# Experimental Study on Drying Characteristics of Alfalfa Hay Bales Using Hot Air Convection
## 3 Results and Discussion  
### Overall Trend of the Decline in the Moisture Content of Hay Bales  
A total of eight drying experiments (numbered 1# to 8#) were conducted on alfalfa hay bales to examine the changes in the moisture content of different bales under various drying methods, drying temperatures, and drying durations, as shown in Tables 2 and 3. And all the data were calculated and plotted using Excel (Ver. 2019, Microsoft, Redmond, WA, USA). The experiment adopted 70 \({}^{\circ}\)C as the drying temperature. The study by [PERSON] [17] pointed out that the drying rate of oven drying at 70 \({}^{\circ}\)C is significantly higher than that at low temperatures (such as 40 \({}^{\circ}\)C), while higher temperatures may lead to nutrient loss (such as protein degradation). Under the same drying temperature, significant differences in drying efficiency occurred among different forms of hay bale drying, which has a significant effect on the drying intensity and ultimately affects the drying efficiency. As is shown in Figures 4 and 5, when the drying intensity is sufficient to allow hot air to penetrate the bales and remove moisture, the initial density of the bales is related to the drying rate, but the impact is relatively small. When the hot air temperature is around 70 \({}^{\circ}\)C and the air velocity is around 2 m/s, with an initial moisture content of about 30%, the average moisture content of two bales weighing 19 kg and 20 kg, as well as one bale weighing 40 kg, can be reduced to 20% within 2 h. The drying efficiency is 20 kg/h of the original grass. For two bales weighing 25 kg each, the average moisture content can be reduced to 17% (w.b.) within 2 h, with a drying efficiency of 25 kg/h of the original grass. For two bales weighing 27 kg each, the average moisture content can be reduced to 17% (w.b.) within 3 h, with a drying efficiency of 18 kg/h of the original grass. However, when the drying intensity is insufficient and hot air cannot penetrate the bales to remove moisture, the initial density of the bales has a significant impact on the drying rate. For two bales weighing 40 kg each, the average moisture content of the upper bale can be reduced to 17% (w.b.) in about 5 h, while the lower bale's moisture content drops to 25% (w.b.) and then changes very slowly. On July 17, during a drying experiment with three bales, the upper and lower bales had a moisture content of about 30% (w.b.) and weighed 33 kg each, while the middle bale was an old, already-dried bale. After 2 h, the moisture content remained at 27% (w.b. ), indicating that it could not be dried further. Therefore, it is evident that when the drying intensity is sufficient, as the bale density and the amount of grass increase, the drying efficiency of the forage decreases. When the drying intensity is insufficient and the bale density is high, such as in the case of drying two 40 kg bales, the drying intensity at the upper outlet is greater than that at the lower outlet. The hot air tends to accumulate at the upper bale outlet, where the density is relatively lower, leading to particularly slow drying of the other bale. In the case of drying three bales weighing 33 kg each, with the middle bale being an already-dried bale, the upper and lower bales dried very slowly, almost at a standstill. These findings underscore the importance of optimizing drying conditions to ensure sufficient drying intensity, as when the drying intensity is insufficient, the initial density of the bales becomes a significant factor, leading to uneven and inefficient drying. This highlights the need for careful control of drying parameters such as temperature, air velocity, and bale density to achieve uniform and efficient drying. Recent studies [18] have indicated that the effect of the initial moisture content on the drying rate is highly dependent on the material's structure and is not universally applicable. The higher the initial moisture content, the longer the required drying time.