Nozzles in gas turbine electrical generators accelerate the combustion gases to

Question

Nozzles in gas turbine electrical generators accelerate the combustion gases to higher velocities by burning a fuel. The combustion products (M = 28 kg-kmol-1, cP = 1.009 kJ-kg-1-K-1) in a natural gas fueled electrical generator enter the nozzles with a negligible velocity at 4.26 MPa, 400 C. They leave at 2 MPa, 338 oC through an exit area of 0.1 m2 1) What is the velocity at the outlet of the nozzles? 2) What is the mass flow rate through the nozzles? 3) The increase in the flow work of the combustion products is:

Explanation / Answer

Nozzles are no work, no heat transfer, steady-flow devices with a single inlet/outlet. With negligible inlet velocity, the first law becomes V22 = -2Dh. For constant specific heats, Dh = cPDT. Presuming uniform flow, mdot = AV / v. The change in the flow work is Dfw = (pv)2 - (pv)1 = RDT where the latter result is from the ideal gas equation of state.

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