Peripheral knowledge of PPH equipment: common sense of fans (3)

Four. Brief introduction of main performance parameters
To understand the performance of the fan, you must correctly grasp the meaning of the main performance parameters of the fan.

1. Status of import standards for ventilators:
It refers to a gas with a pressure of one atmosphere (760 mmHg) at the inlet of the ventilator, a temperature of 20°C, a relative humidity of 80%, and an air density of 1.2Kg/cm.

2. Air volume:
Air volume refers to the volume of air flowing in a unit of time. If there is no shunt and air leakage, this parameter is a constant in the whole process. When the formula system is adopted, the unit generally uses m3/h (cubic meters/hour), but also m3/min (cubic meters/minute) and m3/s (cubic meters/second).
Wind volume (Q): Unit:
1 cubic meter per second (CMS) = 60 cubic meters per minute (CMM) = 3600 cubic meters per hour (CMH)
1 cubic foot/minute (CFM)=1.7CMH, 1 cubic liter/second (L/S)=3.6m3/h.

3. Static pressure, dynamic pressure and total pressure:

In a centrifugal fan, air first enters the central area of ​​the impeller, and then under the push of centrifugation, the air will flow to the outer edge of the impeller, and then the airflow will pass through the blades to the volute, converting part of the dynamic pressure into static pressure, and passing through the outlet discharge.
In the pipeline, the movement of the incompressible fluid obeys the Berlier principle, that is, in addition to the friction loss and the loss of the vortex formed at the variable load surface of the wind pipe, the fluid has three forms of energy, namely total energy, potential energy, The sum of kinetic energy will remain constant.
The total pressure (Pt) refers to the sum of its static pressure and dynamic pressure.
Static pressure (Ps) refers to the force in all directions per unit surface area, and it has nothing to do with the force of speed.
Dynamic pressure (Pd) refers to the pressure represented by the kinetic energy of the gas on the outlet surface of the fan.
In air-conditioning units, the concept of "external pressure" or "outlet pressure" is often mentioned. It refers to the overall static pressure of the air-conditioning box. When converting to the static pressure of the fan, the machine of the air-conditioning box The value of internal resistance loss.
The total pressure of the fan at this time = the resistance loss inside the air-conditioning box + the residual pressure outside the machine + the dynamic pressure of the fan
Remember not to treat the residual pressure outside the machine directly as the static pressure of the fan.
The pressure unit is Pa, and there is also mmAq (millimeter water column). 1mmAq is approximately equal to 9.8Pa. When calculating, it can be calculated as approximately 10Pa.
1 inch of water column (inAq)=25.4mmAq
It is worth noting that in the operating pipe network, the air duct before the inlet of the ventilator is the suction section, and the air duct after the outlet is the air supply section. The static pressure in the suction section is negative, and the static pressure in the air supply section is positive. The dynamic pressure is always positive. The total pressure is the algebraic sum of the two (Pt=Ps+Pd).
Pd=ρV2/2 (Pd is the dynamic pressure, ρ is the air density in the operating state, generally 1.2, and V is the wind speed of the corresponding part of the calculation pipeline)

4. The speed of the fan: the speed of the fan represents the rotation speed of the impeller per second. It is customarily represented by n and the unit is r/min (rpm).

5. Shaft power and installation power:

The power curve in each figure represents the actual power consumption of the fan, that is, the shaft power. The unit is KW (kilowatt) or HP (horsepower). When matching the motor power, to avoid the motor overheating, the transmission loss must be calculated, and the system may appear The resistance change caused by the increase of the actual power consumption of the fan. These losses are generally restricted to 15% to 20%. Therefore, to determine the installed power of the motor, the actual power consumption of the fan must be multiplied by 1.2 (safety factor). When the calculated value is at the critical point, a motor with surplus should be selected to avoid overloading and burning of the motor during use.
Optional dual fan motor: find out the fan shaft power PW, multiply it by the safety factor of 2.15*1.2, and select a commercially available motor specification. 1HP=0.746KW.

6. Noise of centrifugal fan:

The sound level (noise) is measured with a sound level meter A at a distance of 1 meter from the tuyere at an angle of 45 degrees to its axis, and the unit is dB(A).
Sound pressure level (LpS) conversion success rate level (LwS), just add 7db to LpS. The noise increases with the increase of the impeller speed. Experience has shown that for similar fans, the increase in noise is usually accompanied by an increase in speed and a decrease in efficiency. That is to say, try to use those fans with large diameter impellers but slow speed and stable operation, so that the working point of the fan falls in the high efficiency area.

7. Fan efficiency: Efficiency is an important indicator of fan performance, which can be calculated by the following formula.

(N%) efficiency = air volume (CMM) * pressure (MMAQ) / K (6120) * shaft power (KW)
Shaft power (KW)=air volume (CMM)*total pressure (MMAQ)/K(6120)* (n%) above the full pressure efficiency, if the pressure is full pressure, the efficiency is full pressure efficiency; if the pressure is static pressure, then Is the static pressure efficiency.

8. Transmission mode:

There are the following types of fan drive modes:
(1) Type A transmission: the motor is directly connected, that is, the wind wheel is directly mounted on the motor shaft.
(2) Type B transmission: the pulley is installed between the two bearings, and the impeller is cantilevered.
(3) Type C transmission: the impeller is installed on one side of the shaft, and the pulley is on the other side of the shaft.
(4) D-type transmission: the impeller cantilever is installed on one side of the shaft and is driven by a coupling.
(5) E-type transmission: the pulley cantilever installation, the impeller is installed between two bearings, and the pulley cantilever installation.
(6) F-type transmission: the impeller is installed between the two bearings and is driven by a coupling.
In actual use, we commonly use A-type transmission, C-type transmission, and E-type transmission. The fan with A-type transmission is suitable for small installation space. However, due to the fixed speed of the motor, the fan parameters cannot be adjusted. The C-type transmission is a pulley type, mostly used when a single suction fan is used for exhaust. Its advantage is that the fan can be adjusted and the air medium does not pass through the transmission components, such as bearings, pulleys, and belts, which can ensure the service life of the accessories. Type C fans are generally used for high temperature and dust removal fans. The E-type transmission is driven by a belt pulley, and it also has the function of adjustment. The double-suction fan mostly uses this transmission method for air supply. Single suction fans also use this transmission method, and the installation size is relatively small. The disadvantage is that bearing maintenance is difficult and cannot be used in high temperature and dusty conditions.

9. Vibration value requirements: 6.3m/s (5.6m/s, 4.0m/s, 3.2m/s, 2.5m/s)　

10. Air duct size and installation: The actual use size and wind speed of the duct (low, medium and high wind speed) are related (V=Q/N), and the material selection of the duct is also related. It is related to wind speed and wind pressure.