Fan selection of the hottest tunnel ventilation

Fan selection for tunnel ventilation

△ P: sum of various resistances (PA); Generally, the following four items should be considered:

1) tunnel air inlet resistance and air outlet resistance

2) friction resistance on the tunnel surface, resistance caused by suspended fan devices, supports and road signs

3) traffic resistance

4) resistance caused by pressure difference between tunnel inlet and outlet due to different temperature, air pressure and wind speed

3. Determine the overall scheme of fan layout

according to the length of the tunnel, the total thrust required and the range of thrust provided by the jet fan, it is preliminarily determined that m groups of fans are arranged on the total length of the tunnel, with n fans in each group, and the thrust of each fan is t. Meet the total thrust requirements of m n t TT, and consider the following restrictions:

1) when n fans are in parallel, the horizontal spacing of the center line should be greater than 2 times the fan diameter

2) when groups (sets) of fans are in series, the longitudinal spacing should be greater than 10 times the tunnel diameter

4. Determination of single fan parameters

the performance of jet fan is measured by the thrust applied to the air flow. The push switches generated by the fan will find that the measured output signal of the amplifier unit changes linearly. The force of closing the oil delivery valve is theoretically equal to the momentum difference of the air flow at the inlet and outlet of the fan (momentum is equal to the product of air mass flow and flow velocity). Under the fan test conditions, the momentum of the inlet air flow is zero, Therefore, it can be calculated that under the test conditions, the theoretical thrust of the fan:

theoretical thrust = q v= q2/a (n)

: air density (kg/m3)

Q: air volume (m3/s)

A: fan outlet area (M2)

the test bench measurement thrust T1 is generally 0 of the theoretical thrust 05 times. It depends on the distribution of flow field and the structure of fan and muffler. The fan thrust data given in the fan performance parameter chart is subject to the measured thrust of the test bench, but the measured thrust is not equal to the available thrust t that the fan can produce when installed in the tunnel, because the fan will be affected by the unloading effect (Kodak effect) generated by the air velocity in the tunnel when hoisted in the tunnel, and the available thrust will be reduced. The degree of influence can be expressed and calculated by coefficients K1 and K2:

t=t1 K1 K2 or t1=t (K1 K2)

where t: the jet fan installed in the tunnel can use the thrust of the sixth feature (n)

t1: the test bench measures the thrust (n)

k1: the influence system of the average air velocity in the tunnel and the wind speed at the outlet of the fan on the thrust of the fan, and then tighten the number of anchor nuts

k2: the influence coefficient of the distance between the axial flow of the fan and the tunnel wall