Advanced Topics in Heat and Mass Transfer and Fluid Flow Phenomena in Multiphase Systems
Diffusion and Thermal Transport in Bulk and Nano-Materials
Functional Materials: Technological Aspects of Production and Processing
Diffusion in High-Tech Materials
Diffusion Foundations Vol. 16
Diffusion Foundations Vol. 15
Diffusion Foundations Vol. 14
Diffusion Foundations Vol. 13
Multiscale Modelling of Diffusion-Controlled Phenomena in Condensed Matter
Advances in Nonlinear Heat Transfer in Fluids and Solids
Heat and Mass Transfer Processes: New Developments and Applications II
Mass Transport in Advanced Engineering Materials
Progress in Thermodynamics, Diffusion, Ion and Proton Transport of Ionic Compounds and Ion-Conducting Polymer Films
Advanced Topics in Heat and Mass Transfer and Fluid Flow Phenomena in Multiphase Systems
摘要: This chapter aims to present a theoretical study of the fluid flow in porous media, with particular reference to manufacturing of polymer composites reinforced with fibers via resin transfer molding process. The mass and momentum conservation equations, including the effect of resin sorption by the fibers, and Darcy's law, are presented, and the analytical solution of the governing equation is obtained via method of separation of variables. Predicted results of the flow front, velocity, volumetric flow rate and pressure fields of the resin inside the model, during the injection process, are presented, and the effects of the injection pressure, resin viscosity and sorption term, are also analyzed.
摘要: Innovative technologies are needed to attend the increasingly strict requirements for produced water treatment, since most of the separation processes are limited to particles larger than 10 μm. Separation processes using ceramic membranes are attracting great interest from academic and industrial community. Nevertheless, few studies, especially numerical, regarding the inorganic membrane’s application for the polluted water separation have been reported. In the present work, therefore, a study of fluid-flow dynamics for a laminar regime in porous tubes (tubular porous ceramic membrane) has been performed. The mass, momentum and mass transport conservation equations were solved with the aid of a structured mesh using ANSYS CFX commercial package. The velocity of local permeation was determined using the resistance in series model. The specific resistance of the polarized layer was obtained by Carman-Kozeny equation. The numerical results were evaluated and compared with the results available in the literature, where by a good agreement with each other was found. The numerical results, obtained by the proposed shell and tubular membrane separation module, indicate that there is facilitation of mass transfer and hence a reduction in the thickness of the polarized boundary layer occurs.
摘要: This work focuses on the pollutant dispersion problem with particular reference to thermal power plants. A powerful mathematical modeling to predict gaseous pollutant concentration at atmosphere and different CFD simulations results by Ansys CFX® software are presented. The gaseous pollutant dispersion was evaluated by analyzing of different process parameters as wind velocity, gas emission rate and temperature. The study confirms wind velocity as main variable that strongly affecting dispersion phenomena.
摘要: This work provides information about polymer composite manufacturing by using liquid composite material molding, with particular reference to resin transfer molding process (RTM). Herein, several topics related to porous media, fluid flow, mathematical modeling, computational methods, composite manufacturing and industrial applications were presented. Simulation of resin flow into a fibrous (reinforcement) inserted in a parallelepiped mold has been performed, using the Ansys FLUENT® software, and different results of resin volumetric fraction, stream lines and pressure distribution inside the mold, and volumetric fraction always flow rate (inlet and outlet gates) of the resin, as a function of filling time, have been presented and discussed.
摘要: Freezing is a physical treatment commonly used in operations such as drying, conservation and lyophilization of foods. In the processing and potato industries, parameters like dimension and initial moisture content of the product has a great effect on the cooling, freezing and post-freezing kinetics. Therefore, this work presents a transient three-dimensional mathematical modeling including phase change to describe the heat transfer during the process, of cooling and freezing parallelepiped foods. The governing equation was solved numerically using the finite-volume technique and a full implicit formulation. As an application, this methodology was used to describe the freezing process of potato (french-fry). Numerical results of the temperature in the center of the product were compared to the experimental data reported in the literature and a good agreement was obtained. Results of the temperature distribution inside the solid and cooling, freezing and post-freezing kinetics are presented and analyzed. It was verified that, the smaller the dimensions and lower the initial moisture content of the product, the solidification of water inside the solid occurs even faster. The largest temperature gradients were identified in the surface, close to the regions of the borders of the solid.
摘要: Polyethylene (PE) nanocomposites were prepared by melt intercalation, in order to evaluate the flame retardant effect of this material. For the development of nanocomposites were used the montmorillonite clay (MMT), organoclay (OMMT) and flame retardant product (FRP) with the percentage of 1, 3, 6 and 9 wt%. Grafted polyethylene with maleic anhydride (PE-g-MA) was used as a compatibilizer of the systems. PE and its systems were evaluated: XRD, TEM, TG and flammability (UL94HB, oxygen index (LOI) and cone calorimetry). The X-ray diffraction showed a partial intercalation and exfoliation as well as formation of microcomposite. The phase morphology of the systems was observed by TEM that it showed that the system with 1% OMMT clay presented a predominance of exfoliation. Already the system with 3% OMMT showed partial exfoliation and this exfoliation reduced as the clay content increased. By TG it was seen that MMT, OMMT and FRP acted improving the thermal behavior of the nanocomposites compared to PE matrix. The results obtained for the oxygen index showed that both PE and its systems presented flame retardancy behavior. By means of the horizontal flammability tests, it was found that the presence of 1% MMT clay reduced 25% the flammability of PE. By cone calorimetry it was found that the system that contains 9% of OMMT clay decreased by about 33% the flammability of PE.
摘要: Drying is a simultaneous process of heat and mass transfer and dimensional changes. In recent years, cyclones have been used as a modern drying technology. In this sense, this research proposes a numerical study to describe drying of sugarcane bagasse, using the cyclone as dryer. Herein, it was adopted the Eulerian-Lagrangian model in steady state. The Reynolds stress model was considered to describe turbulence of the gas phase, while a transient lumped model was used to describe heat and mass transfer on the particulate phase (sugarcane bagasse). Particles were considered with irregular shape, composed of a binary mixture (solid part and water). The solution of the proposed model was obtained using the commercial software Ansys CFX 12. Results of the moisture content, temperature, dimension variation, and paths of particles, as well as velocity, pressure, and temperature distributions of the gas phase inside the cyclone are presented and analyzed. It has been found that the obtained components for axial and tangential velocity inside the cyclone are in good agreement with experimental data available in the literature, and that the drying kinetics, heating, dimensional variations, and residence time of particles are affected by the velocity of the gas phase, velocity of the particles, and the flow direction of gas and particles at the entrance of the feed duct.
摘要: The ceramic products processing requires a high consumption of energy. Through the drying and firing stages, the molded product is subjected to high temperatures in a kiln, to obtain the product with required levels of rigidity and resistance. This energy consumption must be evaluated to improve the energy efficiency of the process. This work presents the fundamentals of ceramic materials processing and perform a thermal analysis in an intermittent ceramic kiln. This analysis is based on heat transfer measurements, that occur in the kiln during the ceramic production stages, and effects of the thermal insulation thickness on the heat transfer between the kiln and the environment. The results showed that a considerable amount of energy is used to heat the kiln surfaces, that the greatest heat loss occurs by radiation of the kiln walls and that the use of thermal insulation provides considerable reduction in this heat loss, as well as the reduction in kiln external temperature, which minimize thermal discomfort and work accident risks.
摘要: In this work was conducted a theoretical and experimental study of water absorption in polyester matrix composites reinforced with sisal fiber at temperatures of 25, 50 and 70°C. A fiber content 44.6% sisal fibers, and 55.4% polyester matrix were used in the manufacture of the polymer composite. The dimensions of the composite were 20x20x3mm3 and 20x20x6mm3. Water absorption tests were conducted by immersion of the samples in a distilled water bath and the water uptake calculated by weight difference of the samples in the dry and wetted condition at different elapsed time. A three-dimensional mathematical model was developed to predict mass transfer during the water absorption inside the parallelepiped solid. Results of water absorption kinetic and moisture content distribution inside the composites showed the more favorable areas which presents delamination problems due the weakness of the fiber-matrix interface and consequently, reduction in the mechanical properties. It was found that the high water bath temperatures accelerate the absorption process and that the water absorption of the sisal reinforced polymer composite with 3 mm of thickness was faster than the with 6 mm of thickness.