1. Centrifugal fan
Relying on the input mechanical energy, the machine that increases the gas pressure and discharges the gas. It is a driven fluid machine.
Centrifugal fans are widely used in:
①Ventilation, dust exhaust and cooling of factories, mines, tunnels, cooling towers, vehicles, ships and buildings;
②Ventilation and induced air for boilers and industrial furnaces;
③Cooling and ventilation in air conditioning equipment and household appliances;
④ Drying and selection of grains;
⑤The wind source of the wind tunnel and the inflation and propulsion of the hovercraft.
2. Axial fan
It is the air flow in the same direction as the axis of the fan blades, such as electric fans, air conditioners outside the fan is an axial fan. It is called "axial flow" because the gas flows parallel to the fan axis.
Axial fans are usually used in occasions with higher flow requirements and lower pressure requirements.
The axial fan fixes the position and moves the air.
Features:
Small axial fan: low power consumption, fast heat dissipation, low noise, energy saving and environmental protection. Because of its small size, it is widely used.
Large axial flow fan: It has the characteristics of simple structure, stable and reliable, low noise, large air volume, and wide range of functions.
3. Diagonal flow fan/mixed flow fan
The fan between the axial flow fan and the centrifugal fan, the impeller of the diagonal flow fan makes the air do both centrifugal movement and axial movement, and the movement of the air in the shell mixes the two forms of axial flow and centrifugal movement.
Combines the characteristics of axial and centrifugal fans, although it looks more like a traditional axial fan. The curved plate-shaped blade is welded to the conical steel hub. The flow rate is changed by changing the angle of the blades in the inlet casing upstream of the impeller. The housing can have an open entrance, but more commonly, it has a right-angled shape so that the motor can be placed outside the pipe. The drain shell expands slowly to slow down the air or gas flow and convert kinetic energy into useful static pressure.
Mainly used for mine ventilation and tunnel ventilation.
the difference:
1. The centrifugal fan changes the flow direction of the medium in the duct, while the axial flow fan does not change the flow direction of the medium in the duct;
2. The former is more complicated to install.
3. The former motor and fan are generally connected by a belt to drive the rotating wheel, while the latter motor is generally in the fan;
4. The former is often installed at the inlet and outlet of air conditioning units, boiler drums, induced draft fans, and so on. The latter is often installed in the middle of the duct or at the front end of the duct outlet.
5. The former is pressurized after air is collected, and the latter is driven by positive pressure.
Diagonal flow (mixed flow) fan:
1. The wind pressure coefficient is higher than that of axial flow fans, and the flow coefficient is larger than that of centrifugal fans.
2. Fill the gap between the axial flow fan and the centrifugal fan.
3. The installation is simple and convenient.
The difference between centrifugal fan and axial fan at startup:
The operating power of the centrifugal fan increases with the increase in air volume, so the air door of the centrifugal fan should be fully closed when it is started, and then gradually opened to avoid excessive fan current and burn the motor.
The operating power of the axial flow fan decreases with the increase of the air volume, so when the axial flow fan starts, the damper should be fully opened, and then gradually closed to the required air volume value.
Two types of effects
The role of axial fans and centrifugal fans in mechanical ventilation:
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 gap between grain temperature and air temperature and reduce the occurrence of condensation. In the future, the ventilation should be carried out at night as much as possible, because this ventilation is mainly for cooling. At night, the atmospheric humidity is relatively high and the temperature is relatively low, which reduces water loss and makes full use of the low temperature at night to improve the cooling effect. .
2. In the initial stage of ventilation with centrifugal fans, condensation on doors, windows, walls, and even slight condensation on the surface of the grain may occur. Just stop the fan, open the windows, turn on the axial fan, and turn the grain surface if necessary to remove the hot and humid air in the warehouse. Just outside the warehouse. However, if the axial flow fan is used for slow ventilation, there will be no condensation, and only the middle and upper grain temperature will rise slowly. As the ventilation continues, the grain temperature will drop steadily.
3. When the axial flow fan is used for slow ventilation, because the air volume of the axial flow fan is small, and the grain is a poor conductor of heat, it is easy to ventilate some parts slowly at the initial stage of the ventilation. As the ventilation continues, the grain temperature in the whole warehouse will gradually balance. .
4. The advantages of slow ventilation with axial flow fans: good cooling effect; low unit energy consumption, which is particularly important today when energy saving 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 axial flow fan is not suitable for ventilation in high moisture areas.
5. The advantages of centrifugal fans: obvious cooling and precipitation effects, short ventilation time;
Disadvantages: high energy consumption per unit; poor ventilation timing is prone to condensation.
