1 Common ventilation method of tunnels

1.1 Natural ventilation

The so -called natural ventilation is to discharge harmful gases and smoke from the tunnel without the role of fan equipment, all relying on the pistons of the car and the role of natural wind. If the natural wind direction of the tunnel is the same as the driving direction of the car, the natural wind is a helping effect, and the time to exclude harmful gases is faster; if the natural wind direction is the opposite of the driving direction of the car, the natural wind is resisting. long.

Natural wind has a small impact on one -way transportation. Generally, the effect of natural ventilation can be evaluated based on the meteorological data that is mastered; Some cars have a resistance effect. The proportion of two parts is more difficult to determine. In addition, the instability of natural winds makes natural ventilation complicated. Therefore, the length of the tunnel of two -way transportation is very short, or the known natural wind is fixed. And when the wind speed is large, the role of natural ventilation is generally not considered.

1.2 Vertical ventilation

(1) Shooting vertical ventilation

The vertical ventilation is to introduce fresh air from one hole, and it is discharged from the way to pollute the air through another hole, or the direction of air flow in the tunnel is consistent with the vertical axis of the tunnel. In this way, the degree of air pollution increases linearly from the entrance to the exit direction. The pollution concentration at the entrance is the smallest and the contamination concentration in the exit is the largest.

During traffic, the ratio of the traffic volume of up and down continuously changes, but the airflow has a certain inertia. In order to avoid the impact of changes in traffic, a certain backup coefficient should be considered, which is generally 1.2. The firewood fan should be installed as outside the boundary, and the airflow sprayed out has a adverse effect on traffic.

(2) The vertical ventilation of the vertical well

 

Vertical ventilation is the simplest ventilation method. When natural ventilation is not satisfied, it is the most economical to supplement with mechanical ventilation. However, the tunnel is too long, and it is not economically set to make up for this shortcoming. Therefore, the long tunnel is often used to use a well. The ventilation method of vertical wells is mostly used for transport tunnels. For the tunnel to the traffic, the vertical well should be set in the middle of the tunnel. In most cases, it is limited by the terrain conditions. It is difficult to set up a well in the middle. When the two sections of the vertical well are not equal, the ventilation resistance of both ends will occur. It is necessary to balance the two sections of the balancing of the radius to make it the required balance of the required air inlet at the bottom of the air inlet at the bottom of the well, so that the two sections of the air volume must meet the requirements.

(3) Half -horizontal ventilation

The pollution concentration of semi -horizontal ventilation is basically close to the same. Send -high ventilation is a common form of semi -horizontal ventilation. Fresh air passes through the air supply pipe directly to the car's exhaust holes, and the air is directly diluted. This pair of subsequent pairs of subsequent pairs The car is beneficial. The pollution air is not easy to diffuse on the tunnel, and it is discharged through the cave doors at both ends.

When two -way traffic, whether it is delivery or excretion, if the intensity of the traffic is equal, the meteorological conditions of the two holes are the same, and the wind pressure in the tunnel is the largest in the central government. At the middle point of the tunnel, the air is still, and the wind speed is zero, which is called a neutral point. In addition to this, the wind speed increases linearly to the two holes.

During one -way traffic, most of the neutral points of ventilation and ventilation move to the entrance. The neutral point of the exhaust -type type is close to the export. The pollution concentration is the same as the opposite traffic. The pollution concentration near the neutral point is high.

(4) Full horizontal ventilation

The full -horizontal ventilation method is to set up air passages and exhaust channels. The wind of vertical flow is basically not generated in the tunnel, only horizontal wind. The longitudinal wind speed of the direction of traffic is roughly zero, and the concentration of pollutants is basically uniform along the tunnel; in one -way traffic, due to the impact of traffic wind, a certain wind speed will be generated in the vertical direction. The concentration of pollutants increases from the entrance to the exit, and some pollution air is directly discharged from the exit, and sometimes the discharge volume accounts for a large proportion.