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MATHEMATICS, ECONOMICS, SCIENCES INSTRUCTION: Solve the following problems. DO NOT QUESTIONAIRES!
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FINAL COACHING EXAM 05 – MESL PROBS
very probable ANYTHING ON THE
1. Which of the following statements is true for an isentropic steady-flow process? (p is pressure, T is temperature, V is volume, and W is work.) A. p2/p1 = (V1/V2)k * C. p2/p1 = V1/V2 B. W = -V(p2 – p2) D. p2/p1 = (V1/V2) Answer: A
2. Air is compressed from 100 kPa and 40°C in a steady-flow operation. During the compression process, each kilogram of air losses 90 kJ as heat to the environment. Air is discharged at the rate of 10 m3/min. What power is required to drive the compressor? A. 126 kW C. 195 kW B. 180 kW D. 391 kW * Answer: D
3. The state of an ideal gas is changed in a steady-state open process from 400 kPa and 1.2 m3 to 300 kPa and 1.5 m3. The relationship between pressure and volume during the process is pV1.3 = constant. What work is performed? A. 130 kJ * C. 1210 kJ B. 930 kJ D. 9030 kJ Answer: A
4. A gas goes through the following thermodynamic processes: A to B: constant-temperature compression, then B to C: constant volume cooling, and then C to A constant pressure expansion. The pressure and volume at state C are 1.4 bars and 0.028 m3, respectively. The network during C to A process is 10.5 kJ. What is the volume at state A? A. 0.07 m3 C. 0.19 m3 3 B. 0.10 m * D. 0.24 m3 Answer: B
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MATHEMATICS, ECONOMICS, SCIENCES
FINAL COACHING EXAM 05 – MESL PROBS
5. A gas goes through the following thermodynamic processes: A to B: constant-temperature compression, then B to C: constant volume cooling, and then C to A constant pressure expansion. The pressure and volume at state C are 1.4 bars and 0.028 m3 , respectively. The network during C to A process is 10.5 kJ. What is the volume at state A? A. 0.07 m3 C. 0.19 m3 3 B. 0.10 m * D. 0.24 m3 Answer: B
6. A gas goes through the following thermodynamic processes: A to B: constant-temperature compression, then B to C: constant volume cooling, and then C to A constant pressure expansion. The pressure and volume at state C are 1.4 bars and 0.028 m3 , respectively. The network during C to A process is 10.5 kJ. What net work is derived from one complete A-B-C cycle ? A. – 21 kJ C. – 6.5 kJ B. – 8.3 kJ * D. 4.8 kJ Answer: B
9. A Carnot engine receives 100 kJ of heat from a hot reservoir at 370°C and rejects 37 kJ of heat. Determine the temperature of the cold reservoir. A. – 35°C * C. 130°C B. 100°C D. 230°C Answer: A
7. A Carnot refrigerating system receives heat from a cold reservoir at 0C. The power input is 1750 W per ton of refrigeration. The system’s coefficient of performance is: A. 1.4 C. 1.8 B. 1.6 D. 2.0 * Answer: D 10. What is the maximum thermal efficiency possible for a power cycle operating between 600°C and 110°C? A. 47% C. 63% B. 56% * D. 74% Answer: B
8. In a heat treating process, a 2 kg metal part ( specific heat = 0.5 kJ/kg.K) initially at 800C is quenched in a tank containing 200 kg of water initially at 20C. Calculate the total entropy change of the process immediately after the quenching. A. 2.3 kJ/kg (decrease) C. 0.90 kJ/kg (increase) B. 0.65 kJ/kg (decrease) D. 1.6 kJ/kg (increase) * Answer: D
11. A Rankine cycle operates between the pressure limits of 600 kPa and 10 kPa. For saturated liquid water leaving the condenser and a turbine inlet temperature of 300°C, determine the thermal efficiency of the cycle. Note: ( 300C and 0.6 Mpa superheated steam hD = 3061.6 kJ/kg ) then: SE = 7.3724 kJ/kg.K, SF = 0.6491 kJ/kg.K ; SFG = 7.5019 kJ/kg.K, hF = 191.8 kJ/kg, hfg = 2393.0 kJ/kg, VF = 0.00101 T m3/kg A. 13% B. 25% * Answer: B
C. 37% D. 52%
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MATHEMATICS, ECONOMICS, SCIENCES
12. A reversible thermodynamic system is made to follow the Carnot cycle between the temperature limits of 300°C and 75°C. 300 kW of heat are supplied per cycle to the system. What is the change in entropy during heat addition? A. 0.52 kW/K * C. 1.0 kW/K B. 0.86 kW/kg D. 4.0 kW/K Answer: A
13. A system operating on the cycle which uses water as the working fluid. The A-to-B and C-to-D processes are isothermal. The B-C and D-to-A processes are isentropic. The pressure of the process at points A and B is 800 kPa, and the pressure at points C and D is 2 kPa. All the processes are within the liquid-to-vapor region for water. At 800 kPa: hf = 721.1 kJ/kg, hg = 2769.1 kJ/kg, Sf = 2.0466 kJ/kg.K, Sg = 6.6636 kJ/kg.K At 2 kPa: hf = 73.5 kJ/kg, hg = 2533.5 kJ/kg, Sf = 0.2606 kJ/kg.K, Sg = 8.7245 kJ/kg.K. What is the approximate change in entropy from state A to state B? A. 0 kJ/kg.K C. 4.6 kJ/kg.K * B. 2.1 kJ/kg.K D. 8.5 kJ/kg.K Answer: C
FINAL COACHING EXAM 05 – MESL PROBS
14. A system operating on the cycle which uses water as the working fluid. The A-to-B and C-to-D processes are isothermal. The B-C and D-to-A processes are isentropic. The pressure of the process at points A and B is 800 kPa, and the pressure at points C and D is 2 kPa. All the processes are within the liquid-to-vapor region for water. At 800 kPa: hf = 721.1 kJ/kg, hg = 2769.1 kJ/kg, Sf = 2.0466 kJ/kg.K, Sg = 6.6636 kJ/kg.K At 2 kPa: hf = 73.5 kJ/kg, hg = 2533.5 kJ/kg, Sf = 0.2606 kJ/kg.K, Sg = 8.7245 kJ/kg.K. What is the approximate change in entropy from state B to state C? A. 0 kJ/kg.K * C. 4.6 kJ/kg.K B. 2.1 kJ/kg.K D. 8.5 kJ/kg.K Answer: A
15. A system operating on the cycle which uses water as the working fluid. The A-to-B and C-to-D processes are isothermal. The B-C and D-to-A processes are isentropic. The pressure of the process at points A and B is 800 kPa, and the pressure at points C and D is 2 kPa. All the processes are within the liquid-to-vapor region for water. At 800 kPa: hf = 721.1 kJ/kg, hg = 2769.1 kJ/kg, Sf = 2.0466 kJ/kg.K, Sg = 6.6636 kJ/kg.K At 2 kPa: hf = 73.5 kJ/kg, hg = 2533.5 kJ/kg, Sf = 0.2606 kJ/kg.K, Sg = 8.7245 kJ/kg.K. What is the approximate enthalpy at state C? A. 74 kJ/kg C. 1800 kJ/kg B. 720 kJ/kg D. 1900 kJ/kg * Answer: D
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MATHEMATICS, ECONOMICS, SCIENCES
FINAL COACHING EXAM 05 – MESL PROBS
16. In a particular power cycle, 350 MJ of heat are transferred into the system each cycle. The heat transferred out of the system is 297.5 MJ per cycle. What is the thermal efficiency of this cycle? A. 1.0 % C. 7.5% B. 5.0 % D. 15 % * Answer: D
19. A Carnot cycle operates between the temperature limits of 800K and 300K. If the entropy of the low temperature reservoir increases 2.34 kJ/K, what is the work of the cycle? A. 230 kJ C. 670 kJ B. 440 kJ D. 1200 kJ * Answer: D
20. A Carnot cycle refrigerator, operates between – 11°C and 22°C. What is the coefficient of performance? A. 0.25 C. 4.3 B. 1.1 D. 7.9 * Answer: D
17. A refrigeration cycle has a coefficient of performance 80% of the value of a Carnot refrigerator operating between the temperature limits of 50°C and – 5°C. For 3 kW of cooling, what power input is required? A. 0.53 kW C. 0.77 kW * B. 0.62 kW D. 0.89 kW Answer: C
18. A heat pump takes heat from groundwater at 7°C and maintains a room at 21°C. What is the maximum coefficient of performance possible for this heat pump? A. 1.4 C. 5.6 B. 2.8 D. 21 * Answer: D
21. A household window rating of 7.5 kJ/W-h. for the unit? A. 2.1 * B. 5.2 Answer: A
air conditioner has an energy efficiency What is the coefficient of performance C. 7.0 D. 9.4
22. A gas mixture with volumetric proportions of 30% carbon dioxide ( specific heat Cp, of 0.867 kJ/kg.K ) and 70% nitrogen ( Specific heat, Cp of 1.043 kJ/kg.K) is cooled at constant pressure from 150C to 50C. Determine the heat release. A. – 210 kJ/kg C. – 97 kJ/kg * B. – 160 kJ/kg D. – 46 kJ/kg Answer: C
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MATHEMATICS, ECONOMICS, SCIENCES
FINAL COACHING EXAM 05 – MESL PROBS
25. A small distiller evaporates 1 L of water per half hour. Copper tubing exposed to the air serves as a condenser to recover the steam. The outside surface of the tubing is at 99.9°C. The ambient temperature is 20°C. The inside diameter of the tube is 0.75 cm, and the outside diameter is 1.2 cm. The thermal conductivity of copper is 388 W/m-K. hfg for saturated steam at 100°C is 2257 kJ/kg. How long must the tube be to condense all of the steam? A. 0.3 m C. 2.4 m * B. 1.2 m D. 8.3 m Answer: C
23. By weight, atmospheric air is approximately 23.15% oxygen and 76.85% nitrogen. What is the partial pressure of oxygen in the air at standard temperature and pressure? A. 21 kPa * C. 26 kPa B. 23 kPa D. 30 kPa Answer: A
24. A 0.75 m3 tank contains nitrogen at150 kPa ad 40°C. 2.0 kg of oxygen are added to the tank. What is the final volumetric percentage of the nitrogen? A. 14 % C. 38% B. 17% D. 41 % * Answer: D
26. A well-insulated copper rod (thermal conductivity of 388 W/m-K) is 50 cm long and has a cross-sectional area of 10 cm2. One end of the rod is in contact with a block of ice at 0°C, and the other end is in boiling water at 100°C. Heat of vaporization for saturated steam at 100°C is 2257 kJ/kg. The heat of fusion for ice at 0°C is 334 kJ/kg. How much ice is melted in 1 min? A. 0.2 g C. 1.1 g B. 0.5 g D. 13.9 g * Answer: D
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MATHEMATICS, ECONOMICS, SCIENCES
FINAL COACHING EXAM 05 – MESL PROBS
27. A well-insulated solid copper wire 1 m long with a crosssectional area of 0.0839 cm2 connects two reservoirs, one with boiling water at 100°Cand the other with ice at 0°C.How long does it take for 100 cal of energy to move through the wire? A. 3.5 min C. 86 min B. 21 min * D. 240 min Answer: B
30. A 3 m x 3 m plate at 500°C is suspended vertically in a very large room. The plate has an emissivity of 0.13. The room is at 25°C. What is the net heat transfer from the plate? A. 8.3 kW C. 46 kW * B. 24 kW D. 47 kW Answer: C
28. In 1 hr, how much black-body radiation escapes a 1 cm x 2 cm rectangular opening in a kiln whose internal temperature is 980°C? A. 20 kJ C. 130 kJ B. 100 kJ * D. 150 kJ Answer: B
31. At 3:00 p.m in July, a stone wall reaches a maximum temperature of 50°C. The stone has an emissivity of 0.95. What is the radiant heat energy transfer from the wall per square meter of this wall at that temperature? A. 190 W/m2 C. 1100 W/m2 B. 590 W/m2 * D. 3800 W/m2 Answer: B
29. A composite wall constructed of 2.5 cm of steel (k = 60.5 W/m-K) and 5.0 cm of aluminum (k = 177 W/m-K) separates two liquids. The liquid on the steel side has a film coefficient of 15 W/m2-K and a temperature of 400°C. The liquid on the aluminum side has a film coefficient of 30 W/m2-K and a temperature of 100°C. Assuming that steady-state conditions have been reached, what is the approximate temperature at the steel-aluminum interface? A. 150°C C. 250°C B. 200°C * D. 300°C Answer: B
32. Hot air at an average temperature of 100°C flows through a 3 m long tube with an inside diameter of 60 mm. The temperature of the tube is 20°C along its entire length. The convective film coefficient is 20.1 W/m2-K. Determine the rate of convective heat transfer from the air to the tube. A. 520 W C. 910 W * B. 850 W D. 1070 W Answer: C
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MATHEMATICS, ECONOMICS, SCIENCES
FINAL COACHING EXAM 05 – MESL PROBS 35. At the start of compression in an air-standard Otto cycle with a compression ratio of 10, air is at 100 kPa and 40 oC. A heat addition of 2800 kJ/kg is made. What is most nearly the thermal efficiency? A. 52% C. 64% B. 60% D. 67% Answer. B
33. An engine develops a brake power of 30 kW, 40 kW are absorbed by cooling water that is pumped through the water jacket and a radiator. The water enters the top of the engine’s radiator at 95°C. The enthalpy of the water at that temperature is 397.96 kJ/kg. The water leaves the bottom of the radiator at 90°C and with an enthalpy of 376.92 kJ/kg. What is the water flow rate for steady state operation? A.4.2x 10-4 m3/s C. 1.9 x10-3 m3/s * B. 1.4 x 10-3 m3/s D. 3.3 x10-3 m3/s Answer: C
36. . A Carnot refrigerator receives heat from a cold reservoir at 0oC. The power input is 1750 W per ton of refrigeration. What is most nearly the system’s coefficient of performance? A. 1.4 C. 1.8 B. 1.6 D. 2.0 Answer. D
37. A Carnot cycle refrigerator operates between – 11oC and 22oC. What is the coefficient of performance? A. 0.25 C. 4.3 B. 1.1 D. 7.9 Answer. D
34. Two Carnot engines operate in series such that the heat rejected from one is the heat input to the other. The heat transfer from the high-temperature reservoir is 500 kJ. The overall temperature limits are 1000K and 400K. Both engines produce equal work. What is most nearly the intermediate temperature between the two engines? A. 400K C. 700K B. 500K D. 1000K Answer. C
38. 0.8 kg of helium is in a cube-shaped vessel with edges measuring 1.3m. The pressure is two times standard atmospheric pressure. What is most nearly the temperature of the helium? A. 80K C. 160K B. 130K D. 27OK Answer. D
39. A 5.4 kg mixture of nitrogen, oxygen, and butane in a 3 m3 container is at atmospheric pressure and has a temperature of 300K. What is most nearly the molecular weight of the mixture? A. 28 kg/kmol C. 44 kg/kmol B. 32 kg/kmol D. 58 kg/kmol Answer. C
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MATHEMATICS, ECONOMICS, SCIENCES
FINAL COACHING EXAM 05 – MESL PROBS
40. Steam flows into a turbine at a rate of 10kg/s, and 10 kw of heat are lost from the turbine. Elevation and the kinetic energy effects are negligible.
What is most nearly the power output from the turbine? A. 4000 kW C. 4800 kW B. 4400 kW D. 5000 kW Answer. C
41. Steam is quickly compressed by a piston in a cylinder with a compression ratio of 4:1. Before compression, the temperature of the steam is 400K, and the steam is at atmospheric pressure. After compression, the temperature of the steam is 600K. What is most nearly the work per unit mas done by the piston? A. 300 kJ/kg C. 325 kJ/kg B. 315 kJ/kg D. 330 kJ/kg Answer. A
42. . The steady-state heat transfer rate through a 10 cm thick by 1 m2 homogenous wall section is 10 W. What is most nearly the temperature difference between the two wall surfaces if the thermal conductivity of the wall material is 1 W/m.oC. A. 1.0 OC C. 7.8 OC O B. 2.3 C D. 10OC Answer. A
43. An engine operates at a constant temperature of 90oC. Through a reversible process, the engine’s work output is 5.3 kJ, and the heat loss is 4.7 kJ. What is most nearly the change in entropy during the process? A. 0.013 kJ/K C. 0.015 kJ/K B. 0.014 kJ/ K D. 0.016 kJ/K Answer. A
44. By weight, atmospheric air is approximately 23.15% oxygen and 76.85% nitrogen. What is most nearly the partial pressure of oxygen in the air at standard pressure? A. 21 kPa C. 26 kPa B. 23 kPa D. 30 kPa Answer. A
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MATHEMATICS, ECONOMICS, SCIENCES
FINAL COACHING EXAM 05 – MESL PROBS
45. Complete combustion of 13.02 g of a compound (CXHY) produces 40.94 g of CO2 and 16.72 g of H2O. What is the empirical formula of the compound? A. CH C. CH4 B. CH2 D. CH2O Answer. B
48. Theoretically, how many kilograms of air are needed to completely burn 5 kg of ethane ( C2H6 ) A. 0.8 kg C. 81 kg B. 19 kg D. 330 kg Answer. C
46. Theoretically, how many kilograms of air are needed to completely burn 5 kg of ethane ( C2H6 ) A. 0.8 kg C. 81 kg B. 19 kg D. 330 kg Answer. C
47. Eleven grams of propane (molecular weight of 44 g / mol) are burned with just enough pure oxygen for complete combustion. What is most nearly the mass of combustion products produced? A. 31 g C. 41 g B. 39 g D. 51 g Answer. D
49. Octane (C8H18) is burned with 150% theoretical air in a steady combustion process. Combustion is complete. The total pressure is 1 atm. What is most nearly the air-fuel ratio? A.10 kg air / kg fuel C. 23 kg air / kg fuel B. 15 kg air / kg fuel D. 31 kg air / kg fuel Answer. C
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MATHEMATICS, ECONOMICS, SCIENCES
50. Heat flows steadily through a composite wall made up of two materials, A and B, of equal thickness. The thermal conductivity of material A is twice that of material B. If the temperature of the outside surfaces of A and B are 80oC and 25oC, respectively, the temperature of the interface surface between materials A and B is most nearly A. 54 OC C. 62 OC O B. 58 C D. 66 OC Answer. C
…END… SUBMIT THIS TEST QUESTION SET TO YOUR WATCHERS. BRINGING THE TEST QUESTION SET OUT OF THE ROOM WILL BE A GROUND FOR DISCIPLINARY ACTION.
FINAL COACHING EXAM 05 – MESL PROBS