Mechanical Engineering Review Online

1. Determine the enthalpy of air with wet bulb temperature of 28^oC and dry bulb temperature of 33^oC using psychrometric chart.

a. 80

b. 90

c. 85

d. 95

2. Find the enthalpy of air with wet bulb temperature of 25^oC and 80% RH using psychrometric chart.

a. 56

b. 40

c. 66

d. 75

3. Find the dew point temperature of air with dry-bulb temperature of 300 K and RH of 60% using psychrometric chart.

a. 18

b. 16

c. 15

d. 10

4. Find the humidity ratio of air with enthalpy of 50 kJ/kg and RH of 80%. Using psychrometric chart.

a. 0.018

b. 0.020

c. 0.0012

d. 0.012

5. At 32^oC air vapor mixture has a relative humidity of 70%. Find the humidity ratio if the atmospheric pressure is 101 kPa. At 32^oC, P_sat = 4.759 kPa.

a. 0.02122

b. 0.0313

c. 0.0288

d. 0.0312

6. The humidity ratio of air is 0.06. If the barometric pressure is 98 kPa, find the partial pressure of water vapor.

a. 8.6 kPa

b. 7.6 kPa

c. 6.7 kPa

d. 10.8 kPa

7. Air at 32^oC and pressure of 100 kPa has a density of 1.10 kg/m³. Find the humidity ratio of air.

a. 0.0458

b. 0.0478

c. 0.0326

d. 0.00326

8. What is the enthalpy of air-vapor mixture at 75% RH and 34^oC when the barometric pressure is 100 kPa. At 34^oC: Psat = 5.324 kPa, hg = 2563.5 kJ/kg.

a. 89

b. 85

c. 75

d. 100

9. Air-vapor mixture has an enthalpy of 75 kJ/kg at 32^oC. Find the partial pressure of water vapor. At 30^oC: hg = 2556.3 kJ/kg.

a. 2.89

b. 2.78

c. 2.56

d. 2.05

10. Air enters an air-conditioning system at 68% RH with 0.026 specific humidity and leaves at 24^oC db and 17^oC wb. Determine the refrigerating capacity in tons of refrigeration if the mass of air is 12 kg/s. (At 68%RH and 0.026, h=86 kJ/kg, v=0.815 m³/kg. At td=24^oC and tw=17^oC, h=44 kJ/kg).

a. 133.3

b. 123.5

c. 153.4

d. 143.3

11. The initial condition of a 130 kW air conditioner is 42^oC db and 63% relative humidity and exits at 23^oC db and 25% RH. Determine the volume of air entering the system. (At 42^oC and 63%RH, h=113 kJ/kg, SH=0.0125)

a. 1.2

b. 2.2

c. 1.8

d. 1.6

12. 28 kg of air enters a dryer at 25^oC db and 38% RH. If 18 kg of re-circulated air from the dryer has a partial pressure of water vapor of 11 kPa, determine the humidity ratio after mixing. (At 25^oC and 38%RH, SH=0.006)

a. 0.044

b. 0.033

c. 0.023

d. 0.043

13. 60 kg of air with an enthalpy of 78 kJ/kg is mixed with another air x until the mixture is 116 kg and an enthalpy of 72 kJ/kg. Determine the enthalpy of air x before mixing.

a. 60.5

b. 65.5

c. 68.3

d. 84.9

14. A 5 x 6 x 5 room has a pressure of 100 kPa and temperature of 32^oC (Psat = 5.6 kPa), the relative humidity is 68%. Determine the mass of vapor. Take R_V = 0.422 kJ/kg-K.

a. 5.5

b. 4.4

c. 3.3

d. 6.6

15. Water enters the cooling tower at 58^oC and leaves at 32^oC when the heat rejected to air is 125 kW. Determine the capacity of the pump required, in Liters per second for the cooling tower.

a. 1.89

b. 1.66

c. 1.44

d. 1.14

16. A 120 BHP diesel engine has a brake thermal efficiency of 32% and a jacket water loss of 33%. A cooling tower is used to cool the engine with a range of 28^oC. Determine the mass of water leaving the tower, in kg/hr.

a. 3855.8

b. 2834.8

c. 2859.8

d. 2899.3

17. A 100 tons of refrigeration has a COP of 6 is installed with a cooling tower. Air enters the tower at 24^oC db and 52% RH, it leaves at 37^oC db and 78% RH. Determine the volume of air required in m³/hr. (At 24^oC and 52%RH, h=51 kJ/kg, v=0.88m³/kg. At 37^oC and 78%RH, h=110 kJ/kg)

a. 6.1

b. 5.3

c. 7.1

d.8.8

18. An evaporative condenser of an ammonia refrigeration system has water flowing at a rate of 105 kg/s and enters a natural draft cooling tower at 45^oC. The water is cooled to 32^oC by air entering at 26.8^oC db and 24^oC wb. The air leaves the tower as 88% RH and 30^oC db. Find the percent of make-up water needed by the tower. (At td=26.8^oC and tw=24^oC, h=73 kJ/kg, SH=0.0177. At 88% RH and 30^oC, h=100 kJ/kg, SH=0.0274)

a. 2.3%

b. 3.8%

c. 1.9%

d. 4.3%

19. A cooling tower cools water at a rate of 28 kg/s from 40^oC to 23^oC. Air enters the tower at 20^oC at a rate of 38 kg/s. Find the temperature of air at the exit of the cooling tower.

a. 62.3

b. 77.8

c. 72.1

d. 65.3

20. An air conditioning system has a sensible heat load of 123 kW and latent heat load of 23 kW. Determine the sensible heat factor.

a. 84.25

b. 95.32

c. 88.16

d. 73.56

21. Determine the dew point temperature of air with a humidity ratio of 0.0153 kg water per kg of dry air.

a. 18

b. 21

c. 25

d. 32

22. A dryer has 18% moisture wet feed and 2.5% moisture of dried product. Determine the moisture removed for every 6 kg of solids in the final product.

a. 1.116

b. 0.954

c. 0.775

d. 0.658

23. An auditorium is to be supplied with 38 m³/s of air at 15oC db. The total heat load is 330 kW and has a sensible heat factor of 0.80. Determine the temperature inside the auditorium, in degrees Celsius, using air at standard pressure.

a. 20.7

b. 31.7

c. 25.3

d. 28.1

24. A certain coil has an inlet temperature of 52oF and outlet 88^oF. If the mean temperature of the coil is 112^oF, determine the bypass factor of the coil.

a. 0.25

b. 0.54

c. 0.35

d. 0.40

25. Determine the sensible heat factor of an air conditioning system with a sensible heat load of 58 kW and latent heat of 18 kW.

a. 66.3%

b. 79.5%

c. 81.3%

d. 76.3%

Answer Key (Handwritten)