Modeling the effect of shrinkage on fluidized bed drying of orthodox broken type tea

Abstract

Fermented tea particles (dhool) are a polydisperse system subject to shrinkage during fluidized bed drying, which is an important process in the production of orthodox broken type tea. The effect of shrinkage on the physical properties and the minimum fluidization velocity were studied. Five different moisture contents of dhool particles were chosen in the range of 3-106 mass% (dry basis) and the changes in particle diameters and particle densities were measured. For each of the moisture contents, the minimum fluidization velocity was found for three different bed loadings using ambient air at 25?C in a fluidized bed with an area of 351?345 mm2. Since the conventional industrial type fluidized bed dryers operate at 124?C, the new correlations among the Archimedes number, Reynolds number at minimum fluidization and dimensionless moisture content were developed using air properties at 124?C. The results were validated for orthodox broken type tea, drying at 124?C, in a fluidized bed dryer with bed loadings in the range of 44.5 to 50.5 kg/m2. The predicted fluidization velocity was found to be in good agreement with the experimental data and the difference was below 10% for most cases.