HW3b_09 solution

# HW3b_09 solution - ME 18b, HW 3 Due Tuesday April 21, 2008...

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1 ME 18b, HW 3 Due Tuesday April 21, 2008 (accepted until 4 pm) TAs for HW #3: Dan Alvarez, Monday 8-10 pm, SFL 229; Mary Dorman, Monday 7-9 pm SFL 331 1. Cal Tech Power Plant Rankine Cycle analysis: The Cal Tech Power Plant uses two thermodynamic cycles to produce electric power and provide steam for campus use. Examine the following schematic of the power plant’s Rankine cycle. (A better copy of this is posted as a handout on the class website). Using the information given on the diagram you should do a complete thermodynamic analysis of the cycle which includes finding: [Note: Please convert all given values to SI units] a) The heat input of the steam generator (compare the heat lost by the gas turbine exhaust to the heat gained by the water) b) The work produced by the steam turbine, (compare this to the generated electric power of 2.5 MW – how efficient is the turbine/generator system) c) The work of the pump d) The overall Rankine cycle efficiency e) Suggest some ways the plant could become even more efficient

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2 Solution: Determine properties for each state in the cycle. State 1, Pump exit: T1 = 109°C, P1 = 2.41 MPa, mass flow rate = 5.87 kg/s. Using CATT software find h1 = 459 kJ/kg State 2, Steam Generator exit: T2 = 266°C, P2 = 1.97 MPa. Find h2 = 2944 kJ/kg, also s2 = 6.629 kJ/kgK. We’ll need this to evaluate the efficiency of the turbine by comparing the actual output to the ideal turbine. The steam generator heat input is: Q boiler = m(h2 – h1) = 5.87 kg/s(2944 – 459)kJ/kg/1000 Q boiler = 14.6 MW Heat loss by gas turbine exhaust in the heat recovery unit. Assume the exhaust gas has properties similar to air. You could assume it’s mostly a mixture of CO2 and H2O vapor but that makes it more complicated. Q
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## This note was uploaded on 01/08/2011 for the course ME 18b taught by Professor Hunt during the Spring '08 term at Caltech.

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HW3b_09 solution - ME 18b, HW 3 Due Tuesday April 21, 2008...

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