## 3 Results and Discussion  
### The Kinetics and Energy Intensity of Drying  
Figure 2a shows a graph demonstrating the dependence of dimensionless moisture content (\(Y\)) on time (\(t\)). Despite the variations in drying methods, the curve paths are very similar. The characteristic drying periods such as the constant drying-rate period and the falling drying-rate period cannot easily be distinguished, which is typical for biomaterials drying processes [9; 33]. As expected, convective drying alone was the slowest among the methods tested. However, the application of microwaves (MW) or ultrasound (US) significantly reduced the drying time by increasing the rate of drying. Figure 2b illustrates the relationship between the drying rate (\(DR\)) and dimensionless moisture content (\(Y\)) during the process. A comparative analysis of the drying rate curves reveals that the application of microwaves had a significantly greater impact than ultrasound (Figure 2b). The maximum drying rate for the microwave processes (CVMW and CVMWUS) reached a value above 0.03 g/s, while for the convective-ultrasound process (CVUS), the highest observed value was 0.02 g/s. The lowest drying rate was observed for the convection process (CV), with a maximum of approximately 0.015 g/s, which resulted in a prolonged drying time. The shape of the drying rate curves exhibits a similar pattern across the different processes, which enables the essential drying periods to be identified. These include the initial stage, the constant drying rate period, and the falling drying rate period. The values of \(Y_{i}\) at which the transition between the drying periods occurs are slightly different for each process; however, some similarities can be observed between the CV and CVUS processes, as well as between the CVMW and CVMWUS processes. The initial stage of the process lasts from the beginning until a constant drying rate is reached. For the CV-CVUS pair of processes, this period lasted until the dimensionless moisture content reached \(Y_{i}\approx 0.89\), while for the CVMW-CVMWUS pair, it lasted until \(Y_{i}\approx 0.87\). In both instances, this occurred after approximately 1200 s of the process' duration. The relatively prolonged heating period observed in this study may be attributed to two factors: the larger sample batch size compared to other studies on hybrid drying and the initiation of drying on the cold dryer. In this approach, a portion of the heat energy supplied with the hot air was utilized for the heating of the dryer components. The process subsequently entered the constant drying rate period. In the case of the CV-CVUS pair of processes, this period lasted until the material reached a dimensionless moisture content of approximately 0.57, which occurred after 5400 s of the convection (CV) process and 3900 s of the ultrasound-assisted process (CVUS). In the microwave-assisted processes  
Figure 2: Evolution of dimensionless moisture content, \(Y_{i}\) (**a**); drying rate, \(DR_{i}\) (**b**); and temperature of the samples, \(T/T^{*}\) (**c**), for each process. (CVMW, CVMWUS), the constant drying rate period ended at a dimensionless moisture content of 0.47, which was reached after approximately 3600 s, despite the variations in the types of processes. The condition for the end of the period of constant drying rate is the slowing down of the transport of moisture from the inside of the sample to its surface. In all the processes studied, the transport of moisture to the surface of the sample is caused by diffusion. When microwaves are used (CVMW, CVMWUS), the temperature of the samples is higher than in the other processes (CV, CVUS). This facilitates diffusion at lower moisture contents. In addition, internal heating of the material with microwaves causes an increase in moisture pressure, which in turn causes easier transport of moisture to the surface (pressure flow). For these two reasons, the period of constant drying rate is longer in the processes with microwaves (CVMW, CVMWUS) than in the processes without microwaves (CV, CVUS).