Mechanical Engineering Review Online

1. An ideal gas is compressed isothermally. The enthalpy change is:

a. Sometimes negative

b. Zero

c. Sometime positive

d. Always positive

2. An system with paddle work is irreversible, therefore, the change in its entropy

a. Is zero 

b. Greater than zero

c. Positive

d. Negative

3. An ideal gas is compressed in a cylinder so well insulated that there is essentially no heat transfer. The temperature of the gas:

a. Decreases 

b. Remains constant

c. Increases

d. Infinite

4. Name the process that has no heat transfer

a. Isothermal

b. Isentropic

c. Polytropic

d. Adiabatic

5. The first law of thermodynamics

a. Internal energy is due to molecular motions
b. Entropy of the universe is increased by irreversible processes
c. Energy can be neither created nor destroyed
d. Heat energy cannot be completely transformed into work.

6. Enthalpy of an ideal gas is a function only of

a. Entropy

b. Internal energy

c. Temperature

d. Pressure

7. A tank contains 90 ft³ of air at a pressure of 350 psi; if the air is cooled until its pressure and temperature decrease to 230 psi and 60^oF, respectively, what is the decrease in internal energy.

a. -4889.352 Btu

b. -4989.3582 Btu

c. -6578.232 Btu

d. -2830.101 Btu

8. If 12 lbs of water are evaporated at atmospheric pressure until a volume of 300 ft³ is occupied, how much work is done?

a. 634,632.94 lb-ft

b. 653,017.09 lb-ft

c. 643,392.86 lb-ft

d. 662,012.94 lb-ft

9. How much work is done when 23 ft³ of air initially at a pressure of 15 psi and at temperature of 50^oF experience an increase of pressure to 65 psi while the volume remains constant?

a. -6580 Btu

b. 6580 Btu

c. infinite

d. zero

10. In an air standard Otto cycle, the clearance volume is 15% of the displacement volume. Determine the compression ratio and or thermal efficiency.

a. 55.7%

b. 86.2%

c. 65.3%

d. 45.1%

11. Which of the following statement is correct? The relative humidity of an air water vapor mixture :

a. Is the ratio of the partial pressure of the water vapor to the partial pressure of the air.
b. Indicates the mass of water vapor in the mixture
c. Is equal to the mole fraction of the water vapor in the mixture temperature.
d. Is the ratio of the partial pressure of the water vapor to the saturation pressure at the mixture temperature

12. A Reversed Carnot cycle requires 3.5 hp and extracts energy from a lake to heat a house. If the house is kept at 72^oF and requires 2000 Btu per minute, what is the temperature of the lake, in deg F?

a. 497.6

b. 37.63

c. 562.3

d. 65.2

13. A water temperature rise at 20 deg F in the water cooled condenser is equivalent, in deg C to:

a. 10.11

b. 11.11

c.12.22

d. 18.3

14. Is the condition of pressure and temperature at which a liquid and its vapor are indistinguishable

a. Critical point

b. Dew point

c. Absolute humidity

d. Relative humidity

15. If the temperature is held constant and the pressure is increased beyond the saturation pressure, we have a

a. Saturated vapor

b. Compressed liquid

c. Saturated liquid

d. Sub-cooled liquid

16. Steam flows into a turbine at a rate of 15 kg/s and 15 kW of heat are lost from the turbine. Ignoring potential and kinetic energy effects, Calculate the power output from the turbine. (h₁ = 2739.0 kJ/kg, h₂ = 2300.5 kJ/kg)

a. 5662.3 kW

b. 6552.4 kW

c. 6562.5 kW

d. 3452.3 kW

17. The compression ratio of an ideal Otto cycle is 6:1. Initial conditions are 100 kPa and 23^oC. Determine the pressure and temperature at the end of adiabatic compression.

a. 1352.5 kPa, 606.1 K

b. 1228.6 kPa, 706 K

c. 1326.1 kPa, 766.2 K

d. 1228.6 kPa, 606.1 K

18. What pressure is a column of water 120 cm high equivalent to?

a. 11.7 kPa

b. 12.8 kPa

c. 15.3 kPa

d. 10.1 kPa

19. An ideal vapor compression cycle requires 3 kW to power the compressor. You have found the following data for the cycle: The enthalpy of the condenser entrance = 203 kJ/kg, exit = 55; evaporator entrance = 55 kJ/kg, exit = 178. If the mass flow rate of the refrigerant is 0.15 kg/s, then the coefficient of performance of this refrigeration cycle is most nearly:

a. 5.12

b. 6.15

c. 4.98

d. 7.12

20. The internal combustion engines never work on _____ cycle:

a. Rankine

b. Diesel

c. Dual combustion

d. Otto

21. The dividing point between the high pressure and low pressure sides of the refrigeration cycle occurs at the

a. Expansion valve

b. Compressor

c. Condenser

d. Cooling coil

22. A pressure of 1 millibar is equivalent to:

a. 1000 dynes/sq cm

b. 1000 cm of Hg

c. 1000 psi

d. 1000 kg/sq cm

23. The enthalpy of air is increased by 140.543 kJ/kg in a compressor. The rate of air flow is 17.52 kg/min. The power input is 48.5 kW, which of the following values most nearly equals the heat loss from the compressor in kW?

a. 8.4 kW

b. 7.5 kW

c. 6.6 kW

d. 9.1 kW

24. Liquid ammonia at a temperature of 26 deg C is available at the expansion valve. The temperature of the vaporizing ammonia in the evaporator is 2 deg C. Determine the percentage of liquid vaporized while flowing through the expansion valve.

At 2^oC: P = 462.49 kPa; hf = 190.4 kJ/kg; hfg = 1255.2 kJ/kg; hg = 1445.6 kJ/kg

At 26^oC: P = 1033.97 kPa; hf = 303.6 kJ/kg; hfg = 1162 kJ/kg; hg = 1465.6 kJ/kg

a. 9.02

b. 90.98

c. 91.08

d. 8.92 

25. In an air standard diesel cycle, compression starts at 98 kPa and 300 K. The compression ratio is 15 to 1. The maximum cycle temperature is 2050 K. Determine the thermal efficiency.

a. 55.3%

b. 48.2%

c. 58.9%

d. 35.2%

26. Air enters an auditorium at the rate of 28.3 m³/s. The air is at 25^oC dry bulb (hg=2547.7 kJ/kg) and 16^oC wet bulb temperature (hg=2531.0 kJ/kg), and is at 100 kPa. What will be the mass rate of flow of water vapor (kg/min)? Note: Saturation pressure at 16^oC = 1.8181 kPa.

a. 10.5

b. 12.3

c. 16.7

d. 18.0

27. A waste heat recovery boiler produces 4.8 MPa (dry saturated steam from 104^oC feed water. The boiler receives energy from 6 kg/s of 954^oC dry air. After passing through the waste heat boiler, the temperature of the air has been reduced to 343^oC. How much steam in kg is produced per second? NOTE: At 4.8 MPa dry saturated, h=2796.0 kJ/kg.

a. 1.56 kg/s

b. 1.99 kg/s

c. 0.98 kg/sd. 2.02 kg/s

28. A superheat steam Rankine cycle has turbine inlet conditions of 18 MPa and 530^oC expand in a turbine to 0.007 MPa. The turbine and pump polytropic efficiencies are 0.85 and 0.65, respectively. Pressure losses between pump and turbine inlet are 1.5 MPa. What should the pump work in kJ/kg?

a. 25

b. 30

c. 35

d. 40

29. Air enters the compressor of a gas turbine at 100 kPa and 300 K with a volume flow rate of 8 m³/s. the compressor pressure ratio is 11 and its isentropic efficiency is 88%. At the inlet to the turbine, the pressure is 960 kPa and the temperature is 1500 K. The turbine has an isentropic efficiency of 85% and exit pressure is 100 KPa. On the basis of an air-standard analysis, what is the thermal efficiency of the cycle in percent?

a. 25

b. 35

c. 30

d. 40

30. Mechanism designed to lower the temperature of air passing through it

a. Air cooler

b. Air defense

c. Air spillover

d. Air cycle

31. A steam plant operates with initial pressure of 1.70 MPa and 370^oC temperature and exhaust to a heating system at 0.17 MPa. The condensate from the heating system is returned to the boiler at 65.5oC and the heating system utilizes from its intended purpose 85% of the energy transferred from the steam it receives. The turbine efficiency is 75%. If the boiler efficiency is 80%, what is the cogeneration efficiency of the system in percent? Neglect pump work.

Steam properties:

At 1.70 MPa and 370^oC: h=3187.1 kJ/kg, s=7.1081 kJ/kg-K
At 0.170 MPa: hf = 483.20, hfg = 2216, sf=1.4752, sfg=5.7062
At 65.5^oC: hf=274.14

a. 56.3

b. 66.6

c. 58.2

d. 47.9

32. In a cogeneration plant, steam enters the turbine at 4 MPa and 400^oC. One fourth of the steam is extracted from the turbine at 600 kPa pressure for process heating. The remaining steam continues to expand to 10 KPa. The extracted steam is then condensed and mixed with feed water at constant pressure and the mixture is pumped to the boiler pressure of 4 Mpa. The mass flow rate of steam through the boiler is 35 kg/s. Disregarding any pressure drops and heat losses in the piping, and assuming the turbine and pump to be isentropic, how much process heat is required in kW?

Steam properties:

At 4 MPa and 400^oC: h=3213.6 kJ/kg, s=6.7690 kJ/kg-K
At 600 kPa: hf=670.56, hfg=2086.3, sf=1.9312, sfg=4.8288

a. 18255.48

b. 19266.52

c. 20021.35

d. 178113.21

33. A vessel of 0.060 m³ capacity is well insulated and is divided equally by a rigid conducting diaphragm. Initially both halves contain air at pressure of 138.5 kPa and 415.3 kPa and temperature 28^oC and 188^oC, respectively. What is the increase in entropy of the system in kJ/^oC?

a. -0.01887

b. -0.01978

c. -0.01699

d. -0.01578

34. A refrigeration system operates on an ideal vapor-compression using R12 with an evaporator temperature of minus 30^oC and condenser exit temperature of 49^oC and requires 75.5 kW motor to drive the compressor. What is the capacity of the refrigerator in tons of refrigeration? Enthalpy at the condenser entrance=382 kJ/kg, exit=248.15; at the evaporator entrance=248.15, exit=338.14.

a. 5.306

b. 2.0699

c. 3.0678

d. 4.0351

35. What is the total required heating energy in raising the temperature of a given amount of water when the energy applied is 1200 kWh with heat losses of 30%.

a. 1891.3 kW-h

b. 3281.2 kW-h

c. 1613.2 kW-h

d. 1714.3 kW-h

36. Ammonia weighing 25 kgs is confined inside a cylinder equipped with a piston has an initial pressure of 415 kPa at 39^oC. If 3000 kJ of heat is added to the ammonia until its final pressure and temperature 415 kPa and 100^oC, respectively, what is the amount of work done by the fluid in kJ?

a. 645.9 kJ

b. 548.9 kJ

c. 745.9 kJ

d. 447.8 kJ

37. What is the term used to express to express the ratio of specific humidities, actual versus saturated?

a. Relative humidity

b. Absolute humidity

c. Degree of saturation

d. Percent saturation

38. What is the most efficient thermodynamic cycle?

a. Carnot

b. Diesel

c. Rankine

d. Brayton

39. What is a check valve?

a. A valve designed to allow a fluid to pass in one direction only
b. A valve designed to release the excess pressure
c. A valve which allows flow of fluid in either direction
d. A valve used for checking the pressure of fluid

40. A Carnot engine receives 150 Btu of heat from a hot reservoir at 800^oF and rejects 50 Btu of heat, determine the temperature of the cold reservoir, in deg F.

a. 420

b. 40

c. 43

d. -40

41. The maximum thermal efficiency possible for a power cycle operating between 1300oF and 230oF is.

a. 60.8%

b. 55.3%

c. 65.1%

d. 58.2%

42. An ideal gas at 48 psig and 82^oF is heated in a closed container to 140^oF, what is the final pressure.

a. 79.3

b. 82.1

c. 69.4

d. 73.1

43. A Carnot engine requires 38 kJ/sec from the hot source. The engine produces 18 kW of power and the temperature of the sink is 30^oC. What is the temperature of the hot source?

a. 120.3

b. 111.1

c. 100.2

d. 115.7

44. The sun generates 1 kW/m² when used as a solar collectors. A collector with an area of 1m² heat water. The flow rate is 3.5 L/min. What is the temperature rise in the water? Let the specific heat of water is 4.187 kJ/kg-K.

a. 5.32

b. 6.08

c. 4.32

d.4.09

45. Determine the average Cp value in kJ/kg-K of a gas if 540 kJ of heat is necessary to raise the temperature from 320 K to 800 K making the pressure constant.

a. 1.002

b. 1.125

c. 1.321

d. 1.211

46. The thermal efficiency of a particular engine operating on an ideal cycle is 40%.Calculate the heat supplied per 1300 watt-hr of work developed in kJ.

a. 11700

b.12600

c. 11100

d. 11502

47. A large mining company was provided with 3 cubic meters of compressed air tank. Air pressure in the tank drops from 710 kPa to 190 kPa while the temperature remains unchanged at 30 degree C. What percentage has the mass of air in the tank been reduced?

a. 53.7%

b. 63.2%

c. 73.2%

d. 83.2%

48. How much work is necessary to compress air in an insulated cylinder from 0.30 cu m to 0.01 cum. Use T=21 degree C and P₁ = 98 kPa.

a. 200 kJ/kg

b. 213 kJ/kg

c.301 kJ/kg

d. 155 kJ/kg

49. An Otto engine has a clearance volume of 8%. It produces 320 kW of power. What is the amount of energy rejected in kW?

a. 154.3 KW

b. 174.6 kW

c. 182.3 kW

d. 162.3 kW

50. A refrigeration system using R22 has a capacity of 350 kW of refrigeration. The evaporating temperature is minus 10oC and the condensing temperature is 40^oC. Calculate the fraction of vapor in the mixture before the evaporator. Properties of R22 at -10^oC: hg=401.6 kJ/kg, hf=188.426 kJ/kg. At 40^oC: hf=249.6866 kJ/kg

a. 0.2874

b.0.1873

c. 0.3871

d.0.2013

51. In a refrigeration system, the heat absorbed in the evaporator per kg mass of refrigerant passing through is:

a. Equals the increase in enthalpy

b. Does not depend of the refrigerant used

c. Is decreased if pre-cooler is used

d. Equals the increase in volume

52. A gas turbine working on air standard Brayton cycle has air entering the compressor at atmospheric condition and 25^oC. The pressure ratio is 9 and the maximum temperature in the cycle is 1200 deg C. Compute for the cycle efficiency per kg of air in percent.

a. 46.6

b. 40.3

c. 56.3

d. 33.3

53. Ton of refrigeration is heat unit equivalent to:

a. 50.4 kcal/sec

b. 12660 kJ/hr

c. 3413 kWh

d. 2545 Btu/hr

54. A heat engine is operated between temperature limits of 1380 deg C and 250 deg C. Engine supplied with 15145 kJ/kWh. Find the Carnot cycle efficiency in percent.

a. 58.3%

b. 60.3%

c.68.4%

d. 75.3%

55. The amount of sensible heat for a sensible heat ratio of 0.78 and total cooling load of 110 kJ/kg.

a. 80.3

b. 60.6

c. 90.2

d. 85.8

56. 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 deg C. Determine the heat energy supplied per kg of steam supplied in the superheaters. Steam properties are: At 25 bar and 370 deg C: h=3171.8 kJ/kg and At 25 bar and 0.98 dryness: hf=962.11 kJ/kg, hfg=1841.0 kJ/kg.

a. 498.4

b. 305.3

c. 405.5

d. 228.3

57. A closed vessel contains air at pressure of 170 kPa gauge and temperature of 32^oC. The air is heated at constant volume to 65^oC with the atmospheric pressure of 758 mm Hg. What is the final gauge pressure?

a. -101.05

b. 101.05

c. -199.3

d. 199.3

58. The evaporative condenser of an ammonia refrigeration plant has a water flow rate of 130 kg/sec and enters a natural draft cooling tower at 40^oC. The water is cooled to 29^oC by entering at 38^oC db and 24^oC wb. The air leaves the tower as saturated at 40oC db. Calculate the make up water required in kgs per hour. Water properties: At 40^oC: hf=167.48 kJ/kg and At 29^oC, hg=121.43 kJ/kg. Air properties: At 38^oC db and 24^oC wb: h=72.5 kJ/kg, SH=0.013 kgv/kga and At 40^oC db saturated: h=166 kJ/kg, SH=0.0488 kgv/kga.

a. 8251.8

b. 8053.2

c. 7039.1

d. 8591.3

59. An air standard engine has a compression ratio of 22 and a cut-off ratio of 6. If the intake air pressure and temperature are 98 kPa and 28^oC, calculate the work in kJ/kg.

a. 2069.3

b. 2669.2

c. 3066.1

d. 3668.1

60. What is the temperature in degree C of 2 liters of water at 27^oC after 480 calories of heat have been added to?

a. 30.3

b. 27.2

c.37.1

d. 40.2

61. In an open feed water heater for a steam power plant, saturated steam at 7 bar is mixed with subcooled liquid at 7 bar and 25 deg C. Just enough steam supplied to ensure that the mixed steam leaving the heater will be saturated liquid at 7 bar when heater efficiency is 95%. Calculate the mass flow rate of subcooled liquid if steam flow rate is 0.870 kg/s. Steam properties: At 7 bar, saturated vapor: hg=2763.5 kJ/kg. At 7 bar and 25 degree C: hf=105.5 kJ/kg. At 7 bar, saturated liquid: hf=697.22 kJ/kg.

a. 1.886

b. 3.881

c. 2.886

d. 4.001

62. A volume of 460 cc of air is measured at a pressure of 743 mm Hg absolute and a temperature of 25^oC. What is the volume in cc at 760 mm Hg absolute and 0^oC?

a. 300.1

b. 259.3

c. 405.3

d. 411.9

63. What should be the temperature of both the water and steam whenever they are present together?

a. Saturation temperature for the existing pressure 

b. Boiling point of water at 101.325 kPa

c. Superheated temperature

d. One hundred degree C

64. What is the function of steam separators?

a. Trapping the steam and letting water through 

b. Throttling

c. Changing direction of the steam flow

d. Steam metering

65. A manometer is an instrument used to measure:

a. Air pressure

b. heat radiation

c. Condensate water level

d. Air volume

66. The relationship of water vapor in the air at the dew point temperature to the amount that would be in the air if the air were saturated at the dry-bulb temperature is:

a. Partial pressure actual at dew point 

b. Percentage humidity

c. Relative humidity

d. Partial pressure of water

67. The law that states entropy of all perfect crystalline solids is zero at absolute zero temperature.

a. Newtons Law 

b. Third law of thermodynamics

c. Second Law of thermodynamics

d. First Law of thermodynamics

68. Reversed Carnot refrigeration used to produce ice at 0^oC, water is available at 310 K, brine mixture is -15oC, determine the coefficient of performance.

a. 3.3

b. 2.9

c. 5.8

d. 4.9

69. The relative humidity becomes 100% and where the water vapor starts to condense

a. Critical point

b. Saturated point

c. Dew point

d. Cloud point

70. A 30 kg iron was put in a container with water. The water is at 10^oC and the iron has an initial temperature of 450 K, until the iron was in thermal equilibrium with water. Find the change in entropy (Cp for iron = 0.42 kJ/kg-K)

a. 5.84

b. 6.84

c. -5.84

d. -6.84

71. Determine the bypass factor of an air heating coil if the mean coil temperature is 120^oF and it heats air from 65^oF to 95^oF

a. 0.2525

b. 0.4545

c. 0.3532

d. 0.6431

72. When hot sopu was served in a cup during a dinner, an engineer was so eager to drink it. Since it was hot, he added cube of ice to cool the soup and stirred it. He noticed that moisture starts to form on the outermost surface oc the cup. He wanted to chech the temperature of the outermost surface of the cup. What is the temperature equal to?

a. Superheated temperature

b. Zero

c. Standard temperature

d. Dew point temperature

73. In a Rankine cycle, steam enters the turbine at 2.5 MPa and 250^oC (enthalpies and entropies given) and the condenser pressure of 50 kPa (properties given). What is the thermal efficiency of the cycle? At 2.5 Mpa and 250oC: h₁=2880.1 kJ/kg, s₁=6.4085 kJ/kg-K and at 50 kPa: h_f=340.49, h_g=2645.9, s_f=1.0910, s_fg=6.5029, s_g=7.5939, v_f=0.00103

a. 25.7%

b. 20.1%

c. 32.5%

d. 20.1%

74. A 4m x 4m x 4m room has a relative humidity of 85%. The pressure in the room is 110 kPa and temperature is 38oC (P=5.628 kPa). What is the mass of vapor in the room? (Rv=0.4615 kPa-m3/kg-K)

a. 2.133

b. 1.133

c. 2.991

d. 3.218

75. The process in which heat is transferred to a thermal energy storage device is known as

a. Adiabatic

b. regeneration

c. intercooling

d. isentropic

76. A simultaneous generation of electricity and steam (or heat) in a single power plant

a. Gas turbine

b. Steam turbine – gas turbine plant

c. waste heat recovery

d. cogeneration

77. At atmospheric pressure of 750 mm of mercury at sea level with temperature of 23^oC, what is the specific weight of air?

a. 1.97 kN/m³ 

b. 1.18kN/m³

c. 1.00 kN/m³

d. 2.09 kN/m³

78. What is meant by brake horsepower?

a. Power developed by the engine cylinder 

b. Final horsepower delivered to the equipment

c. Actual horsepower delivered to the engine shaft

d. Work required to raise weight of 33000 lbs at 1-foot height in one minute time.

79. The pressure and temperature entering the turbine are 1800 kPa and 380^oC. The pressure leaving the turbine is 20 kPa. The quality of steam entering the condenser is 85%. What is the turbine work? Steam properties: At 1800 kPa and 380^oC: h=3207.2kJ/kg. At 20 kPa: hf=251.40, hg=2609.7

a. 900.2 kJ/kg

b. 951.2 kJ/kg

c. 1000.8 kJ/kg

d. 869.1 kJ/kg

80. In Sterling and Erickson cycle, regeneration can

a. hinder efficiency

b. decrease efficiency

c. increase efficiency

d. limit efficiency

81. The engineer was tested to design the air-conditioning system for a ballroom dance hall. Considering that this involve a lot of activity from its users. The engineer would design that it will require ______.

a. Maximum attainable effective temperature 

b. Higher effective temperature

c. Constant effective temperature

d. Lower

82. The ratio of compressor work to the turbine work of gas turbine is called

a. Compression ratio

b. Back work ratio

c. Cut-off ratio

d. Pressure ratio

83. The ideal cycle based on the concept that the combustion process is both diesel and gasoline in the combination of heat transfer process that is constant pressure and constant volume

a. Ericsson cycle

b. Dual cycle

c. Brayton cycle

d. Rankine cycle

84. An engine operates on the air standard Otto cycle. The cycle work is 910 kJ/kg. The maximum cycle temperature is 3000^oC and the temperature at the end of isentropic compression is 620^oC.Determine the engines compression ratio.

a. 5.5

b. 8.4

c. 6.7

d. 4.3

85. R22 is

a. Dichlorodiflouromethane

b. Monochlorodiflouromethane

c. Methyl chloride

d. Trichlorodiflouromethane

86. A Diesel engine is operating on a 4-stroke cycle, has a heat rate of 11310.1 kJ/kW-hr brake. The compression ratio is 14, the cut-off ratio is 2.5, and using k=1.33, calculate the brake engine efficiency.

a. 63.7%

b. 53.8%

c. 40.5%

d. 71.2%

87. Heat absorbed by a liquid in changing it to gas

a. Heat of fusion

b. Heat of vaporization

c. Calorie

d. Heat of conduction

88. A steam condenser receives 12 kg/s of steam with an enthalpy of 2580 kJ/kg. Steam condenses into a liquid and leaves with an enthalpy of 180 kJ/kg. Cooling water passes through the condenser with temperature increase from12^oC to 25^oC. Determine the water flow rate in kg/s.

a. 500

b. 629

c. 529

d. 459

89. Number of molecules in a mole of any substance is a constant called:

a. Rankine cycle

b. Avogadro’s number

c. Otto cycle

d. Thompson constant

90. An adiabatic feed pump in a steam cycle delivers water to a steam generator at a temperature of 200^oC and a pressure of 10 MPa. The water enters the pump as a saturated liquid at 180^oC. If the power supplied to the pump is 80 kW, determine the mass flow rate. Steam properties: At 180^oC: hf=763.33 kJ/kg, vf=0.0011274 m³/kg, Psat=1.0021 MPa.

a. 7.89

b.8.88

c. 6.53

d. 9.11

91. What is the unit of electromagnetic wave frequency

a. Volts

b. Horsepower

c. Hertz

d. Knot

92. Which of the following materials is suitable for tubing in refrigeration application where refrigerant ammonia is employed?

a. Plastic

b. Brass

c. Steel

d. Copper

93. When the number of reheat stages in reheat cycle is increased, the average temperature

a. Increases

b. Decreases

c. Zero

d. Constant

94. During sensible heating, the absolute humidity remains constant but the relative humidity

a. Increases

b. Decreases

c. Zero

d. Constant

95. Recirculated air of 9 kg/sec with 55 kJ/kg enthalpy and outside air of 3 kg/s with 92 kJ/kg enthalpy enters the conditioning unit. Determine the air conditioning capacity of supply enthalpy to conditioned space is 45 kJ/kg.

a. 200

b. 255

c. 231

d. 210

96. Outside air of an air conditioning system is 30% of recirculated air. Determine the mass of outside air if mass of supply air is 16 kg/s.

a. 3.0

b. 3.7

c. 4.1

d. 5.1

97. At 30^oC, air-vapor mixture has a relative humidity of 75%. Find the humidity ratio if barometric pressure is 100kPa. At 30^oC, Psat=4.245 kPa.

a. 0.02045

b. 0.01053

c. 0.02111

d. 0.02981

98. The humidity ratio of air is 0.048. If barometric pressure is 100 kPa, calculate the partial pressure of water vapor.

a. 6.21

b. 7.16

c. 8.32

d. 9.31

99. Air at 36^oC and pressure of 100 kPa has a density of 1.10 kg/m³. Find the humidity ratio of air.

a. 0.0215

b. 0.0299

c. 0.01561

d. 0.03145

100. What is the enthalpy of the air-vapor mixture at 65% RH and 35^oC when the barometric pressure is 102 kPa? At 35^oC: Psat=5.628 kPa, hg=2565.3

a. 90.33

b. 84.31

c. 74.99

d. 94.57

Answer Key (Handwritten)