Research Of Coupled Heat And Moisture Transfer In Hygroscopic And Respiration Grain Bulk During The Warehousing Storage

Temperature and moisture content are the two most important parameters while grain storage for a long time, and they have important influence to the stored grain fever mildew, and decide good or bad of the grain quality. Seasonal temperature changes in the external environment and grain itself has respiration are the main factors causing the heat transfer and moisture migration within the grain bulk. In view of this, choose wheat to grain moisture, moisture absorption and respiration solution stack moisture and temperature-induced changes.In the grain bulk, because of temperature gradient, moisture moves from the high-temperature region to the low-temperature region, which can cause low-temperature region’s moisture over the grain bulk safe moisture, and microorganism in grain bulk increase rapidly,bring the deterioration of the grain bulk. Extreme case, when air encountered cold air grain bulk surface, even lower than the dew temperature, can cause moisture to condense on the wall or surface of the grain barn, and increase the moisture content of this region. This time, we need to take measures (such as ventilation, drying) to reduce moisture content, and prevent wheat mildew.Based on macroscopic volume method and local heat balance principle, this paper analyzes the effect of natural convection which caused by atmospheric temperature, and considers the impact of respiration to temperature and moisture, and then construct a mathematical model of moisture migration and temperature transfer in the grain bulk. This research is a 5 m radius,10 m height cylindrical bin. The cylindrical bin is a symmetric figure, so we select cylindrical bin s half axial section as a geometric model to be calculated in this paper. Compared with the results by Kosher K. KhanKari verified the feasibility of the model established in this paper.We studied two types of winter and summer conditions in this paper, outside ambient temperature taken daily temperature changes with 100 days as a cycle. When the initial temperature of the grain bulk is-10 ℃, approximate seen in winter conditions; when the initial temperature of the grain bulk is 30 ℃, approximate seen in summer conditions. Whether it is winter or summer conditions are both simulated initial moisture of 12% and 14% of the cases, all cases areas divided consider the respiratory source term and does not consider respiratory source two cases for comparative analysis moisture and temperature changes caused by respiration of wheat. In winter cases, temperature throughout the period were lower than the temperature placed in granary(30 ℃),because of the temperature gradient between the external environment and the grain bulk, over time, grain bulk temperature decreases from the inside out; In summer cases, temperature throughout the period were higher than the temperature placed in granary(-10 ℃),over time, similar to winter conditions, formed temperature gradient between the external environment and the grain bulk, grain bulk temperature gradually increased from the inside out. Temperature gradient is an important factor causing moisture migration. In winter cases, the internal temperature of the grain bulk is higher but lower on the boundary, moisture move to the upper boundary and right boundary of the simulation region, and the moisture gradient focused on upper boundary, right boundary and bottom boundary, this can provide guidance for the security grain storage. So in winter cases, we need to focus on the upper and the boundary of grain bulk.In summer cases, moisture move from the upper boundary and right boundary to the simulation region, and the moisture gradient focused on upper boundary, right boundary and bottom boundary, this can provide guidance for the security grain storage.Because of steam conservation and fluid flow,the moisture content in boundary area are lower than other areas.But summer cases are not obvious than winter cases.In summer cases,the initial temperature is lower than winter,so the respiration of wheat is weak, produced less water.