Study on temperature field of grain piles in underground grain silos lined with plastic

Abstract: This study aims to explore the temperature changes of grain piles in underground grain silos during storage. The research object was taken as a corn grain pile with 23% high moisture content and a weight of 15 tons, while the underground grain silo with an inner diameter of 3m and a height of 5 m. Firstly, the change of temperature field was analyzed experimentally under static storage conditions. Secondly, the multi-physics software COMSOL was selected to simulate the grain bins with the same size, boundary conditions and height using the theory of heat transfer in porous media. The actual pile height was also utilized to fully consider the influence of grain respiration on the distribution of temperature field in the pile during simulation. A comparison between numerical simulation and experimental data was made to investigate the influence of different initial grain temperatures, grain types and loading seasons on the temperature field in the warehouse. The results show that the grain respiration was strong during the static storage stage. Specifically, the grain pile started to heat up at the bottom, and gradually formed a high-temperature heat core with 22.5 ℃ locating on the place, where was 1m radial and 2m axial from the physical core. Then, the position of heat core moved gradually to the middle and upper part of grain pile, and finally stabilized at the place where was 1m below the grain loading line, resulting in the obvious stratification in the temperature of grain pile. Furthermore, the spatial domain of air temperature descended from 15.1 to 12.2 ℃ in the bin at ambient temperature. The temperature changes of grain layers in the whole experiment chamber were almost unaffected by the air domain temperature, except the fourth layer of grain stack. More importantly, there was a great increase in the temperature of grain pile under various initial grain temperature (5, 15, 25 and 35 ℃). Specifically, the final temperatures of grain pile in the silo were 9.5 and 16.8 ℃, with an temperature increase of 4.5 ℃ and 1.8 ℃, when the initial grain temperatures were 5 and 15 ℃, respectively. The peak values of stack temperature in the silo were 19.2, 26.3 and 41.1 ℃, when the initial grain temperatures were 17.9, 25 and 35 ℃, respectively. The highest increase in temperature was 6.1 ℃ for the grain pile in the warehouse, when the initial grain temperature was 35 ℃. Nevertheless, the temperature declined after the peak. Among five kinds of grain pile (corn, rapeseed, soybean, wheat, and rice), the highest increase in the average temperature was 1.6 ℃ in the rapeseed pile, whereas, the lowest increase was 1.2 ℃ in the corn pile. External environment temperature in different seasons (spring: 17th April to 10th May; Summer: 17th July to 9th August; Autumn: 17th October to 9th November; Winter: 17th January to 9th February) presented little effect on the grain pile temperature in the silo, indicating that the temperature of grain pile in the silo behaved a consistent trend of change under different seasonal conditions. Consequently, the finding can provide a sound reference for practical engineering during storage of high moisture grain in underground silos.