mech3020-s11-hw04 - efficiency as pressure ratio → 1...

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MECH 3020 Thermodynamics II: Homework set #4, due Wednesday 1. Say an ideal gas turbine cycle has a maximum temperature of 2000 K and an inlet temperature of 300 K. Will the power output for this cycle, for a fixed mass flow rate and pressure ratio, depend on whether or not a regenerator (assumed ideal) is installed? 2. Sometimes the simplifying and idealized assumptions used in thermodynamic analysis can lead to predictions that are obviously impossible. Consider such a case: an ideal gas turbine, with an ideal regenerator, has a fixed heat input of q H = 900 kJ/kg. Inlet conditions are 300 K, 1 atm. Specific heat is assumed constant. (a) Try to predict the temperature at the exit of the combustor. What happens? (b) If, for the ideal regenerator, w T = q H (as discussed in class), what would happen to the thermal
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Unformatted text preview: efficiency as pressure ratio → 1. Remember: q H is fixed at 900 kJ/kg. 3. A gas turbine cycle is required to produce a power of ˙ W = 5 MW. The turbine and compressor have isentropic efficiencies of η C = η T = 0 . 85, and the regenerator has an effectiveness of ± = 0 . 9. The maximum temperature in the cycle is 1800 K, and the pressure ratio is 8. Calculate: (a) The thermal efficiency of the cycle. (b) The cycle exit temperature (the temperature of the gases exhausted to the atmosphere), and (c) The volumetric flow rate of the air entering the compressor. Solve the problem two ways, using 1) the air tables, and 2) constant specific heat. Note that when using the air tables, the definition of the regenerator effectiveness is given by Eq. (9-23) in the text. 1...
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This note was uploaded on 09/24/2011 for the course MECH 3020 taught by Professor Mackowski during the Spring '11 term at Auburn University.

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