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of the monitor well, carefully avoiding any vacuum leaks . An <br /> orifice plate restricts the flow causing a pressure drop across <br /> the orifice . By measuring the resulting pressure change across <br /> the orifice it as possible to calculate the air flow rate The <br /> flow rate is calculated by the pressure drop (millimeters (mm) <br /> mercury or water) across a square edge orifice plate <br /> Ve = CK sgr (P) Q = AVe <br /> Where <br /> Ve= velocity in feet per minute (fpm) <br /> C = Orifice Coefficient = 0 65 (for orifice used) <br /> K = Constant = 794 . 6 for mm water or 2929 8 for mm <br /> mercury <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 multiplied <br /> by the volume of air produced an one day <br /> The lab reports the Concentrations (C) of the air sampling an <br /> gg/liter The first step is to convert this value to lbs/cf (pounds <br /> per cubic foot) 1 ug/l x 0 000001g/ug x 0 0022051/g x 28 . 321/cf = <br /> 0 0000000621lb/cf <br /> The volume of air produced an one day, equals the flow rate (Q) x the <br /> time of flow. <br /> V = Q x T : cf/day = cf/man x 1440min/day <br /> The volume must be corrected to standard temperature and <br /> pressure (STP) <br /> P = Pressure = 14 7 lb/ane @ STP <br /> V = Volume cf <br /> T = Temperature an degrees above absolute Zero W 491 58OR Q <br /> STP <br /> USI-- the Tdea1 Gas Law P1V1/T1 = P2V2/T2 <br /> Solving for V2 =P1V1T2/P2T1 <br /> Assuming P1 = P2 = 14 . 7 lb/inx , P cancels from the equation <br /> leaving V2 = VIT2/T1 <br /> vi = Q -f/m x 1440 man/dav <br /> T2 = 491 . 58oR T1 = 459 58� + ToF at site <br /> V2 = Q cf/man x 1440 min/day x 491 58oR/ (459 . 580 + TOF) <br /> X lb/day = C ug/l x 0 0000000621 lb 1/ug cf x Q cf/min x 1440 <br /> 6 R603 APPEND E <br />