The existence of a first drying stage for potato proved by two independent experimental evidences
2007
Perré , Patrick (INRA (France). UMR 1093 Laboratoire d'Etude et Recherche Sur le Matériau Bois) | May , Bee (RMIT University, VICTORIA(Australie). School of Applied Sciences)
During convective drying, the existence of a constant drying rate period (first drying period) is of great importance as it denotes an efficient internal mass transfer through capillary forces. Below the domain of free water, internal moisture movement is much slower and the mechanical properties may change, leading to a significant effect on product quality. The existence of this first drying period is usually demonstrated by the observation of a constant drying rate stage. However, with highly deformeable materials, the overall drying rate is misleading due to the substantial decrease of the exchange surface. The drying flux is a more useful quantity to consider, but it requires both the exchange surface area and the overall drying rate to be determined during the entire drying process. Another proof of evidence of a first drying stage lies in the sample temperature, which should stay equal to the wet bulb temperature. In this paper, we proposed a new experimental set-up that allows the existence of a first drying stage to be proved by two independent experimental data. Using a climatic chamber, a microbalance and two contactless methods (two laser beam micrometers and an infrared thermometer) the sample dimensions, the drying rate and the surface temperature can be collected simultaneously versus time. The results obtained from both methods on different products are consistent and confirm the existence of a constant drying flux period for potato.
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