# Drying Characteristics of Chicken Manure Under a Variable Temperature Process
## 3 Results and Discussion  
### Drying Characteristics at Different Drying Temperatures  
The drying of chicken manure was carried out in two stages. The drying temperature in the first stage was maintained at 20 \({}^{\circ}\)C. When the moisture content of the chicken manure dropped to 45%, the drying temperature increased to 45, 50, 55, 60, and 65 \({}^{\circ}\)C in the different experimental groups, with an air velocity of 1.2 m/s throughout the drying process. As shown in Figure 3, the drying time gradually decreased with increasing drying temperature during the second stage. [PERSON] et al. found that temperature was the primary factor influencing the hot-air drying rate of porous materials such as sludge, and increasing temperature can improve the dehydration rate [16]. The results of the experiments demonstrated that as the drying temperature increased by 5 \({}^{\circ}\)C each time, the duration taken to reduce the moisture content of the manure to 10% was reduced by 3.2, 4.3, 2.5, and 1.3 h. When the drying temperature in the second stage reached 55 \({}^{\circ}\)C, the effect on reducing drying time was significantly greater than at other temperatures (\(p<0.05\)). This can be explained by the evaporation dynamics of water in chicken manure. At the early stage of drying, the primary water removed is free water on the surface, which evaporates easily. In the middle and later stages, the primary water removed includes capillary water, adsorbed water, and bound water, which require higher heat energy to evaporate [17; 18; 19]. Although increasing the drying temperature enhances the drying rate, once the moisture content drops below 30%, the remaining water is primarily bound water, and the effect of temperature on increasing the drying rate diminishes. Therefore, the experimental data indicated that the drying times for the drying temperatures of 55 \({}^{\circ}\)C, 60 \({}^{\circ}\)C, and 65 \({}^{\circ}\)C were not significantly different (\(p>0.05\)). Consequently, to effectively shorten the drying time at a lower temperature, the optimal drying temperature for the second stage was determined to be 55 \({}^{\circ}\)C.  
Since the experiment aimed to simulate the real drying conditions, the energy consumption in the first drying stage was calculated based only on the fan's energy consumption. In contrast, in the second drying stage, the total energy consumption was determined by measuring the combined energy usage of both the fan and the electric heater. According to the experimental results shown in Figure 4, when the drying temperatures in the second stage were set at 45, 50, 55, 60, and 65 \({}^{\circ}\)C, the corresponding energy consumption values were 2.79, 2.52, 2.36, 2.48, and 2.87 kWh, respectively. The analysis of the results revealed that energy consumption was significantly higher at drying temperatures of 45 \({}^{\circ}\)C and 65 \({}^{\circ}\)C (\(p<0.05\)). At 45 \({}^{\circ}\)C, the energy consumption peaked because the drying time was the longest, leading to the increase in fan energy usage. The longer the drying time, the higher the fan's energy consumption. On the other hand, as the temperature increases, the power  
Figure 3: Effect of drying temperature in the second stage on drying time of the variable temperature process. Notes: Different letters (a, b, c) are significant (\(p<0.05\)). The same letters are not significant. of the electric heater rises. The experimental results further indicated that when the drying temperature exceeded 60 \({}^{\circ}\)C, energy consumption again began to rise. Therefore, to achieve optimal energy efficiency, the most suitable drying temperature for the second stage was determined to be 50-60 \({}^{\circ}\)C. Using traditional drying methods, we could see that previous studies had concluded that drying temperature was generally positively correlated with energy consumption. For example, [PERSON] et al.