Abstract
Characteristics of cassava drying were investigated by using a microwave hot-air drying system. Two waveguides were installed on a single plane of the microwave cavity. The drying experiments were carried out at two levels of sample surface temperature set-points, 70℃ and 80℃respectively. Cassava (Rayong-9) with 2.5 kg weight and 61% moisture content on wet basis was dried in the dryer for about 300 - 340 minutes until the final values of moisture content of about 20% db were achieved. It was found that the drying time decreased with an increase in sample-surface temperature set point. Approximately 87% of the moisture was removed during the drying period. It was found that there was a rapid decrease in moisture ratio values followed by the gradual decline period in all experiments. With regard to drying kinetics, 5 commonly used mathematical models were examined with the experimental data. It was found that Page’s and diffusion models provided a good agreement between the experimental and predicted moisture ratio values for all temperature set-points. The regression results indicated that highest values of coefficient of determination and adjusted coefficient of determination as well as lowest value of standard error of estimation were reported for the case of Page’s model at 80℃ temperature set-point.
Highlights
Thermal drying may be defined as the process of thermally removing moisture to yield a solid product
Drying time decreased with an increase in sample-surface temperature set point
87% of the moisture was removed from the sample during the 300 - 340 minutes drying-period
Summary
Thermal drying may be defined as the process of thermally removing moisture to yield a solid product. Two processes simultaneously take place during thermal drying. These processes are the evaporation of surface moisture and the internal moisture transferring of the drying product. The energy from the surrounding environment, as a result of convection, conduction, radiation, or the combination of these effects, is transferred to the drying product to evaporate the surface moisture. The movement of internal moisture to the surface of the drying product may occur through several mechanisms such as diffusion, capillary effect as well as an increase in internal pressure of the material. A least square method was used for drying model fitting in order to minimize the standard error between the experimental data and the calculated values
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