Worded-problems-in-thermodynamics-1-2.docx

1. If the °F scale is twice the °C scale, what is the reading in the Fahrenheit scale? a. 160° c. 140° b. 320° d. 280° 2. Water enters the condenser at 30°C and leaves at 60°C. What is the temperature difference in °F? a. 16.67 c. 54 b. 48.67 d. 22 3. A cylinder and piston arrangement contains saturated water vapor at 110°C. The vapor is compressed in a reversible adiabatic process until the pressure is 1.6 Mpa. Determine the work done by the system per kg of water. At 110°C, S 1 = 7.2387 kJ/kg-K, U1 = 2518.1 kJ/kg and at 1.6 Mpa, S2 = 7.2374 kJ/kg-K, U2 = 2950.1 kJ/kg, T2 = 400°C. a. -500 kJ/kg c. -632 kJ/kg b. -432 kJ/kg d. -700 kJ/kg 4. Helium is compressed isothermally from 14.7 psia and 68°F. The compression ratio is 4. Calculate the change in entropy of the gas given that RHelium = 0.4961 Btu/lbm-°R. a. -0.688 Btu/lbm-°R c. 0.688 Btu/lbm-°R b. -2.76 Btu/lbm-°R d. 2.76 Btu/lbm-°R 5. Steam at a pressure of 9 bar (hf = 743 kJ/kg, hfg = 2031 kJ/kg) is generated in an exhaust gas boiler from feedwater at 80°C (h = 334.9 kJ/kg). If the dryness fraction of the steam is 0.96, determine the heat transfer per kilogram of steam. a. 2357.86 c. 1357.86 b. 3357.86 d. 5357.86 6. If wet saturated steam at 8 bar (hfg = 2048 kJ/kg) requires 82 kJ of heat per per kg of steam to completely dry it, what is the dryness fraction of the steam? a. 0.76 c. 0.96 b. 0.86 d. 0.66 7. Wet saturated steam at 17 bar (hf = 872 kJ/kg, hfg = 1923 kJ/kg) dryness 0.97 is produced from feedwater at 85°C (h = 335.9 kJ/kg). Find the heat energy supplied per kg. a. 4381.41 kJ/kg c. 2381.41 kJ/kg b. 1381.41 kJ/kg d. 3381.41 kg 8. A turbo-generator is supplied with superheated steam at a pressure of 30 bar and temperature 350°C (h = 3117 kJ/kg). The pressure of the exhaust steam from the turbine is 0.06 bar (hf = 152 kJ/kg, hfg = 2415 kJ/kg) with a dryness fraction of 0.88. If the turbine uses 0.25 kg per second, calculate the power equivalent of the total enthalpy drop. a. 109.95 kW c. 309.95 kW b. 209.95 kW d. 409.95 kW 9. Steam enters the superheaters of a boiler at a pressure of 20 bar (hf = 909 kJ/kg, hfg = 1890 kJ/kg, ѵg = 0.09957 m³/kg) and dryness 0.98 and leaves at the same

pressure at a temperature of 350°C (h = 3138 kJ/kg, ѵ = 0.01386 m³/kg). Find the percentage increase in volume due to drying and superheating. a. 12.04 c. 32.04 b. 22.04 d. 42.04 correct ans. 10. Steam at the rate of 500 kg/hr is produced by a steady flow system boiler from feedwater entering at 40°C. Find the rate at which heat is transformed in kCal/hr if the enthalpy of steam is 600 kCal/kg and of steam 50 kCal/kg. a. 275,000 kCal/hr c. 375,000 kCal/hr b. 175,000 kCal/hr d. 475,000 kCal/hr 11. A pump discharge 50 tons of water per hour to a height of 8m, the overall efficiency of the pumping system being 69%. Calculate the output and input power. a. 1.09 kW & 1.58 kW c. 1.09 kW & 2.58 kW b. 2.09 kW & 2.58 kW d. 2.09 kW & 1.58 kW 12. A condenser vacuum gauge reads 715 mm Hg when the barometer stands at 757 mm Hg. What is the absolute pressure in the condenser in kPa. a. 196.25 kPa c. 5.60 kPa correct answer b. 100.92 kPa d. 95.33 kPa 13. Oil flows bore at a velocity of 2 m/s through a nest of 16 tubes in a single pass cooler. The internal diameter of the tubes is 30 mm and the density of the oil is 0.85 g/li. Find the volume flow in liters per second. a. 20 c. 22 b. 21 d. 23 14. Calculate the quantity of heat to be transferred to 2.25 kg of brass to raise its temperature from 20°C to 240°C taking the specific heat of the brass as 0.394 kJ/kg-K. a. 519.03 kJ c. 195.03 kJ b. 159.03 kJ d. 591.03 kJ 15. Three cubic meter of air at a pressure of 20 kPag is compressed at constant temperature to a pressure as 425 kPag. Calculate the final volume of the air. a. 0.80 m³ c. 0.92 m³ b. 0.69 m³ d. 0.96 m³ 16. The pressure of the air in a starting air vessel is 40 bar and the temperature is 24°C. If a fire in the vicinity causes the temperature to rise to 65°C, find the pressure of the air. Neglect any increase in volume of the vessel. a. 45.52 bar c. 42.55 bar b. 54.52 bar d. 44.55 bar 17. One cubic meter of a perfect gas at a constant pressure of 1 bar and temperature of 17°C are compressed to a volume of 0.50 m³ and the final pressure is 6 bar. Calculate the final temperature. a. 870°C c. 597°C b. 560°C d. 860°C c.

18. An air compressor delivers 0.20 m³ of air at a pressure of 850 kPa and 31°C into an air reservoir. Taking the gas constant of air as 0.287 kJ/kg-K, calculate the mass of air delivered. a. 1.59 kg c. 5.91 kg b. 1.95 kg d. 5.19 kg 19. An oxygen cylinder of volume 2.3 ft³ has a pressure of 2200 psig and is at 70°F. Determine the mass of oxygen in the cylinder. a. 26.66 lbs c. 28.66 lbs b. 26.86 lbs d. 28.88 lbs 20. What is the power of a steam jet 15mm in diameter moving at 750 m/s? Steam condition, 1.4 kg/cm², dry and saturated ( v=1.256 m³/kg). a. 29.67 kW c. 19.67 kW b. 39.67 kW d. 49.67 kW 21. Steam leaves an industrial boiler at 827.4 kPa and 171.6°C (h f = 727.25 kJ/kg, hfg = 2043.2 kJ/kg). A portion of the steam is passed through a throttling calorimeter and is exhausted to the atmosphere when the calorimeter pressure is 101.4 kPa and a temperature of 115.6°C (h = 2707.6 kJ/kg). How much moisture does the steam leaving the boiler contain? a. 2.08% c. 4.08% b. 3.08% d. 5.08% 22. During the polytropic process of an ideal gas, the state changes from 138 kPa and 5°C to 827 kPa and 171°C. Find the value of n. a. 1.354 c. 1.345 b. 1.253 d. 1.234 23. For an ideal gas, what is the specific molar entropy change during an isothermal process in which the pressure changes from 200 kPa to 150 kPa? a. 2.39 J/mol-K c. 3.39 J/mol-K b. 1.39 J/mol-K d. 4.39 J/mol-K 24. Water enters the heater at 25°C and leaves at 80°C. What is the temperature change in °F? a. 55 c. 11 b. 99 d. 65 25. The suction pressure of a pump reads 600 mm Hg vacuum. What is the absolute pressure in kPa? a. 11.33 c. 21.33 b. 31.33 d. 41.33 26. One kilogram of wet steam at a pressure of 8 bar (ѵ = 0.2404 m³/kg, ѵ f = 0.0011148 m³/kg) and dryness 0.94 is expanded until the pressure is 4 bar (ѵg = 0.4625 m³/kg, ѵf = 0.0010836 m³/kg). If expansion follows at the lower pressure. a. 0.9072 c. 0.2260 b. 0.4197 d. 0.2404 27. 2.5 liters of superheated steam at 25 bar and 400°C (ѵ = 0.1252 m³/kg) is expanded in an engine to a pressure of 0.1 bar (ѵg = 14.674 m³/kg, ѵf =

0.0010102 m³/kg) when its dryness fraction is 0.9. Find the final volume of the steam. a. 163.74 liters c. 363.74 liters b. 263.74 liters d. 463.74 liters 28. A 1.5 kg of wet steam at a pressure of 5 bar (h f = 640 kJ/kg, hfg = 2109 kJ/kg) dryness 0.95 is blown into 70 liters of water of 12°C (h = 50.4 kJ/kg). Find the final enthalpy of the mixture. a. 74.80 kJ/kg c. 94.80 kJ/kg b. 84.80 kJ/kg d. 104.80 kJ/kg 29. Wet saturated steam at 16 bar (hf = 859 kJ/kg, hfg = 1935 kJ/kg) reducing valve and is throttled to a pressure of 8 bar (hf = 721 kJ/kg, hfg = 2048 kJ/kg). Find the dryness fraction of the reduced pressure steam. a. 0.8833 c. 0.9933 b. 0.7733 d. 0.6633 30. A vessel of volume 8.7 m³ contains air and dry saturated steam at a total pressure of 0.06 bar and temperature 29°C (Psat = 0.04 bar, ѵ = 34.80 m³/kg). taking R for air as 287 J/kg-K, calculate the mass of steam and the mass of air in the vessel. a. 0.25 kg, 0.204 kg c. 0.25 kg, 350 kg b. 0.35 kg, 0.204 kg d. 0.35 kg, 0.45 kg 31. A water temperature rise of 18°F in the water cooled condenser is equivalent in °C to: a. -9.44 °C c. 10°C correct answer b. 263.56 K d. 7.78°C 32. Steam flows into a turbine at the rate of 10kg/s and 10kW of heat are lost from the turbine. Ignoring elevation and kinetic energy effects, calculate the power output from the turbine. Note: h1= 2739.0 kJ/kg and h2= 2300.5 kJ/kg a. 4605 kW c. 4375 kW correct answer b. 4973 kW d. 4000 Kw 33. The enthalpy of air is increased by 139.586 kJ/kg in a compressor. The rate of air flow is 16.42 kg/min. The power input is 48.2 kW. Which of the following values most nearly equals the heat loss from the compressor in kW? a. -10 c. -9.95 b. 10.2 d. 9.95 34. A Carnot engine requires 35 kJ/s from the hot source. The engine produces 15 kW of power and the temperature of the sink is 26°C. What is the temperature of the hot source in °C. a. 245.57 c. 250.18 b. 210.10 d. 260.68 35. The maximum thermal efficiency possible for a power cycle operating between 1200°F and 225°F is: a. 58% c. 57.54%

b. 58.73% d. 57.40% 36. A Carnot engine receives 130 Btu of heat from a hot reservoir at 700°F and rejects 49 Btu of heat. Calculate the temperature of the cold reservoir. a. -21.9 °F c. -20.8 °F b. -24.2 °F d. -22.7 °F 37. A tank contains 80 ft³ of air at a pressure of 350 psi. If the air is cooled until its pressure and temperature decrease to 200 psi and 70°F respectively, what is the decrease in internal energy? a. 4575 c. 5552 b. -5507 d. 0 38. If 10 lbs of water evaporated at atmospheric pressure until a volume of 288.5 ft³ is occupied, how much work is done? a. 610,358 ft-lb c. -610,358 ft-lb b. 0 d. 550,000 ft-lb 39. A reverse Carnot cycle requires 3 Hp and extracts energy from a lake to heat a house. If the house is kept at 70°F and requires 2000 Btu per minute, what is the temperature of the lake? a. 35°F c. 39°F b. 36°F d. 40°F 40. A pressure gage registers 50 psig in a region where the barometer is 14.25 psia. Find the absolute pressure in psia. a. 64.25 c. 151.325 b. 443 d. 35.75 41. After series of state changes, the pressure and volume of 2.286 kg of Nitrogen are each doubled. What is ∆S? a. 2.807 kJ/kg-K c. 2.987 kJ/kg-K b. 2.268 kJ/kg-K d. 3.407 kJ/kg-K 42. The temperature of 4.82 lb of Oxygen occupying 8 ft³ is changed from 110°F to 200°F while pressure remains constant at 115 psia. Determine the final volume. a. 7.26 ft³ c. 9.26 ft³ b. 8.26 ft³ d. 10.26 ft³ 43. Twenty grams of oxygen gas (O2) are compressed at a constant temperature of 30°C to 5% of their original volume. What work is done on the system? Use R of air , 0.0619 Cal/gm-K a. 824 Cal c. 944 Cal b. 924 Cal d. 1124 Cal 44. Helium (R = 0.4968 Btu/lbm-°R) is compressed isothermally from 14.7 psia and 68°F. The compression ratio is 4. Calculate the work done by the gas. a. -364 Btu/lbm c. -187 Btu/lbm b. -124 Btu/lbm d. -46.7 Btu/lbm 45. Gas is enclosed in a cylinder with a weighted piston as the top boundary. The gas is heated and expands from a volume of 0.04 m³ to 0.10 m³ at a constant pressure of 200 kPa. Calculate the work done by the system.

a. 8 kJ c. 12 kJ b. 10 kJ d. 14 kJ 46. A piston cylinder system contains a gas which expands under a constant pressure of 1200 lb/ft². If the piston is displaced 1 ft during the process, and the piston diameter is 2 ft. What is the work done by the gas on the piston? a. 1768 ft-lb c. 3768 ft-lb b. 2387 ft-lb d. 4000 ft-lb 47. Gas is enclosed in a cylinder with a weighted piston as the top boundary. The gas is heated and expands from a volume of 0.04 m³ to 0.10 m³. The pressure varies such that PV = constant and the initial pressure is 200 kPa. Calculate the work done by the system. a. 6.80 kJ c. 9.59 kJ b. 7.33 kJ d. 12 kJ 48. In an isentropic process, P1 = 200 psia, P2 = 300 psia and T1 = 700°R. Find T2 using k= 1.4. a. 576°R c. 786°R b. 680°R d. 590°R 49. Nitrogen (k = 1.4) is expanded isentropically. Its temperature changes from 620°F to 60°F. Find the pressure ratio (P1/P2). a. 0.08 c. 26.2 b. 12.91 d. 35.47 50. Nitrogen is expanded isentropically. Its temperature changes from 620°F to 60°F. The volumetric ratio is (V1/V2) = 6.22 and the value of R for nitrogen is 0.0787 Btu/lbm-°R. What is the work done by the gas? a. -100.18 Btu/lbm c. -110.18 Btu/lbm b. 120.27 Btu/lbm d. -120.27 Btu/lbm 51. An air bubble rises from the bottom of a well where the temperature is 25°C, to the surface where the temperature is 27°C. Find the percent increase in the volume of the bubble if the depth of the well is 5 m. Atmospheric pressure is 101,528 Pascals. a. 49.3 c. 41.3 b. 56.7 d. 38.6 52. An ideal gas is 45 psig and 80*F is heated in a closed container to 130*F. What is the final pressure? a. 54 psia c. 75 psia b. 65 psia d. 43 psia 53. How much work is necessary to compress air in an insulated cylinder from 0.20 m³ to 0.01 m³. Use Tˌ= 20°C and P̩=100 kPa. a. 113.4 Kj c. 110.1 kJ b. 121.4 kJ d. 115.7 kJ 54. A heat engine is operated between temperature limits of 1370°C and 260°C. Engine is supplied with 14,142 kJ/kwh. Find the Carnot cycle efficiency in percent.

a. 70.10 c. 67.56 b. 65.05 d. 69.32 55. A closed vessel contains air at a pressure of 160 kN/m² gauge and temperature of 30°C. The air is heated at constant volume to 60°C with the atmospheric pressure of 759 mm Hg. What is the final gauge pressure? a. 174 c. 167 b. 186 d. 172 56. What is the temperature in °C of 2 liters of water at 30°C after 500 Calories of heat have been added? a. 35.70 c. 38 b. 30.2 d. 39.75 57. A volume of 450 cm³ of air is measured at a pressure of 740 mm Hg absolute and a temperature of 20°C. What is the volume in cm³ at 760 mm Hg absolute and 0°C? a. 516.12 c. 620.76 b. 408.25 d. 375.85 58. Assuming compression is according to the law PV= constant. Calculate the initial volume of gas at a pressure of 2 bar which will occupy a volume of 6 m³ when it is compressed to a pressure of 42 bar. a. 126 m³ c. 130 m³ b. 120 m³ d. 136 m³ 59. A steam condenser receives 1okg per second of steam with an enthalpy of 2,570 kJ/kg. Steam condenses into liquid and leaves with an enthalpy of 160 kJ/kg. Cooling water passes through the condenser with temperature increases from 13°C to 24°C. Calculate the cooling water flowrate in kg/s. a. 533 c. 523 b. 518 d. 528 60. A steam expands adiabatically in a turbine from 2000 kPa, 400°C to 400 kPa, 250°C. What is the effectiveness of the process in percent assuming an atmospheric temperature of 15°C. Neglect changes in kinetic and potential energy. Properties of steam: At 2000 kPa and 400°C ( h= 3,247.6 kJ/kg, S= 7.1271 kJ/kg-K ) and at 400 kPa and 250°C ( h= 2,964.2 kJ/kg, S= 7.3789 kJ/kg-K. a. 82 c. 80 b. 84 d. 86 61. Find the change in internal energy of 5 lbm of oxygen when the temperature changes from 100°C to 120°F, Cᵥ= 0.157 Btu/lbm-°R. a. 14.70 Btu c. 16.80 Btu b. 15.70 Btu d. 147 Btu 62. Water (Specific heat, Cᵥ = 4.2 kJ/kg-K) is being heated by 1500-W heater. What is the rate of change in temperature of 1kg of water. a. 0.043 Kelvin/s c. 0.357 Kelvin/s correct b. 0.179 Kelvin/s d. 1.50 Kelvin/s

63. One kilogram of water (Cᵥ = 4.2 kJ/kg-K) is heated by 300 Btu of energy. What is the change in temperature in K? a. 75.36 K c. 73.80 K b. 125.20 K d. 17.96 K 64. Determine the change in enthalpy per lb mass of nitrogen gas as its temperature changes from 500°F to 200°F. (Cp = 0.2483 BTU/lbm°R) a. -74.49 Btu/lbm c. -68.47 Btu/lbm b. -72.68 Btu/lbm d. -63.78 Btu/lbm 65. Calculate the change in enthalpy as 1kg of nitrogen is heated from 1000K to 1500K, assuming the nitrogen is an ideal gas at a constant pressure. The temperature dependent specific heat of nitrogen is Cp = 39.06-512.79 Tˉ¹·⁵ + 1072.7 Tˉ² - 820.4Tˉ³ where Cp is in kJ/kg-mol, and T is in K. a. 600 kJ c. 800 kJ b. 697.27 kJ d. 897.27 kJ 66. What is the resulting pressure when one pound of air at 15 psia and 200°F is heated at constant volume to 800°F? a. 15 psia c. 36.4 psia b. 28.6 psia d. 52.1 psia 67. The temperature of an ideal gas remains constant while the absolute pressure changes from 103.4 kPaa to 827.2 kPaa. If the initial volume is 80 liters, what is the final volume? a. 5 li c. 15 li b. 10 li d. 20 li 68. For a certain ideal gas, R = 0.277 kJ/kg-K and k = 1.384. What are the values of Cp and Cᵥ? a. 0.9984 kJ/kg-K, 0.7214 kJ/kg-K c. 0.7124 kJ/kg-K, 0.8124 kJ/kg-K b. 1 kJ/kg-K, 0.8124 kJ/kg-K d. 0.9984 kJ/kg-K, 0.6124 kJ/kgK 69. A mixture is formed at 689.48 kPaa, 37.8 °C by bringing together these gases each volume before mixing measured at 689.48 kPaa, 37.8 °C; 3 mol CO 2, 2 mol N2, 4.5 mol O2. Find the partial pressure of CO2 after mixing. a. 217.73 kPaa c. 326.60 kPaa b. 145.15 kPaa d. 445.15 kPaa 70. An air with mass of 0.454 kg and an unknown mass of CO 2 occupy an 85 liters tank at 2068.044 kPaa. If the partial pressure of the CO 2 is 344.74 kPaa, determine its mass. a. 0.138 kg c. 0.183 kg b. 0.238 kg d. 0.283 kg 71. Steam enters the superheaters of a boiler at a pressure of 25 bar and dryness of 0.98 and leaves at the same pressure at a temperature of 370°C. Calculate the heat energy supplied in the superheaters. Properties of steam: At 25 bar and 370°C ( h= 3,171.8 kJ/kg ) and at 25 bar and o.98 dryness (h= 962.11 kJ/kg, h= 1,841.01 kJ/kg ).

a. 407.46 c. 405.51 correct answer b. 408.57 d. 406.54 72. The thermal efficiency of a particular engine operating on an ideal cycle is 35%. Calculate the heat supplied per 1200 watt-hr of work developed in kJ. a. 12,343 c.14,218 b. 10,216 d. 11,108 73. Determine the average Cp value in kJ/kg-K of a gas if 522 kJ of heat is necessary to raise the temperature from 300 K making the pressure constant. a. 1.440 c. 1.038 b. 1.044 d. 1.026 74. Determine the force in Newtons required to produce an acceleration of 0,30 m/s² on a 0.05 kg mass. a. 0.018 N c. 0.015 N b. 0.025 N d. 0.200 N 75. Ammonia weighing 22kg is confined inside a cylinder equipped with a piston has an initial pressure of 413 kPa at 38°C. If 2900 kJ of heat is added to the ammonia until its pressure and temperature are 413 kPa and 100°C, respectively. What is the amount of work done by the fluid in kJ? a. 667 c. 420 b. 304 d. 502 76. What is the total required heating energy in raising the temperature of a given amount of water when the energy supplied is 1000 kwh with heat losses of 25%? a. 1000 c. 1333 b. 1500 d. 1250 77. A vessel of 0.058 m³ capacity is well insulated and is divided equally by rigid conducting diaphragm. Initially both halves contain air at pressure of 137.8 kPa and 413.4 kPa and a temperature of 27°C and 177°C respectively, What is the increase of entropy of the system in kJ/°C. a. 1.002 c. 0.00173 b. 0.5080 d, 0.1080 78. A certain gas at 101.325 kPa and 16°C whose volume is 2.83 m³ are compressed into a storage vessel contained the gas at a pressure and temperature of 137.8 kPa and 24°C. After admission, the pressure has increased to 1171.8 kPa. What should be the final temperature of the gas in the vessel in Kelvin? a. 298.0 c. 180 b. 319.0 d. 420 79. Steam enters a throttling calorimeter at a pressure of 1.03 Mpa. The calorimeter downstream pressure and temperature are respectively 0.100 Mpa and 125°C. What is the percentage moisture of the supply steam? Properties of the steam: P= 1.03 Mpa hg= 2779.25 kJ/kg hfg= 2010.7 kJ/kg At 0.100 Mpa and 125°C: h= 2726.6 kJ/kg

a. 2.62 c. 3.15 b. 5.21 d. 1.98 80. What pressure is column of water 100cm high equivalent to? a. 9807 dynes/cm² c. 0.10 Bar b. 9807 N/m² d. 98100 N/m² 81. Determine the average constant pressure specific heat of steam at 10 kPa and 45.8°C. Note: From steam table, at 47.7°C, h= 2588.1 kJ/kg and at 43.8°C, h= 2581.1 kJ/kg. a. 1.79 kJ/kg°C c. 30.57 kJ/kg°C b. 10.28 kJ/kg°C d. 100.1 kJ/kg°C 82. A 10m³ vessel initially contains 5m³ of liquid water and 5m³ of saturated vapor at 100 kPa. Calculate the internal energy of the system. Properties of liquid water and saturated vapor: At 100 kPa, Vf = 0.001043 m³/kg; Vg = 1.6940 m³/kg; Uf = 417.3 kJ/kg; Ug = 2506.1 kJ/kg a.2.0x 10 83. A vessel with a volume of 1 m³ contains liquid water and water vapor in equilibrium at 600 kPa. The liquid water has a mass 1 kg. Calculate the mass of the water vapor. Properties of liquid water and water vapor at 600 kPa : V f=0.001101 m³/kg Vᶢ=0.3157 m³/kg a. 1.57kg c. 2.54kg b. 1.89kg d. 3.16kg 84. If 6 liters of a gas at a pressure of 100 kPaa are compressed reversibly according to PV²=C, until the volume becomes 2 liters. Find the final pressure. a. 600 kPaa c. 900 kPaa b. 800 kPaa d. 1000 kPaa 85. The flow energy of 124 liters per minute of fluid passing a boundary to system is 108.5 kJ/min. Determine the pressure at this point. a. 875 kPa c. 975 kPa b. 675 kPa d. 575 kPa 86. Work done by a substance in reversible nonflow manner in accordance with V = 100/P ft³, where P is in psia. Evaluate the work done on or by the substance as the pressure increases from 10 psia to 100 psia. a. 33 157.22 ft-lb c. 43 157.22 ft-lb b. -33 157.22 ft-lb d. -43 157.22 ft-lb 87. A closed gaseous system undergoes a reversible process during which 25 Btu are rejected, the volume changing from 5 ft³ to 2 ft³, and the pressure remains constant at 50 psia. Find the change of internal energy. a. -57.76 Btu c. 2.76 Btu b. -2.76 Btu d. 52.76 Btu 88. Assume 8 lb of a substance receive 240 Btu of heat at constant volume and undergo a temperature change of 150°F. Determine the average specific heat of the substance during the process.

a. 0.5 Btu/lb°F c. 0.40 Btu/lb°F b. 0.3 Btu/lb°F d. 0.20 Btu/lb°F 89. The following expressions relate to a particular gaseous mass: PV = 95T, h= 120+0.60T where these units obtain in psf, V in ft³/lb, T in °R and h in Btu/lb. If the specific heats are temperature dependent only, find Cp and Cᵥ. a. 0.6 Btu/lb°R, 0.28 Btu/lb°R c. 0.60 Btu/lb°R, 0.7 Btu/lb°R b. 0.5 Btu/lb°R, 0.50 Btu/lb°R d. 0.50 Btu/lb°R, 0.48 Btu/lb°R 90. Calculate the entropy of steam at 60 psia with a quality of 0.60./ Properties of steam at 60 psia: Sf = 0.4274 Btu/lb°R & Sfg = 1.2172 Btu/lb°R. a. 0.4247 Btu/lb°R c. 0.7303 Btu/lb°R b. 1.1577 Btu/lb°R d. 0.896 Btu/lb°R 91. How much power is there in the kinetic energy of the atmosphere ( density=1.217 kg/m³) at 56 kph wind velocity? Consider the section that passes through a 3m diameter circular area normal to the velocity. a. 10.21 kW c. 16.21 kW b. 15.21 kW d. 17.21 kW 92. An electric heater is to heat 11 kg of oil per min. from 4.5°C to 65.5°C. Specific heat of the oil is 2.1 J/gm-°C. How many watts should this heater consume? a. 20 448 W c. 20 400 W b. 33 448 W d. 23 442 W 93. Find the enthalpy of 1kg of wet saturated steam at a pressure of 0.20 bar and dryness fraction of 0.85. At 0.20 bar, hf= 251 kJ/kg, hfg= 2358 kJ/kg a. 2200 kJ/kg c. 2255.30 kJ/kg b. 2525 kJ/kg d. 2000 kJ/kg 94. If the specific enthalpy of wet saturated steam at a pressure of 11 bar is 2681 kJ/kg, find its dryness fraction. At 11 bar, hf=781 kJ/kg & hfg=2000 kJ/kg a. 0.75 c. 0.95 correct answer b. 0.85 d. 0.65 95. Find the heat transfer required to convert 5kg of water at a pressure of 20 bar and temperature of 21°C into steam of dryness fraction 0.90 at the same pressure. Properties of steam: P=20 bar; hf=909 kJ/kg; hfg= 1890 kJ/kg Note: for water at 21°C1 h=88 kJ/kg a. 10 610 kJ c. 12 610 kJ b. 11 610 kJ d. 15 610 kJ 96. A closed vessel contains air at a pressure of 140 Kpag and temperature of 20°C. Find the final gauge pressure if the air is heated at constant volume to 40°C. Take atmospheric pressure as 759 mm Hg. a. 156.46 c. 136.46 b. 146.46 d. 126.46

97. Water substance at 70 bar and 65°C enters a boiler tube of constant inside diameter of 25mm. The water leaves the boiler tube at 50 bar and 700K at velocity 100 m/s. Calculate the inlet volume flow in li./sec. At 70 bar & 65°C, v1=0.001017 m³/kg, at 50 bar & 700K, v2=0.06081 m³/kg. a. 0.75 c. 0.82 correct answer b. 0.64 d. 0.96 98. A group of 50 persons attend a secret meeting in room which is 12m wide by 10m long and a ceiling height of 3m. The room is completely sealed off and insulated. Each person gives off 150 kCal per hour of heat and occupies a volume of 0.20 m³. Then room has an initial pressure of 101.3 kPa and temperature of 16°C. Calculate the room temperature after 10 minutes. ͮ Use R= 0.287 kJ/kg-K and Cᵥ= 0.171 kCal/kg-K. ͫͫͫͫͫͫͫͫͫͫͫͫͫͫͫͫ ͫͫͫͫͫͫͫͫͫͫͫͫͫͫͫͫ a. 33.1 °C c. 38.7 °C ͫͫͫͫͫͫͫͫͫͫͫͫͫͫͫͫ b. 37.7 °C d. 31.7 °C ͫͫͫͫͫͫͫͫͫͫͫͫͫͫͫͫ 99. Steam at 1000 lbᶠ/ft² pressure and 300°R has specific volume of 6.5 ft³ lbm and a specific enthalpy of 9800 ft-lbᶠ/lbm. Find the internal energy per pound mass of steam. a. 2500 ft-lbf/lbm c. 5400 ft-lbf/lbm ͫͫͫͫͫͫͫͫ b. 3300 ft-lb f /lb m d. 6900 ft-lbf/lbm ͣͥͣͣͣͣͥͣͣͣ ͣͥͣͣͣ 100. Three pounds mass of air are contained at 25 psia and 100°F. Given that ͣͥͣͣͣ Rair= 53.35 ft-lbf/lbm. What is the volume of the container? a. 10.7 ft³ c. 20.6 ft³ b. 15 ft³ d. 24.9 ft³