Thin Layer Drying Model for Cooked Soybeans

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The drying characteristics (changes in moisture content and volume of sample during drying) of cooked soybeans (boiled soybeans) were measured at selected operating conditions. The sample was dried by the two kinds of drying methods; the hot air drying method and the continuous vacuum drying method. From the observed relationship between the drying rate and moisture content of the sample, we estimated that the continuous vacuum drying process of the sample was composed of the two periods; the constant rate period and the falling rate period. The hot air drying process of the sample was in the falling rate period. In the constant rate period for the continuous vacuum drying (above 100 % d.b.), the moisture contents of the sample decreased with elapsed time and represented as a linear function of elapsed time. The falling rate period for the continuous vacuum drying (below 100 % d.b.) was in the first falling rate period, and the measured moisture contents of the sample agreed well with the values calculated from the exponential model. The Page equation could be used to estimate the changes in moisture content of the sample for the hot air drying process. An Arrhenius-type equation was used to relate the dying rate constant of the sample for each drying method and period to temperature. Volume changes of the sample during drying were determined by measuring particle density. An empirical equation relating the moisture content of the sample and temperature to specific volume was derived.