Cinética de congelamento do feijão (Phaseolus vulgaris L.) a baixas temperaturas

Abstract

R ESU M OO objetivo neste trabalho foi obter as curvas de congelamento do feijão, cultivar 'gordo', nas temperaturas de -25, -50, -170 e -196 °C e determinar sua difusividade térmica efetiva. Com vista à obtenção das curvas de congelamento das sementes nas temperaturas de -25 e -50 °C utilizou-se um freezer criogênico horizontal; para a temperatura de -170 °C, o vapor de nitrogênio e, para a temperatura de -196 at low temperatures A B ST R A C T The objective of this study was to obtain the freezing curves of beans, variety 'gordo' at temperatures of -25, -50, -170 and -196 °C, and determine their effective thermal diffusivity. For the curves of freezing beans seeds at temperatures of -25 and -50 °C a cryogenic horizontal freezer was used, for temperature of -170 °C, nitrogen vapor was used and at temperature of -196 °C seeds were submerged in liquid nitrogen. To express the kinetic behavior of the freezing of bean seeds, the Fourier model was used taking into account the first term of the series and; Cavalcanti-Mata & Duarte model I and II. The results indicate that the three models satisfactorily represent the experimental data of the kinetics of freezing, though with Model II of Cavalcanti-Mata & Duarte highest coefficient of determination were obtained. It is concluded that time necessary to freeze the seeds of beans at temperature of -25 °C was of 1200 min; at temperature of -50 °C the equilibrium was reached with 480 min; at -170 °C the time was 180 min and at -196 °C it was 30 min.