Drying results
Preliminary tests indicated that it is necessary a pre-drying step of papaya seeds to obtain seeds with around 40 g/100 g of moisture content (w.b.). This process allows the initial movement of the bed and guarantee to reach of 11–13 g/100 g of moisture in the end of process to appropriated storage. However, the amount of moisture was still considered high and with great moisture percentage on seeds surface. Also, before drying, the minimum spouted velocity was determined for pre-dried papaya seeds. The obtained value was 8.4 m s−1.
Fig. 3 shows the dimensionless air relative humidity (UR/UR0) as a function of time for the experiments 15, 16 and 17 (V = 10.50 m s−1, T = 70 °C and t = 2.25 h), which correspond to the central point of the experimental design. It can be seen in Fig. 3, that at the beginning of experiment, there is a peak in the values of dimensionless relative humidity. This phenomenon may be related to the load stage. Comparing the curves, a similar behavior can be observed. Within 5 min the dimensionless relative humidity decreased with the time. In this step, the influence of convective drying process was observed. After 20 min, there was a less pronounced curve, being this step dominated by diffusion.