## 3 Results  
### Kinetic and Drying Time  
First, HD tests were performed to dry the carrot slices and considered as the standard for evaluation. Then, the effects of other dryers (single, hybrid and with US pretreatment) on the carrot slice drying were evaluated by studying the drying kinetics (drying time) (Table 4). Figure 1 shows the drying kinetics of the carrot slices dried by different dryers. Evidently, HD drying took significantly longer than the other methods (190 \(\pm\) 10 min) (\(p<\) 0.05). According to Table 4, the use of MWD and INFD resulted in the faster drying process (55% and 23%, respectively). The use of MW radiation significantly affected the drying kinetics and accelerated the evaporation [31]. When INF-HD and MW-HD were employed, the carrot slices were dried at a higher pace at 28% and 50%, respectively. This shows that both MW radiation and INF illumination can accelerate the evaporation process. INFD and MWD waves, in combination with HD, can penetrate into the product and produce heat at the water sites, and this will displace the moisture from the center to the surface [29].  
According to Figure 1 and the drying times reported in Table 4, the application of US pretreatment can reduce the drying time. This can be attributed to the cavitation phenomenon inside the product resulting in severe expansion and contraction which will eventually make the product texture spongy. Such a spongy texture can accelerate the moisture elimination compared to the conditions without the US pretreatment, and thus the application of ultrasound can decline the drying time [32; 33]. The US+MW-HD was the most rapid drying technique since it dried the carrot slices 73% faster (compared to the HD method). This method benefited from the advantages of hybrid MW-HD as well as the US pretreatment resulting in a significant reduction of drying time. Different letters for the same segment represent statistically significant differences at a confidence level of 95%.  
By investigating the walnut kernel drying by different methods (HD, MWD with US pretreatment), [PERSON] et al. [12] concluded that US pretreatment can shorten the drying time in both methods. According to [PERSON] et al. [34], who studied the drying carrot by different methods (HD and MVD with US pretreatment), the longest drying time was observed in the samples dried by the HD method. They declared that the US pretreatment can shorten the drying time. Similar results were also reported by the other researchers, for instance: [PERSON] et al. [28] for drying raspberries, [PERSON] et al. [35]  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**No** & **Drying Method** & **Drying Time (min)** & **Reduced Drying Time (\%)** & **D\({}_{\text{eff}}\) (m\({}^{2}\)/s)** & **SEC (MJ)/kg** \\ \hline
1 & HD & 190 \(\pm\) 10g & - & 7.12 \(\times\) 10\({}^{-9}\) & 297.29 \(\pm\) 11.21i \\
2 & INFD & 145 \(\pm\) 7e & 23 & 9.50 \(\times\) 10\({}^{-9}\) & 120.83 \(\pm\) 9.22f \\
3 & MWD & 85 \(\pm\) 5c & 55 & 1.79 \(\times\) 10\({}^{-8}\) & 42.5 \(\pm\) 3.22b \\
4 & INF–HD & 135 \(\pm\) 10d & 28 & 1.39 \(\times\) 10\({}^{-8}\) & 186.49 \(\pm\) 10.99h \\
5 & MW–HD & 95 \(\pm\) 6c & 50 & 1.43 \(\times\) 10\({}^{-8}\) & 164.47 \(\pm\) 8.24g \\
6 & US+HD & 170 \(\pm\) 9f & 10 & 8.28 \(\times\) 10\({}^{-9}\) & 265.99 \(\pm\) 4.44k \\
7 & US+INFD & 130 \(\pm\) 6d & 31 & 1.16 \(\times\) 10\({}^{-8}\) & 54.58 \(\pm\) 3.75c \\
8 & US+MWD & 70 \(\pm\) 3b & 63 & 2.09 \(\times\) 10\({}^{-8}\) & 23.75 \(\pm\) 2.22a \\
9 & US+INF–HD & 60 \(\pm\) 4b & 68 & 2.37 \(\times\) 10\({}^{-8}\) & 111.9 \(\pm\) 6.31e \\
10 & US+MW–HD & 50 \(\pm\) 2a & 73 & 2.78 \(\times\) 10\({}^{-8}\) & 103.23 \(\pm\) 4.89d \\ \hline \end{tabular}
\end{table}
Table 4: Influence of the different drying methods on the drying parameters of carrots.  
for drying broccoli floret, [PERSON] et al. (2020) for drying red beetroot, and [PERSON] et al. (2020) for drying _Kelussia odoratissima_.