2
$\begingroup$

I am reading Rocket Propulsion Elements by George P. Sutton & Oscar Biblarz, 9th Edition. In the fifth chapter, I was introduce to the specific heat ratio k for the perfect gas mixture, Eq. 5-7:

(1) $k_{\text{mix}} = \frac{(C_{p})_{\text{mix}}}{(C_{p})_{\text{mix}}-R'}$

Since,

(2) $k_{j} = \frac{(C_{p})_{\text{j}}}{(C_{v})_{\text{j}}}$

(3) $R_{j} = \frac{R'}{\mathfrak{M}_{j}} $ $\text{&}$

(4) $R_{j} = (C_{p})_{\text{j}} - (C_{v})_{\text{j}}$

It seems to me that this equation should instead include the mixture gas constant $R_{\text{mix}}$ in the place of the Universal gas constant, $R'$.

I tried to derive it without success. Can someone clarify this to me?

$\endgroup$
3
  • $\begingroup$ The question doesn't seem to be a bad one, however, I believe it is not really suited for this site... For chemistry questions, check out chemistry.stackexchange.com $\endgroup$ – finnmglas Sep 17 '20 at 15:50
  • 2
    $\begingroup$ On topic here, on topic on chemistry (or physics?). OP decides where to post in that case. And OP posted here. $\endgroup$ – SE - stop firing the good guys Sep 17 '20 at 16:12
  • 1
    $\begingroup$ Good question and congrats on going through the details. My 4th edition doesn't have these equations in it. And I learned something. $\endgroup$ – Organic Marble Sep 17 '20 at 20:32
2
$\begingroup$

Universal gas constant R' is correct. Sutton uses $C_p$ for molar specific heat and $c_p$ for mass specific heat. See table of symbols at end of chapter (I have the 7th ed.).

$\endgroup$
1
  • 3
    $\begingroup$ Since $C_{p}$ is the molar specific heat, my mistake is equation (4). It should be: $R' = (C_{p}) - (C_{v})$ $\endgroup$ – John Ortiz Sep 17 '20 at 19:48

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.