Good day. I am using ideal gases (CO2, H2O,N2,O2,SO2) to model the products (flue gases) of coal combustion. I need to develop a lookup table of the enthalpies of the ideal gases at different temperatures. I know how to calculate the volumes of the different ideal gases, but I struggle to calculate the volumetric heat capacity of each ideal gas. An example of how I need to calculate the enthalpy of CO2 is the following:
HCO2 = CpCO2 * T * VCO2,
where HCO2 is the enthalpy (kJ/kg) of CO2 at temperature T, CpCO2 is the volumetric heat capacity (kJ/m^3.K), T is the temperature (K), and VCO2 is the specific volume (m^3/kg) of CO2.
How does one calculate CpCO2 (kJ/m^3.K)?
There are different papers and ESA reports by Capitelli et al where you can find these quantities. I attach one report. You can also give a look to the book
M. Capitelli, G. Colonna A. D'angola, Fundamental Aspects of Plasma Chemical Physics: Thermodynamics.
You can also give look to this site http://phys4entrydb.ba.imip.cnr.it/EquilTHETA/refs.php
I forget something. The equation you are writing is wrong, because Cp is a function of the temperature, as you will see from the references I suggest in my previous comment. Therefore the enthalpy should be calculated integrating your equation from T=0 to T or from T1 and T2.
There is a really good book on syngas manufacture called "Concepts in Syngas manufacture" if you can get hold of it it has temperature dependant heat capacities for all of your molecules of interest to fairly high temperatures.
Here is a link with some information about the book, but not the book itself. I would expect most technical universities to have it available. http://www.worldscientific.com/worldscibooks/10.1142/p717
Also, Cp = dH/dT at constant pressure. To calculate change in enthalpy then you need to integrate both sides. Thus you integrate the polynomial ideal heat capacity equation. (It is generally a polynomial).
To be a little more specific, you get a reference temperature (there are plenty of tables with reference enthalpies at 298 Kelvin) and then you calculate the change in enthalpy from that reference temperature to the temperature of interest via the above mentioned integration of the ideal heat capacity polynomial equation.
Elliott and Lira (Introductory Chemical Engineering Thermodynamics) give the Enthalpy of formation of CO2 as being -393.51KJ/mol and they give the ideal heat capacity equation as being CP(J/mol*K)= A+B(T)+C(T^2)+D(T^3), and for CO2 the constants are given by them as A=1.980E+1, B=7.344E-2, C=-5.602E-5, D=1.715E-8. They have values for all of your other molecules too.
I still recommend using the values given by "Concepts in Syngas manufacture" by Jens Rostrup-Nielsen, it is probably the best textbook you will find on the subject.
- Badges
- Science topic
- Similar topics
- Engineering
- Materials Engineering