Why does the return air shaft enter the air when the coal mine is naturally ventilated?

In the case of natural ventilation in coal mine, the phenomenon of air intake in return air shaft is usually caused by the difference of air pressure. This phenomenon is due to the air flow caused by the air pressure difference inside and outside the mine. The following are some possible reasons for air intake in the return air shaft:

1. temperature difference: the temperature in the underground mine may be lower than the ground, which will cause the air in the return air shaft to become heavier than the air outside, thus generating downward airflow. This phenomenon of cold air sinking may lead to air intake in the return air shaft.

2. Air pressure difference: When the air pressure in the mine is lower than the ground, the outside air will be "sucked" into the mine. This may be due to the influence of weather, such as low-pressure weather system, or the difference of mine depth and height.

3. Influence of terrain and buildings: The surrounding terrain, the layout of buildings and other factors may change the direction of airflow, resulting in a certain wind pressure difference, leading to air intake in the return air shaft.

4. The mine seal is not tight: if the mine seal is not tight enough, the air pressure and temperature around the return air shaft will be closer to the outside world, reducing the possibility of air intake. But if there is air leakage in the mine, it will affect the airflow of the return air shaft and make it enter the air.

The interaction of these factors may lead to the air intake phenomenon of the return air shaft. For the safe operation of the mine, it is necessary to monitor and manage the airflow scientifically and reasonably to ensure the normal operation of the mine ventilation system and maintain the safety and stability of the mine working environment.