This paper is about a comparative study of some parameters related to natural solar drying of cassava, ripe(I) or raw(II) plantain banana and mango. The comparative study was carried out by investigating the constant rate period, the falling rate period and the transition between these two periods. For the constant rate period, the product temperature Tp and the ambient temperature Ta were analysed in relation with the initial moisture content Wi. Then the maximum temperature difference DTmax between Ta and Tp was investigated, and found to decrease exponentially with Wi. In the constant rate period, parameters such as hc/λ, dm/dt and the mass transfer coefficient hm were reported and discussed. A new parameter was then introduced and termed the specific rate Rsp, which strongly correlated to Wi and DTmax. The critical point Wc was also taken into account. As for the falling rate period, the study was carried out by means of the overall resistance to diffusion Rds. The next step was the analysis of the drying rhythms. Finally, the investigation about the rewetting behaviour of the four products was made by using the desorption and sorption velocities (Vdes and Vsor), and the rewetting rate, too.
Objectives of this research were to develop and evaluate a drying process for peeled longan using combined microwave-hot air (MWHA). Each experiment employed the peeled ‘Dor’ longan to be dried to final moisture content of 18% (dry basis). Hot air temperature was regulated for three levels: 40, 50, and 60 °C, coupled with MW regulated for four levels: 100, 180, 300 and 450 W. Results show that MWHA drying process yielded a unique convex-shaped drying rate period, followed by a falling rate period. A step-wised drying process using 40 °C hot air with 450 W-MW power for 1.7 h, followed by 60 °C hot air with 300 W-MW power for 3.3 h provided the maximum drying efficiency. Compared to the 65 °C hot air drying to obtain the golden brown flesh, combined MWHA process reduced drying time by 64.3% and specific energy consumption by 48.2%.