## 3 Results and Discussions
### The Thermal Efficiency of the Drying System  
Thermal efficiency (\(\eta\)) is defined as the ratio of the effective output energy to the total energy input into a specific thermal system [41], which was widely used to evaluate the thermal performance of the agricultural product drying system [42]. In order to investigate the thermal performance of the key components of the drying system, the variations of the thermal efficiency of CC (\(\eta_{CC}\)), HE (\(\eta_{HE}\)), DC (\(\eta_{DC}\)), RA (\(\eta_{RA}\)) and the whole drying system (\(\eta_{S}\)), with drying time for the three drying processes, are depicted in Figure 7.  
As can be seen from the above Figure 7, the \(\eta_{HE}\) for the drying process of \(\alpha=75^{\circ}\), \(\alpha=90^{\circ}\) and optimized drying process were ascertained to be varied within the ranges of 85.03-89.56%, 77.57-82.01% and 81.08-95.21%, respectively, and the \(\eta_{CC}\) for the three processes were all above 93%. By comparing Figure 7a-c, it can be found that the \(\eta_{HE}\) and \(\eta_{DC}\) for the optimized drying process were higher than that of the other two drying processes under the same drying time (especially in the 1 st drying cycle), respectively, indicating that the optimized drying process showed a better thermal performance in the HE and DC. Additionally, DC was the key component for evaporating moisture from the wet corn material, and \(\eta_{DC}\) was one of the most important indexes for evaluating the drying capacity of the whole drying system. It can be seen from the above three figures that \(\eta_{DC}\) decreased with the increase of drying time and that the variation range of \(\eta_{DC}\) for the drying processes of \(\alpha=75^{\circ}\), \(\alpha=90^{\circ}\) and optimized drying process were ascertained to be 4.09-35.43%, 2.49-30.49% and 6.81-41.71%, respectively. Furthermore, in order to obtain a better understanding of the energy saving performance of the optimized drying process, the total energy input into the drying system and the \(SHC\) for the three drying processes, respectively, were depicted in Figure 8a,b. As can be seen from Figure 8a, the total energy consumption of the optimized drying process was lower than that of the other two processes. On the other hand, \(SHC\) was the key index for evaluating the drying difficulty of the corn in the drying system and could be calculated by the Equation (31); the calculation results are shown in the following Figure 8b. It can be seen from the figure that the average \(SHC\) for the optimized drying process, \(\alpha=75^{\circ}\) and \(\alpha=90^{\circ}\) were 7290.269, 8068.129 and 8881.118 MJ, respectively, indicating that the drying difficulty of the optimized drying process was lower than that of the other two processes.  
Figure 6: The heat loss characteristics (**a**) and the total heat loss (**b**) of the drying system for the three drying processes.  
Figure 8: The total energy input into the drying system (**a**) and the specific heat consumption (**b**) of the drying system for the three drying processes.  
Figure 7: The thermal efficiency of the key components for the drying process of \(\alpha=75^{\circ}\)(**a**), \(\alpha=90^{\circ}\)(**b**) and the optimized drying process (**c**).