ME 200 Thermodynamics 1 Spring Exam 2

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1 Last Name: First Name: Thermo no. ME 200 Thermodynamics 1 Sprg Exam 2 Circle your structor s last name Ardekani Fisher Hess Naik Sojka (onle and on campus) INSTRUCTIONS This is a closed book and closed notes exam. Equation sheets and all needed tables are proided. Significant credit for each problem is gien if you identify your system and its boundary, draw the releant EFD, start your analysis with the basic equations, list all releant assumptions, and hae appropriate units. 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 receie credit for your answers. Do not write on the back of any page because it makes it ery easy for gradg mistakes to occur. If you need extra paper raise your hand and a proctor will supply it. Maximum credit for each problem is dicated below. IMPORTANT NOTE The use of PDAs, Blackberry-type deices, 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 deice 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 reactiated only after you leae 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 are allowed.

2 Problem Possible Score Total 100

3 1. Answer the followg questions by circlg all (and only all) correct answers. (a) A piston-cylder deice contas a substance that is compressed at constant pressure. Assume changes ketic and potential energy are negligible. Which of the followg statement(s) is (are) always true for such a process? q = h w < 0 T > 0 u > 0 Compression work done on the substance w < 0 Energy balance: QW U KEPE Q PV U H q h (b) For a throttlg process, the pressure decreases from let to exit. If the fluid flowg through the ale is liquid (compressible) at let and exit, what happens to temperature durg the throttlg process? Increases Decreases Remas same Insufficient formation Throttlg is isenthalpic: h 0 up ct P T P/ c 0 (c) Which of the followg assumptions is (are) required to calculate the change specific enthalpy as: h = p? Ideal gas Incompressible Constant temperature process Adiabatic process Incompressible: h up ct P (d) An entor claims that an ideal gas flows steadily through an adiabatic turbe producg work put. Assume changes ketic and potential energy are negligible. Is this claim true? Yes Energy balance: de dt system No Q W m hke pe m hke pe W m h h

2. The Ericsson cycle has been proposed for ternal combustion (IC) enge use. The workg fluid is an ideal gas, often He. The P- diagram and data at each state are proided below.

4 2. The Ericsson cycle has been proposed for ternal combustion (IC) enge use. The workg fluid is an ideal gas, often He. The P- diagram and data at each state are proided below. State T, C p, bar u, / h, /, m / (a) Compute the specific olume at each of the four states. Report your answers m /. (b) Determe the specific work and specific heat transfer for all four processes the cycle. Report your answers /. System

5 Problem 2 (contued) Assumptions No other work except mog boundary work Neglect friction Quasi-equilibrium process Ignore KE and PE changes Helium behaes as an ideal gas Basic Equations Wboundary pdv de Q W m h ke pe m h ke pe dt system Integratg: QW U KE PE Solution (a) Specific enthalpy: h u p1 h u h u h u p p m kpa m kpa p h u m kpa p2 h u m kpa p4 (b) Mog boundary work durg expansion of the gas from 1 to 2: 2 m w12 pd p1 p kPa w w 12 > 0 sce the gas expands Considerg energy balance for the gas from 1 to 2: q12 w12 u2 u1 q q Mog boundary work durg expansion of the gas from 2 to : m m w2 pd p22 p ln 16100kPa ln 2 2 m q 12 > 0 heat transfer to the gas

6 Problem 2 (contued) w2 801 w 2 > 0 sce the gas expands Considerg energy balance for the gas from 2 to : q2 w2 u u2 q w q 2 > 0 heat transfer to the gas Mog boundary work durg compression of the gas from to 4: 4 m w4 pd p p kPa w w 4 < 0 sce the gas is compressed Considerg energy balance for the gas from to 4: q4 w4 u4 u q q Mog boundary work durg expansion of the gas from 4 to 1: m m w41 pd p44 p1 1ln kPa.96 ln 4 4 m.96 q 4 > 0 heat transfer from the gas w w 41 < 0 sce the gas is compressed Considerg energy balance for the gas from 4 to 1: q41 w41 u1 u4 q w q 41 > 0 heat transfer from the gas

7 . A compressor, condenser, throttlg ale, and eaporator are strung together to make a refrigeration system. The workg fluid is R14a, with data at each state proided the table below. Mass flow rate of R14a is 2 /s. State x p, bar T, C, m / u, / h, / n/a (a) Compute the compressor power. Report your answer kw. (b) Fd the eaporator heat transfer rate. Report your answer kw. (c) Calculate the coefficient of performance for the cycle. (d) Sketch the p- diagram for the cycle. Label all states and constant temperature les. (e) If the eaporator pressure is kept constant and the condenser pressure is creased, will the coefficient of performance crease, decrease, or rema the same? You must proide support to receie credit for your answer. Assumptions Steady state One-dimensional flow Quasi-equilibrium process Ignore KE and PE changes Insulated compressor: Q 0 Passie (rigid) eaporator: W 0

8 Problem (contued) Basic Equations dm dt system m m m m m m m R-14a de dt system Q W m h ke pe m h ke pe Solution (a) Considerg energy balance for the compressor (CV I): W comp m R-14a h1h W comp 46 kw s (b) Considerg energy balance for the eaporator (CV II): Q eap m R-14a h1h Q s (c) Coefficient of performance for the refrigeration cycle: COPR 6.1 (d) P- diagram for the cycle is shown below. eap 280 kw COP Q Q L eap R W net, W comp 280 kw 46 kw (e) If eaporator pressure remas constant and condenser pressure is creased, the coefficient of performance will decrease sce more power is required to operate the compressor.

Circle your instructor s last name

Circle your instructor s last name 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