Design of auxiliary ventilation systems for long drivages

Auxiliary ventilation relies upon fabricated ducting for the passage of either intake or return air. Because of the nature of the ducting and the numerous joints, complete elimination of leakage from or into the ducting is impossible in practice. The methods available for analysing the airflow problems in a leaky duct are given. When a ventilation duct in a development end is extended, as the face advances, the air volume flow rate reaching the face gradually decreases due to both the increasing resistance of the duct and the increasing leakage. When the face air volume flow rate has decreased to the minimum acceptable value, one or more additional fans are installed in series. If all these fans are placed at the one end of the duct, the air volume flow rate does increase but leakage also increases on account of the high combined pressure. Alternatively, placing one or more fans along the ducting within the drivage reduces the pressure differences that induce leakage, but hazards of recirculation could occur in an uncontrolled fashion along the duct if the fans are located arbitrarily along the duct. The design principles involving multiple fans spaced in series in long ducts are given. The solution for one typical problem is also given.