Question

A small air turbine with an isentropic efficiency of 80% should produce 120 Btu/lbm of work. The inlet temperature is 1800 R and it exhausts to the atmosphere. Find the required inlet pressure and the exhaust temperature. 

Answer 1

 C.V. Turbine actual energy Eq

 w = h_i - h_e,ac = 120

If constant heat capacity was used

T_e = T_i - w/C_p = 1800 - 120/0.24 = 1300 R

T_e,s = T_i - w_s/C_p = 1800 - 150/0.24 = 1175 R

The constant s relation is Eq