# Experimental Study on Drying Characteristics of Alfalfa Hay Bales Using Hot Air Convection
## 1 Introduction
Although they have higher energy consumption compared to microwave drying and other technologies, they are more favorable for preserving nutrients such as proteins [18]. By optimizing drying parameters, drying efficiency can be further improved, and the quality of alfalfa can be better retained [19]. [PERSON] [20] pointed out that different drying management methods have a significant impact on alfalfa hay production. Alfalfa hay dried in the sun and turned over has poorer quality, mainly due to leaf shedding, which reduces the proportion of nutrient-rich leaves in the final hay, thereby lowering its overall nutritional content. [PERSON] [21] studied the drying process of high-moisture whole alfalfa bales and found that time has the greatest impact on bale moisture content, followed by temperature and then air velocity. The interaction between air velocity and drying time is the most significant. [PERSON] [22] evaluated color differences and protein solubility and concluded that the optimal temperature for hot air drying is 175 \({}^{\circ}\)C, at which the quality and nutritional content of alfalfa are better preserved. [PERSON] [23] conducted hot air drying experiments on alfalfa at temperatures of 40 \({}^{\circ}\)C and 120 \({}^{\circ}\)C and found that when the medium temperature increases by 10 \({}^{\circ}\)C, the drying speed can be increased by 10-15%. [PERSON] [24] found through computer simulation and field experiments that when the inlet air temperature is between 500 \({}^{\circ}\)C and 800 \({}^{\circ}\)C, the temperature of the drying grass segments can reach 90 \({}^{\circ}\)C or even higher, indicating that high-temperature drying media can significantly improve drying efficiency. The relative humidity of hot air also has a certain impact on the quality of alfalfa and drying efficiency. [PERSON] et al. [25] found that when the relative humidity of hot air is 20% (w.b. ), the drying time of the samples is the shortest, while at a relative humidity of 40% (w.b. ), the color difference \(\Delta\)E is the smallest when compared to the fresh sample. [PERSON] [26] found that the moisture concentration at different depths of the leaves during the drying process has a significant impact on the drying mechanism, with more moisture removed near the surface than in the middle layer, indicating a high initial moisture removal rate that gradually decreases as the drying process continues. Despite numerous studies discussing optimization methods for the uniformity of alfalfa hay bales, involving the initial moisture content, drying temperature, and other processes and parameters, there is still a lack of systematic research on how to precisely control drying parameters to achieve the best drying effect for alfalfa with different initial states. This study uses hay bale drying and test equipment to systematically investigate the effects of the initial moisture content (25-30%), bale density (110-180 kg/m\({}^{3}\)), drying temperature (50-90 \({}^{\circ}\)C), and air velocity (1-3 m/s) on the drying performance of alfalfa hay bales, including drying rate and uniformity, analyzes energy consumption patterns under different drying conditions, and discusses the relationship between bale density and airflow resistance. This work aims to provide valuable references for the production of high-quality alfalfa hay in livestock production.