Fan selection general steps

1, calculate the venues to determine the ventilation

The fan air volume is defined as the product of the wind speed V and the cross-sectional area of the air passage F. The large fan can accurately calculate the air volume because it can accurately measure the air volume with the anemometer, so the air volume calculation is very simple.

The number of fans is determined according to the number of ventilation of the selected room. Calculate the total amount of wind required for the plant. Then calculate the number of fans. Formula: N = V × n / Q Where: N-- fan number (units), V-- Ventilation volume (m3), n - Ventilation times (times / hour), Q - Single fan volume (m3 / h) of the selected fan model. Fan model selection should be based on the actual plant. Size of the fan model to match the fan and wet curtain as far as possible to maintain a certain distance (as much as possible, respectively, installed in the plant on both sides of the gable) to achieve good ventilation effect of the exhaust side try not to close to nearby buildings. Nearby households, such as from the indoor air contains pollution of the environment can be installed in the tuyere spray device. Near absorption of pollutants concentrated recovery. Do not pollute the environment

 2, calculate the total thrust required

It = ΔP × At (N)

Among them, At: tunnel cross-sectional area (m2)

△ P: the sum of the resistance (Pa); generally should take into account the following four:

1) Tunnel inlet resistance and outlet resistance;

2) the frictional resistance of the tunnel surface, hanging fan device, brackets and road signs caused by the resistance;

3) Traffic resistance;

4) resistance between the entrance and exit of the tunnel due to pressure difference caused by temperature, pressure and wind speed.

3, to determine the overall layout of the fan program

According to the length of the tunnel, the total thrust required and the scope of the thrust provided by the jet fan, a preliminary set of m fans are arranged on the total length of the tunnel with n units in each group. The thrust of each fan is T.

Satisfy the total thrust requirement of m × n × T≥Tt, taking into account the following restrictions:

1) n typhoon juxtaposed, its horizontal centerline spacing should be greater than 2 times the fan diameter

2) m group (Taiwan) fan series, the longitudinal spacing should be greater than 10 times the tunnel diameter

4, single fan parameters to determine

The performance of a jet fan is measured by its thrust force applied to the airflow. The thrust generated by the fan is theoretically equal to the difference in momentum between the airflow at the inlet and outlet of the fan (the momentum is equal to the product of the mass flow rate of the air flow and the flow rate). In the fan test condition, Momentum is zero, so you can calculate the theoretical thrust of the fan under test conditions:

Theoretical thrust = p × Q × V = pQ2 / A (N)

P: Air density (kg / m3)

Q: Air volume (m3 / s)

A: fan outlet area (m2)

The test bench thrust measurement T1 is generally 0.85-1.05 times the theoretical thrust, which depends on the flow field distribution and the structure of the fan and the silencer. The fan thrust data given in the fan performance parameter diagram are measured on the test bench , But the measured thrust is not equal to the available thrust T that can be generated by the fan in the tunnel because of the effect of unloading the fan when it is hoisted in the tunnel due to the airflow velocity in the tunnel (Kodana effect) , The available thrust decreases.The degree of influence can be expressed and calculated by the coefficients K1 and K2:

T = T1 × K1 × K2 or T1 = T (K1 × K2)

Where T: installed in the tunnel jet fan available thrust (N)

T1: Test bench measurement thrust (N)

K1: Average airflow velocity in the tunnel and the effect of fan outlet velocity on fan thrust

K2: The coefficient of influence of the axial distance between the fan shaft and the tunnel wall