Why is a circular airway more effective for ventilation?

A circular airway is more effective for ventilation primarily because it minimizes turbulence and friction. In a circular cross-section, air flows more smoothly compared to other shapes, such as square or rectangular ducts, where corners can interrupt airflow. By reducing turbulence, the air can travel more efficiently through the airway, allowing for better exchange and circulation of air within the mine. This smoother flow contributes to maintaining adequate ventilation, which is crucial for the safety and health of miners by ensuring the dilution and removal of harmful gases and dust.

In terms of surface area, while a circular airway does have a good ratio of enclosed volume to surface area, the effectiveness for ventilation specifically hinges on the airflow dynamics. The ability to escape air plays a lesser role in the context of efficient ventilation, as the design focus is typically more aligned with controlling flow patterns rather than just air escape. Lastly, construction ease is not a determining factor for the effectiveness of ventilation; the shape's impact on airflow characteristics is the critical consideration.