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sample-exam - RYERSON UNIVERSITY Department of Mechanical...

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Unformatted text preview: RYERSON UNIVERSITY Department of Mechanical and Industrial Engineering APPLIED THERMODYNAMICS - MEC514 FINAL EXAM DATE: 17 December 2009 SECTIONS: 011-051 TIME: 3 hours EXAMINER: Prof. R.S. Budny ASSOCIATE: Prof. J. Dimitriu INSTRUCTIONS: 1. OPEN BOOK EXAM. Suggested aids for your own personal use are: course textbook; class notes + assignments + solutions (as sold at Alicos); non-communicating electronic calculator; drawing instruments (i.e., “rolling” ruler, set squares, protractor, small magnifying glass, pens and pencils). 2. Prohibited items include: cell-phones (text and/or video display), pagers and other wireless devices, Palm-pilots, laptop computers, radios/video/music players etc.. These must be switched off and left at the front of the exam room. 3. Leave all bags and brief cases at the front of the exam room. Traveling back and forth to bags and brief cases while the exam is in progress is NOT permitted. 4. Candidates may not borrow or lend any materials while the exam is in progress. 5. Answer all five (5) questions. Marks are as indicated beside each question. 6. Answer questions in the space provided. You may use the back of the page if required. 7. Candidates must layout their work clearly and legibly at all times; otherwise, marks may be lost. Illegible answers will not be graded. 8. Full marks will be awarded for correct answers using the correct method. Marks will be deducted for incorrect units. 9. Use engineering judgment when answering questions. If you feel that there is a genuine error or omission in any question then make an assumption and draw this to the attention of the examiner right on the test paper and continue with the solution. 10. DO NOT detach any sheets from the exam paper. Question Name: Student ID: Section: Seat #: 1. (Write your student I.D. number) 1 2 3 4 5 2. (Circle your section number) 3. (Seat number) 4. 5. Total Mark / / / / / MEC514.F09 - 2 of 8 - Final Exam 5 QUESTION 1. Dry air is contained in a tank at a stagnation pressure of 7 ×10 Pa (absolute) and a stagnation temperature of 500 K and is allowed to flow through a converging-diverging nozzle. The nozzle throat area is 5 cm2. The air passes through the nozzle and finally exits into a large chamber maintained at constant back pressure pb. For the above conditions a stationary normal shock wave stands in the exit plane and the temperature just upstream of the shock wave is 254 K. Assume adiabatic frictionless flow with constant specific heat values and that the flow is 5 isentropic, except where the shock stands. Local atmospheric pressure is 1 ×10 Pa. For each of the following questions circle the (one) most appropriate answer which may have been rounded off and pay attention to the units. Questions may be answered using any combination of formulas or tables. Use the back of the page for rough work but this will not be marked. All questions are of equal value [1 mark each]. A) The temperature in the throat section is: (i) 417°C; (ii) 417 K; (iii) 600 K (iv) 600°C; (v) 500 K. B) The mass flow rate through the nozzle throat section is: (i) 0.02 kg/s; (ii) 6,300 kg/s; (iii) 0.63 kg/s; (iv) 200 kg/s; (v) 1 kg/s because it's "choked". C) The Mach number just upstream of the shock wave is: (i) 0.55; (ii) 4.8; (iii) 1.57; (iv) 2.5; (v) 2.2. D) The Mach number just downstream of the shock wave is: (i) 0.71; (ii) 0.3; (iii) 2.2; (iv) 0.55; (v) 1. E) The temperature at the exit plane is: (i) 472 K; (ii) 472°C; (iii) 500 K; (iv) 330 K; (v) 254 K. MEC514.F09 - 3 of 8 - Final Exam QUESTION 2. Propane, C3H8, is burned completely with the theoretical amount of dry air. Balance the combustion equation shown below and solve for unknowns a, b, c, d, and e. [5 marks] C3 H8 a O2 b N 2 c CO2 d H2 O e N2 MEC514.F09 - 4 of 8 - Final Exam QUESTION 3. A system consisting of two well-insulated tanks is shown in the figure below. Initially the valve between the two tanks is closed. After the valve is opened the oxygen (O2) and hydrogen (H2) gases mix together uniformly and eventually reach steady-state conditions. Using the ideal gas laws and assuming constant cv values, determine the following for the final gas mixture when the valve is opened: [1 mark for each part below] (a) The percent molar analysis. (b) The temperature, T, in Kelvin. (c) The apparent molecular weight (i.e., atomic weight), M, in kg/kmol. (d) The mixture specific heat, cv, in kJ/(kg·K). (e) The mixture pressure, p, in kPa (absolute). m = 1.5 kg of O2 V = 3 m3 T = 500 K cv = 0.712 kJ/(kg·K) m = 0.5 kg of H2 V = 2 m3 T = 300 K cv = 10.183 kJ/(kg·K) Initial conditions shown when the valve is closed MEC514.F09 - 5 of 8 - Final Exam QUESTION 4. A real refrigeration cycle is shown below and uses refrigerant HFC-134a. The mass flow rate of refrigerant is 0.006 kg/s. A one-cylinder single-acting compressor is used and has a total displacement volume of 140 cm3. You may assume that there is no heat transfer from the compressor to the surroundings and that bearing frictional losses may be ignored. You may also ignore pressure losses in the condenser, evaporator, and pipe lines. [1 mark for each part below]. (a) Draw the system p-h diagram on the attached HFC-134a chart and label all points according to their location on the schematic diagram. Number the points as 1, 2, etc.. (b) Calculate the heat removed in the condenser, in kW. (c) Calculate the cycle coefficient of performance (COP). (d) Calculate the compressor isentropic efficiency, in percent. (e) Calculate the compressor speed, in RPM, if the volumetric efficiency is 60%. 3 0.8 MPa (abs) 2 o 10 C condenser 70oC mR=0.006 kg/s ˙ compressor V = 140 cm3 throttle valve evaporator 4 0.1 MPa (abs) 1 -10oC MEC514.F09 - 6 of 8 - Final Exam Revised HFC-134a Chart (Dupont Chemicals version). Uses specific volume instead of density. MEC514.F09 - 7 of 8 - Final Exam QUESTION 5. An adiabatic air duct is used to mix together two different air streams. You may assume that the air is at standard atmospheric pressure and that the air at points 1 and 2 is adiabatically mixed together by the time it reaches point 3. [1 mark for each part below] (a) Plot and label the location of point 1 on the attached psychrometric chart and determine the value of h1, in Btu/lba. (b) Plot and label the location of point 2 on the attached psychrometric chart and determine the value of h2, in Btu/lba. (c) Determine the value of h3, in Btu/lba and plot and label the location of point 3 on the attached psychrometric chart. (d) What is the dew point temperature, in °F, at point 3? (e) Determine the volumetric air flow rate at point 3, in CFM (i.e., ft3/min). 2 76oF DB φ = 80% ma= 42 lb a / min ˙ 3 1 99oF DB 60oF WB ma=58 lb a / min ˙ MEC514.F09 - 8 of 8 - Final Exam ASHRAE Chart has enthalpy lines + wet-bulb lines. Also uses W in lbw/lba (NOT GRAINS). ...
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This note was uploaded on 09/28/2010 for the course MEC MEC 309 taught by Professor Habiba during the Spring '10 term at Ryerson.

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