ME 200 Thermodynamics 1 Fall 2016 Final Exam

Size: px

Start display at page:

Download "ME 200 Thermodynamics 1 Fall 2016 Final Exam"

Kelly Pierce
5 years ago
Views:

1 Last Name: First Name: Thermo no. ME 200 Thermodynamics 1 Fall 2016 Final Exam Circle your instructor s last name Ardekani Bae Fisher olloway Jackson Meyer Sojka 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 EFD, start your analysis with the basic equations, list all relevant assumptions, and have 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 receive credit for your answers. Do not write on the back of any page because it you will not receive credit for that work. If you need extra paper raise your hand and a proctor will supply it. Maximum credit for each problem is indicated below. 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 during examinations. Doing so is cheating. If you bring a smart watch, cell phone, or other communication device to the examination, it must be turned off prior to the start of the exam, placed in your backpack, and the backpack must be stored below your seat. It shall be reactivated only after you leave the examination room for the final time. Otherwise it is a form of cheating and will be treated as such. SECOND IMPORTANT NOTE The only calculators allowed for use on this exam are those of the TI-30X series. No others.

2 Problem Possible Score Total 200

3 1. A. [10 points] A water drop is place in a sealed and insulated vessel containing only air. The drop is observed to evaporate completely. What happens to the air temperature? (Circle the correct answer) - the temperature rises - the temperature remains the same - the temperature falls B. [10 points] A container of water is boiling in a kitchen. The air pressure throughout the kitchen is 1 bar and its temperature is 25 C. What is the water pressure immediately above the boiling surface? (Circle the correct answer). - >1 bar - =1 bar - <1 bar C. [10 points] Consider the same kitchen and container of boiling water that s in 1B. What is the water vapor temperature immediately above the boiling surface? (Circle the correct answer). - T = 100 C - T = 25 C - 25 < T < 100 C

2. [60 points] Waste heat from one power producing cycle can be used as the source for another. One example is using the exhaust from an IC (diesel) engine to boil water in a steam cycle power plant.

4 2. [60 points] Waste heat from one power producing cycle can be used as the source for another. One example is using the exhaust from an IC (diesel) engine to boil water in a steam cycle power plant. A hardware diagram is provided below, with relevant properties provided in the corresponding table. Use that information to answer the following questions. - What is the steam mass flow rate? Report your answer in kg/s. - What is the overall energy efficiency of this combined IC enginesteam cycle system? Report your answer in %. state d kg/s of air exits at 1.68 bar and 505 K state a kg/s of air enters at 1 bar and 300 K Air leaves at 1 bar and 500 K

5 State p, bar T, K h, kj/kg u, kj/kg s, kj/kg-k a b c d

6 3. [60 points] The gas Brayton cycle gas turbine engine was developed for aircraft propulsion. One example is the so-called turbo-jet engine. The turbo-jet engine consists of an inlet diffuser, a compressor, a combustor, a turbine (whose sole purpose is to drive the compressor), and a nozzle. See diagram below. In this problem the engine is attached to an aircraft moving at 260 m/s through air at -50 C and 0.7 bar. The compressor pressure ratio is 20:1 and the combustor exit temperature is 2000 K. Calculate the following, all the while assuming all devices are ideal The air pressure and temperature as it exits the diffuser The air pressure and temperature as it exits the compressor The specific compressor power consumption The rate of specific heat addition in the combustor The turbine exit temperature and pressure The nozzle exit velocity. -50 C, 0.5 bar diffuser compr essor nozzle 0.5 bar

7 4. [50 points] A weird piston-cylinder device is shown below. It holds kg of R134a that is initially half liquid at 20 C. The 24 V resistance heater embedded in the R134a is supplied with a current of 0.75 A for a duration of 3 min. During that time the piston moves upward against atmospheric pressure (1 bar) and the spring (k=4 kn/m) until it reaches the stops. 5.0 cm dia mpiston =? 0.6 kg of R-134a T1=20 C, x1=0.5 Calculate the following: a. The work associated with the resistor. b. The R134a pressure when the piston hits the stops. c. The final R134a temperature. d. The entropy generation associated with the resistor, the spring, the piston and the R134a.

8 Work Relations W boundary = pd Welectrical I t 1 st Law and Mass Conservation Relations E = U+ KE + PE 2 nd Law Relations, PROPERTY RELATIONS FOR ME 200 Pressure, Temperature and Energy Relations p mrt / u h c = cp k cp / c T T p 1 hu p ht (, p) h ( T) v ( T)[ p p ( T)] Entropy Relations (and isentropic processes) Tds du pd Tds dh dp f f sat dt d dt dp ds c R ds cp R T T o o s s s Rln( p / p ) s cln( T p / T1) p / p p / p 2 1 s r2 r1 v / v v / v 2 1 s r2 r1 EFFICIENCY AND CYCLE RELATIONS FOR ME 200 Device Efficiencies and Cycle Analyses 2 2 turbine wact wisen comp pump wisen wact η nozzle = V 2,act /V 2,isen Wnet,out Q L Q th COPR COPP Q W W th,rev T 1 T L COP R,rev net,in TL T T L COP P,rev net,in T T T L T T C Q Q C rev

FINAL EXAM. ME 200 Thermodynamics I, Spring 2013 CIRCLE YOUR LECTURE BELOW:

FINAL EXAM. ME 200 Thermodynamics I, Spring 2013 CIRCLE YOUR LECTURE BELOW: ME 200 Thermodynamics I, Spring 2013 CIRCLE YOUR LECTURE BELOW: Div. 5 7:30 am Div. 2 10:30 am Div. 4 12:30 am Prof. Naik Prof. Braun Prof. Bae Div. 3 2:30 pm Div. 1 4:30 pm Div. 6 4:30 pm Prof. Chen Prof.