CYLINDER LEAK DOWN TESTER

Forum about flow calculators available on pipeflowcalculations.com and how to find solution for your fluid flow problem.
admin
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Joined: Mon Feb 08, 2010 7:47 pm

Re: CYLINDER LEAK DOWN TESTER

Post by admin »

Air in pressurized cylinder is heated due to compression, but while going through restriction it is cooled due to sudden drop in pressure.
Pipe flow calculations - since 2000
HenriMalcorps
Posts: 8
Joined: Wed Mar 20, 2013 1:27 pm

Re: CYLINDER LEAK DOWN TESTER

Post by HenriMalcorps »

Indeed, when the velocity increases pressure has to go down, this is a direct consequence of Bernoulli (or the conservation of energy), as it is used in the ventury of our old carburettors. If the pressure goes down, internal energy has to be used and temperature decreases. Of course, if the process is not adiabatic, some energy is escaping (or entering) the system and Bernoulli has to take this into account.
The leak down tester is constructed out of metal and is not thermally isolated. The question to me remains, is the isothermal approximation a reasonable approach or not? To get the answer on this question, I think I will have to "ask nature" and do the experiment. In fact I don't need exact results, but sufficient understanding about the way a tester works, to find out how it should be constructed and used.
It is not clear to me if the gas discharge is supposed to be adiabatic. If I would have to make a suggestion for the documentation of pipeflowcalculations, I would suggest to better highlight the hypotheses which are underlying for each calculator: adiabatic? Isothermal? laminar or turbulent? Compressible or not?...
I enjoy very much the discussions on this forum and the discussions with admin are very enlightening and passionating.
admin
Site Admin
Posts: 375
Joined: Mon Feb 08, 2010 7:47 pm

Re: CYLINDER LEAK DOWN TESTER

Post by admin »

Pressure is dropping not only due to change in pipe diameter but also due to local reistance losses in restriction and friction in pipe. In Bernolli equation flow is considered with no energy loss, but in real system it is not the case.
Because of that you must add parts of equation that takes care about losses - local losses with K factor and friction losses, but in short pipes like your (10 mm in length) friction effect is much less important than losses due to sudden contraction and enlargement.
Pipe flow calculations - since 2000
HenriMalcorps
Posts: 8
Joined: Wed Mar 20, 2013 1:27 pm

Re: CYLINDER LEAK DOWN TESTER

Post by HenriMalcorps »

This is one of the important conclusions for the construction of the leak down tester, if results obtained with different instruments have to be comparable. The length of the obstruction is not very important; at the contrary the diameter, or more general the ratio between both diameters, is very important. Making a hole of 1mm with a precision of 0.05mm or better, may be a challenge for an amateur.
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