1 Due to the large difference between air temperature and grain temperature, the first ventilation time should be selected during the day to reduce the difference between grain temperature and temperature and reduce the occurrence of condensation. The future ventilation should be carried out at night as much as possible, because this ventilation is mainly for cooling, and the atmospheric humidity is relatively high and the temperature is low at night, which not only reduces the water loss, but also makes full use of the low temperature at night, which improves the cooling effect. .
2. In the early stage of ventilation with centrifugal fans, condensation may occur on doors and windows, walls, and even slight condensation on the grain surface. Just stop the fan, open the window, turn on the axial flow fan, and turn the grain surface if necessary to remove the hot and humid air in the bin. It can be done outside. However, there will be no condensation when the axial flow fan is used for slow ventilation, only the grain temperature in the middle and upper layers will rise slowly, and the grain temperature will drop steadily as the ventilation continues.
3 When using the axial fan for slow ventilation, due to the small air volume of the axial fan and the fact that the grain is a poor conductor of heat, it is easy to cause slow ventilation in individual parts in the early stage of ventilation. As the ventilation continues, the grain temperature of the whole warehouse will gradually balance.
4 Grain for slow ventilation must be cleaned by a vibrating screen, and the grain entering the warehouse must be cleaned in time for the impurity area caused by automatic classification, otherwise it is easy to cause uneven local ventilation.
5 Calculation of energy consumption: The axial flow fan in No. 14 warehouse has been used for a total of 50 days of ventilation, with an average of 15 hours per day and 750 hours of sharing. h/t.°C. Warehouse No. 28 has been ventilated for 6 days for a total of 126 hours, the moisture content has dropped by 1.0% on average, the temperature has dropped by 20.3 degrees on average, and the unit energy consumption is: 0.038kw.h/t.℃.
6 Advantages of slow ventilation with axial fans: good cooling effect; low unit energy consumption, which is particularly important today when energy conservation is advocated; ventilation timing is easy to grasp, and condensation is not easy to occur; no separate fan is required, which is convenient and flexible. Disadvantages: Due to the small air volume, the ventilation time is long; the precipitation effect is not obvious, and the high-moisture grain should not be ventilated with an axial flow fan.
7 Advantages of centrifugal fans: obvious cooling and precipitation effects, short ventilation time; disadvantages: high unit energy consumption; poor ventilation timing is prone to condensation.
8 Conclusion: In the ventilation for the purpose of cooling, the axial flow fan is used for safe, efficient and energy-saving slow ventilation; in the ventilation for the purpose of precipitation, the centrifugal fan is used.
