PRESSURE CHANGE IN VESSEL
PRESSURE CHANGE IN VESSEL
(OP)
A 5 Gallon Pressure Vessel(non-vented) is completely filled with Diesel Fuel #2.The vessel is pressurized to 500 psig, the temperature of the Diesel is 90 Degrees F. If the Diesel is heated to say 140 Degrees F, What is the equation to calculate the pressure rise?





RE: PRESSURE CHANGE IN VESSEL
You need a databook for those two constants.
A general equation would look something like this:
expansion coeeficient: a (ft3/deg F)
Compressibility: b (ft3/psi)
at constant volume: dP (psi) = a*dT/b
Best Regards
Morten
RE: PRESSURE CHANGE IN VESSEL
Is this some kind of homework problem !!???
I cannot immagine any kind of real or practical use for such a set-up.....but, I can imagine this being a homework problem dreamed up by an instructor
Come back and tell us this is real !!??
MJC
RE: PRESSURE CHANGE IN VESSEL
Best Regards
Morten
RE: PRESSURE CHANGE IN VESSEL
No, this is not a homework question.
We are a division of JohnCrane Mechanical Seals.We manufacture the Seal Lubricator Systems that supply the barrier fluid to "cool" and "lubricate" the seal(s).
This question relates to a unit we built. This unit uses Diesel Fuel as the barrier fluid (to "lubricate" the seal).
It is stored and circulated through a pressure vessel. The question had been posed as to what pressure increase would be seen in this unit with increased temperature.
I still have not found the answer or information.
Regards, Tom
RE: PRESSURE CHANGE IN VESSEL
RE: PRESSURE CHANGE IN VESSEL
I think my first post covers is EXCEPT for the coefficients. Try to find them in a databook.
Now in order to make up for my impollite insinuations i even checked google for you (www.google.com) a great search engine.
I found a chevron datapage: http://www.chevron.com/prodserv/fuels/bulletin/diesel/L2_4_6_rf.htm
Here the linear thermal expansion coefficient is 0.00046 /deg F
The compressability is however more difficult. I took the first reference that i could find (not quite sure its diesel no. 2 but it is diesel). The value i found at this link http://www.amesim.com/de/pdf/fuel_113.pdf is approx 1/15000 bar = 1/217500 psi
A 50 def F temp increase should therefore lead to a increase in pressure of 0.00046*50*217500 psi=5000 psi pressure increase (the correspond OK with Butelja's rule of thumb where 1 def F means 60-70 psi increase since .00046*217500 equals 100 psi/deg F).
Best Regards
Morten
PS: Try a seach engine like GOOGLE if you are looking for physical properties. I used the search terms "expansion coeeficient diesel" and "bulk modulus diesel" to find these sites
RE: PRESSURE CHANGE IN VESSEL
If this vessel is pressurized to 500psig and part of a closed circuit there must be a reason for this pressure (it must be higher than that of the secondary side of the seal i suppose)
Then how is the pressure maintained in case of a leakage thru the seal? If there is nothing to maintain this pressure, then the system will be useless after the first incidence of leakage, because there's no overpressure left.
On the other hand if there is something to maintain this pressure, then there is also the possibility to allow relieving any overpressure, fex. thru a thermal relief valve.
Another possibility could be to allow a volume of nitrogen at the top of the vessel large enough to cope for thermal expansion of the diesel and large enough to maintain pressure in case of a seal leakage. Same system is used on accumulator backup vessels for hydraulic systems, enabling emergency hydraulic operation if the power unit breaks down.
Also consider that should the pressure rise to abnormal levels, there's a good chance the seal will be blown away (into where it wasn't meant to go) possibly before the vessel bursts.
Regards
Mogens
RE: PRESSURE CHANGE IN VESSEL
RE: PRESSURE CHANGE IN VESSEL
The Mathcad spreadsheet I mentioned in my earlier post does take the pressure expansion as well as the thermal expansion of the container into account. The algebra equating the volume change of the fluid as a function of pressure and temperature to the volume change of the container as a function of pressure and temperature gets a little messy.
RE: PRESSURE CHANGE IN VESSEL
We built a small vessel from 2" pipe for actual testing, the 60-70 PSI increase / 1Degree rise is almost exact
Pressure is maintained to the vessel through a "piston pot",
with different areas on each side of the piston, thus creating a +10% differential on the lubricator side(reference pressure from the inboard side of seal is on opposite side of piston)
Thanks, Tom