Metodologia numérica para análise de secagem de grãos em leito fixo pela primeira e segunda Lei da Termodinâmica / Numerical methodology for analyzing deep bed grain drying by first and second laws of Thermodynamics

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

This work presents a methodology for analyzing deep bed grain dryers by means of the first and second laws of thermodynamics. The thermodynamic modeling is a more complex extension of a literature-available thermodynamic modeling of fluidized bed dryers, which involves a system of lumped mass and energy equations. Thus, the present analysis involved a system of four non-linear partial differential equations (PDE) with pure advection forms, describing one-dimensional deep bed drying. The numerical solution involved solving the system of PDEs by making use of a recently available numerical method, the Radial Basis Function (RBF) method. Among the many existing radial basis functions, the multiquadrics function (MQ) was employed. The MQ function requires the use of a shape function for accurate results. The method was tested by solving the highly complex benchmark problem of pure advection equation. The resulting solution accuracy was excellent. After that, the method was extended to the solution of deep-bed grain drying. Although there is some criticism concerning the empirical approach for using the shape function, its value was rather easy to be obtained. It suffices to use a shape function value immediately above the value below which the solution diverges. Simulation results and analyses were presented, by considering a reference drying condition of air temperature, humidity ratio and air velocity, respectively, equal to 50 oC, 0.0061 kg/kg and 0.2 m/s. The deep bed initial values were corn kernel moisture content of 0.33, decimal, dry basis, 20 oC and air moisture ratio equal to 0.01021 kg of water/kg of dry air. A parametric study was carried on by spanning air temperature and velocity in the respective ranges of 30-70 oC and 0.2-0.6 m/s and initial bulk grain moisture contents ranging from 0.25 to 0.33, db. The results included time and spatial profiles for air and corn temperatures, bed moisture ratios and most important, corn moisture content. Additionally, curves are presented for time variation of average corn moisture content and air dryer outlet temperature. Comprehensive data on air availability and first and second law efficiencies, as integrated along the drying operation are presented. Therefore, this work should be of value to dryer designers and for future drying research objectives.

ASSUNTO(S)

energia energy secagem armazenamento de produtos agricolas termodinâmica simulation grãos grain drying thermodynamics simulação

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