Review Course Final Exam – PM

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41. Calculate the latent load in cooling 27,250 cfm of air with humidity ratios of 136 and 57.

42. Calculate the total heat rejected by a 15000 cfm cooling tower operating at an outdoor air temperature of 90°Fdb/80°Fwb (enthalpy = 139.1 gr/lb), return condenser water of 105°F, and a supply condenser water of 87°F. The air leaving the cooling tower is saturated at 97°F (enthalpy = 273.2 gr/lb).

43. Calculate the amount of makeup water required for a cooling tower due to evaporation. The flow rate of water is 200 gpm, the humidity ratio of the air entering the cooling tower is 0.009 lb/lb, and the humidity ration of the air leaving the cooling tower is 0.054 lb/lb.

44. A 1,920,000 Btuh steam boiler is capable of providing __________ lbs/hr of steam.

45. An existing 1100 rpm, 5 hp fan rated for 4.5”wg static pressure is to be used in a new application with a static pressure of 6.75”wg. Calculate the new required horsepower?

46. Calculate the heat transfer rate required in a heat exchanger to heat 100 gpm of water from 165°F to 200°F. The heat transfer coefficient for the heat exchanger is 115 Btu/hr-ft2-°F and the specific heat of water is 1 Btu/lbm-°F.

47. Calculate the log mean temperature difference (LMTD) for the heat exchanger in question 46. The entering hot fluid temperature is 250°F and the leaving hot fluid temperature is 210°F. The heat exchanger is parallel flow.

48. Calculate the heat exchange surface area for the heat exchanger in question 46.

49. Calculate the static pressure loss in a 12” diameter duct carrying 680 cfm?

50. Calculate the flow rate for an existing pump with an 8” impeller and a flow rate of 500 gpm that is retrofitted with a new 9” impeller.

51. A 500 gpm centrifugal pump’s speed is increased from 1100 rpm to 1750 rpm without changing any other parameters. What water flow is the pump now capable of delivering?

52. Calculate the sensible load in cooling 27,250 cfm of air from 95°F to 55°F.

53. Calculate the total load in cooling 27,250 cfm of air from 95°F to 55°F with enthalpies of 46.9 Btu/lb and 22.7 Btu/lb

54. Electronic temperature sensors are classified as: I. Resistance Temperature Devices (RTD), II. Thermostats, III, Thermistors, IV. Thermocouples

55. __________ are temperature sensitive semiconductors that exhibit a large change in resistance over a relatively small range of temperature.

56. In a simple thermodynamic refrigerant cycle, what is the state of the refrigerant between the evaporator and the compressor?

57. Refrigerant enters a refrigerator compressor at 22.39 psi, 16°F, and at a rate of 9.5 ft3/min. The refrigerant exits the compressor at 143.8 psi. The compressor efficiency is 72%, the specific volume of the refrigerant at the compressor suction is 2.29 ft3/lb, the enthalpy of the refrigerant at the compressor suction is 76.32 Btu/lb, and the enthalpy of the refrigerant at the compressor discharge is 91.75 Btu/lb. Calculate the mass flow rate of refrigerant thru the compressor.

57. What is the heat removal rate of the refrigeration system in question 57?

59. Determine the mass flow rate of air for 50,000 cfm of air being conditioned from 105°F/50%RH down to 52°F/100%RH. Assume the density of air (ρ) = 0.0749 lb/ft3

60. An existing supply air fan is required to move an additional 2,000 cfm. Determine the increase in fan speed (RPM) needed to move the additional air. The fan is currently operating at 1,000 rpm and is delivering 8,500 cfm.

61. What hp motor is required to operate a fan delivering 12000 cfm at a velocity of 50 ft/s? Fan heat is 5°F. Neglect frictional and motor drive losses. Air density = 0.075 lbm/ft3

62. How much steam is required to humidify 1,000 cfm of air if the required grains per ft3 = 0.50?

63. Calculate the discharge velocity of a 2” pipe with water traveling at 6 ft/sec and 60 psi pressure. Assume no change in elevation. Water density = 1.94 slugs/ft3, atmospheric pressure = 14.696 psi.

64. Calculate the volumetric flow rate of water flowing through a 4” diameter pipe at 11.3 fpm. The hydraulic diameter of 4” pipe is 4.03”.

65. Calculate Reynold’s number for the pipe in question 64. Kinematic viscosity = 0.000011ft2/sec

66. The flow in the pipe in question 64 is __________.

For questions 67 thru 69, use the following schematic and T-S Diagram for an ideal refrigeration cycle using R-134a operating between 21.29 psi and 123.35 psi. The mass flow rate of the refrigerant is 0.17 lbs/sec.

At 21.29 psi, hf = 12.2 Btu/lb, hfg = 94.7 Btu/lb, and hg = 106.1 Btu/lb

At 123.35 psi, hf = 45.9 Btu/lb, hfg = 76.0 Btu/lb, and hg = 121.5 Btu/lb

67. What is the power input to the compressor?

68. What is the rate of heat removal from the space?

69. What is the rate of heat rejection to the environment?

70. The situation where liquid refrigerant enters the compressor through the suction line is known as liquid __________.

71. Calculate the required counterflow heat exchanger area if the hot side fluid is water entering at 235°F and leaving at 185°F, the cold side fluid is water entering at 115°F and leaving at 160°F, and the heat transfer coefficient is 100 Btu/hr-ft2-°F. Heating load = 1,000,000 Btuh.

72. A 70% efficient heat recovery wheel is capable of recovering __________ Btuh sensible heat when the exhaust air temperature is 78°F, the outdoor air temperature is 90°F, and the airflow is 18,500 cfm (exhaust and makeup air).

73. What amount of steam is required for a heating load of 3,395,000 Btuh?

74. What size boiler would be required to provide the steam in question 73?

75. Calculate the Net Positive Suction Head for a pump located 120 feet below a roof-mounted, atmospheric tank. The piping losses between the holding tank and the pump inlet are 19.95 psi. Atmospheric pressure is 14.696 psi, the specific weight of water is 62.17 lb/ft3, and the vapor pressure of water is 0.5947 psi.

76. Interior spaces intended to be occupied by humans are to have active or passive heating systems that can maintain a minimum indoor temperature of _______ at 3 feet above the floor on the design heating day.

77. A 2” copper pipe routed 175 feet horizontally would require how many pipe supports?

78. What is the code mandated, minimum distance a cooling tower discharge plume be from a ventilation inlet to a building?

79. Calculate the spring constant for a spring loaded with 37 lbs. that stretches 12.25 inches.

80. The mass of a wall would have to be increased by a factor of _____ to increase its Sound Transmission Class (STC) from 10 dB to 20 dB.


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