EF 152 Exam 3 - Fall, 2018 Page 1 Version: A Copy 50 Name: Section: Seat Assignment: Specify your EXAM ID on the right. Use 000 if you do not know your exam ID. 0 0 0 1 1 1 2 2 2 3 3 3 4 4 4 5 5 5 6 6 6 7 7 7 8 8 8 9 9 9 Instructions Do not open the exam until instructed to do so. Do not leave if there is less than 5 minutes to go in the exam. When time is called, immediately stop writing, remain seated, and pass your exam to the center aisle. Working after time is called results in an automatic deduction. Turn your equation sheets in with your exam. Guidelines Assume 3 significant figures for all given numbers unless otherwise stated Show all of your work no work, no credit Write your final answer in the box provided Include units for all answers
EF 152 Exam 3 - Fall, 2018 Page 2 Version: A Copy 50 1. (2 pt) What is the second law of thermodynamics? U= Q - W Natural process move toward greater disorder PV=nRT For a fixed amount of gas, volume increases when pressure decreases 2. (2 pt) For a given mass of H 2 0, which requires more heat energy? increase in temperature from -55 C to -5 C increase in temperature from 5 C to 55 C Phase change from solid to liquid state at 0 C Phase change from liquid to gas state at 100 C 3. (2 pt) What is true for a diesel cycle? It has spark plugs Heat is added at constant pressure Heat is added at constant volume 4. (2 pt) An internal combustion engine (Otto Cycle) operates with a compression ratio of 9:1. It s efficiency is in what range? 10-20% 20-30% 30-40% 40-50% 50-60% 60-70% 5. (2 pt) In a particular engine cycle there are 650 Joules of heat added, 250 Joules of heat exhausted and the total net work is 400 Joules. What is the thermal efficiency? 250/400 250/650 400/650 400/900 400/250 650/250 6. (2 pt) In a particular freezer cycle, in one second there are 650 Joules of heat exhausted to the room, 400 Joules of heat extracted, and the freezer consumes 250 Watts of electricity. What is the coefficient of performance? 250/400 250/650 400/650 400/900 400/250 650/250 7. (2 pt) In a Carnot heat engine, heat is added during which type of process? Constant Volume Constant Temperature Constant Pressure Adiabatic Parang
EF 152 Exam 3 - Fall, 2018 Page 3 Version: A Copy 50 Use figure at right for questions on this page p 500 kpa B C 100 kpa Constant Temperature A V 0.05 m 3 0.25 m 3 8. (2 pt) What is the work done in process BC? 0 400 kpa (0.20 m 3 ) -400 kpa (0.20 m 3 ) 500 kpa (0.20 m 3 ) 500 kpa (0.05 m 3 ) ln (.05/.25) 9. (2 pt) What is the change in internal energy in process AB? 0 400 kpa (0.20 m 3 ) -400 kpa (0.20 m 3 ) 500 kpa (0.20 m 3 ) 500 kpa (0.05 m 3 ) ln (.05/.25) 10. (2 pt) What is the change in internal energy in process ACB? 0 500 kpa (0.20 m 3 ) -500 kpa (0.20 m 3 ) 600 kpa (0.20 m 3 ) 600 kpa (0.05 m 3 ) ln (.25/.05)
EF 152 Exam 3 - Fall, 2018 Page 4 Version: A Copy 50 11. (6 pt) Carbon fiber ABS filament has =60x10 6 / C and E=5260 MPa. If expansion is constrained, what is the thermal stress when the temperature changes by 90 C? 12. (6 pt) A 5 kg iron block at 80 C is dropped into a tank that contains 500 g of liquid water at 25 C. The temperature is 50 C when thermal equilibrium is reached. Determine the energy lost to the surroundings. Specific heat of iron: 0.11 cal/g C, specific heat of water: 1 cal/g C 13. (6 pt) A power plant takes in steam at 777 K to power turbines and then exhausts the steam at 300 K. The heat input is 100 MW. What is the theoretical maximum possible power output of the power plant?
EF 152 Exam 3 - Fall, 2018 Page 5 Version: A Copy 50 For the problems on this page, use the following properties for air: =1.4, =0.026 W/m C, M=29g/mole 14. (6 pt) A 0.5 x 0.5 meter window is composed of 2 panes of glass (R=0.0038 m 2 C/W per pane) with 20 mm of airspace between. What is the thermal resistance of the window? 15. (6 pt) A chamber contains 5 m x 5 m x 2 m of air at Standard Temperature and Pressure (STP). What is the mass of air in the chamber?
EF 152 Exam 3 - Fall, 2018 Page 6 Version: A Copy 50 16. (16 pt) An insulated cooler has a surface area of 1.2 m 2 and a wall thickness of 3 cm. The temperature of the inner surface is 0 C, and the temperature of the outside surface is 28 C. The cooler is made out of a material that has a thermal conductivity of 0.06 W/m K. If 5 kg of ice at 0 C are put in the chest, how long (in minutes) will it take for the ice to melt? Water has a specific heat of 1 cal/g C, a latent heat of fusion of 79.6 cal/g, and a latent heat of vaporization of 540 cal/g.
EF 152 Exam 3 - Fall, 2018 Page 7 Version: A Copy 50 Use Figure and Table for questions on this page γ=1.4, c' v =20.78 J/mol K, and c' p =29.1 J/mol K. p (kpa) Q H P (kpa) V (m 3 ) T (K) 2292 B C A 110 0.07 630 Wab= Qab= B 2292 0.008 1500 Q C Wbc= 142.1 kj Qbc= 497.4 kj C 2292 0.07 110 A Wca= Qca= 0.008 0.07 V (m 3 ) 17. (6 pt) What is the temperature at C? 18. (4 pt) What is the magnitude of the heat exhausted during process CA? 19. (8 pt) What is the efficiency?
EF 152 Exam 3 - Fall, 2018 Page 8 Version: A Copy 50 20. (16 pt) A freezer that operates at 25% of the ideal COP maintains a low temperature of 18 C inside a 25 C room. In one day, 8000 kj of heat are extracted. If the cost of electricity is $0.09 per kw hr ($0.09 per 3600 kj) determine the cost to run the refrigerator for 1 day.