Secagem em camada fina e espessa de grãos de arroz vermelho em casca: avaliação experimental, modelagem e simulação.

Abstract

The present research work had as objectives to study the behavior of the apparent and real specific masses; intergranular porosity by liquid displacement method and the specific heat determined by the method of mixtures for water contents ranging from 11.6 to 30.06%, wet basis; determining the equilibrium desorption isotherms hygroscopic by the static method with use of saturated salt solution, using four temperature levels 10, 20, 30 and 40 ° C and five levels of relative humidity of t he air ranging from 11.15 to 84,32%; for the analysis of experimental data seven mathematical models were used: Henderson modified by Cavalcanti Mata, Henderson modified by Thompson, Chung-Pfost, modified Halsey, Cavalcanti Mata and Henderson; determining, experimentally, the latent heat of vaporization of water from red rice as a function of water content and temperature , using the method Othmer; analyzing the drying kinetics of a thin layer using a fixed bed drier with forced ventilation in five temperatures: 40, 50, 60, 70 and 80 ° C for initial water contents of 20, 25 and 30% by applying to the experimental data five mathematical models: Henderson modified by Cavalcanti Mata, Henderson modified by Thompson, Henderson, Fick, Page and Thompson; to perform drying and mathematical simulation in a thick layer at temperatures of 40, 50, 60 and 70 ° C and water levels established in the thin layer. The results showed that the apparent and real specific masses, the intergranular porosity and specific heat increased with increasing water content and that the behavior physical properties of red rice can be represented depending on the water content of the simple linear model. It was observed that the equilibrium water content, to the same hygroscopic relative humidity, decreased with temperature elevation, as to the same temperature, the hygroscopic equilibrium water content increases with increasin g relative humidity, following the same trend of most agricultural products. Based on statistical parameters, models Henderson modified by Cavalcanti Mata and Henderson modified by Thompson were the best represented the hygroscopicity of red grains of rice in husk. The effective diffusivity of red rice grains, estimated by Fick model, increased with increasing drying air temperature. It was also found that for each temperature examined the effective diffusivity increases with increasing initial water content. Through the drying kinetics curves, it was found that increasing temperature is a decrease in drying time, while for the initial water content, the greater will be its highest drying rate early in the process. Among the models analyzed in the drying kinetics, the Cavalcanti Mata was the best set to the experimental data at all temperatures and initial water contents studied. The simulation of the thick layer drying used the Thompson model, in which it showed a concordance between the experimental and simulated datas for the average values of the layers, having the lowest average final deviation with temperature of 60 ° C and initial water content equivalent to 20% b.u.