Modelagem e simulação de secagem de feijão macassar (Vigna unguiculata (L.) Walp.): contração volumétrica da camada espessa.

Abstract

The deep thick layer cowpea, variety "manteiguinha", drying experiments with initial water contents between 233% and 193%, dry base, were realized using a fixed bed dryer with temperatures of 52 and 28°C, and drying air of 0,5 mxs"1, for simulation with Thompson's model considering the volumetric contraction of the layer. The principal objective of this work was to compare the experimental and the simulated data using Thompson model and CAVALCANTI MATA (2003) proposed model considering the volumetric contraction versus its water content, of the cowpea beans layer. The equations of heat and mass balance for studied beans were obtained and introduced to the mathematical simulation program SoFeiMa, developed by computing technicians of the Storage and Processing of Product Agricultural Laboratory. According to the obtained results, it was concluded that: a) To the same relative humidity, the equihbrium water content increases with the decrease of the temperature and can be expressed by the equation: Xe = (ta(l-UR)/-0,009688xT0^76015)0-75530 with the correlation coefficient of 98,9%; b) The latent heat of vaporization increases with the decrease of the water content of the product, from 25 to 5% dry base and with the decrease of the temperature from 50 to 20 °C, and can be represented by the equation hfg = (606-0,57xT) x (l+0,23822xexp(- 0,0469xXe)) with a correlation coefficient of 98,7%; c) The specific heat of the cowpea beans varies linearly with its water contents, obtaining the follow equation cp = 0,357 + 0,00178x(Xbu) with a correlation coefficient of 99,9%; d) The Page's equation for thin layer best fits to the experimental data with correlation coefficient varying from 97,8 to 99,9% when compared to Thompson's equation, with correlation coefficient varying from 96,7 to 99,7%; e) The water content of cowpea beans, and the temperature profiles simulated by SoFeiMa, when the layer volumetric contraction is considered, have less relative mean deviation than the Thompson's model simulated data; f) The drying time simulated by the proposed model approached better to the experimental data for the two studied temperatures; g) the compatibility between the experimental and simulated data, confirms the validity of the proposed model Cavalcanti Mata (2003) for cowpea beans, variety ''manteiguinha", drying at thick layer.