Gas Compression as Vessel Level Rises
Gas Compression as Vessel Level Rises
(OP)
i have a nitrogen blanketed water storage vessel. If the vessel is initially 25% full of water and then filled to 50% full, how can i calculate the final temperature and pressure of the compressed nitrogen gas?
This query is based on an upset scenario where the vessel is filled but no gas vented from the vessel.
Thanks.
This query is based on an upset scenario where the vessel is filled but no gas vented from the vessel.
Thanks.





RE: Gas Compression as Vessel Level Rises
If the process takes more than a few seconds, then you can calculate the heat of compression, convert that to energy using the specific heat of the gas, transfer that heat in its entirety to the water and calculate a new water temp. Water temp will most likely go up by a small fraction of a degree.
In my GasBuster, I use inflow of water to compress gas about 5 compression ratios, and the CFD models that I had run do not show a measurable temperature increase because of the heat transfer into the water. In the field we cannot detect any temperature change during the process (and it is really fast).
David Simpson, PE
MuleShoe Engineering
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"
RE: Gas Compression as Vessel Level Rises
You will get a more accurate calculation using z factor and proper software, but I doubt it will be more than 1-2 psi difference asuming these values are correct.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Gas Compression as Vessel Level Rises
I used to calculate the temperature this formula:
T2 = T1 x (P2/P1)^((k-1)/k)
T1, T2 are the initial, final temperature respectively (deg K)
k = Cp/Cv assumed constant = 1.4
P2/P1 = 1.5
So for example if the initial temperature is 15 deg C, the resulting is 50 deg C assuming a fast compression process and prior to any tangible heat exchange yet with the water.
Any comments or correction as the formula I have used is the one I use for dynamic compressors just setting the polytropic efficiency to 100% assuming it should be equal to adiabatic reversible process (am I right) ?
RE: Gas Compression as Vessel Level Rises
David Simpson, PE
MuleShoe Engineering
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"
RE: Gas Compression as Vessel Level Rises
Do you think the dynamic is identical if you consider a lower pressure ratio (say 1.5 to 2) that will keep the temperature sufficiently below water evaporation point ? So you would have heat exchange only between Liquid water and Nitrogen.
I have no experience with such Gasbuster and the question is just out of curiosity.
RE: Gas Compression as Vessel Level Rises
I have found the equation you showed to be a reasonable approximation to reality at 1.1 compression ratios and less (it even matches reality reasonably well in expansion). The boundary conditions of the equation are all centered around loosing or gaining heat to/from the environment and the reversibility of the reactions. Not the magnitude of any term. It doesn't work at all with an irreversible process like phase change or with a heat sink the magnitude of a vessel full of liquid.
David Simpson, PE
MuleShoe Engineering
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"
RE: Gas Compression as Vessel Level Rises
It will take me time to understand but I continue reading.
It is a fascinating invention really.
RE: Gas Compression as Vessel Level Rises
David Simpson, PE
MuleShoe Engineering
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"