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FLOW RATES <br /> Flow rates are measured at the site by use of orifice plates A <br /> one inch orifice is placed in line for each well and two one inch <br /> orifices in parallel are used to measure the total flow. <br /> An orifice plate restricts the flow of air across <br /> restriction causes a it . This <br /> pressure drop across the orifice . By <br /> measuring the resulting pressure change across the orifice it is <br /> Possible to calculate the air flow rate <br /> The flow rate is calculated by the pressure drop (millimeters <br /> (mm) water) across a square edge orifice plate . <br /> Ve = CK sgr (P) Q = AVe <br /> WherVe= velocity in feet per minute (fpm) <br /> C = Orifice Coefficient = 0 . 65 (for orifice used) <br /> K = Constant = 794 6 mm water <br /> P = Pressure differential across the orifice <br /> Q = Flow rate in cubic feet per minute (CFM) <br /> A = Area orifice in square feet . 1" = 0 00545 ft2 <br /> Q = A X 0 65 X 794 6 X sqr (P) <br /> CALCULATIONS <br /> To calculate the pounds (lb) per day the concentration is <br /> multiplied by the volume of air produced in one day. <br /> The lab reports the Concentrations (C) of the air sampling in <br /> ug/liter. The first step is to convert this value to lbs/cf <br /> (pounds per cubic foot) <br /> 1 ug/l x 0 . 000001g/ug x 0 0022051g/g x 28 321/cf <br /> 0 00000006211b/cf The volume of air produced in one day, equals the flow rate (Q) x <br /> the time of flow <br /> V = Q x T = cf/day = cf/min x 1440min/day <br /> The volume must be corrected to standard temperature and <br /> pressure (STP) <br /> P = Pressure = 14 7 lb/in2 @ STP <br /> V = Volume cf <br /> T = Temperature in degrees above absolute Zero = 491 . 58oR Q STP <br /> Using the Ideal Gas Law P1V1/T1 = P2V2/T2 <br /> Solving for V2 =P1V1T2/P2T1 <br /> Assuming P1 = P2 = 14 7 lb/int, P cancels from the equation <br /> leaving V2 = V1T2/T1 <br /> Page 4 of R604, 10/21/93 <br />