Mechanical Engineering Review Online

A water tube boiler evaporated 6.05 kg of water per second from a feed water temperature of 104.44 deg C to steam at 1241.1 kPa and quality of 0.95: weight of coal fuel per second is 0.58 kg: high heating value of the coal as fired 11,900 Btu/lb. Steam properties: At 104.44 deg C: hf=437.78. At 1241.1 kPa: hf=805.29, hfg=1980.6

1. Determine the rate of the heat absorption in kJ/sec.

a. 12605.8

b. 13606.9

c. 15600.2

d. 18507.1

2. Find the boiler horsepower

a. 1286.8

b. 1487.1

d. 1386.8

d. 1152.8

3. What is the boiler efficiency?

a. 84.9%

b. 89.8%

d. 75.3%

d. 79.7%

A 680 bhp diesel engine uses fuel oil of 28 deg API at 45 deg C, fuel consumption is 0.78 lbs per bhp-hr. cost of fuel is P6.65 per liter.

4. What is the density of the fuel oil used in kg/li?

a. 0.783

b. 0.869

c. 0.683

d. 0.801

5. What is the fuel consumption in liters per hr?

a. 200.3

b. 285.3

c. 274.9

d. 255.3

6. Determine the minimum volume of the required day tank

a. 7588.21 L

b. 6998.42 L

c. 6008.53 L

d.6599.21 L

7. Find the cost of fuel per day.

a. 49945.7

b. 40398.8

c. 45368.9

d. 43884.7

A reheat steam cycle has 13.85 MPa throttle pressure at the turbine inlet and a 2.8 MPa reheat pressure, the throttle and reheat temperature of the steam is 540 deg C, condenser pressure is 3.4 kPa, engine efficiency of high pressure and low pressure is 80%. Steam properties: At 13.85 MPa and 540 deg C: h=34341. At 2.8 MPa and 540 deg C: h=3538.5. At 2.8 MPa: h=2974.9. At 0.0034 MPa: h=2204.5, hf=109.84, vf=0.0010032

8. Determine the enthalpy at the entrance to the boiler, in kJ/kg

a. 135.7

b. 115.4

c. 148.3

d. 123.7

9. Find the reheat cycle turbine work, in kJ/kg

a. 1578.5

b. 1477.2

c. 1674.6

d. 1832.1

10. Find the pump work, in kJ/kg

a. 10.89

b. 13.89

c. 14.87

d. 12.07

11. What is the heat added in the boiler and reheater, in kJ/kg

a. 3873.97

b. 4864.87

c. 5811.23

d. 2974.21

12. Determine the reheat cycle thermal efficiency?

a. 42.9%

b. 38.7%

c. 28.9%

d. 47.6%

13. The ratio of the sum of the individual demands of the system to the overall maximum demand of the whole system:

a. Diversity factor

b. Demand factor

c. Utilization factor

d. Load factor

14. The ratio of the kW-hr generated to the product of the capacity of the plant in kW to the number of hours the plant has been in actual use.

a. Load factor

b. Demand factor

c. Diversity factor

d. Utilization factor

15. Load curves refers to the plot of

a. Load versus time 

b. Load versus current

c. Load versus generating capacity

d. Load versus cost of power

16. The ratio of the average load to the peak load over a designated period of time is called:

a. Reactive factor

b. Load factor

c. Diversity factor

d. Plant use factor

An ammonia refrigeration compressor takes its suction from the evaporator at a temperature of -20 deg F (-28.9 deg C) and a quality of 96%. The compressor discharges at a pressure of 100 psi (689.5 kPa), liquid ammonia leaves the condenser at 50 deg F (10 deg C). Properties of Ammonia: At 689.5 kPa (tsat=13.3 deg C) h=1568. At 10 deg C, hf=246.531. At -28.9 deg C: hf=68.5, hg=1424.5, sf=0.49366, sg=6.0452

17. Find the heat absorbed by the evaporator, in kJ/kg

a. 1023.73

b. 1123.73

c. 1243.81

d. 1300.92

18. Find the heat rejected to the condenser, in kJ/kg

a. 1308.21

b. 1083.17

c. 1321.47

d. 1451.82

19. Find the COP

a. 4.35

b. 6.78

c. 5.68

d. 3.91

20. Find the horsepower per ton of refrigeration

a. 0.5381

b. 0.8296

c. 0.6617

d. 0.7197

21. Determine the quality of refrigerant upon entering to the evaporator

a. 10.34%

b. 11.24%

c. 9.87%

d. 13.13%

An air-standard engine operating on the diesel cycle when the suction pressure is 98 kPa and the fuel is injected 5% of the stroke, the clearance volume is 7% of the stroke. Assume k=1.4.

22. Determine the air standard efficiency

a. 52.1%

b. 58.3%

c. 62.15%

d. 48.31%

23. Determine the compression ratio

a. 14.32

b.15.28

c. 13.11

d. 16.81

24. Determine the cut-off ratio

a. 1.71

b. 2.01

c. 3.12

d. 2.99

25. What is the clearance ratio as a percentage of the piston volume displacement?

a. 6%

b. 7%

c. 8%

d. 9%

26. The level of the water in an enclosed water tank is 45 m above the ground. The pressure in the air space above the water is 130 kPa. The average density of water is 998 kg/cm³. What is the pressure of the water at the ground level?

a. 501.45 kPa

b. 458.31 kPa

c. 571.45 kPad. 553.21 kPa

27. A vertical cylinder containing argon is fitted with a piston of 35 kg mass and cross section area of 0.030 m². The atmospheric pressure outside the cylinder is 98 kPa and local gravitational acceleration is 9.80 m/s². What is the argon pressure inside the cylinder?

a. 100.45 kPa

b. 118.45 kPa

c. 98.12 kPa

d. 109.45 kPa

28. In order that cavitation will not take place in the suction line of a pump what should be the sum of the velocity head and pressure head at suction compared to the vapor pressure of the liquid?

a. Adequately greater

b. Sufficiently lower

c. Constant

d. Equal

29. An engineer inspected an air-conditioning unit. He found out that the unit does not produce any cooling effect, however, the air-conditioning unit is running. He checked the temperatures of the condenser and evaporator and had the unit run. He found out that there was no change in the temperature. What should he do?

a. Replace fuse

b. Replace relay

c. Adjust door seal

d. Charge with new refrigerant

30. A rapid increase in boiler pressure occurs when there is:

a. Moderate drop in steam load 

b. Constant drop in steam load

c. Abrupt drop in steam load

d. Gradual drop in steam load

31. Dry air can be approximated as ___% oxygen and ___% nitrogen.

a. 30% and 70%

b. 21% and 79%

c. 70% and 30% d

d. 79% and 21%

32. When H₂O in the products of combustion is in liquid form, the heating value is known as

a. Higher heating value 

b. Lower heating value

c. Lower and higher heating value

d. Low and medium heating value

33. In an experiment airplane flying at 22,000 m (g=9.71 m/s²), the airflow in a piece of apparatus is measured by using a mercury manometer. The difference in the level is 290 mm. At sea level and the same temperature, mercury has a density of 13,600 kg/m³. Determine the pressure drop across the orifice.

a. 38.30 kPa

b. 40.41 kPa

c. 35.31 kPa

d. 42.12 kPa 

34. The height of mercury manometer column which is used to measure a vacuum is 710 mm, and the barometer reads 98 kPa. Determine the gas pressure.

a. -2.43

b. 3.34 kPa

c. 4.12 kPa

d. -3.34 kPa

35. A manometer contains a fluid having a density of 810 kg/m³. The difference in height of the column is 305 mm. What pressure difference is indicated?

a. 1.82 kPa

b. 2.42 kPa

c. 3.01 kPa

d. 4.08 kPa

36. A pressure gage reads 2.50 MPa, and the barometer reads 98 kPa. Calculate the absolute pressure.

a. 2598 kPa

b. 2087 kPa

c. 2118 kPa

d. 2873 kPa

37. A piston has an area of 450 mm². What mass must the piston have if it exerts a pressure of 60 kPa above atmospheric pressure on the gas enclosed in the cylinder. Assume standard gravitational acceleration.

a. 1.82 kg

b. 3.28 kg

c. 2.75 kg

d. 4.01 kg

Air at a pressure of 98 kPa has a volume of 0.40 m³. The air is compressed in a reversible adiabatic manner until the temperature is 200^oC. The reversible work is -65 kJ/kg. Determine

38. The initial temperature, in K

a. 109.54

b. 300.28

c. 382.55

d. 207.31

39. The air mass, in kg

a. 1.821

b. 0.994 3

c. 0.5141

d. 0.3838

40. The change of internal energy, in kJ

a. 34.25

b. 20.21

c. 28.34

d. 24.95

Air is compressed polytropically from 100 kPa and 24^oC and delivered to a tank at 1400 kPa and 180^oC. Determine per kilogram of air

41. The heat removed during compression, in kJ/kg

a. -101.31

b. -153.14

c. -123.41

d. -184.38

42. The reversible work, in kJ/kg

a. -201.32

b. -248.32

c. -235.15

d. -283.21

43. A piston cylinder containing air receives heat at a constant temperature of 480 K and an initial pressure of 210 kPa. The initial volume is 0.018 m³ and the final volume is 0.088 m³. Determine the heat and work, in kJ.

a. 8.31

b. 7.52

c. 6.00

d. 5.17

44. A closed rigid container has a volume of 1 m³ and holds air at 355.6 kPa and 273 K. Heat is added until the temperature is 610 K. Determine the heat added and the final pressure.

a. 1000.12 kJ and 794.56 kPa 

b. 1099.11 kJ and 794.56 kPa

c. 1099.11 kJ and 854.34 kPa

d. 1211.15 kJ and 764.51 kPa

45. An ideal gas occupies a volume of 0.55 m³ at a temperature of 350 K and a given pressure. The gas undergoes a constant-pressure process until the temperature decreases to 280 K. Determine the final volume and work if the pressure is 130 kPa.

a. 0.44 m³ and -14.30 kJ 

b. 0.55 m³ and -18.51 kJ

c. 0.48 m³ and -16.31 kJ

d. 0.58 m³ and -15.99 kJ

46. A 1.5 kg gaseous system is in a piston-cylinder and receives heat at constant pressure of 360 kPa. The internal energy increases to 180 kJ and the temperature increases to 60 K. If the work done is 130 kJ, determine the specific heat and change in volume.

a. 2.84 kJ/kg-K and 0.3611 m3 

b. 3.44 kJ/kg-K and 0.3611 m³ 

c. 5.82 kJ/kg-K and 0.3611 m³ 

d. 6.11 kJ/kg-K and 0.3611 m³

47. An insulated, constant volume system containing 1.43 kg of air receives 55 kJ of paddle work. The initial temperature is 28oC. Determine the final temperature, in K.

a. 300.21 K

b. 314.21 K

c. 321.82 K

d. 354.52 K

48. A 6 m³ tank contains chlorine (R=0.1152) at 300 kPa and 310 K after 2.8 kg of chlorine has been used. Determine the original mass and pressure if the original temperature is 320 K.

a. 33.51 kg and 300.3 kPa 

b. 53.20 kg and 309.7 kPa

c. 50.82 kg and 305.87 kPa

d. 48.31 kg and 401.65 kPa

49. An electric calorimeter samples steam with a line pressure of 0.175 MPa. The calorimeter adds 230 watts of electricity to sampled steam having a resultant pressure of 100 kPa, temperature of 100^oC and a flow rate of 13 kg/h. Determine the main steam quality. At 0.175 MPa: hf=486.99, hfg=2213.6. At 100 kPa and 100^oC: h=2676.2

a. 0.9889

b. 0.8739

c. 0.9001

d. 0.8871

50. The barometer reads 30.0 inches of mercury. What is the absolute pressure if a vacuum gage reads 9.8 psi?

a. 6.82

b. 3.87

c. 7.99

d. 4.94

51. An Otto cycle has a compression ratio of 9.0 and an air conditions at the beginning of compression of 98 kPa and 24^oC. The heat added is 1400 kJ/kg. Determine the work done.

a. 821.34 kJ/kg

b. 800.52 kJ/kg

c. 818.66 kJ/kg

d. 857.88 kJ/kg

52. In an air standard diesel cycle the compression starts at 100 kPa and 28^oC. The compression ratio is 13 and the maximum temperature is 2000 K. Determine the thermal efficiency.

a. 50.34%

b. 48.31%

c. 56.08%

d. 45.87%

53. A spherical fuel oil tank 2.3 m diameter is filled to a height of 0.60 m from the top of the tank. The fuel tank is used to supply the engine at the rate of 0.3 kg/s. How many hours to consume the available fuel? (SG=0.85)

a. 4.68 hrs

b. 3.62 hrs

c. 5.51 hrs

d. 2.89 hrs

54. An air conditioning system delivers 25 kg/s of air to a theater which is to be maintained at 18^oC. Air from outside is mixed with recirculated air which is 5 kg/s more than the recirculated air. If the temperature of air after mixing is 30^oC, determine the temperature of outside air, in deg C.

a. 35

b. 38

c. 36

d. 37

55. A refrigeration system is to be used to cool 45,000 kg of water from 30^oC to 15^oC in 5 hours. The refrigerant is ammonia and the operating conditions are 616 kPa evaporating pressure and 1737 kPa liquefaction pressure. Determine the quantity of cooling water in the condenser for an increase in temperature of 8^oC. Enthalpy at the condenser entrance=1650 and exit=410.4kJ/kg. Evaporator entrance=410.4, exit=1471.6 kJ/kg.

a. 5.48 kg/s

b. 6.88 kg/s

c. 4.58 kg/s

d. 7.01 kg/s

56. Flow of fluids wherein its particles do not have definite paths and the paths of the individual and distinct particles cross one another is:

a. Turbulent flow

b. Laminar flow

c. Non-uniform flow

d. Unsteady flow

57. What do you call a conversion technology that yields electricity straight from sunlight without the aid of a working substance like gas or steam without the use of any mechanical cycle?

a. Power conversion 

b. Solar thermal conversion

c. Sterling cycle conversion

d. Photovoltaic-energy conversion

58. A property of lubricating oil that measures the thickness of the oil and will help determine how long oil will flow at a given temperature is known as?

a. Flash point

b. Pour point

c. Cloud point

d. Viscosity

59. A boiler has a bursting pressure, Bp, of 600 kPa and a factor of safety, FS, of 8 is employed in design. As an engineer, would you advise to have a working pressure, Wp, of 500 kPa?

a. No, Wp is only 75 kPa at FS of 8 

b. No, Wp must be higher than 500 kPa

c. Yes, since Bp is 600 Pa

d. Yes, to attain better efficiency

60. What is the area of the diagram from the relation of temperature and entropy plane?

a. Heat

b. Work

c. Energy

d. Power

61. In refrigeration system has the following condition: condenser entrance=1720 kJ/kg, exit=350.2 kJ/kg. Evaporator entrance=350.2 kJ/kg, exit=1462 kJ/kg. Find the COP of the system.

a. 4.3

b. 3.3

c. 5.1

d. 6.0

62. If 780 Btu of heat is added to a substance at constant temperature of 160^oF, what is the change in entropy, in Btu/oR?

a. 1.26

b. 2.26

c. 3.26

d. 4.26

63. A substance at a pressure of 1MPa and specific volume of 0.653 m³/kg has an enthalpy of 9000 kJ/kg. What is its internal energy?

a. 5347 kJ/kg

b. 8347 kJ/kg

c. 6841 kJ/kg

d. 7814 kJ/kg

64. What is the enthalpy of a substance at a pressure of 480 kPa, specific volume of 1.010 m³/kg and internal energy of 2590 kJ/kg?

a. 4071

b. 3074

c. 2118

d. 5871

65. Convert 12 tons of refrigeration to kcal/min.

a. 599.3

b. 681.1

c. 604.8

d. 879.7

66. An ideal gas is compressed isothermally from 100 kPa and 0.55 m³ to a final pressure of 500 kPa, what is the final volume, in m3?

a. 0.88

b. 0.22

c. 0.11

d. 0.33

67. A Carnot cycle operates between the temperature limits of 900 K and 250 K. If the entropy of the low temperature reservoir increases to 2.4 kJ/K. Find the work of the cycle.

a. 1860 kJ

b. 1270 kJ

c. 1007 kJ

d. 1560 kJ

68. Convert vacuum pressure of 110 mm Hg into absolute pressure in meters of water if the atmospheric pressure is 12.22 meters of water. SG of mercury = 13.6

a. 12.35

b. 15.35

c. 9.87

d. 10.72

69. The ice making capacity is always

a. Directly proportional to the refrigerating effect 

b. Greater than the refrigerating effect

c. Equal to the refrigerating effect

d. Less than the refrigerating effect

70. The ratio of cross-sectional area of flow to the wetted perimeter

a. Hydraulic lead

b. Hydraulic mean depth

c. Hydraulic gradient

d. Hydraulic power

71. In pipe specification, schedule number is used; when the pipe is specified as “Schedule 80,” the pipe corresponds to the:

a. Allowable stress 

b. Internal pressure

c. “Extra standard” weight

d. “Old standard” weight

72. The effect of superheating the refrigerant is:

a. High COP

b. Decrease COP

c. Maintain COP

d. Increase COP

73. When the air saturated, the wet bulb depression is:

a. Zero

b. Indefinite

c. Unity

d. 100%

74. Calculate the horsepower required to compress 12 lbm/sec of air from 1 atm and 100^oF to 3 atm and 1300^oF. For low pressure air: T=560^oR, h=134 Btu/lbm, T=1760^oR, h=439 Btu/lbm.

a. 3660

b. 5176

c. 6871

d. 5289

75. Air is compressed in a piston-cylinder arrangement 1/10 of its initial volume. If the initial temperature is 120^oF and the process is frictionless and adiabatic. What is the final temperature, in deg R?

a. 1805

b. 1779

c. 1456

d. 1387

76. A mass of 0.30 kg of metal having a temperature of 120^oC is plunged into a 0.05 kg of water at 23^oC. The temperature of water and metal becomes 50^oC. Assuming no heat loss to the surroundings, determine the specific heat of the metal in kJ/kg-K.

a. 0.1189

b. 0.2998

c. 0.3879

d. 0.2692

77. Gas initially at 120 psia and 300^oF receives 15500 ft-lb_f of work while 45 Btu of heat are removed from the system. Calculate the internal energy change for the system.

a. -20.35 Btu

b. -22.31 Btu

c. -28.31 Btu

d. -25.08 Btu

78. An air receiver with a volume of 2600 L initially contains atmospheric air at 30^oC. How many kilogram of air are added into the tank if the final conditions are 1600 kPa and 38^oC?

a. 49.64

b. 45.65

c. 43.58

d. 40.87

79. Air flowing through a pipe losses 12 kJ/sec of heat to the surroundings so that its temperature is reduced by 15^oC. What is the mass flow in kg/s?

a. 0.831

b. 0.795

c. 0.812

d. 0.710

80. One pound of air is compressed from a volume of 1.5 ft³ and a pressure of 12 psia to a volume of 0.156 ft³ and a pressure of 120 psia. Assuming that the compression follows the law PVⁿ=constant, find the work done during the compression process, in lb-ft.

a. -5993

b. -5084

c. -6174

d. -5783

81. A condenser vacuum gage reads 580 mm Hg when the barometer reads 758 mm Hg. What is the absolute condenser pressure in kN/m²?

a. 20.71

b. 18.34

c. 25.31

d. 23.73

82. A Carnot engine receives 110 Btu of heat from a hot reservoir at 800^oF and rejects 40 Btu of heat. Determine the temperature of the cold reservoir.

a. -2.82

b. -7.82

c. -3.87

d. -1.82

A certain coal has the following ultimate analysis by weight: C=70.5, H₂=4.5%, O₂=6.0%, N₂=1.0, S=3.0%, Ash=11%, moisture=4.0%. A stroker fired boiler of 180,000 kg per hour steaming capacity uses this coal as a fuel. Calculate:

83. The weight of air in kg needed per kg of coal when this coal is burned with 25% excess air.

a. 11.91

b. 13.51

c. 10.87

d. 15.01

84. Volume of air in cubic meters per hour with air at 60^oF and 14.7 psia pressure.

a. 189310

b. 200668

c. 297115

d. 255017

85. Weight in metric tons of coal needed for 24 hours operation at rated capacity if boiler efficiency is 80% and factor of evaporation is 1.20.

a. 400.63

b. 351.68

c. 494.52

d. 458.85

A pelton type turbine was installed 35 meters below the head gate of the penstock. The head loss due to friction is 18 percent of the given elevation. The length of the penstock is 85 meters and coefficient of friction is 0.00085. Determine.

86. The diameter of the penstock, in meters

a. 1.82

b. 1.32

c. 1.01

d. 1.58

87. The power output, in kW

a. 9095.8

b. 8007.3

c. 9907.1

d. 8971.3

88. The crank shaft of a double-acting steam engine rotates at 240 rpm. The bore and stroke of the steam engine is 300 mm x 450 mm, and the mean effective pressure acting upon the piston is 5 kg/cm². Determine the indicated horsepower or the horsepower developed in the cylinder.

a. 155.3

b. 187.3

c. 167.3

d. 149.3

89. Fish weighing 12000 kg with a temperature of 18^oC is brought to a cold storage and which shall be cooled to -5^oC in 12 hours. Find the required plant refrigerating capacity in tons of refrigeration if the specific heat of fish is 0.8 above freezing and 0.29 below freezing point which is -2^oC. The latent heat of freezing is 56.1 kcal/kg.

a. 20.97

b. 18.99

c. 25.31

d. 23.94

Water from a reservoir is pumped over a hill through a pipe 850 mm in diameter and a pressure of one (1) kg/cm² is maintained at the pipe discharge where the pipe is 80 meters from the pipe center line. The pump has a positive suction head of 8 meters. Pumping rate of the pump at 1000 rpm is 2.0 m³/s. Friction losses is equivalent to 2 meters of head loss. Compute:

90. The amount of energy that must be furnished by the pump in kW

a. 1550.4

b. 1660.5

c. 1487.8

d. 1588.8

91. If the speed of the pump is 1300 rpm, what is the new value of the discharge, in m3/s?

a. 2.6

b. 3.6

c. 4.6

d. 5.6

Air enters a fan through a duct at a velocity of 6.5 m/s and an air inlet static pressure of 2.8 cm of water less than atmospheric pressure. The air leaves the fan through a duct at a velocity of 12 m/s and a discharge static pressure of 7.8 cm of water above atmospheric pressure. If the specific weight of the air is 1.18 kg/m³ and the fan delivers 9.56 m³/s, determine:

92. The fan air power, in kW

a. 10.52

b. 11.68

c. 12.87

d. 13.77

93. The efficiency, in percent if the power input to the fan is 14 kW at the coupling

a. 75.11%

b. 78.21%

c. 80.12%

d. 65.35%

94. A temperature measurement in an ordinary thermometer which has constant specific humidity

a. Dew point temperature 

b. Critical temperature

c. Wet bulb temperature

d. Dry bulb temperature

95. At what temperature wherein an oil of any grade becomes cloudy and it freezes, thus its application is limited

a. Cold point

b. Pour point

c. Freezing point

d. Flash point

96. For reciprocating compressor, slip at positive/negative displacement

a. Cd=1

b. Cd<1

c. Cd>1

d. Cd=0

97. The size of steam reciprocating pump is generally designated by a three-digit number such as 646. What would be the first number designates?

a. Stroke of the pump 

b. Percent clearance

c. Number of cylinders

d. Inside diameter of the steam cylinder measured in inches

98. What is the required base area, in m² of the foundation to support an engine with specific speed of 1300 rpm and weight of 10,000 kg. Assume bearing capacity of soil as 48.876 kPa. Use C=0.11

a. 8.77

b. 6.89

c. 9.97

d. 5.99

99. A liquid dominated geothermal plant with a single flash separator receives water at 204^oC. The separator pressure is 1.04 MPa. A direct contact condenser operates at 0.034 MPa. The turbine has a polytropic efficiency of 0.80. For a cycle output of 60 MW, what is the mass flow rate of the well-water in kg/s? Steam properties: At 204oC: hf=870.51 kJ/kg. At 1.04 MPa: hf=770.38, hfg=2009.2, hg=2779.6, sg=6.5729. At 0.034 MPa: hf=301.40, hfg=2328.8, sf=0.9793, sfg=6.7463

a. 2548.75

b. 2749.75

c. 2846.88

d. 2987.31

100. The hot combustion gases of a furnace are separated from the ambient air and its surroundings, which are at 24^oC, by a brick wall 0.18 m thick. The brick has a thermal conductivity of 1.3 W/m-K and a surface emissivity of 0.80. Under steady state conditions and outer surface temperature of 110^oC is measured. Free convection heat transfer to the air adjoining this surface is characterized by a convective coefficient of 20 W/m²-K. What is the brick inner surface temperature, in ^oC?

a. 424.41

b. 401.81

c. 454.51

d. 488.64

Answer Key (Handwritten)