Papers by Keyword: Mass Transfer

Abstract: The microstructure of aluminum nanopowder combustion crystalline products in air and the influence of a constant magnetic field (with induction of 0.3 T) on their structures have been studied. It was revealed that in the combustion products of free-poured aluminum nanopowder two-level whiskers are present. Hexagonal single crystals are formed by combustion in air in a homogeneous magnetic field, and in case of inhomogeneous magnetic field (with induction of 0.3 T) faceted elongated crystals of micron size are generated. The crystallites of such structure are formed due to the mass transfer of the combustion products in the direction of thermal flows. Ordered six-sided crystal structures are formed by overcooling the oxidation products by the action of magnetic field and by increasing the mobility of their structural units in recrystallization thermal wave. According to electron- microscope investigation the formation of the faceted crystals is possible with optimal sizes of combustion product particles.

Abstract: Mathematical models of ignition of condensed substances considering interconnected processes of a heat and mass transfer in systems “composite propellant – hot particle – gas”, “liquid fuel – hot particle – air” and “gel-like fuel – hot particle – gas” were developed. As a result of numerical modeling modes of ignition for solid, liquid and gel-like condensed substances characterized by ignition delay time and arrangement of ignition zone relative to local energy source were established. Liquid fuel has 3 ignition modes, composite propellant and gel-like fuels have 1 ignition mode

Abstract: A non-stationary mathematical model of desublimation UF₆ in vertical tanks considers the movement of gaseous uranium hexafluoride contains in the article. Results of calculation of time dependence of the linear velocity desublimation, the thickness of the resulting layer of the solid phase, the temperature distribution in the tank wall - desublimation layer, filling dynamics of vertical tank B-12 by solid UF₆ are presented. Calculations have shown that the 70% of B-12 tank is filled desublimation UF₆ by 250 hours, which is in good agreement with the experimental data

Abstract: Ore samples, believed to be low grade manganese ore were characterized using XRD, XRF and SEM, before being ground further into very fine particle sizes going through a preliminary leaching process. Sulfuric acid was chosen as the leachant, and leaching was done without any presence of reducing agents.

Abstract: Microdialysis, being a well-established sampling technique, still suffers from mass transfer limitations. Arguably, the biggest contributor to mass transfer limitation in this case is the membrane layer. To reduce limitations to mass transfer, and at the same time, increasing the performance of microdialysis probes, a concise mass transfer analysis must be done. For microdialysis probes, being relatively small in size and operating under possibly stringent biological conditions, an experimental route of analysis is less preferred compared to a computational route. This paper looks at the needs of computational mass transfer studies, and provides an idea why a comprehensive physical characterization effort is imperative for computational mass transfer studies.

Abstract: : The effects of mixed convection with thermal radiation and chemical reaction on MHD flow of viscous, incompressible and electrically conducting fluid on a moving inclined heated porous plate is analyzed. The non-linear coupled partial differential equations are solved by perturbation technique. The influence of different pertinent parameters such as Grashof number (Gr), modified Grashof number (Gm), magnetic field parameter (M), heat source parameter (), chemical reaction parameter (γ), Schmidt number (Sc) and angle of inclination () on velocity, temperature and concentration distribution have been studied and analyzed with the help of graphs. An analysis of the coupled heat and mass transfer phenomena is provided in detail. We observed that velocity decreases for increasing values of the angle of inclination α. The results of the present study are compared with the results obtained by Chaudhary et al. [1], and Dulal et al. [4] in the absence of angle of inclination, our results appear to be in good agreement with the existing results. Key words: Heat and mass transfer, Viscous and Ohmic dissipation, Radiation, Chemical reaction, Inclined, Porous plate.

Abstract: Utilization of advanced materials in civil engineering motivates research in both experimental and computational methods of reliable identification of their material characteristics, as e.g. the thermal conductivity and diffusivity in semilinear evolutionary equations of heat conduction, coming from the energy balance in classical thermodynamics, or the capillary transfer coefficient in similar equations, coming from the mass balance. The paper presents mathematical preliminaries of such inverse analysis and an overview of computational approaches with references to practical applications.

Abstract: In this manuscript, we have investigated the influence of radiation absorption on an unsteady MHD convective heat and mass transfer flow of a Newtonian fluid past a vertical porous plate in the presence of thermal radiation and chemical reaction. The non dimensional governing equations have been solved by using a multiple perturbation method, subject to the corresponding boundary conditions. The effects of various physical parameters such as velocity, temperature and concentration are studied through graphs. The expressions for local skin friction, Nusselt number and Sherwood number are derived and discussed with the help of a table. It is noticed that velocity increases when an increase in modified Grashof number Gm, radiation absorption parameter χ, Sorret number S₀, time t whereas it decreases when an increase in Schmidt number Sc, chemical reaction parameter Kr and radiation parameter F. Temperature increases with an increase in radiation parameter χ and Sorret number S₀ whereas it decreases with an increase in chemical reaction parameter Kr, F and ϕ. Concentration is observed to be decreased when chemical reaction parameter Kr and Schmidt number Sc increase whereas it increases with an increase in Sorret number S₀. Skin friction increases with an increase modified Grashof number Gm, radiation parameter χ and Sorret number S₀ whereas it has reverse effect in the case of Schmidt number Sc, chemical reaction parameter Kr. Nusselt number increases with an increase in Sc, S₀, χ whereas it has reverse effect in the case of Kr. Sherwood number gets decreased when Sc, χ and Kr both are increased whereas it has shown revere effect in the case of S₀.

Abstract: The freeze-drying rate is essentially low, since it is controlled by internal moisture diffusion. In addition, the application of vacuum and low temperature during the process presents a higher energy demand. Therefore, the search for new strategies to improve water mobility during freeze-drying constitutes a topic of relevant research. The aim of this work was to evaluate the use of power ultrasound to improve freeze-drying characteristics of açai, quantifying the influence of the applied power on both the drying and rehydration kinetics of the material. Açai (Euterpe oleracea Martius) samples were sonicated with two different frequency levels, 20 kHz and 40 kHz, and two sonication times, 3 min and 10 min. Page’s equation considering internal and external resistances to mass transfer provided a good fit of freeze-drying kinetics, while the Peleg’s equation was found to be suitable for describing the rehydration kinetics of freeze-dried açai. Pretreatment of açai with ultrasound waves was not effective. Ultrasound-induced structural disruption in the açai skin hindered the mass transfer during both freeze-drying and rehydration processes.

Abstract: A modified large-size MOCVD reactor is developed to produce uniform and large-volume epitaxy thin film layer of gallium nitride (GaN). The full governing equations for continuity, momentum, energy and chemical species are solved numerically. It is investigated how thermal flow field, and the operating parameters affect molar concentration of each reactant, and the thin film uniformity. These parameters are involved such as the chamber pressure (100-700 torr), susceptor rotation rate (100-800). In this paper, the simulation results from these listed parameters shows that an optimum epitaxy layer can be achieved in the large-size reactor.