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How to convert PPMw (by weight) to PPMv(Volume) for H2S & moisture(H2O) in gas mixture?
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Submitted Chris Haslego, Nov 21 2011 11:21 AM | Last updated Nov 21 2011 01:29 PM

Category:	Fluid Dynamics
Question:	How can I determine the choked or sonic flow in an orifice?
Keywords:	v1i17,choked,choke,sonic,flow,gas,orifice,calculate,determine,calculation
Answer:	Choked flow (also known as sonic flow) occurs when the ratio of the upstream gas pressure to the downstream gas pressure is equal to or greater than [(k + 1) / 2]^{k / ( k - 1)} , where k is the specific heat ratio (C_p / C_v). For many gases, k ranges from about 1.1 to about 1.4, and so choked gas flow usually occurs when the upstream pressure is about twice the downstream pressure. The equation for choked flow is: Q = C A (g k d P_U )^1/2 [2 / (k + 1)]^{(k +1) / (2k - 2)} If the ratio of upstream to downstream gas pressure is less than [(k + 1) / 2]^{k / ( k - 1)},then the flow is non-choked (i.e., sub-sonic) and the equation for non-choked flow is: Q = C A (2 g d P_U)^1/2 [k / (k - 1)]^1/2 [(P_D / P_U)^2/k - (P_D / P_U )^{(k + 1) / k} ]^1/2where: Q = mass flow, lb/s C = discharge coefficient (usually about 0.72) A = orifice hole area, ft² g = 32.17 ft/s² gravitational acceleration k = C_p / C_v = (specific heat at constant pressure) / (specific heat at constant volume) d = gas density, lb/ft³, at upstream pressure P_U = upstream pressure, lbs/ft² P_D = downstream pressure, lbs/ft²