Page 219 - Advanced thermodynamics for engineers

9.7 PROBLEMS 205

Specific heat at constant pressure c p,m in J/kmol K, with T in K
3
CO 2 c p;m ¼ 21 10 þ 34:0T
3
H 2 O c p;m ¼ 33 10 þ 8:3T
3
O 2 c p;m ¼ 28 10 þ 6:4T
3
N 2 c p;m ¼ 29 10 þ 3:4T
3
[0.9986 10 þ 0.2105T; 28.71; 895.7 K; 1.591 bar]
P9.11 The products of combustion of a jet engine have a molecular weight, m w , of 30 and a molar
4
specific heat at constant pressure given by c p,m ¼ 3.3 10 þ 15T J/kmol K where T is the
gas temperature in Kelvin. When the jet pipe stagnation temperature is 1200 K the gases
leave the nozzle at a relative speed of 600 m/s. Evaluate the static temperature of the gas at
the nozzle exit and estimate the total to static pressure ratio across the nozzle. Assume that the
products of combustion behave as an ideal gas and that the flow is isentropic.
In a frictional nozzle producing the same mean outlet speed from the same inlet gas
temperature, what would be the effect on
(a) the mean outlet static temperature, and
(b) the total to static pressure ratio?
[1092 K; 1.732; (a) unaffected; (b) increased]