Project ForgeThermodynamics
First Law of Thermodynamics
GATE 2017
Hard
The pressure ratio across a gas turbine (for air, specific heat at constant pressure Cp = 1040 J/kg·K and ratio of specific heats γ = 1.4) is 10. If the inlet temperature to the turbine is 1200 K and the isentropic efficiency is 0.9, the gas temperature at turbine exit is __________ K.
679.5 K(± 4.5 accepted)
Explanation
Isentropic exit temp: T2s = T1×(1/rp)^((γ-1)/γ) = 1200×(0.1)^0.2857 ≈ 1200×0.518 = 621.6 K. Actual exit temp from isentropic efficiency: T2 = T1 - η(T1-T2s) = 1200 - 0.9×(1200-621.6) ≈ 1200-520.6 = 679.4 K.
Source: GATE ME 2017 Session 1 (ME-1) (2017)
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