Problem An anemometer is held in a 6 x 16-foot airway for 1-3/4 minutes and the reading is found to be 700. What is the quantity of air passing through the airway? = Q = A x V = 96 x 400 38,400 cu. ft. per min. It would be well to keep the following in mind when working ventilation problems dealing with quantity of air flow: a. flowing. Measurement Required to Determine Quantity of Air Dimensions of cross-section through which the air is b. Time in minutes in which the anemometer reading was recorded. c. Linear feet of air travel as measured by the anemometer. Ventilation Openings to Coal Mines Types of Openings The openings to a seam of coal used for haulage or hoisting purposes are also used for ventilating purposes. The types of openings include shafts, slopes, and drifts. Shafts are the most expensive type of opening to construct, and as a result, slopes are rapidly taking over in use in modern coal mining. Drift openings are the cheapest of the three types, but the topographical features may not always permit their use. Frequently, the openings in any particular mine will be similar, that is, in a mine with a flat seam which outcrops, the ventilation openings may all be drifts. Mines where the coal lies beneath the surface are usually developed from slopes or shafts, and these openings are used for ventilation purposes. Sometimes the extent of deep-lying flat seam 47-135 O 719 workings may be such that additional shafts for ventilation purposes must be sunk several miles from the main hoisting shafts or slopes. Size and Construction Drift and slope openings driven in the coal are of a size which is determined by the thickness of the seam and the size of the mine equipment used. The height is usually that of the seam, although in thin seams some roof or bottom rock may be removed to provide sufficient clearance. The width is usually just enough to provide adequate track clearance and possibly a traveling path at one side. The width is governed by the nature of the roof and floor structure, the character of the coal seam, and, to some extent, by the method of mining that is employed. The entrances to many drifts and slopes are concrete or masonry-built portals to support the loose rock or dirt above the entrance. The shape or drift and slope openings are usually rectangular and, in some instances, are trapezoidal. In certain sections of the airway, such as an overcast, the shape may either be semi-circular, or have an arched roof with a rectangular base. Shaft openings used for ventilation purposes may also be used for hoisting, either of coal or supplies. The size of hoisting shafts is necessarily governed by the service for which the shaft is intended. Main shafts may have one, two, or more compartments for hoisting coal, and the balance of the shaft area may be taken up with steam pipes, electrical cables, or a stairway. Shafts sunk for air purposes only may be unlined or may be lined with masonry or concrete. They are usually much smaller in size than hoisting shafts since their only purpose is to carry air, although escape stairways are sometimes placed in them. The shapes of shaft openings are of many forms and variations of geometric figures. Some of the more common shapes are illustrated on the following page. Airways in mines have cross-sections that are usually geometrical in pattern, and an airway area can be calculated in most instances by substituting known values in a formula for that particular form of cross-section. The most common type of cross-section is the rectangle, but the square, arched, and the trapezoidal sections are also encountered. The circular form is more commonly found in air shafts than in underground passages. Area is the product of the two linear dimensions of any plane surface or cross-section, expressed in square units. The following symbols and their meanings will be helpful in calculations of area and perimeters of airways. A = Area in square feet. 0 = Perimeter in feet. 1 = Length in feet. W = Width in feet. D= Diameter in feet. r = Radius in feet. s = Side in feet. The following calculations of areas will illustrate the symbols and their use: |