## 3 Results and Discussion
### The Kinetics and Energy Intensity of Drying
As the drying rate during this period is determined primarily by the internal transport of moisture, the value of this parameter continues to decrease (Figure 2b) and falling drying rate period occurs. The notable occurrence of a constant drying rate period may be somewhat unexpected. A review of the literature reveals numerous reports concerning materials of plant origin for which a constant drying rate period is not observed, and the entire drying process occurs during the period of falling drying rate [9]. However, some researchers have reported the presence of a constant drying rate period. [PERSON] et al. reported similar drying curves for carrot [35] and red pepper [36]. On the other hand, [PERSON] et al. [15] did not observe a constant drying rate period during the drying of carrot using multiple techniques. The underlying reason behind this discrepancy remains unclear. [PERSON] and [PERSON] [33] hypothesized that this phenomenon may be linked to a variation in the mass exchange area resulting from material shrinkage during the drying process. However, determining exchange surface area is extremely difficult and requires advanced experimental techniques. In Figure 3, the average drying rate, \(DR_{av}\); time, \(DT_{av}\); and specific energy consumption, \(SEC_{av}\), for each particular drying process are presented. The average drying rate obtained during the hybrid processes was visibly higher compared to the convective process (Figure 3a). In the case of the fastest drying procedure (CVMWUS) the average drying rate increased by 140% compared to CV, while for other hybrid programs, namely ultrasound-assisted (CVUS) and microwave-assisted (CVMW) convective drying, the increase equaled 13% and 112%, respectively. These changes were reflected in the value of the average drying time, which exhibited reductions of 10%, 53%, and 59% for CVUS, CVMW, and CVMWUS, respectively (Table 2). A strong positive correlation ([PERSON]'s \(r=0.99\)) was identified between the \(DR_{av}\) and \(DT_{av}\) values; a finding that is also evident in the graphical representation (Figure 3a). Figure 3: Average drying rate, \(DR_{av}\) and time, \(DT_{av}\) (**a**); and specific energy consumption, \(SEC_{av}\) (**b**) for each process. On the basis of the obtained results, microwaves were found to be a more efficient enhancement agent compared to ultrasound; this follows from the different mechanisms of interaction they have with the material being dried. Microwaves heat the entire volume of the sample, thereby significantly intensifying the transport of moisture within the body (through the intensification of diffusion and evaporation). Furthermore, the application of MW radiation typically results in a reduction in the temperature gradient within the material, which additionally enhances the drying process (through the reduction of thermodiffusion) [34]. The obtained results are in good agreement with the reports of other authors. [PERSON] et al. [15] also observed a 50% reduction in drying time for microwave-assisted hot air drying of carrot. [PERSON] et al. [37] noted a fivefold decrease in drying time during the microwave-assisted convective processing of this vegetable. The influence of ultrasound on the material being dried is very limited and depends strictly on the acoustic impedance mismatch between the sample material and the surrounding air. Several authors have proposed different mechanisms for ultrasound interaction, for example, cavitation, the \"sponge effect\", microstreaming, the formation of microchannels, disturbance in the boundary layer, etc. [26]. The proposed phenomena may accelerate the drying operation by reducing both the internal and external resistances. On the basis of the results obtained during the authors' previous research [38; 39], it can be stated that in the case of the presented drying system, ultrasound influences the kinetics of the process rather by reducing external resistance factors such as the laminar boundary layer.