Enthalpy and Heat Calculation
Enthalpy and Heat Calculation
(OP)
Hello!!
I was wondering if i might be able to get some help/advice on this query I have. I have an excel spreadsheet which calculates the enthalpy change and heat required when chnaging the pressure of a gas sample in a gas pipeline. However I am unable to fully understand where some of the figures are being taken from:
This is the formula that appears to be being used to calculate the enthalpy of the gas coming in:
H= [(c-E1)*Tin]+[D(Tin^2)]+[(A-E2)*P1]-[B*P1/(Tin^2)]
Where:
Tin = Temp. of the gas entering
Pin= Pressure of the gas entering
A= -0.00792078
B= 950.85
C= 0.0314566
D= 0.000009138
E1= 0.000358
E2= 0.001391
There is also a figure called ERF (which I presume is some type of correction factor) which is added to the enthalpy, this is calculated by:
ERF=E3*(P1^2)+(E4*P1*Tin)+(E5*Tin*P1^2)+E6
Where:
E3= 0.0003572
E4= 0.000008397
E5= 0.00000119
E6= 0.0845
the Change in enthalpy is found by taking the total enthalpy (including correction factor) of the gas leaving the pressure changer from that of the gas entering the pressure changer.
I cannot understand what the values A,B,C,D, E1 ...... etc. are. They are simply numbers in the spreadsheet I have been given.
Any help or advice on where they might have come from would be much appreciated - Sorry for the long post!
Aisers





RE: Enthalpy and Heat Calculation
Good luck,
Latexman
RE: Enthalpy and Heat Calculation
RE: Enthalpy and Heat Calculation
Sorry its for a natural gas pipeline, The person who gave me the spreadsheet cannot identify where they have come from either as this is a very old calculation.
I have found one other person who seems to be using these forumlae on another forum - His question was about the actual coding of the program and not the theory. I have messaged him but have gotten no reply.
htt
RE: Enthalpy and Heat Calculation
you've definitely been faster than me
RE: Enthalpy and Heat Calculation
Good luck,
Latexman
RE: Enthalpy and Heat Calculation
strange that the (c-E1) value is not a single constant (must be pre-determined). typically, the constants for enthalpy equations are different for each hydrocarbon gas (methane, ethane, etc.) and then further calculations are accomplished to obtain the enthalpy value at the respective P & T. i wonder if the equation provided is for a single hydrocarbon gas.
the suggestion by Latexman is recommended.
good luck!
-pmover
RE: Enthalpy and Heat Calculation
Hey Guys!
Thanks for your feedback - I really appreciate you having a look at it, I know there is next to nothing to go on.
I believe this equation/calculation has been used in the gas industry for a good number of years by companies such as british gas etc.
It just seems weird that no one is able to place it or decipher where it comes from.
Thanks for your help,
Aisers
RE: Enthalpy and Heat Calculation
RE: Enthalpy and Heat Calculation
The suggestion to purchase a simulator to verify a formula could appear, at least, exaggerate.
RE: Enthalpy and Heat Calculation