Studies on Drying Characteristics of Some Crops in a Portable Tapered Fluidized Bed Dryer and Its Design Optimization

Abstract

The drying characteristics for different crops (grains and vegetables) are analyzed using a fluidized bed dryer with respect to the moisture content, diffusivity and physical properties of grains and vegetables. Temperature dependence of mass transfer coefficients is established in terms of Arrhenius type of relation. Drying constant and shrinkage constant of different shaped samples are also studied. Simple mathematical expressions are developed relating volumetric shrinkage constant with drying constant. Dimensionless groups viz. Reynolds number, Schmidt number, and Sherwood number are determined at different drying conditions. With the knowledge of diffusivity and dimensionless groups, mass transfer coefficients are determined. The physical properties of samples are also analyzed at different levels of moisture contents. The performance of fluidized bed dryer measured in terms of its efficiency is investigated by using different samples. The effects of different system parameters (viz. temperature, time, and density of material and fluid velocity) on the drying performances i.e. on moisture content, diffusivity and efficiency of the samples are also studied through different mathematical expressions.
Artificial Neural Network and Taguchi analysis are used to validate the developed correlations for drying characteristics. The chi square (χ2), correlation coefficient (R2) and root mean square error (RMSE) findings indicate that ANN and Taguchi analysis optimize the system parameters of the fluidized bed drying more effectively than regression analysis. Thus the developed correlations can be used for parameter-optimizations over a wide range thereby providing a better platform for efficient operations. Again a portable tapered fluidized bed dryer is designed to provide drying in turn storing opportunity to farmers. Thus the present work lays foundation for an efficient dryer to be designed effectively which can further be scaled up suitably for industrial applications.