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Sign below to indicate compliance with the University Honor Code Possible Score Problem #1 45 Problem #2 45 Problem #3 10 100 Name: 1. Consider the reheat-regenerative Rankine cycle as shown with water as the working fluid. The working fluid experiences no irreversibilities as it passes through the turbines, pumps, steam generator, reheater, and condenser. The net power output of the cycle is 12 MW. There is no stray heat transfer. A. Complete the table below. B. Determine the thermal efficiency. C. Determine the mass flow rate of the steam entering the first turbine. State p (MPa) T (˚C) ṁ / ṁ1 (use y' and y") h (kJ/kg) s (kJ/kg-K) x (-) 1 8 480 (1) 3348.4 6.6586 ------- 2 2 ------- (y') 2963.5 ------- 3 0.7 2741.8 0.9895 4 0.7 440 3353.3 7.7571 ------- 5 0.3 ------- ( y") 3101.5 ------- 6 0.008 7 0.008 0 8 0.3 ------- ------- 9 0.3 561.47 0 10 8 ------- 569.73 ------- 11 8 205 882.4 ------- ------- 12 2 908.79 0 13 0.3 ------- 0.1605 Name: 2. A piston-cylinder assembly contains air and executes a 3 processes in the following manner: 12 T1=27°C , V1=2m3 and P1=1bar; Heat is added at a constant pressure to a temperature T2=202°C 23 Adiabatic Expansion to State 3 such that Pv1.4=constant until T3=27°C 34 An exhaust valve then opens and Isothermal compression occurs until V4=V3/10. Air leaves the cylinder at the same temperature and pressure as in the cylinder, which remains the same. Texit=T3=T4 and Pexit=P3=P4 Assume ideal gas with R=0.287 kJ/kgK, k=1.4 A. Fill in the Tables below. B. Sketch the states on a P-v diagram. C. What is the initial mass m1=m2=m3? D. What is the final mass m4? E. If 100kJ of total heat is added during the process what is the work in kJ from 34 during the exhaust process? Process Q/m (kJ/kg) W/m (kJ/kg) Δu (kJ/kg) Δs (kJ/kgK) 12 23 T K P bar V m 3 1 1 2 2 3 4 m1=m2=m3(kg) m4(kg) Wtot 34(kJ) Name: 3. Short Answers: A. Shown is a regenerative gas turbine power cycle with intercooling and reheat. Assuming an air-standard model Assuming that you have already determined the enthalpy at EVERY state (h1-h10, including isentropic and non-isentropic states), develop expressions for the following in terms of those enthalpy values: • Overall cycle efficiency (ηcycle ) • The regenerator efficiency (ɳregenerator) B. A 5kg block of copper at 100°C is submerged in 10kg of water at 10°C. What is the final temperature after steady state equilibrium is attained? What is the entropy change to the universe in kJ/K? Does this make sense? Assume both materials are incompressible with Cp,Cu=0.385kJ/kgK and Cp,water=4.18 kJ/kgK

Name: Number ENPM 672 Thermodynamics Spring 2016 Final EXAM March 2016 Open Book, Open Notes Dr. Kristen Hines University of Maryland, College Park Sign below to indicate compliance with the University Honor Code Possible Problem #1 45 Problem #2 45 Problem #3 10 100 Score Name: 1. Consider the reheat-regenerative Rankine cycle as shown with water as the working fluid. The working fluid experiences no irreversibilities as it passes through the turbines, pumps, steam generator, reheater, and condenser. The net power output of the cycle is 12 MW. There is no stray heat transfer. A. Complete the table below. B. Determine the thermal efficiency. C. Determine the mass flow rate of the steam entering the first turbine. State 1 p (MPa) 8 T (˚C) 480 ṁ / ṁ1 (use y' and y") (1) h (kJ/kg) 3348.4 2 2 ------- (y') 2963.5 ------- 3 0.7 2741.8 0.9895 4 0.7 440 5 0.3 ------- 6 0.008 7 0.008 8 0.3 9 0.3 10 8 11 8 12 2 13 0.3 3353.3 ( y") s (kJ/kg-K) 6.6586 7.7571 3101.5 x (-) ------- ------------- 0 ------- ------561.47 0 ------- 569.73 ------- 205 882.4 ------- 908.79 ------0 ------- 0.1605 Name: 2. A piston-cylinder assembly contains air and executes a 3 processes in the following manner: 1 2 3 T1=27°C , V1=2m3and P1=1bar; Heat is added at a constant pressure to a temperature T2=202°C Adiabatic Expansion to State 3 such that Pv1.4=constant until T3=27°C An exhaust valve then opens and Isothermal compression occurs until V4=V3/10. Air leaves the cylinder at the same temperature and pressure as in the cylinder, which remains the same. Texit=T3=T4 and Pexit=P3=P4 Assume ideal gas with R=0.287 kJ/kgK, k=1.4 2 3 4 A. B. C. D. E. Fill in the Tables below. Sketch the states on a P-v diagram. What is the initial mass m1=m2=m3? What is the final mass m4? If 100kJ of total heat is added during the process what is the work in kJ from 3 exhaust process? Process 1 2 2 3 T P V K bar m 1 2 1 2 3 4 m1=m2=m3(kg) m4(kg) Wtot 3 Q/m (kJ/kg) 4(kJ) 3 W/m (kJ/kg) Δu (kJ/kg) 4 during the Δs (kJ/kgK) Name: 3. Short Answers: A. Shown is a regenerative gas turbine power cycle with intercooling and reheat. Assuming an air-standard model Assuming that you have already determined the enthalpy at EVERY state (h1-h10, including isentropic and non-isentropic states), develop expressions for the following in terms of those enthalpy values: • Overall cycle efficiency ( ηcycle ) • The regenerator efficiency (ɳregenerator) B. A 5kg block of copper at 100°C is submerged in 10kg of water at 10°C. What is the final temperature after steady state equilibrium is attained? What is the entropy change to the universe in kJ/K? Does this make sense? Assume both materials are incompressible with Cp,Cu=0.385kJ/kgK and Cp,water=4.18 kJ/kgK Name:
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