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‣ On the validity of lumped capacitance approaches for the numerical prediction of heat and mass transfer in desiccant airflow systems

Ruivo, C. R.; Costa, J. J.; Figueiredo, A. R.
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica Formato: aplication/PDF
Português
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In the present work, a detailed model of simultaneous heat and mass transfer through a desiccant micro-porous medium of a channel wall of compact heat and mass exchangers, such as desiccant wheels, was developed. The relevant phenomena considered by this model within the porous medium are surface diffusion of the adsorbed water, Knudsen diffusion of water vapour, heat conduction and the sorption process. A one-dimensional formulation of this model is used to investigate the validity of two simplifying approaches based on the lumped-capacitance method. One consists of neglecting the transversal heat and mass transfer resistances within the porous medium, the other of cancelling only the thermal resistance.; http://www.sciencedirect.com/science/article/B6VT1-4NDDT7N-2/1/03da119a5957dd37fdfb381ac8936208

‣ Transferência de calor e massa no escoamento bifásico em torno de aerofólios equipados com sistemas de antigelo aeronáuticos.; Heat and mass transfer in two-phase flow around airfoils with aeronautical anti-ice systems.

Silva, Guilherme Araújo Lima da
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 02/02/2009 Português
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Há a necessidade de prevenir formação de gelo nas asas e nos estabilizadores de aeronaves, pois as formas de gelo podem causar a degradação do desempenho aerodinâmico, o aumento de peso, bem como dificuldades de controle e manobra que, em casos críticos, leva a uma diminuição da margem de segurança operacional. Quando as aeronaves atravessam nuvens com gotículas de água sub-resfriadas, ou seja, em equilíbrio metaestável, o crescimento de gelo ocorre nas superfícies não protegidas. Usualmente, os sistemas antigelo térmicos de aerofólios são projetados, desenvolvidos e certificados com o auxílio de programas de simulação numérica. O presente trabalho visa desenvolver e implementar um modelo matemático para prever a transferência de calor e massa no escoamento bidimensional bifásico em torno de aerofólios de uso aeronáuticos, equipados com sistema de antigelo térmico operando em regime permanente. Em condições de formação de gelo, é necessário aquecer o bordo de ataque e controlar a temperatura da região protegida para que não ocorra formação de gelo. O sistema de aquecimento compensa os efeitos do resfriamento imposto principalmente pelos mecanismos acoplados de evaporação e transferência de calor por convecção...

‣ Modelagem e simulação de um reator catalítico de membrana inerte permseletiva a hidrogênio com transferência de calor e massa; Modeling and simulation of a catalytic reactor with a permselective to hydrogen inert membrane with heat and mass transfer

Germano Possani
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 18/02/2011 Português
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Dentre os termoplásticos mais utilizados atualmente na indústria, pode-se mencionar o estireno, principal responsável pela produção de plásticos e borrachas. No processo de fabricação de estireno, a principal rota química é por meio da desidrogenação de etilbenzeno, com o hidrogênio como subproduto. A conversão de etilbenzeno nesta reação é em torno de 50,0 %, devido ao equilíbrio termodinâmico. Para deslocar esse equilíbrio e aumentar a produtividade de estireno,foram desenvolvidas novas configurações de reatores, tal como os reatores com membrana. eatores equipados com membranas de paládio fornecem uma seletividade maisalta ao estireno uando comparados com reatores equipados apenas com membranas porosas. Para explorar o otencial desse tipo de reator, modelagens matemáticas foram desenvolvidas a fim de determinar os parâmetros cruciais que regem esses processos. O objetivo deste trabalho foi modelar e simular um reator de leito fixo catalítico, envolto por uma membrana inerte permseletiva ao hidrogênio com transferência de calor e massa, sendo composta por uma camada de aço inoxidável de 1,6 mm de espessura, a qual serviu de suporte para a deposição de um filme de 20 µm de paládio. Para essa modelagem foram utilizados os métodos de Runge-Kutta-Gill para o cálculo das variáveis no sentido axial...

‣ Micro direct methanol fuel cell: experimental and modelling studies

Falcão, D. S.; Rangel, C. M.; Pinto, A. M. F. R.
Fonte: Laboratório Nacional de Energia e Geologia Publicador: Laboratório Nacional de Energia e Geologia
Tipo: Conferência ou Objeto de Conferência
Publicado em //2013 Português
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The Direct Methanol Fuel Cell (DMFC) has attracted much attention due to its potential applications as a power source for transportation and portable electronic devices. Based on the advantages of the scaling laws, miniaturization promises higher efficiency and performance of power generating devices and the MicroDMFC is therefore an emergent technology. In this work, a set of experiences with a MicroDMFC of 2.25 cm2 active area are performed in order to investigate the effect of important operating parameters. The cell is presented in Fig. 1. The experimental rig consists in a rotameter for air flow, a peristaltic pump (Control CO) for methanol flow and an electrochemical station (Zahner) to obtain polarization curves. The effect of the methanol concentration on the cell performance, between 3 and 5 M was studied. All the experiments were performed at room temperature, a condition of special interest with view to portable applications. Maximum power density achieved was 32.6 m /cm2 using a 4 M methanol concentration at room temperature. Polarization curves are compared with mathematical model simulations in order to achieve a better understanding of how parameters affect performance. The one-dimensional model used in this work takes in account coupled heat and mass transfer...

‣ Modeling and simulation of direct contact evaporators

Campos,F.B.; Lage,P.L.C.
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2001 Português
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A dynamic model of a direct contact evaporator was developed and coupled to a recently developed superheated bubble model. The latter model takes into account heat and mass transfer during the bubble formation and ascension stages and is able to predict gas holdup in nonisothermal systems. The results of the coupled model, which does not have any adjustable parameter, were compared with experimental data. The transient behavior of the liquid-phase temperature and the vaporization rate under quasi-steady-state conditions were in very good agreement with experimental data. The transient behavior of liquid height was only reasonably simulated. In order to explain this partial disagreement, some possible causes were analyzed.

‣ Modeling heat and mass transfer in the heat treatment step of yerba maté processing

Peralta,J. M.; Schmalko,M. E.
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2007 Português
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The aim of this research was to estimate the leaf and twig temperature and moisture content of yerba maté branches (Ilex paraguariensis Saint Hilaire) during heat treatment, carried out in a rotary kiln dryer. These variables had to be estimated (modeling the heat and mass transfer) due to the difficulty of experimental measurement in the dryer. For modeling, the equipment was divided into two zones: the flame or heat treatment zone and the drying zone. The model developed fit well with the experimental data when water loss took place only in leaves. In the first zone, leaf temperature increased until it reached 135°C and then it slowly decreased to 88°C at the exit, despite the gas temperature, which varied in this zone from 460°C to 120°C. Twig temperature increased in the two zones from its inlet temperature (25°C) up to 75°C. A model error of about 3% was estimated based on theoretical and experimental data on leaf moisture content.

‣ Simultaneous heat and mass transfer in packed bed brying of seeds having a mucilage coating

Prado,M. M.; Sartori,D. J. M.
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2008 Português
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The simultaneous heat and mass transfer between fluid phase and seeds having a mucilaginous coating was studied during packed bed drying. To describe the process, a two-phase model approach was employed, in which the effects of bed shrinkage and nonconstant physical properties were considered. The model took into account bed contraction by employing moving coordinates. Equations relating shrinkage and structural parameters of the packed bed with moisture content, required in the drying model, were developed from experimental results in thick-layer bed drying. The model verification was based on a comparison between experimental and predicted data on moisture content and temperature along the bed. Parametric studies showed that the application of correlations capable of incorporating changes in bed properties gives better data simulation. By experimental-theoretical analysis, the importance of shrinkage for a more accurate interpretation of heat and mass transfer phenomena in the drying of porous media composed of mucilaginous seeds is corroborated.

‣ Analysis of heat and mass transfer during microwave drying of food products

Haghi,A. K.; Amanifard,N.
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2008 Português
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Microwave (MW) drying is a rapid dehydration technique that can be applied to specific foods. Increasing concerns over product quality and production costs have motivated the researchers to investigate and the industry to adopt microwave drying technology. The advantages of microwave drying include the following: shorter drying time, improved product quality, and flexibility in producing a wide variety of dried products. Drying is influenced by heat and mass transfer between drying airflow and product, as well as the complex moisture transport processes which take place in the product.. This paper presents an analytical approach for the drying of potato. The laws of moisture content change in the food product as a function of mass transfer are used for the theoretical approach. The study gives a brief description of efforts made to obtain basic drying parameters under different microwave drying conditions. This computational method can be used as a tool for microwave drying of potato slabs more efficiency.

‣ Solution of porous media inverse drying problems using a combination of stochastic and deterministic methods

Lugon Junior,Jader; Silva Neto,Antônio J.
Fonte: Associação Brasileira de Engenharia e Ciências Mecânicas - ABCM Publicador: Associação Brasileira de Engenharia e Ciências Mecânicas - ABCM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2011 Português
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In the present work the inverse problem of simultaneous heat and mass transfer modeled by Luikov equations is studied using a hybrid combination of the Levenberg-Marquardt (LM), Simulated Annealing (SA) and Artificial Neural Network (ANN) methods. The direct and inverse problems are described, formulated and solved. After the use of an experiment design technique, the hybrid combination ANN-LM-SA yielded good estimates for the heat and mass transfer problem of interest. The proper choice of the set of parameters to be estimated allowed the design of an experiment with higher sensitivity coefficients. One ANN was used to generate the initial guess for the LM, another one to approximate the gradient needed by LM, and, finally, the global minimum was searched using the SA. The experimental data considered in the inverse problem was generated using the solution for the direct problem with the addition of noise.

‣ Transferencia de calor e massa em colunas de destilação a vacuo : uma abordagem Euleriana-Lagrangeana; Heat and mass transfer in vacuum towers : an Eulerian-Lagrangian

Karolline Ropelato
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 18/12/2008 Português
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A compreensão dos fenômenos existentes em equipamentos industriais é de extrema importância para o seu projeto e otimização. O uso de colunas de destilação é conhecido antes mesmo do século XX. Desde o seu surgimento até os tempos atuais, significativos avanços ocorreram. A literatura apresenta diversos trabalhos considerando o estudo de colunas de destilação com pratos ou recheios. No entanto, pouca atenção tem sido dada para colunas com vazios. O presente trabalho apresenta uma metodologia para o estudo da transferência de calor e massa em colunas de destilação com distribuidores do tipo sprays em processos de destilação, considerando uma abordagem Euleriana-Lagrangeana. Neste tipo de abordagem, as gotas são modeladas individualmente a partir de trajetórias na fase contínua. O modelo k-e ?foi empregado para predizer o comportamento da fase vapor. O equilíbrio termodinâmico é modelado considerando a lei de Raoult. Utilizando conjuntamente conhecimentos de Termodinâmica, Processos de Separação (destilação) e de Fluidodinâmica Computacional (CFD), um modelo matemático é proposto. A aplicação das escalas características de tempo como metodologia de análise e compreensão dos resultados é proposta; The understanding of fluid dynamic phenomena in industrial equipments are extremely important for new projects and their optimization. Distillation columns are being used even before the XX century. Since that time many advances have happened. The literature presents different studies as far as plates or packed columns are concerned...

‣ Experimental and modeling studies of a micro direct methanol fuel cell

Falcão, D. S.; Rangel, C. M.; Pinto, A. M. F. R.
Fonte: Laboratório Nacional de Energia e Geologia Publicador: Laboratório Nacional de Energia e Geologia
Tipo: Conferência ou Objeto de Conferência
Publicado em //2013 Português
Relevância na Pesquisa
97.68776%
The Direct Methanol Fuel Cell (DMFC) has attracted much attention due to its potential applications as a power source for transportation and portable electronic devices. Based on the advantages of the scaling laws, miniaturization promises higher efficiency and performance of power generating devices and the MicroDMFC is therefore an emergent technology. In this work, a set of experiences with a MicroDMFC of 2.25 cm2 active area are performed in order to investigate the effect of important operating parameters. Maximum power density achieved was 32.6 mW/cm2 using 4M mehanol concentration at room temperature. Polarization curves are compared with mathematical model simulations in order to achieve a better understanding of how parameters affect performance. The one-dimensional model used in this work takes in account coupled heat and mass transfer, along with the electrochemical reactions occurring in a direct methanol fuel cell and was already developed and validated for DMFC in previous work [1-3]. The model is also used to predict some important parameters to analyze fuel cell performance, such as water transport coefficient and methanol crossover. This easy to implement simplified model is suitable for use in real-time MicroDMFC simulations.

‣ ANALYSIS OF INTERFACIAL AND MASS TRANSFER EFFECTS ON FORCED CONVECTION IN GAS-LIQUID ANNULAR TWO-PHASE FLOW

Nogueira, E.; Dantas, B. D.; Cotta, R. M.
Fonte: UFPR Publicador: UFPR
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; Peer-reviewed Article Formato: application/pdf
Publicado em 28/10/2004 Português
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In a gas-liquid annular two-phase flow one of the main factors influencing the determination of heat transfer rates is the average thickness of the liquid film. A model to accurately represent the heat transfer in such situations has to be able of determining the average liquid film thickness to within a reasonable accuracy. A typical physical aspect in gas-liquid annular flows is the appearance of interface waves, which affect heat, mass and momentum transfers. Existing models implicitly consider the wave effects in the momentum transfer by an empirical correlation for the interfacial friction factor. However, this procedure does not point out the difference between interface waves and the natural turbulent effects of the system. In the present work, the wave and mass transfer effects in the theoretical estimation of average liquid film thickness are analyzed, in comparison to a model that does not explicitly include these effects, as applied to the prediction of heat transfer rates in a thermally developing flow situation.

‣ Heat and mass transfer in MHD free convection along a vertical wavy plate with variable surface heat and mass flux

Mahdy,A.; Mohamed,R.A.; Hady,F.M.
Fonte: Latin American applied research Publicador: Latin American applied research
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/2009 Português
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The problem of combined heat and mass transfer in buoyancy-induced MHD natural convection flow of an electrically conducting fluid along a vertical wavy plate with power-law variation of both heat and mass flux was investigated. The resulting transformed governing equations are solved numerically by an implicit finite-difference scheme. The results are presented for the major parameters including the wave amplitude a, the magnetic parameter Mn, the buoyancy ratio between species and thermal diffusion Br, the Lewis number Le, and the power-law parameter ?. A systematic study on the effects of the various parameters on flow, heat and mass transfer characteristics is carried out.

‣ Dufour and Soret effects on unsteady MHD convective heat and mass transfer flow due to a rotating disk

Maleque,Kh. A.
Fonte: Latin American applied research Publicador: Latin American applied research
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2010 Português
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An unsteady three dimensional MHD convective heat and mass transfer flow in an incompressible fluid due to a rotating disk is studied by taking into account the Dufour and Soret effects. The system of axial symmetric non-linear partial differential equations governing the unsteady flow, heat and mass transfer is written in cylindrical polar coordinates and reduced to nonlinear ordinary differential equations by similarity transformations. The resulting system of ordinary nonlinear differential equations is then solved numerically by a shooting method using Range-Kutta six order integration scheme. The flow, temperature and concentration fields are affected by the magnetic interaction parameter M, Rotational parameter R, Soret Number S0 and Dufour number Df respectively. The results of the numerical solution are presented graphically in the form of velocity, temperature and concentration profiles. The results for the wall flow, temperature and concentration gradients obtained are presented in tabular form for various values of the parameters M, R, S0 and Df.

‣ Soret and dufour effects on heat and mass transfer due to a stretching cylinder saturated porous medium with chemically-reactive species

El-Kabeir,S. M. M.
Fonte: Latin American applied research Publicador: Latin American applied research
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/2011 Português
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The diffusion-thermo and thermal-diffusion effects on heat and mass transfer by boundary layer flow over a stretching cylinder embedded in a porous medium have been studied numerically in the a presence of chemical reaction effect. The governing nonlinear partial differential equations are transformed into a set of coupled ordinary differential equations, which are solved numerically by using Runge-Kutta method with shooting techniques. Numerical results are obtained for the velocity, temperature and concentration distributions, as well as the skin friction coefficient, local Nusselt number and local Sherwood number for several values of the parameters, namely, the Reynolds number, Darcy number, chemical reaction parameter, Dufour and Soret numbers. The obtained results are presented graphically and the physical aspects of the problem are discussed.

‣ Soret and dufour effects in a mixed convection couple stress fluid with heat and mass fluxes

Srinivasacharya,D.; Kaladhar,K.
Fonte: Latin American applied research Publicador: Latin American applied research
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/2011 Português
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An analysis is presented to investigate the Soret and Dufour effects on the mixed convection heat and mass transfer along a semi-infinite vertical plate embedded in a couple stress fluid with flux distributions. The governing non-linear partial differential equations are transformed into a system of ordinary differential equations using similarity transformations and then solved numerically. Profiles of dimensionless velocity, temperature and concentration are shown graphically for various values of Dufour number, Soret number and Couple stress parameter.

‣ Analysis of heat and mass transfer in a mixed convective diffusion flame attached to a vertical fuel surface

Bula,A. J.; Rahman,M. M.
Fonte: Latin American applied research Publicador: Latin American applied research
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2008 Português
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Analysis of heat and mass transfer in a burning vertical surface exposed to a fluid flow parallel to the surface is presented. The combustion process considered is steady and the burning surface is in equilibrium vaporization. A fast gas phase reaction is assumed to occur between the fuel and the oxidizer. The flame sheet approximation is used to describe the reacting flow. The governing equations describing the conservation of mass, momentum, energy, and species concentrations were solved numerically along with appropriate boundary conditions. Schvab-Zeldovich variables were used to eliminate the mass and energy generation terms from the governing equations. Calculations were done for two different fuels and for a range of Reynolds number. Computed results included the distributions of velocity components, enthalpy, and concentration of fuel, oxidizer, products, and inert gas, and the position of the flame sheet.

‣ Fluctuating thermal and mass diffusion on unsteady free convection flow past a vertical plate in slip-flow regime

Sharma,P. K.
Fonte: Latin American applied research Publicador: Latin American applied research
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/2005 Português
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The unsteady free convective viscous incompressible flow past an infinite vertical porous flat plate with periodic heat and mass transfer in slip-flow regime is discussed. Assuming variable suction at the porous plate, approximate solutions are obtained for velocity, skin-friction, temper-ature, heat transfer and species concentration. During the course of discussion, the effects of Gr (Grashof number based on temperature), Gc (modified Grashof number based on concentration difference), Sc (Schmidt number), A (suction parameter) and ω (frequency) for Pr=0.71 (air) have been presented.

‣ Thermophoresis and chemical reaction effects on mhd mixed convective heat and mass transfer past a porous wedge in the presence of suction

Muhaimin,I.; Kandasamy,R.; Kamis,A. B.
Fonte: Latin American applied research Publicador: Latin American applied research
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2010 Português
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The effects of thermophoresis and MHD mixed convection flow with heat and mass transfer over a porous wedge are presented here, taking into account the homogeneous chemical reaction of first order. The governing fundamental equations are approximated by a system of nonlinear ordinary differential equations and are solved numerically by using the Runge Kutta Gill and shooting methods. The steady-state velocity, temperature and concentration profiles are shown graphically. It is observed that due to the presence of first-order chemical reaction, the concentration decreases with increasing values of the chemical reaction parameter. The results also showed that the particle deposition rates were strongly influenced by thermophoresis and the strength of the magnetic field in the presence of buoyancy force, particularly for opposing flow and hot surfaces. Numerical results for the skin-friction coefficient, wall heat and mass transfer are obtained and reported graphically for various parametric conditions to show interesting aspects of the solution.

‣ Influence of heat- and mass-transfer coupling on the optimal performance of a non-isothermal chemical engine

Yanhua,Cai; Guozhen,Su; Jincan,Chen
Fonte: Sociedad Mexicana de Física Publicador: Sociedad Mexicana de Física
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/2010 Português
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The cyclic model of a non-isothermal chemical engine operated between two reservoirs with different temperatures and chemical potentials is established, in which the irreversibilities resulting from the heat and mass transfer between the working fluid and the reservoirs are taken into account. Expressions for the power output and efficiency of the engine are analytically derived and used to analyze the performance characteristics of the engine at the maximum power output. The general characteristics of the efficiency of the engine are searched in detail. The optimal criteria for some important parameters, such as the power output and efficiency, are obtained and the reasonably operating region of the engine is determined. Some interesting cases are specially discussed. The results obtained here can reveal the performance characteristics of a non-isothermal chemical engine affected by the irreversibilities of heat- and mass-transfer coupling.