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1 Last Name: First Name: Thermo no. ME 200 Thermodynamics 1 Fall 2018 Exam Circle your structor s last name Division 1 (7:0): Naik Division (1:0): Wassgren Division 6 (11:0): Sojka Division 2 (9:0): Choi Division 4 (8:0): Holloway Division 7 (2:0): Vuppuluri Number of extra papers used if any Division 8 (12:0): Buckius INSTRUCTIONS Do not remove staples from any page. If you use extra paper, attach it at the end of the exam with a paper clip and dicate above how many extra sheets were attached. Do not write on the back of any page because it will not be scanned so will not be graded. This is a closed book and closed notes exam. Equation sheets and all needed tables are provided. Significant credit for each problem is given if you identify your and its boundary, draw the relevant energy flows on a diagram i.e. Energy Flow Diagram (EFD), start your analysis with the basic equations, list all relevant assumptions, and have appropriate units and use three significant figures. There is no need to re-write the given and fd. Do not hesitate to ask if you do not comprehend a problem statement. For your own benefit, please write clearly and legibly. You must show your work to receive credit for your answers. IMPORTANT NOTE The use of PDAs, Blackberry-type devices, cell phones, laptop computers, smart watches or any other sources of communication (wireless or otherwise) is strictly prohibited durg examations. Dog so is cheatg. If you brg a smart watch, cell phone, or other communication device to the examation, it must be turned off prior to the start of the exam, placed your backpack, and the backpack must be stored below your seat. It shall be reactivated only after you leave the examation room for the fal time. Otherwise it is a form of cheatg and will be treated as such. SECOND IMPORTANT NOTE The only calculators allowed for use on this exam are those of the TI-0X series. No others. 1

2 1. [20 pots] Circle the correct answer (no partial credit) for (a) to (d). (a) [2 pots] For a constant mass, a reversible and adiabatic process is always isentropic. (True or False) (b) [2 pots] For a constant mass, an isentropic process is always reversible and adiabatic. (True or False) (c) [2 pots] At a given temperature, entropy the liquid phase of a substance is always larger than entropy the vapor phase of the same substance. (True or False) (d) [2 pots] Coefficient of performance is always less than one. (True or False) (e) [6 pots] Liquid water, considered as an compressible substance, enters a reversible and adiabatic pump at 0C and flows with negligible changes KE and PE. The pump has one let and one let and operates at steady state. What is the temperature (C) of liquid water at the exit of the pump? Show supportg calculations. ds Q j ms ms generation s s 0 j Tj,boundary T For an compressible substance: s Cln 0 T T T 0 C T (f) [6 pots] An ventor claims that the maximum efficiency of a power cycle operatg between hot and cold reservoirs of temperatures 1000C and 500C, respectively, is equal to 50%. Is this claim possible? (Yes or No) Justify usg an equation. Maximum efficiency for a reversible power cycle: T K C th, rev TH K It is impossible to atta an efficiency of 50% for a power cycle operatg between hot and cold reservoirs of temperatures 1000C and 500C 2

3 2. [40 pots] Air (m = 0.4 ) contaed a piston-cylder device undergoes a constant pressure process at an absolute pressure of 86.5 kpa. The temperature of air changes from 427C to 77C durg the process. Molecular weight of air: /kmol Use the closest value ideal gas table; do not terpolate. (a) Calculate the itial and fal volume of air. Report your answers m. (b) Fd the work durg the process. Report your answer. (c) Determe the heat transfer durg the process. Report your answer. (d) Calculate the total entropy generation for the and its surroundg. Assume a surroundg temperature of 27C. Report your answer /K. Identify appropriate or s, show mass/energy teractions (EFD), list any assumptions and basic equations, and provide your solution. There is no need to re-write the given and fd. System/EFD Assumptions Quasi-equilibrium Ignore KE change Ignore PE change Air behaves as an ideal gas Neglect friction No other work except boundary work Closed m = constant

4 Extra Space for Problem 2 Basic Equations dm m m Integratg: m constant de Q W m h ke pe m h ke pe Integratg: QW U KE PE ds Q j ms m s T Integratg: generation j j,boundary Q S T boundary Solution (a) PV mr T ; air R air 8.14 R kmol-k MW air K kmol Initial volume of air: V Fal volume of air: V mr T K -K air 1 1 P kpa mr T K -K air 1 2 P kpa V1 1m V2 0.5 m (b) Boundary work durg the process: W PdV W P P V V boundary W kpa 0.5 1m W W < 0 work done on the (c) Considerg energy balance for the : Q12 W12 mu2 u Q Q < 0 heat transfer of the 4

5 Extra Space for Problem 2 (d) Considerg entropy balance for the and its surroundg: generation generation Q Q P ms s1 ms2 s1 Rair ln Tboundary Tsurroundg Tboundary Tsurroundg P K generation > 0 irreversible process K 5

6 . [40 pots] A power plant consists of an adiabatic pump, a boiler, an adiabatic turbe, and a condenser. The wor fluid is water/steam, with data at each state provided the table below; all the pressure values are absolute. Q boiler m 2 m W turbe W pump m 1 m Q 1 condenser State P, bar T, C u, / h, / s, /-K P, bar T sat, C u f, / u g, / h f, / h g, / s f, /-K s g, /-K (a) Calculate the isentropic efficiency of the turbe. Report your answer %. (b) Determe the specific heat transfer for the boiler and the condenser. Report your answers /. (c) Fd the specific entropy generation for the entire power cycle. Assume heat transfer occurs to the boiler at a boundary temperature of 500C while heat transfer occurs from the condenser to an environment at a temperature of 0C. Report your answer /-K. (d) Show the cycle on T-s diagram relative to the vapor dome and the relevant les of constant pressure. Label the axes and four states and dicate the process directions with arrows. For water: T critical = 74C, P critical = 221 bar. Identify appropriate or s on the sketch provided, show mass/energy teractions (EFD), list any assumptions and basic equations, and provide your solution. There is no need to re-write the given and fd. m 4 m 4 6

7 Extra Space for Problem Assumptions Steady state, steady flow One-dimensional, uniform flow Ignore KE change Ignore PE change Boiler and condenser: W CV 0 Turbe and pump: Q 0 CV Basic Equations dm m m de ds Q W m h ke pe m h ke pe Q j generation j Tj,boundary ms m s Solution (a) Mass balance for the turbe: m m4 m steam Energy balance for the actual turbe: wactual h h For the isentropic process through the turbe: s s4s K s f,45c < s 4s < s g,45c saturated liquid-vapor mixture s4 s s f,45 C For saturated liquid-vapor mixture: x4s 0.86 s s g,45 C f,45 C h4 h s f,45 C h x s s h4 s h h g,45c f,45c Energy balance for the isentropic turbe: wisentropic h h4s wactual Isentropic efficiency of the turbe: turbe turbe 90% w isentropic

8 Extra Space for Problem (b) Mass balance for the boiler: m2 m m steam Energy balance for the boiler: qboiler h h qboiler 020 q > 0 heat transfer to the Mass balance for the condenser: m4 m1 m steam Energy balance for the condenser: qcondenser h1h qcondenser 2060 q < 0 heat transfer of the (c) Entropy balance for the entire power cycle: qboiler qcondenser cycle T T K 0 27 K boiler condenser cycle K Alternatively Considerg entropy balance for the pump: pump s2 s K Considerg entropy balance for the boiler: 020 qboiler boiler s s Tboiler K -K -K Considerg entropy balance for the turbe: turbe s4 s K Considerg entropy balance for the condenser: 2060 qcondenser condenser s1s Tcondenser 0 27K -K -K Specific entropy generation for the entire heat pump cycle: cycle pump boiler turbe condenser cycle K 8

9 Extra Space for Problem (e) T-s diagram 9

ME 200 Thermodynamics 1 Fall 2017 Exam 3

ME 200 Thermodynamics 1 Fall 2017 Exam 3 ME 200 hermodynamics 1 Fall 2017 Exam Circle your structor s last name Division 1: Naik Division : Wassgren Division 6: Braun Division 2: Sojka Division 4: Goldenste Division 7: Buckius Division 8: Meyer