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Mixed-mode ventilation systems use both mechanical and natural processes. The mechanical and natural components may be used at the same time, at different times of day, or in different seasons of the year. [4] Since natural ventilation flow depends on environmental conditions, it may not always provide an appropriate amount of ventilation.
is the area of the duct, is the velocity of the fluid. The practicalities of mine ventilation led Atkinson to group some of these variables into one all-encompassing term: Area and perimeter were incorporated because mine airways are of irregular shape, and both vary along the length of an airway.
Round duct is made using a continuous spiral forming machine which can make round duct in nearly any diameter when using the right forming die and to any length to suit, but the most common stock sizes range evenly from 4" to 24" (10-60 cm) with 6"-12" (15-30 cm) being most commonly used. Stock pipe is usually sold in 10' (300 cm) joints.
However, they are seldom used as the actual basis of design or calculation. For example, residential ventilation rates are calculated based on area of the residence and number of occupants. [5] Non-residential ventilation rates are based on floor area and number of occupants, or a calculated dilution of known contaminants. [6]
Cross-breezes work when two windows are opposite of each other. Cross ventilation is a natural phenomenon where wind, fresh air or a breeze enters upon an opening, such as a window, and flows directly through the space and exits through an opening on the opposite side of the building (where the air pressure is lower).
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Orifice plate showing vena contracta. An orifice plate is a thin plate with a hole in it, which is usually placed in a pipe. When a fluid (whether liquid or gaseous) passes through the orifice, its pressure builds up slightly upstream of the orifice [1] but as the fluid is forced to converge to pass through the hole, the velocity increases and the fluid pressure decreases.