Abstract
Characteristics of cassava microwave hot-air drying were investigated in a 2-planes microwave hot-air dryer. The drying experiments were carried out at two levels of sample surface temperature set-points viz. 70 and 80°C respectively. Cassava (Rayong-9) with 2.5 kg weight and 61% moisture content on wet basis was dried in the dryer for about 5-5.3 h. It was found that the drying time decreased with an increase in sample-surface temperature set point. Approximately 89% of the moisture was removed during the drying period. The rapid decrease in moisture ratio values followed by the gradual decline period was found 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. The regression results indicated that high values of coefficient of determination and adjusted coefficient of determination as well as low value of standard error of estimation were reported for the case of these two models.
Highlights
Thermal drying may be defined as the process of thermally removing moisture to yield a solid product
The rapid decrease in moisture ratio values followed by the gradual decline period was found in all experiments
The regression results indicated that high values of coefficient of determination and adjusted coefficient of determination as well as low value of standard error of estimation were reported for the case of these two models
Summary
Thermal drying may be defined as the process of thermally removing moisture to yield a solid 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. According to the conventional hot-air dryer, several kinds of materials have been investigated with regard to their drying characteristics. Some examples of fruits/vegetables drying characteristics namely Borneo Canarium Odontophyllum, tomato and lemon grass were investigated (Basri et al, 2012; Brooks et al, 2008; Ibrahim et al, 2009)
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