How do I calculate flow rate from pressure drop?
How do I calculate flow rate from pressure drop?
(OP)
Hi. I have a digital manometer measuring pressure in units of inch h20. I'm trying to measure flow rate of air (in cc/min) over 60 seconds. I can record the pressure drop in inch h20 over that time period, how can I calculate the flow rate in cc/min? The manometer I'm using only has a pressure display, so my only knowns are pressure drop and time period. What other data do I need? I don't work with manometers much... I was trying to use PV=nRT but I'm not sure how to find n. Not sure if that's the best formula to use or not. Please help!
thanks!
thanks!





RE: How do I calculate flow rate from pressure drop?
RE: How do I calculate flow rate from pressure drop?
Assuming the ideal gas law applies to your pressure and temperature range,
V2 = P1 * V1 / T1 * T2 / P2
Volume lost = V1 - V2
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RE: How do I calculate flow rate from pressure drop?
I guess the volume is constant and known. You can measure the pressure and temperature. Re-cast your PV = nRT formula to be n = (PV)/(RT). Everything on the right hand side is known or measurable. This will tell you the change in n (the number of moles) from one set of measurements to the next. Convert the change in moles to whatever units you want to report in.
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RE: How do I calculate flow rate from pressure drop?
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"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain
RE: How do I calculate flow rate from pressure drop?
http://virtualpipeline.spaces.msn.com
"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain
RE: How do I calculate flow rate from pressure drop?
I don't think you can calculate the flow rate based on pressure drop. I think your best bet is to use the capture method.
You would need to encapsulate the leaking seal such that the leaking air is captured by a capsule of known volume. You would need to measure the temperature and the pressure (use a manometer) in the capsule, and the time duration to collect the leaking air. Now, since the capsule volume is known and you measured the temperature and pressure of the air, you can calculate the standard volume of the air. The standard air volume divided by the time duration to collect the air will give you the average leakage rate.