Project ForgeAir (ideal gas) enters a perfectly insulated compressor at a temperature of 310 K. The pressure ratio of the compressor is 6. Specific heat at constant pressure for air is 1005 J/kg.K and ratio of specific heats at constant pressure and constant volume is 1.4. Assume that specific heats of air are constant. If the isentropic efficiency of the compressor is 85 percent, the difference in enthalpies of air between the exit and the inlet of the compressor is __________ kJ/kg (round off to nearest integer).
Explanation
T2s = T1×PR^((γ−1)/γ) = 310×6^(0.2857) ≈ 310×1.6684 ≈ 517.2 K. Δh_isentropic = Cp(T2s−T1) = 1005×(517.2−310) ≈ 208.2 kJ/kg. Actual Δh = Δh_isentropic/η = 208.2/0.85 ≈ 245.0 kJ/kg.
Source: GATE ME 2020 Session 1 (ME-1) (2020)
This question is part of a 15-day revision cycle — sign in and Project Forge will bring it back the day before you'd forget it.