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1 ME 00 Thermodynamics Fall 07 Exam Circle your structor s last name Division : Naik Division : Wassgren Division 6: Braun Division : Sojka Division 4: Goldenste Division 7: Buckius Division 8: Meyer INSTRUCTIONS 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 system 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. Do not write on the back of any page because it will not be scanned so will not be graded. If you need extra paper raise your hand and a proctor will supply it. 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.

2 . [0 pots] Circle all (and only all) correct answers. (a) Consider a lightbulb powered by electricity. Assume positive sign for heat transfer to the system and for work put from the system. Which of the followg is true considerg lightbulb as the system? W > 0, Q > 0 W > 0, Q < 0 W < 0, Q > 0 W < 0, Q < 0 (b) Which of the followg is (are) true for a fixed state contag only vapor? T < T sat T > T sat (Both must be correct) P < P sat P > P sat (c) What is the quality for a saturated liquid-vapor mixture? Ratio of volume occupied by vapor phase to total volume of the mixture Ratio of volume occupied by liquid phase to total volume of the mixture Ratio of mass occupied by vapor phase to total mass of the mixture Ratio of mass occupied by liquid phase to total mass of the mixture (d) A steel ball at 00C is itially held stationary 00 m above the ground. The ball is then released, and the ball accelerates and cools durg its fall to the ground. Assume air friction to be negligible. When is the total energy of the ball highest? The stant it is released Just before it hits the ground Just after it hits the ground The energy remas constant (e) Which of the followg is (are) not true for change specific ternal energy durg a process with itial and fal states havg only liquid? u u P, T u P, T uu P u P f f uct T u u T u T f f

3 . [40 pots] A piston-cylder device contas a gas (which remas a gas through) undergog a cycle with the followg three processes: Process -: Constant pressure expansion at 0 bar absolute pressure Process -: Constant volume coolg Process -: Lear pressure crease from 5 bar absolute pressure (State ) back to 0 bar absolute pressure at State The data at various states the cycle is provided table below. State P, bar V, m U, kj (a) Sketch the three processes on a P-V diagram. Label the axes and all three states and dicate the process directions with arrows. (b) Calculate the boundary work (kj) for the gas durg each process. (c) Determe the heat transfer (kj) for the gas durg each process. (d) Is this a power cycle or a refrigeration cycle? Justify your answer with appropriate calculation. (e) Calculate thermal efficiency or coefficient of performance for the cycle. Identify the system, 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. (Show boundary and identify system) Assumptions Quasi-equilibrium Ignore KE change Ignore PE change Neglect friction No other work except boundary work

4 Extra Space for Problem Basic Equations Wboundary pdv de dt system Integratg: QW U KE PE Solution (a) P-V diagram Q W m h ke pe m h ke pe P (bar) (No vapor dome) + (Correct states) P = P = 0 bar (b) Boundary work durg the constant pressure process from to : V =0.5 m V = V = m W pdv p p V V 000 kpa 0.5 m W 500 kj + Boundary work durg the constant volume process from to : W pdv W 0 Boundary work durg the process from to : W pdv Area under the curve(le)from to p pvv + W kpa 0.5 m W 75 kj + (c) Considerg energy balance, heat transfer for each process: V (m ) + Q W U U Q Q 700 kj Q W U U Q Q 00 kj + + Q W U U Q Q 75 kj +

5 Extra Space for Problem (d) Net work durg the cycle: Wnet W W W Wnet 5 kj W 0 power cycle net (e) For a power cycle, thermal efficiency: Wnet, 5 kj th QH Q Q 700 kj th 7.9%

6 . [40 pots] A closed, rigid tank with a volume of 0.5 m itially contas refrigerant R-4a at an absolute pressure of 6 bar and temperature of 60C (State ). The refrigerant is stirred with a paddle wheel device and the tank is cooled at the same time. The paddle wheel performs 0 kj of work on the refrigerant. The refrigerant temperature drops to C (State ) due to the given energy teractions. (a) Determe the mass (kg) of R-4a the tank. (b) What is the fal pressure (bar) of R-4a the tank? (c) Fd the heat transfer (kj) for R-4a durg the process. (d) Show the process on P-v diagram relative to the vapor dome and the les of constant temperature for the two states. Label the axes and two states and dicate the process direction with arrow. Identify the system, 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. Assumptions Quasi-equilibrium Ignore KE change Ignore PE change Closed m = constant Rigid V = constant W b = 0 (Show boundary and identify system) (Show energy teractions Q and W) Basic Equations de dt system Integratg: QW U KE PE Q W m h ke pe m h ke pe

7 Extra Space for Problem Solution (a) For R-4a: T sat (6 bar) =.6C T > T sat superheated vapor + Usg superheated vapor table: m v kg V 0.5 m Mass of R-4a: m m 6.04 kg v m kg V (b) m = constant and V = constant v constant m For R-4a: T = C, v = v = m /kg v f,c < v < v g,c saturated liquid-vapor mixture p p 4.4 bar p sat C + (c) Considerg energy balance, heat transfer durg the process: Q W U U W W m u u b other Paddle wheel performs work on R-4 W 0 kj Usg superheated vapor table: For saturated liquid-vapor mixture: x other kj u 75. kg f, C u u u g, C f, C x v v f, C v v g, C f, C u u u 67.8 kj kg (uf, ug values) kj Q 0 kj 6.04 kg kg Q 5. kj (vf, vg values)

8 Extra Space for Problem (d) P-v diagram (Vapor dome) (Correct states) (Correct isotherms)

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