different temperatures with the use of ultrasonic radiation, kinetic laws of the process and to select rational operating parameters and extraction process intensification, a series of experiments and experimental data processing were carried out. On the basis of the obtained data the process modeling is carried out and the model of mass transfer while inulin extraction is calculated. After have been analyzed the obtained results, in particular, fields of inulin concentration in Jerusalem artichoke and kinetic curves of extraction, it was concluded that in the process of extraction there are slight gradients of concentrations observed, which cause "soft" extraction modes. Furthermore, ultrasonic treatment application at the frequency of radiation 20-22 kHz reduces the duration of the extraction process and significantly increases specific output of inulin. The equations obtained are necessary not only to determine the duration of extraction and its rational mode parameters, but also to model the extraction process mathematical results. These research results can be used in the field of food science and industry, as well as in the development and design of food equipment.

Abstract: The paper presents research into heat and mass transfer in agglomerated particles exposed to the thermal plasma flow. The dynamic motion, heating and melting are considered for agglomerated particles. It is shown that the surface temperature of porous particles rather rapidly reaches the value of T_sur>T_melt starting from the area of their introduction into the plasma flow. This effect is determined by the low conductivity of porous particles and indicates to a great temperature difference between the particle surface and its nucleus. It is shown that hollow particles can be obtained from silica sand treated by thermal plasma at 6700 K and 515 m/s velocity. The particle surface displays no clear defects. According to the analysis of X-ray diffraction patterns, the obtained hollow particles have no diffraction peaks.