On 10 Jul 2003 16:48:01 -0700, in sci.space.tech
(Iain McClatchie) wrote:

I just got the book "Mechanics and Thermodynamics of Propulsion",
mostly on the recommendations found in the sci.space.tech archives. I
turned to Appendix 2 to find tables with specific heat vs temp for the
various gases that you find in a rocket engine (O2, CO2, CH4, H2, H2O,
that sort of thing). Hooray!

Imagine my disappointment when I noticed that the tables were
specifically for gases at low pressure -- 1 atm. That pressure
doesn't come up very often in simulations of rocket engines and
hypervelocity guns.

I've looked on the web, but have not found a reference for specific
heats of these gases at high pressures. I'm mostly interested in the
100 - 1000 atm range.

Am I just being stupid or unread? Is there some bog-standard
adjustment that I'm supposed to make to these specific heats to
account for pressure? Or did some guy in 1886 prove that specific
heats are completely independent of pressure?

How accurate are you trying to be? In my copy of NASA SP-3045,
Compressed Gas Handbook, the variation of the Cp of air as a function
of pressure is small at higher temps. Data eyeballed off graph:

T (F) Cp @ 0psia (Btu/Lbm) Cp @ 15,000psia (Btu/Lbm)
500 0.248 0.289
1000 0.265 0.288
2000 0.283 0.2835
3000 0.295 0.301
4000 0.3045 0.3065

FWIW, this data is courtesy of the Cornell University, Engineering
Experiment Bulletin No.30. Where the data included for other gases
also came from.