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Finding flow rate exiting blow tube

Finding flow rate exiting blow tube

Finding flow rate exiting blow tube

(OP)


Hi guys,

       For the past weeks i have been trying to come up with a decent setup to calculate the volume flow going through a blow head.  I am dealing with air at pressure from 30psi – 60psi, have a 488 gallon air tank, air regulator, and 3 gauges upstream (one on regulator) Here is what I have tried so far.

1.    placed the 488 gallon tank to a certain psi (30-60psi) and see measure the drop after a minute with data for every 10 seconds. The problem here is that the pressure drops fast and my equation shows higher losses in 30seconds than in 1 minute.  The equation used is [(Volume * DP)/(Time * P(atm,14.7psi))].  I got this equation from the Dept. of Energy website while doing some compressor leakage surveys so I am not sure if it is valid in this case.
2.    I tired to get the downstream pressure by strapping the blow tube to a hose with a  small connector T pipe and gage but I wasn't getting any readings.  After reading and talking with some folks I figured that the reason I wasn't getting reading is because air follows the path of least resistance so I attached a second tube of the inner diameter as the hose and connector attached to blow tube.  I got pressure readings but not sure if this accurate.
3.    My next idea is to pretty much reverse trial 1 by pushing a known pressure through the blow head and strapping the tank to the end of the blow tube and seeing how much air pressure the tank has after 1 minute.  Then by using the equation in trial 1 I should be able to get a CFM

I have been reading up on orifices within the website and just brought the recommended book by Crane. My questions to you all are:

1.    Is trial 1 equation valid?
2.    Is any of the trials valid (trial 1,2 3)?
3.    Should I just look into orifice setups for accurate data?

My end goal is to get a method that is accurate to measure the CFM at different psi for these blowheads.

I linked a picture of setup 2 and the blowtube.

http://i30.tinypic.com/bg4j79.jpg

http://i30.tinypic.com/nxroyg.jpg

Any help, thought suggestions, will be appreciated.  If the idea is crappy let me know as well I have tough skin.
 

RE: Finding flow rate exiting blow tube

(OP)
hi Ted,

Thanks for the reply, I believe the equation you are talking about is on page 42 (VCP(a)/P1-P2).  When you rearrange that formula to solve for C you get the same equation i am using stated in trial 1.  I guess for the information i need i have to try my trial 3 to get the amount of air used and a certain PSI and then use the equation.  Atleast i know i am not going in the wrong direction.

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