Mauri Fortes

NUMERICAL SIMULATION OF INTERMITTENT AND CONTINUOUS DEEP-BED DRYING OF BIOLOGICAL MATERIALS

Abstract This paper presents a simulation study of dryers. A two-dimensional deep-bed drying model, which incorporates modifications in existing one-dimensional models, has been developed and has the capability of handling both non-uniform velocity profiles and material properties dependence on temperature and moisture content. A corn drying system was simulated in order to analyze its temporal and spatial drying behavior. Both intermittent and continuous drying were simulated. The results showed that continuous drying is more efficient than intermittent drying with respect to drying time. However, intermittent drying led to more uniform temperature and moisture distributions, which improve grain quality. The model can be easily extended to three-dimensional drying analysis.

CONJUGATE ANALYSIS OF NATURAL CONVECTIVE DRYING OF BIOLOGICAL MATERIALS

ABSTRACT This paper presents a numerical analysis of heat and mass transport during natural convective drying of an extruded com meal plate. The conjugate problem of drying and natural convection boundary layer Is modeled. The finite volume technique was used to discretize and solve the highly nonlinear system of coupled differential equations governing the transport inside the plate. The boundary layer solution was obtained by means of a finite difference software package that utilizes Runge-Kuttas 5th order method to solve the inherent transport equations. A methodology for evaluating the heat and mass transfer coefficients during the numerical simulation was developed and successfully implemented. The results showed that there is no analogy between heat and mass transfer coefficients for this type of problem.

Modelagem de um condicionador de ar de alta precisão para uso em processamento agrícola

In this work, a detailed procedure for the analysis of an accurately controlled air conditioner is presented. A computer program, that allows predicting the behavior of the system under different psychrometric conditions and different input air mass flow rates, was developed. The global physical-mathematical model includes mass and energy conservation equations for three different control volumes that compose the conditioner. Thus, the processes of mixture of air, simultaneous evaporation (or condensation) from a water surface and from a drop, and the air-stream heating are modeled separately. Simple semi-empiric expressions for heat and mass coefficients inherent to the evaporation process on a water surface are proposed as well a simplified model for the spray system. Experimental tests made on an air-conditioner allowed to obtain the constants that appear in the expressions for the heat and mass transfer coefficients and to validate the global model, within an engineering acceptable precision level.

Numerical Simulation Techniques for Optimizing Thermodynamic Efficiencies of Cereal Grain Dryers

As a first objective, this study addresses a novel approach to drying efficiency analysis through transient models based on both the first and second laws of thermodynamics. As a second objective, we developed a numerical meshless scheme based on cubic radial basis functions to solve the associated nonlinear coupled advection-dominated set of partial differential equations. The simulated results showed excellent accuracy when compared with available literature data on drying. Finally, and most significantly, this study presents an original methodology for optimizing dryers based on energy and exergy efficiencies and the associated controllable operational parameters: drying air velocity (flowrate) and temperature.

The one-dimensional transient diffusional method: finite element adaptive solutions to convection-diffusion problems

Abstract The diffusional method, a new, simple and natural concept, is introduced for solving convection-diffusion equations. The inherent formulation leads to the variational scheme for one-dimensional steady-state problems; however, the formulation is general and can be directly used in multidimensional analysis. Additionally, a lumped capacitance (mass) matrix first-order time integration technique is presented that is unconditionally stable in its implicit form and conditionally stable for Courant numbers less than one in its explicit form. The explicit form is shown, by comparison with a two-step Taylor-Galerkin scheme, to present an excellent performance for solving transient boundary layer problems and Burgers non-linear equation. Because of dampening due to first order accuracy of the time integrator, the method is not well suited to solve advection dominated problems involving travelling waves at high Peclet numbers; in this respect, a brief analysis is made on the explicit form of the Taylor-Galerkin scheme. This work also presents a performance analysis of the method when used in conjunction with adaptive time stepping procedures. The resulting adaptive PMGV scheme works very well for boundary layer problems and for solving Burgers non-linear viscous and non-viscous equations.

Guest Editorial: Back to the Roots—The Context of Drying and Drying Theories

This Guest Editorial aims at keeping updated or introducing the novice or younger researchers, scholars, and professionals to a few concepts from the highly market-demanded, challenging, and modern area of drying. Drying has existed since the dawn of humanity. Initially present as a purely practical procedure, today it is impressively present in most industry and agricultural processes. Academically, after a non-systematic but important beginning in the decades of 1920–1970, drying science erupted at the 1978 International Drying Symposium at McGill University, led by the young A. S. Mujumdar, at the beginning of his academic career. Subsequent drying development under Mujumdar’s leadership is a well-known history, which deserves further reading. That event served to open or disseminate, systematically, newer techniques for drying analysis techniques beyond statistics and diffusional approaches and newer professional practices. By this time, given its industrial and agricultural importance, researchers were anxious to have drying established as a science. Fast development was the consequence of this movement, which, up to today, has been transforming drying into one of the most challenging engineering areas. Now let us emphasize briefly a few significant and not well-established key points of modern drying concepts. An effort is made to make this text readable rather than complete in view of the limited space available. The issues discussed here were chosen because they need careful review; some of the related aspects may give marginal reason to doubt or even criticize my opinion. Therefore, the idea behind this brief presentation is to furnish some ‘‘food for thought.’’ The line of reasoning starts by positioning drying in the philosophical context. We will start from the general to some of the more specific issues.

Exergy Analysis applied to the design of grain dryers with air flow recirculation

The potential for energy conservation by using the technique of exhaust air recirculation has been known for a few decades. The state-of-art knowledge, including available experimental data associated to drying with recirculation, is rather incomplete and does not allow proper engineering design.

Energy and exergy efficiencies as design criteria for grain dryers

ABSTRACT We devised a novel methodology for optimizing cereal grain dryers grounded on the transient spatial–temporal first and second laws of thermodynamics and associated balance equations. Model equations were solved using a special time-adaptive radial basis function. Comprehensive sensitivity tests show the quantitative effects of initial moisture content, air velocity, and drying air temperature on the temporal profiles of outlet air temperature and moisture content and temporally integrated energy and exergy efficiencies. Drying temperature is the most efficacious parameter in the drying range of 50–90°C. Finally, selected examples show optimized dryer operation points under unrestrained and restrained conditions. Second law efficiency is well suited for expressing drying performance, portraying time, noble energy expenditure, and intrinsic sustainability. Three decision tables, based on simulation results, can be used to define dryer design under normal technical choice. First law efficiency and the specific moisture extraction rate are concepts more adequate for designing in-bin low-temperature dryers. Second law efficiency is indicated when exergy recuperation is at stake: higher drying temperatures, shorter drying times, recirculation drying, and other processes.

Irreversible thermodynamics analysis of ellipsoidal wheat kernel drying, aiming at the evaluation of phenomenological properties

ABSTRACT Literature data have revealed that wheat kernel stress–strain relationships, thermal conductivity, and specific heat support the assumption of isotropy. Accepting this premise, we show that drying complexity can be reduced by properly defining the kernel shape and an accurate model. Therefore, we present an irreversible thermodynamics procedure for obtaining transport properties of a wheat kernel. The numerical solution of the associated nonlinear conservation equations was based on the Radial Basis Functions method. Drying behavior of both prolate ellipsoidal and spherical grain kernels is presented and compared. The predicted moisture and temperature profiles correlated favorably with experimental drying profiles, obtained for two temperatures of 47 and 67.5°C.

Simulação do processo de triagem neonatal usando modelagem por eventos discretos

Desenvolveu-se um modelo de simulacao por eventos discretos para predicao do fluxo operacional do processo de triagem neonatal. O modelo foi validado utilizando dados coletados no Nucleo de Acoes e Pesquisa de Apoio ao Diagnostico da Faculdade de Medicina da Universidade Federal do Estado de Minas Gerais. O modelo foi testado no Laboratorio de Triagem Neonatal da Faculdade de Medicina da Universidade Federal de Minas Gerais, responsavel pelo processamento das amostras coletadas pelo Programa de Triagem Neonatal do estado, que busca a realizacao dos exames em todos os nascidos vivos. O modelo proposto possibilita ao gestor do laboratorio uma visao operacional do fluxo do programa. Portanto, o modelo oferece ao gestor do laboratorio a possibilidade de realizar predicoes e a conducao de experimentos sem a necessidade de interferir na produtividade dos recursos humanos do sistema real.