The role of axial fans and centrifugal fans in mechanical ventilation

1. Due to the large difference between the temperature and the grain temperature, a ventilation time should be selected during the day to reduce the difference between the grain temperature and the temperature and reduce the occurrence of condensation. In the future, ventilation should be carried out at night as much as possible, because this type of ventilation is mainly for cooling. At night, the atmospheric humidity is relatively high and the temperature is low, which not only reduces the loss of water, but also makes full use of the low temperature at night to improve the cooling effect.

2. In the early stage of centrifugal fan ventilation, there may be condensed water on doors, windows, walls and even surfaces. As long as the fan is stopped, the window is opened, the axial flow fan is turned on, and the grain surface is rotated when necessary to exhaust the hot and humid air in the warehouse. When the axial fan is used for slow ventilation, there will be no condensation, only the grain temperature in the middle and upper layers rises slowly, and the grain temperature drops steadily after continuous ventilation.

3. When using the axial fan for slow ventilation, due to the small air volume of the axial fan and the poor thermal conductivity of the grain, the ventilation of individual parts in the early stage of ventilation is easy to be slow, and the grain temperature of the entire warehouse will gradually balance with the continuous ventilation.

4. Grain with slow ventilation must be cleaned with a vibrating screen, and the grain entering the warehouse must be cleaned in time. The impurity area is caused by automatic classification, otherwise it is easy to cause uneven local ventilation.

5. Calculation of energy consumption: Warehouse No. 14 was ventilated by axial flow fan for 50 days, an average of 15 hours a day, a total of 750 hours. The average moisture content decreased by 0.4%, and the average grain temperature decreased by 23.1 degrees. The unit energy consumption is 0.027kw. H/T.°C. Warehouse 28 was ventilated for 6 days and 126 hours. The average moisture content decreased by 1.0%, and the average temperature decreased by 20.3℃. The unit energy consumption is 0.038kw. H/T.°C.

6. The advantages of low-speed ventilation with axial fans are: good cooling effect; low unit energy consumption, which is particularly important today when energy conservation is advocated; ventilation timing is easy to grasp, and dew condensation is not easy; 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 fan: obvious cooling and precipitation effect, short ventilation time; disadvantages: high unit energy consumption; poor ventilation timing, easy to cause condensation.

8. Conclusion: In order to reduce the ventilation temperature, the axial flow fan should be used for safe, efficient and energy-saving slow ventilation; for the precipitation ventilation, the centrifugal fan should be used.

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