mech3020-s11-hw04

# 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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