## 3 Results and Discussion
### Drying Kinetics
If the drying time of MW1 and MW2 is related to the CVUS schedule, then the advantage equals 41% and 63%, respectively. Additionally, the temperature of the sample surface (T\({}_{\text{m}}\)), measured with an IR camera, increased violently at the beginning of the process, then stabilized for a short period of drying, and finally  
Figure 2: Evolution of the relative moisture content (MR) and temperature of samples (T\({}_{\text{m}}\)) and the drying agent (T\({}_{\text{a}}\)) during: (**a**) convective drying (CV—schedule No. 1) and (**b**) convective drying assisted with ultrasound of a power P\({}_{\text{US}}\) = 200 W (CVUS—schedule No. 2). increased again, meaningfully exceeding the temperature of the drying agent (Ta). At the end of drying, the temperatures of the sample surfaces were equal to T\({}_{\text{a}}\) = 350 K and 370 K for the CVMW1 and CVMW2 schedules, respectively. It doubtless resulted from the action of the microwaves, which are recognized as one of the most effective sources of energy. Application of this kind of radiation during drying of products rich in moisture, such as fruits and vegetables, was found to be very advantageous and usually leads to high kinetic benefits [25; 26; 27]. Unfortunately, such great increases in the samples' temperature may lead to many deteriorative processes, such as local overheating (\"hot spots\"); thermal decomposition of nutrients; changes in color, taste, and smell; and texture degradation, deformations, etc. [6; 7; 9]. For this reason, the quality of the products was analyzed in detail and is discussed in the next section. In Figure 4, the drying curves obtained for the last and the most complex schedule are presented. In this case, the convective process was enhanced with both microwave and ultrasound radiation of a power P\({}_{\text{MW}}\) = 100 W and P\({}_{\text{US}}\) = 200 W, respectively. One can see the time of drying was, in this schedule, significantly longer in comparison to CVMW2 (41% growth, cf. Figure 5a) but slightly shorter than that observed during CVMW1 (11% reduction, cf. Figure 5a). Nevertheless, in comparison to convective (CV) or even ultrasonically-assisted convective (CVUS) processes, the drying time was still shorter and the advantages were equal to 52% and 47%, respectively (cf. Figure 5a). If temperature curves are considered, it can be stated that their course is more similar to those  
Figure 4: Evolution of the relative moisture content (MR) and temperature of samples (T\({}_{\text{m}}\)) and the drying agent (T\({}_{\text{a}}\)) during convective drying assisted with microwaves (P\({}_{\text{MW}}\) = 100 W) and ultrasound (P\({}_{\text{US}}\) = 200 W, CVMWUS—schedule No. 5). Figure 3: Evolution of the relative moisture content (MR) and temperature of samples (T\({}_{\text{m}}\)) and the drying agent (T\({}_{\text{a}}\)) during convective drying assisted with microwaves of power: (**a**) P\({}_{\text{MW}}\) = 100 W (MW1—schedule No. 3) and (b) P\({}_{\text{MW}}\) = 250 W (MW2—schedule No. 4). observed for CVMW processes than to CV or CVUS ones. At the beginning of the process, the temperature of the material rose rapidly to some equilibrium value; next, it remained stable for a short period of drying, and after the 50 th minute of the process, it started to rise again. At about the 90 th min of the process, the temperature exceeded the value registered for ambient air and finally attained 355 K, which is 12-15 K higher compared to the temperature of the drying agent. This kind of curved course suggests a dominant influence of microwaves over ultrasound on the kinetics of convective drying. In Figure 5 the average values of the drying rate and time, specific energy consumption are presented respectively. Both presented in Figure 5a parameters exhibited the expected trend observed in the drying kinetics curves (Figures 2-4). The convective-microwave drying process (CVMW2), carried out at higher microwave power, was the shortest drying process, which also had the highest average drying rate.