I have been using the Redlich-Kwong EOS to calculate the compressibility factor for nitrogen. I am currently running an Excel VBA that performs the calculation. I have noticed that the process of calculation fails at temperatures of 92 F and below at 10,000 psia. However, it works at a temperatures of 93 F and above, at 10,000 psia. I have also shown it to work for a temperature and pressure envelope of 60 F to 600 F and 14.7 psia to 9,000 psia, respectively. By failure, I mean to say that Excel cannot converge on an answer and the program crashes. I am not sure if this failure is due to the capabilities of Excel, my computer, or if it is due to the limitation of the Redlich-Kwong EOS.
The macro I am using comes from Peress, J.:"Working with Non-Ideal Gases," CEP Magazine March 2003 p. 39. Unfortunately, I have only managed to obtain this macro, I have not been able to get this article to read for myself. The macro, the process to calculate z (compressibility factor), is shown below.
So my questions are:
- Are there pressure and temperature limits to the Redlich-Kwong equation of state? If so, what are they?
- What other factors need to be considered in understanding the limitations of the Redlich-Kwong eos?
- Is there a more robust EOS that can be used to solve for the compressibility factor, specifically for nitrogen, and can be implemented in Microsoft excel?
- Do you have access to the "Working with Non-Ideal Gases" article referenced and can I get a copy from you, please?