Talk:Compressibility factor (gases)/Draft

There is an article of the same name on Wikipedia

Despite the same name, this article was written completely from scratch. Any similarity with the WP article is purely coincidental. - Milton Beychok 21:15, 2 April 2008 (CDT)

EOS

Milton, would it be possible to sketch briefly the pros and cons of the different EOS's? I finished reading and I'm ready to approve the article. --Paul Wormer 12:50, 5 April 2008 (CDT)

Paul, thanks very much for findimg all those typos and for adding a few bits information as well. I must have read it a dozen times and I still had some typos!! I would still like to wait, at least a week for other editors (if any) who may have comments, before you nominate the article for approval.

As for a comparison of the EOS's, I tried that when I was writing the article but couldn't come up with anything that I liked. Some are better in certain areas but not as good in certain other areas. So I decided to say no more than the following (in the section on "Modified versions of the van der Waals equation"):

Perhaps the most commonly used equations of state by engineers working in petroleum refining, petrochemical production, natural gas processing, cryogenic distillation and related industries are: the Redlich-Kwong equation developed in 1949, the Soave-Redlich-Kwong equation developed in 1972 and the Peng-Robinson equation developed in 1976. Those three equations are essentially modified versions of the van der Waals equation.

If you have some wording to suggest other the above, I would be pleased to have you send it to me. Milton Beychok 21:15, 5 April 2008 (CDT)

Notation of powers

You write $T^{2.5},\quad T^{0.5}$ instead of $T^{2}{\sqrt {T}}$, and $\quad {\sqrt {T}}.$ The first notation implies that other powers are OK too, say T^2.6, but I can imagine that dimensionality arguments only allow exact square roots. If that is the case then the second notation is preferable. If the exponents (2.5 and 0.5) are more or less coincidental (i.e., give best fits) then the first notation is preferable, but a remark about this would be in order. --Paul Wormer 13:31, 14 April 2008 (CDT)

Paul, thanks for your comment and it is good to hear from you again. I will change the notation to $T^{2}{\sqrt {T}}$ and $\quad {\sqrt {T}}$, if you so wish.

But I honestly don't see the difference. My calculator gives me the same numerical answer for either notation.

Perhaps, some readers might possibly imply that $T^{2.5}$ means other powers are okay also. However, if they use the equation as written (without pondering any implications), they will get the correct numerical answer.

I referenced those Redlich-Kwong equations to Chapter 3 of Ji Lin Wang's doctorate thesis (reference 19) and to Jean Vidal's book (reference 20). Wang wrote the equations exactly as I did and, on page 114 of his book, Vidal used $T^{2.5}$ also just as I did. However, be that as it may, I repeat that I will change the notation to $T^{2}{\sqrt {T}}$ and $\quad {\sqrt {T}}$, if you so wish. Just let me know. Regards, - Milton Beychok 15:53, 14 April 2008 (CDT)

You are an engineer, that is clear. As I said above, for a physicist/mathematican T^0.5 has a different connotation than $\scriptstyle {\sqrt {T}}$. You will be surprised, but T^1/2 and T^5/2 are OK, too. To me the decimal notation implies 2 significant digits and not an exact value.--Paul Wormer 16:18, 14 April 2008 (CDT)