Temperature dynamics of the heat-pipe low-temperature grain storage with fluorine-free refrigerant HCR22

Abstract: Storage quality has posed a great influence on the grain security in recent years. It is of great social significance to improve the management level of warehousing for the high quality of stored grain. Traditional grain storage cannot fully meet large-scale production, due to the high energy consumption and environmental problems. It is necessary to develop the green technology of low-temperature grain storage by mechanical refrigeration. In this study, an environment-friendly low-temperature granary was designed using the natural coldness resource. The cold storage was used as the heat pipe with the fluorine-free refrigerant HCR22. The heat-pipe low-temperature grain storage was mainly composed of the grain warehouse, heat pipe group, real-time temperature detection system, dewing control system, and pressure detector. The new fluorine-free hydrocarbon refrigerant HCR22 was selected as the circulating medium of the heat pipe group, rather than the traditional Freon refrigerant R22. A test granary was installed to verify the practical feasibility of the low-temperature heat-pipe system. The test position was selected in the middle and high latitudes with a temperate monsoon climate, located in the Chengyang District, Qingdao, Shandong Province, China (120°12′ E, 36°20′ N). The dynamic parameters of grain temperature were measured in the different positions at the evaporation section of the HCR22 and R22 heat-pipe warehouse using a multi-channel temperature recorder during 365-day grain storage. The warehouse without a heat pipe was set as the control group. An electrical conductivity meter was also utilized to detect the moisture content of wheat and the conductivity of grain leaching solution. The results showed that the HCR22 refrigerant performed the lower temperature grain storage with the natural cold source in the heat-pipe cold storage, compared with the Freon refrigerant R22. The running time of the HCR22 heat-pipe warehouse was from November 25 to March 10 of the next year (a total of 108 days of cold storage). The cyclic process of the heat-pipe cold storage was characterized by the steam rising and the condensate dropping. The external and natural cold source was then accumulated gradually into the grain pile, indicating the "cold core" phenomenon. The accumulated cold energy was diffused finally into each grain layer. The lowest and average temperatures of wheat were achieved at -3.10 ℃ and lower than 16 ℃, respectively, after the 365-day grain storage in the HCR22 heat-pipe warehouse. There was an even and gentle drop of temperature in the different positions inside the granary, indicating the low or quasi-low temperature storage. There was lower water loss of wheat grains and lower damage of membrane lipid peroxidation on the seed cell membrane under the quasi-low temperature environment in the HCR22 heat-pipe warehouse. Specifically, the moisture content of wheat decreased by 0.29%, whereas, the conductivity of grain leaching solution increased by 4.20 μS/cm during storage. The energy-free and environmentally friendly grain storage can be expected for the middle and high latitudes. The finding can provide a scientific basis to upgrade technology in green grain storage.