1) The type of fan is determined according to the nature of the conveying gas, the air volume and resistance of the system. For example, general fans shall be used to transport clean air; Explosion proof fan shall be used to transport gas or dust with explosion hazard
2) Considering the air leakage of air duct and equipment and the inaccuracy of resistance calculation, the fan shall be selected according to the following air volume and pressure: Pf · Kp· Δ P Pa Lf=KL · L m3/h, where Pf -- air pressure of fan, Pa; Lf -- air volume of fan, m3/h; Kp -- additional coefficient of wind pressure, general air supply and exhaust system Kp=1.1~1.15; Dedusting system Kp=1.15 ～ 1.20; KL -- additional coefficient of air volume, general air supply and exhaust system KL=1.1; Dedusting system KL=1.1 ～ 1.15; Δ P -- total resistance of the system, Pa; L -- total air volume of the system, m3/h
(3) When the fan works in non-standard state, the fan performance shall be converted according to the following formula, and then select the fan type from the sample with this parameter Lf - fan air volume in standard state, m3/h—— Fan air volume under non-standard state, m3/h; Pf -- wind pressure of fan under standard state, Pa—— Fan air pressure under non-standard state, Pa—— Air density in non-standard state, kg/m3. When the air state changes, the actual required motor power will change, so it is necessary to check whether the motor power matched on the sample meets the requirements.
Fan performance can also be expressed by dimensionless flow coefficient, pressure coefficient and power coefficient. The conversion formulas of these dimensionless performance parameters (also called dimensionless coefficients) are derived from the similarity theory. Fans of the same type are similar (including geometric similarity, kinematic similarity and dynamic similarity), so dimensionless performance parameters of fans of the same type are equal. I.e
Where α、β、γ—— Flow coefficient, pressure coefficient, power coefficient, dimensionless;
ρ—— Air density, kg/m3;
D -- outer diameter of fan impeller, m;
U - tangential velocity around the impeller, m/s;
H -- air pressure of fan, Pa;
Q -- air volume of fan, m3/s.
According to the similarity theory and the dimensionless coefficient formula above, the conversion formula of fan performance of the same type can be obtained as follows:
Q/Q' = ( D/D')3(n/n')
H/H' = ( ρ/ρ') ( D/D')2(n/n')2 (7-2-4)
N/N' = ( ρ/ρ') ( D /D ')5(n/n')3
In the formula, Q, Q '- air volume of two fans to be converted, m3/s;
H. H '- wind pressure of two fans to be converted, Pa;
N. N '- power of two fans to be converted, kw;
D. D '- Impeller straight diameter of two fans to be converted, m;
n. N '- rotating speeds of two fans to be converted, rpm;
ρ、ρ'—— Is the air density of the two fans to be converted, kg/m3.
The above formula can be used for conversion of performance parameters between any two fans of the same type, and also for analysis of performance changes of the same fan under different speeds and air densities.
The purpose of measuring the fan characteristics is to comprehensively use the measurement methods and technologies of wind pressure parameters and fan motor electrical parameters to test the aerodynamic performance of the fan, draw the fan operation characteristic curve and analyze it, so as to evaluate whether the operation state of the ventilation and dust removal system meets the ventilation requirements.
① Air flow parameter measurement: including fan air volume and air pressure measurement. It is required to master the test methods and specifications of the fan aerodynamic performance measurement system, and master the zero point setting, working principle, measurement operation and pressure calculation of the pressure gauge.
② Fan motor power parameters: including motor power, current, voltage and revolutions. It is required to master the measuring methods and instrument operation of revolutions, power, current and voltage
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