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SHRINKAGE AND DENSITY VARIATIONS OF FRESH GREEN BEANS DURING DRYING IN AN INERT MEDIUM FLUIDIZED BED

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Abstract

ABSTRACT

In this article, the shrinkage and density variations of cylindrical fresh green beans were investigated in a fluidized bed dryer with energy carriers. A pilot-scaled fluidized bed dryer was set up for performing the drying experiments. Glass bead particles were used as inert materials. The drying experiments were done with fresh green beans of several lengths using hot air as a heating agent with the temperature range of 30–50C, and the effects of various parameters, such as the presence of inert materials, temperature and sample length, were investigated. It was found that the shrinkage or volume changes, and radial and axial contractions of fresh green beans could be well correlated as linear functions of moisture content during drying. Calculated and experimental values were in good agreement with mean absolute errors (MAEs) of 3.56, 2.48 and 1.22 for volume changes, and axial and radial contractions, respectively. By considering that the change in the volume of the samples was equal to the volume of evaporated water, mathematical models were proposed for volume and density variations. Comparison of the predicted values for volume and density by the proposed model with experimental date showed that the uniform model of shrinkage could explain the shrinkage and density variations of fresh green beans with MAEs of 5.190 and 4.250 for volume and density variations, respectively. The shrinkage coefficients were evaluated by considering their measurement uncertainties.

PRACTICAL APPLICATIONS

Any attempt to characterize drying behavior must inevitably address the physical parameters of the material such as shrinkage and density. The shrinkage phenomenon occurring during the drying process affects the physical properties of the solids, as well as the transport phenomena properties. The shrinkage of vegetables during drying is important not only from the viewpoint of material end use but also for simulation problems.

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