Time to pressurise air vessel
Time to pressurise air vessel
(OP)
Hi All
Hopefully someone can help shed some light on a little problem - what is the best way for me to calculate how long it will take for an empty pressure vessel (at atmospheric) to reach the pressure of my compressed air main? What do I need to know/derive?
To me it appears this is like charging a capacitor - no? Can I draw direct comparisons?
Thanks in advance for any help.
rmacp
Hopefully someone can help shed some light on a little problem - what is the best way for me to calculate how long it will take for an empty pressure vessel (at atmospheric) to reach the pressure of my compressed air main? What do I need to know/derive?
To me it appears this is like charging a capacitor - no? Can I draw direct comparisons?
Thanks in advance for any help.
rmacp





RE: Time to pressurise air vessel
Then it gets ugly. There isn't a closed-form equation that will let you predict the last half because all of the flow equations (other than choked flow) start with a differential pressure and length - your differential pressure changes substantially from second to second.
You can approximate it with an equation like the AGA compressible-flow equation that you recalculate every 5 psi or so, but I've never been close doing that.
David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
The Plural of "anecdote" is not "data"
RE: Time to pressurise air vessel
RE: Time to pressurise air vessel
If so, consider that for a perfect gas, const specific heats and an adiabatic tank, the energy equation yields
E-Einitial =Hsource(stagnation)*(Mass-Mass initial)
where Mass is mass in tank.
Cv*(Mass*T)-Massinitial*Tinitial)=Hsource(mass-massinitial)
The pressure in the tank is then calculated from:
Ptank*Vtank/R=Minitial*Tinitial+GAMMA*Tstagsource(Mass-Massinitial)
RE: Time to pressurise air vessel
?f your pressure vessel is the only unit that consumes compressed air than you have to calculate the total volume (pipe line and the pressure vessel ) and than multiply with the determined pressure you will reach. That will be the total air you will need to reach the desired pressure. Of course temperature is a nother figure to consider but effect will be minimum.Than come to he compressor capacity. ?f your compressor is a screw or piston type compressor the capacity will not change some much (not more than % 5) due the pressure output.Only the power demand will change. Than divide the air need to the compressor capacity in liter/ sec than you will find the time to reach to that pressure.But if your compressor is a centrifugal compressor you have to consider that Centrifugal compressors capacity changes due to the pressure output. So the the compressing prosses of an emty wessel is dynamic not linear.
RE: Time to pressurise air vessel
I'll devote more thinking time to it - I may even have to resort to experimentation!
RE: Time to pressurise air vessel