What are zone ventilation (parallel ventilation), series ventilation and diffusion ventilation?

Sectional ventilation refers to the ventilation mode in which the return air from each underground wind site directly enters the return air lane or the total return air lane in the mining area. Series ventilation refers to the ventilation mode in which all or part of the return air from underground wind sites re-enters other wind sites. Diffusion ventilation refers to the ventilation mode that uses the natural diffusion movement of air molecules in mines to ventilate local places.