Pressure Increase Due To Temperature Increase
Pressure Increase Due To Temperature Increase
(OP)
Anyone know how to calculate the pressure increase due to temperature increase for a liquid in a closed, sealed system? I have the formula: CoTE x temperature increase x copmpressibility, but I can't get the compressibility factor for the liquid I'm using.





RE: Pressure Increase Due To Temperature Increase
Also, to be complete you should make sure you account for the expansion (both thermal expansion and pressure-induced expansion) of whatever the walls of your system are made of.
RE: Pressure Increase Due To Temperature Increase
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RE: Pressure Increase Due To Temperature Increase
David
RE: Pressure Increase Due To Temperature Increase
RE: Pressure Increase Due To Temperature Increase
RE: Pressure Increase Due To Temperature Increase
RE: Pressure Increase Due To Temperature Increase
RE: Pressure Increase Due To Temperature Increase
RE: Pressure Increase Due To Temperature Increase
What do you know about the initial conditions? Pressure? Temp? Volume?
What do you know about the final conditions? Heat flux? Total heat input? Final temperature?
Maybe you could also give some description of how this container is used, and why you're interested in determining the pressure increase. Is this to size a thermal relief valve? Are you concerned with overpressurizing a sealed container? Tell us what you can about the situation.
RE: Pressure Increase Due To Temperature Increase
I did some calcs based on the expansion of the oil to determine how much to fill the vessel to allow it to expand to fill the void.
The initial conditions are ambient or atmospheric pressure and ambient temperature (70F).
I'm heating to 400F with a Firerod cartridge heater. Trying to transfer the heat evenly and quickly to the outside of the vessel.
The vessel is a welded stainless steel cylinder with at least 1/2" wall thickness.
I found some discussion online that concerned me. A guy was doing something similar with a petrol based oil and stated that his pressure increase was roughly 60-70 psi per F degree. If this holds true for my application, I'm approaching 22,000 psi. The last thing I want is a stainless steel bomb in my R&D lab.
A colleague suggested filling the vessel and heating to 400F in an oven, then sealing it off, thus relieving the pressure and filling the void.
RE: Pressure Increase Due To Temperature Increase
Dow and Solutia make competing products. They may have a database which would help.
Last resort: Perry's Handbook, Section on Prediction and Correlation of Physical Properties, Sub Section "Coefficient of Expansion" in mine it's p. 3-227
RE: Pressure Increase Due To Temperature Increase
RE: Pressure Increase Due To Temperature Increase
RE: Pressure Increase Due To Temperature Increase
Patricia Lougheed
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RE: Pressure Increase Due To Temperature Increase
A quick Google search gives typical values for thermal expansion for various types of mineral oil from .00035 to .00054 /F.
Ref:
http://www.multitherm.com/multitherm-ig-1.html
http://www.therminol.com/pages/products/xp.asp
http://www.pantherlubes.com/tl_6.html
If it were me, I'd add a safety factor on top of that, but for the worst case (.00054), a dT from 70 to 400 F will increase volume 17.8%. Round that up to 20% - 25% if you want to be sure.
The remaining volume will be your gas (air?). Assume ideal gas behavior if air and use the change in gas volume and increase in temperature to determine final pressure. That will be your increase in pressure as long as the calculated volume isn't completely displaced.
RE: Pressure Increase Due To Temperature Increase
CoTE = rho1 x (1/rho1-1/rho2) / (T2-T1)
or an EOS. Then you can calculate W (flow requirement) for this scenario using CoTE, Q(heat input), and Cp:
W = CoTE x Q / Cp
As Compositepro said "This is why all fluid heat transfer systems contain an expansion tank." You do not want to build a system expecting it to pop the PSV, but the PSV needs to be there when someone or something goes wrong.
Good luck,
Latexman
RE: Pressure Increase Due To Temperature Increase
1. Add on the vapor pressure of the fluid at the max. temperature to whatever you calculated for thermal-expansion pressure rise.
2. And then ask what happens if the temp. sensor fails, and the heater goes open loop? Ask the heater supplier for a resistance-vs-temp curve, do some heat transfer calcs, and see if there is a peak temperature the device will reach if the operator falls asleep. If you can't guarantee fail-safe operation with this, you may want to consider a relief system like vpl notes - and then you must worry about where you are going to vent a hot hydrocarbon fluid/gas mixture to (hopefully nowhere near my cubical).