Interestingly, after measuring the actual flow from the output of the compressor (using McM #41945K56, I get much lower flow than the rate provided by the factory:
Plugging this measured flow rate into the predicted ADIABATIC equation (green line), I get similar results to using the manuf...
BTW: To share a little about the project, the air bladder is our partner's proprietary design but it requires a large volume of air to go from full deflation (such as CPR mode) to full inflation (about 8CF @ 1psig). Hence the large high pressure air tanks. My guess is that bedroom air...
Great replies. This is helpful!
May I walk through my assumptions and see if they are correct?
So the rapid action of the compressor results in the gas quickly heating up. Before heat is transferred to the cylinder walls, the gas is sent downstream (hence adiabatic). As the pulse of gas...
Aborting this thread. Disappointed that I asked a simple question and was barraged with unrelated advice about inflatable beds and accusations of posting homework. Will later document my measurement of tank fill time and predictions based on the manufacturers FAD curve in case it helps another.
Sure, I'll take the abuse, as I am a novice when it comes to pneumatics and I highly respect the engineers that lend their expertise here.
For this problem, it does not matter what the air is used for as the first stage is filling an air tank. But yes, it will be later used to inflate the bed...
What gave you the impression this is homework? Because I tried to lay out the problem clearly?
This project is for a phase I prototype of an inflatable hospital bed. Assuming adiabatic expansion, I am off by a factor of 2 in estimating tank fill time. I cannot simply go up in size because...
A colleague pointed out that there are two compression stages taking place, that inside the compressor and that inside the air tank. However, it would seem to me that both would fall under adiabatic compression. Unless the air cooled in the tank and heat was absorbed by the tank wall which...
A colleague pointed out that there are two compression stages taking place, that inside the compressor and that inside the air tank. However, it would seem to me that both would fall under adiabatic compression. Unless the air cooled in the tank and heat was absorbed by the tank wall which...
Found another helpful reference from Montemayor, who states that a reciprocating cylinder is very close to an isentropic cycle (thus adiabatic). If this is the case, why do some compressor manufacturers estimate fill time based on isothermal assumptions? I ask because setting k=1 gets me the...
Problem: Starting with an air compressor with a known free air displacement, how long would it take to fill a 5 gallon air tank to 95psig? See below for more detail.
Method: Use (PV^n = constant) to convert free air displacement (in standard atmosphere units SCFM) into resulting pressure built...
Duh! Thank you.
So finishing up, for the initial condition:
Pchoke = 8.5psia
Xt = 0.472
Y = 0.942
Flow = 8.56 SCFM (converted from SCFH)
Iterating every 0.2 sec... I get the following graph of inlet pressure for a valve of Cv = 2.0
Is this a close approximation I can trust?
Would that equation for Xt still apply to non-choked flow?
So using the equation to find the critical pressure: Pchoke = 27.83 psia (air exhausting to atmosphere)
Then Pressure Drop Ratio: Xt = (16psia - 27psia) / 16psia = -0.688
I need to size a valve to relieve air from a pressurized tank to drop pressure from 16psia to 14.76psia within 5 seconds. As the outlet pressure is greater than .5283 of the inlet pressure, this will occur as non-choked (i.e. sub-critical) flow. (Note that specification is not critical to...
That is my understanding as well. Increasing inlet pressure will increase mass flow, but not velocity (M). Thanks for the helpful posts... perhaps some time I will be faced with the challenge of a 3ft diameter jet engine and will put this to the test!
Thank you for the quick and thoughtful confirmation. Still seems odd that you could achieve sonic velocity through a 4" hole with inlet pressure of 25psia to 14.7 psia.
Does orifice diameter affect critical pressure through a converging nozzle, or is it entirely dependent on the ratio of inlet and outlet pressure? (assume Isentropic flow of air). References from other forum posts listed at the bottom.
I've seen many references for testing for choked flow...
To designate only the counterbore having positional tolerance, would I simply move the GD&T frame to the right of the counterbore instruction? (I will likely substitute looser tolerance bushings, but this will be helpful in the future.
How about my GD&T, am I going in the right direction here?
http://files.engineering.com/getfile.aspx?folder=0019b32f-b3b0-46c2-a103-cba0ce070d9c&file=DRW-016-A-4120-A.PDF
