2 - Air Flow in Mine Airways

Abstract

The chapter deals with the fundamentals of fluid flow in pipes and mine airways. Basic pressure loss equation is derived and various ways to estimate the friction factor, λ, are presented. In fully turbulent flow only the degree of roughness determines the friction factor. However, mine airways are very different from conventional pipes. Atkinson's equation is developed further, and a large collection of friction factors from the US and British coal mines are presented. Mine airways are typically rectangular and also have a lot of obstructions that cannot be theoretically analyzed. Actual data with experience alone can yield reliable results. Airflow in ventilation ducts made of steel or fiberglass are discussed. Shock losses owing to obstructions and changes in airway directions are also discussed. Total resistance of a mine to airflow, R, is used to create a “characteristic curve” for the mine. It is useful in determining the correct fan size for the mine (to be discussed later in the book). The concept of “equivalent orifice” is mathematically analyzed and used to determine the area of a regulator in a mine airway to restrict the air flow to a predetermined value. Mine airways change the cross section many times owing to geology or ground control conditions. Such airways are treated as “airways in series.” Similarly, often two to five airways are needed in parallel to carry a given volume of air. Both “series” and “parallel” airways are mathematically analyzed for air flow distribution and pressure losses. Finally, an equation is provided to estimate the horsepower needed to run a fan that can provide a prescribed ventilation air volume at a required pressure differential.