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Liquid nitrogen to gas

Liquid nitrogen to gas

Liquid nitrogen to gas

(OP)
Hi,

How to calculate how many BTUs it takes to convert one gallon of liquid nitrogen (LN2) into gas?
We use heat exchanger with  280F hot water. Output gas temperature  70F

TIA
 

RE: Liquid nitrogen to gas

At what pressure?

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying " Damn that was fun!" - Unknown>>

RE: Liquid nitrogen to gas

(OP)
95 to 100 psi

Thanks

RE: Liquid nitrogen to gas

Have you looked at the Nitrogen phase diagrams yet?  

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying " Damn that was fun!" - Unknown>>

RE: Liquid nitrogen to gas

(OP)
No, where I can find it?

Thanks

RE: Liquid nitrogen to gas

Google it, probably there or in the library. Just look for a pure substance phase diagram (unless you have a mix). That will answer your question. If not let us know and we'll help more

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying " Damn that was fun!" - Unknown>>

RE: Liquid nitrogen to gas

hi Chunia, any luck?

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying " Damn that was fun!" - Unknown>>

RE: Liquid nitrogen to gas

(OP)
Guys,

Sorry for not getting back here sooner, just was busy with electrical problems.
Thank you for pointing me to the right direction, Google is really good source of information, but I did not find an answer to my question. I will keep looking.
 

RE: Liquid nitrogen to gas

You might have overlooked dcasto's post. Go to NIST webbook and check the saturation data of nitrogen. The enthalpy difference between the gaseous state at required condition and the liquid condition gives you btu required per lb.

RE: Liquid nitrogen to gas

(OP)
According to the table out of  NIST webbook it takes 85 Btu to convert pound of liquid Nitrogen to gas (1 deg. delta)
Am I correct?
 

RE: Liquid nitrogen to gas

At 70ºF and 100 psi, are you sure you have liquid nitrogen?

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying " Damn that was fun!" - Unknown>>

RE: Liquid nitrogen to gas

(OP)
Unotec,

It just for converging from liquid to gas. Now I need to warm up the gas from -319F to +70F at 100psi.
 

RE: Liquid nitrogen to gas

And your goal is to keep the pressure constant? I am sure you have considered it already, but with the volume expansion you will have a pressure increase.
If I am not mistaken, the 85BTU you came up with will just be the energy for the phase change, right? You still need the energy to go from -319ºF to boiling (sub cooled liquid) and the energy after boiling to 70ºF (superheated gas)

Have you considered those? (I can't open the NIST page for some funky reason)

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying " Damn that was fun!" - Unknown>>

RE: Liquid nitrogen to gas

(OP)
Yes, you are absolutely correct. Thanks. I saw the formula somewhere ( Btu for warming  gas) just need to find it.  

RE: Liquid nitrogen to gas

Seems to be a problem with your data. Enthalpy of LN2 at -319C is -51.79 btu/lbm and enthalpy of N2 at 100 psia and 70F (isobaric process) is 130.73 btu/lbm. So, you require 182.72 btu/lbm of N2, approximately.

RE: Liquid nitrogen to gas



Take the Btu/lb estimated by quark and multiply it by 6.71 lb/USG (@ 100 psia and -319oF) to obtain the requested Btu figure for one gallon of liquid nitrogen.

RE: Liquid nitrogen to gas

(OP)
Thanks to everybody for the inputs.

Warming the gas:

Q= 1.08 X CFM X (t1-t2)

1 gal of liquid nitrogen = 93.11 cubic feet

Q= 1.08 X 93.11 X (319+70) = 39117 Btu/gal of liquid or Btu/ 93.11 cfm of gas

Latent heat of vaporization
86.6 Btu/lb = 583.5 Btu/gal

Total: 39700 Btu/gal

According to Quark it suppose to be 182.72 Btu/lbm X 6.7347 = 1230.6 Btu/gal

I made a mistake somewhere, I think in the formula....
 

RE: Liquid nitrogen to gas

Yup, and more than one.

First, the formula deals with flow rate and not volume. Secondly, the formula is valid for atmospheric pressure (even you need to revise is for change in atmospheric pressures due to change in elevation). Third, it assumes sensible heat at 70F and thus valid for temperatures not far above and below it. Fourth and not very critical one is that it is for air.

Still, since air is mostly nitrogen, considering 0.24btu/lbF specific heat and .075 lb/cu.ft air density,
0.24x.075x93.11x(319+70) = 651.95 btu/gal, plus 583.5 btu/gl of latent heat equals 1235.45 btu/gal

RE: Liquid nitrogen to gas

(OP)
Quark,

Thank you for spending your time to explain all details of the process to me. I do not want spend any more of everybody's time on the issue.

The answer is : To convert one gallon of liquid nitrogen to the gas at 70F and 100 psi takes 1235.5 Btus

Again, thanks to everybody who helped me to find answer to the question.

Best regards
Chunia
 

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