The difference between centrifugal fan, axial flow fan and mixed flow fan
Relying on the input mechanical energy, a machine that increases the gas pressure and discharges the gas, it is a driven fluid machine.
Centrifugal fans are widely used in:
①Ventilation, dust removal and cooling of factories, mines, tunnels, cooling towers, vehicles, ships and buildings;
②Ventilation and induced draft of boilers and industrial furnaces;
③ Cooling and ventilation in air conditioning equipment and household appliances;
④Drying and selection of grains;
⑤ The wind source of the wind tunnel and the inflation and propulsion of the hovercraft.
2. Axial flow fan
It is the airflow in the same direction as the axis of the fan blade, such as electric fans, air conditioner outdoor fans are axial flow fans. It is called "axial flow" because the gas flows parallel to the fan axis.
Axial flow fans are usually used in applications with high flow requirements and low pressure requirements.
Axial fans fix the position and move the air.
Small axial fan: low power consumption, fast heat dissipation, low noise, energy saving and environmental protection, etc. Due to 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 function options.
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 allows the air to perform both centrifugal motion and axial motion, and the movement of the air in the shell mixes the two motion forms of axial flow and centrifugal.
Combines the features of axial and centrifugal fans, although it looks more like a traditional axial fan. Weld the curved plate blades on the conical steel hub. The flow is varied by changing the angle of the blades in the inlet casing upstream of the impeller. The enclosure can have an open inlet, but more often it has a right-angled bend shape that allows the motor to be placed outside the duct. The drain shell expands slowly to slow the flow of air or gas and convert kinetic energy into useful static pressure.
Mainly used for mine ventilation and tunnel ventilation.
1. The centrifugal fan changes the flow direction of the medium in the air duct, while the axial flow fan does not change the flow direction of the medium in the air duct;
2, the former installation is more complicated.
3. The former motor and the fan are generally connected by a belt driven rotating wheel, and 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, etc. The latter is often installed in the air duct, or at the front end of the air duct outlet.
5. The former is pressurized after the air is received, and the latter is driven by positive pressure.
Diagonal flow (mixed flow) fan:
1. The wind pressure coefficient is higher than that of the axial flow fan, and the flow coefficient is larger than that of the centrifugal fan.
2. It fills the gap between the axial flow fan and the centrifugal fan.
3. Simple and convenient installation.
The difference between centrifugal fan and axial fan at startup:
The operating power of the centrifugal fan increases with the increase of the air volume, so the air door of the centrifugal fan should be fully closed when it is started, and then gradually open to avoid the excessive current of the fan and the burning of the motor.
The operating power of the axial flow fan decreases with the increase of the air volume, so when the axial flow fan is started, the damper should be fully opened, and then gradually closed to the required air volume value.
Two types of action
The role of axial fans and centrifugal fans in mechanical ventilation:
1. Due to the large difference between 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, there may be condensation 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 warehouse. Just outside the warehouse. 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 an 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 some parts in the early stage of ventilation. As the ventilation continues, the grain temperature of the whole warehouse will gradually balance. .
4. 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 axial flow fan should not be used for ventilation in places with high moisture content.
5. Advantages of centrifugal fan: obvious cooling and precipitation effect, short ventilation time