Effect of impurity and content of imperfect grains on heat and carbon dioxide transfer characteristics during self-heating process of imported corn grain bulk

To study the transfer characteristics of heat and carbon dioxide during local heating of imported corn piles with different content of impurities and imperfect grains, imported corn with high moisture (water content of wet base 20.0%) was added to the center of imported corn piles (water content of wet base 14.0%) with different content of impurities and imperfect grains (1%+8%, 3%+11%, 5%+15%) under laboratory conditions to simulate the mildew and heat of grain caused by high moisture in local grain piles, and stored in indoor environment at 20-25℃ for 40 days. The experimental results showed that the temperature of each monitoring point increased first and then decreased. With the increase of the distance from the center hot spot, the temperature rise rate of each monitoring point decreased, and the maximum grain temperature and the final grain temperature decreased. With the increase of the content of impurities and imperfect grains in the grain heap, the increase rate of the central hot spot temperature decreased, and the maximum grain temperature and the final grain temperature increased. The temperature rise rate of other monitoring points decreased, and the maximum grain temperature also decreased, but the final temperature increased. The overall CO₂ gas diffusion rate of the grain pile was:middle layer > lower layer > upper layer. With the increase of the content of impurities and imperfect particles in the grain pile, the CO₂ concentration of each monitoring point increased faster and the highest concentration increased. After 40 days of storage, the fatty acid value and mold number of the central hot spot increased and the moisture content decreased with the increase of the content of impurities and imperfect grains in the grain pile. The research results can further provide basic data for the discovery, monitoring and control of grain stacking hotspots, and provide guidance for the monitoring and prevention of abnormal grain conditions during the storage of imported corn.