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engineer23
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All the JANAF tables I have present values for 1 atm. But what if the reactants or products are at a temperature other than 1 atm (say 10 atm or .5 atm)? Is there a way to scale the JANAF tables for different pressures?
Yes, I believe there are. I did some calculations on chemical rocket propulsion which used JANAF data, and the code had equations for temperature and pressure. I thought JANAF tables were available at different pressures, much like steam tables. Unfortunately, it's been more than 20 years since I did that work, and I haven't kept up with it.engineer23 said:All the JANAF tables I have present values for 1 atm. But what if the reactants or products are at a pressure other than 1 atm (say 10 atm or .5 atm)? Is there a way to scale the JANAF tables for different pressures?
engineer23 said:All the JANAF tables I have present values for 1 atm. But what if the reactants or products are at a temperature other than 1 atm (say 10 atm or .5 atm)? Is there a way to scale the JANAF tables for different pressures?
engware said:Hi there:
This is a good question, but it is a tricky one.
With dealing with steam, you have steam tables and there is no problem. Physical properties are given as a function of both pressure and temperature. Such values have been experimentally measured.
When dealing with gases, combustion, it is another ball game.
Knowing that for ideal gas one can use the state equation as pv = RT, enthalpy values are given as a function of temperature only -- h = u + pv = u + RT = cpT.
View attachment 13422
For basic combustion calculations this is just fine when calculating the flame temperature.
However, when dealing with combustion products over a huge pressure and temperature range, this is not acceptable. In order to get aceptable numerical values, the minimization of Gibbs free energy for the combustion products is used. Such values are given as function of both pressure and temperature. Such calculations cannot be done by hand.
Here are s few URLs that can be of some help to you:
Technical background information on the physical properties
http://members.aol.com/engware/properties.htm
Physical properties online calculator
http://members.aol.com/engware/calc1.htm
Technical background information on combustion
http://members.aol.com/engware/components.htm
Combustion online calculator
http://members.aol.com/engware/calc4.htm
Thanks,
Gordan
PS
If you need additional explanation on the subject matter, I am here to help you out and share a few sample problems with you. Again, this is not an easy subject matter and it takes time to realize and digest what is at stake ...
JANAF tables, also known as the JANAF Thermochemical Tables, are a collection of thermodynamic data for chemical compounds. They were published by the Joint Army-Navy-Air Force (JANAF) Committee in 1970 and have since been used by scientists and engineers to calculate the thermodynamic properties of chemical reactions and processes.
JANAF tables contain a variety of thermodynamic data, including enthalpy, entropy, heat capacity, and Gibbs free energy values. These values are given at various temperatures and pressures, allowing for calculations to be made at different conditions.
JANAF tables are organized by chemical compound and arranged in alphabetical order based on their chemical formula. Each compound has its own table, which contains the thermodynamic data for that compound at different temperatures and pressures. There are also tables for different phases of a compound, such as solid, liquid, and gas.
JANAF tables are used by scientists and engineers in a variety of fields, including chemistry, physics, and engineering. They are used to calculate the thermodynamic properties of chemical reactions and processes, which is essential for understanding and predicting the behavior of chemical systems.
Yes, JANAF tables are still being updated and maintained by the National Institute of Standards and Technology (NIST). The most recent version, JANAF Thermochemical Tables, Fourth Edition, was published in 1998 and is available online.