Abstract
The aim of this work was to compare the results of the liquid diffusion model with respect to bean (Phaseolus vulgaris L.) drying when taking into account or neglecting grain shrinkage. Bean grains were harvested with a moisture content of 0.92 kg water/kg dry matter and dried at air temperatures of 25-55 deg C and relative humidities of 20-75%. The volume of each grain, understood as a sphere, was determined several times over the drying process, taking the diameter to be the mean length of the three orthogonal axes. Grain shrinkage was determined by examining the relationships between the volume associated with each moisture content and the initial volume. The results show that the liquid diffusion model describes the drying kinetics of beans satisfactorily, and that grain shrinkage can be ignored. The diffusion coefficient increases with air temperature, with values ranging between 10.8 x 10-10 and 67.0 x 10-10 square m sE-1. This is described by the Arrhenius equation, with an activation energy of 40.08 kJ molE-1.
Highlights
Water is the main component of most agricultural products and it has enormous influence on their physical
Resende et al / Span J Agric Res (2007) 5(1), 51-58 of agricultural products were developed without taking into account the importance of volumetric contraction during dehydration (Brooker et al, 1992)
Due to the importance of the study of the drying of tropical agricultural products, and the lack of theoretical information regarding the phenomena that occur during bean drying, the aim of this work was to compare the results of the liquid diffusion model under different conditions, taking into account or neglecting grain shrinkage
Summary
Water is the main component of most agricultural products and it has enormous influence on their physical properties. Agricultural products are usually dried to ensure their quality and stability. Diminishing moisture levels lead to a reduction in biological activity and induce chemical and physical changes in grains. According to Prado et al (2000), the removal of water during the drying of grains leads to a reduction in the tension inside cells, promoting product shrinkage. The majority of the models used to predict the drying. O. Resende et al / Span J Agric Res (2007) 5(1), 51-58 of agricultural products were developed without taking into account the importance of volumetric contraction during dehydration (Brooker et al, 1992). According to Ramos et al (2005), this should be included in models for a complete description and analysis of the phenomenon to be made
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