Liquid Oxygen Vaporization Question

[rrbierl]

Hello,

I have a cryogenic pipe with liquid oxygen flowing through it. Pressure = 120psia, Temp = -180 Celsius. I want to determine the increase in pressure if 28.5kJ of heat was added to the system, assuming there would be some vaporization of liquid. Any help would be much appreciated. Thank you.

 

[EnergyMix]

I hate problems that are mixed units. They always make me think schoolwork. Especially for new users. You're not a student, looking for help on an assignment, are you?

 

[rrbierl]

Not gonna lie, I kind of wish I was back in school. But no, I just have a little side project at work and it has been ages since I did any sort of heat transfer. For some reason the company I work for is unable to decide on one type of units. Thankfully I have a nifty little converter executable.

 

[Latexman]

It sounds more like a thermo problem, not heat transfer. There also seems to be some confusion whether it is an open or closed system. You mentioned flowing liquid oxygen, that would lead me to believe you need a Power input (kJ/time) to solve the problem, not an energy input (kJ).

Good luck,
Latexman

 

[ione]

Some ideas to work on.
I don’t want to investigate the way the energy (heat) you’ve quoted in your OP is “added to the system” and assume the whole 28.5 kJ heat up the liquid oxygen.
Now the first point is to know the amount of liquid oxygen (mol) in the system or its mass flow (mol/s). Then consider that at 120 psia oxygen will be in the liquid state up to – 156.7 °C.
You then need the specific heat of liquid oxygen (take an average value in the range -180 °C/-156.7 °C for a ballpark estimate) and check whether your system reaches saturation conditions with 28.5 kJ added.
I doubt there could be a change of phase, anyway this again depends on the amount of liquid oxygen heated. To check whether there will be a change of phase consider that the latent heat of vaporization at 120 psia and -156.7 °C is 5.7523 kJ/mol or 179.765 kJ/kg (source webbook nist).
In order to evaluate pressure increase for a trapped liquid system you can follow the procedure described by valuable member prex (

http://www.eng-tips.com/faqs.cfm?fid=1339).

 

[MortenA]

@rrbierl,
First of all theres is one uncertaincy at least: Is it an enclosed space. If no - then no pressure increae at all (it will just expand). You could check the webdatabook at NIST.org, they have a lot of pure component data incl heat capacity as a funtion of temperature and vapour pressure etc. (i think this is (still) free.

 

[rrbierl]

Thank you all for the help, it is much appreciated.