Refrigeration and air conditioning objective type questions - Set 17

Practice Test: Question Set - 17

1. The unit of thermal diffusivity is
    (A) m/hK
    (B) m/h
    (C) m²/h
    (D) m²/hK

2. The comfort conditions in air conditioning are at (where DBT = Dry bulb temperature, and RH = Relative humidity)
    (A) 25°C DBT and 100% RH
    (B) 20°C DBT and 80% RH
    (C) 22°C DBT and 60% RH
    (D) 25°C DBT and 40% RH

3. The pressure at the outlet of a refrigerant compressor is called
    (A) Suction pressure
    (B) Discharge pressure
    (C) Critical pressure
    (D) Back pressure

4. The bypass factor, in case of sensible cooling of air, is given by (where td₁ = Dry bulb temperature of air entering the cooling coil, td₂ = Dry bulb temperature of air leaving the cooling coil, and td₃ = Dry bulb temperature of the cooling coil)
    (A) (td₁ -td₃)/( td₂ -td₃)
    (B) (td₂ -td₃)/( td₁ -td₃)
    (C) (td₃ -td₁)/( td₂ -td₃)
    (D) (td₃ -td₂)/( td₁ -td₃)

5. The operating temperature of a cold storage is 2°C. The heat leakage from the surrounding is 30 kW for the ambient temperature of 40°C. The actual C.O.P. of refrigeration plant used is one fourth that of ideal plant working between the same temperatures. The power required to drive the plant is
    (A) 1.86 kW
    (B) 3.72 kW
    (C) 7.44 kW
    (D) 18.6 kW

6. In chemical dehumidification process,
    (A) Dew point temperature decreases
    (B) Wet bulb temperature decreases
    (C) Dry bulb temperature increases
    (D) All of these

7. Environmental protection agencies advice against the use of chlorofluorocarbon refrigerants since
    (A) These react with water vapour and cause acid rain
    (B) These react with plants and cause greenhouse effect
    (C) These react with oxygen and cause its depletion
    (D) These react with ozone layer

8. When the lower temperature of a refrigerating machine is fixed, then the coefficient of performance can be improved by
    (A) Operating the machine at higher speeds
    (B) Operating the machine at lower speeds
    (C) Raising the higher temperature
    (D) Lowering the higher temperature

9. The bypass factor of a cooling coil decreases with
    (A) Decrease in fin spacing and increase in number of rows
    (B) Increase in fin spacing and increase in number of rows
    (C) Increase in fin spacing and decrease in number of rows
    (D) Decrease in fin spacing and decrease in number of rows

10. A mixture of dry air and water vapour, when the air has diffused the maximum amount of water vapour into it, is called
    (A) Dry air
    (B) Moist air
    (C) Saturated air
    (D) Specific humidity

11. The total pressure exerted by the mixture of air and water vapour is equal to the sum of pressures which each constituent would exert, if it occupied the same space by itself. This statement is called
    (A) Kinetic theory of gases
    (B) Newton's law of gases
    (C) Dalton's law of partial pressures
    (D) Avogadro's hypothesis

12. The relative humidity lines on a psychrometric chart are
    (A) Vertical and uniformly spaced
    (B) Horizontal and uniformly spaced
    (C) Horizontal and non-uniformly spaced
    (D) Curved lines

13. The C.O.P. of a heat pump working on a reversed Carnot cycle is
    (A) T₁/(T₂ - T₁)
    (B) (T₂ - T₁)/T₁
    (C) (T₁ - T₂)/T₁
    (D) T₂/(T₂ - T₁)

14. A vapour absorption refrigeration system
    (A) Gives noisy operation
    (B) Gives quiet operation
    (C) Requires little power consumption
    (D) Cools below 0°C

15. A refrigerating system operating on reversed Brayton refrigeration cycle is used for maintaining 250 K. If the temperature at the end of constant pressure cooling is 300 K and rise in the temperature of air in the refrigerator is 50 K, then the net work of compression will be (assume air as working substance with Cp = 1 kJ/kg)
    (A) 25 kJ/kg
    (B) 50 kJ/kg
    (C) 100 kJ/kg
    (D) 125 kJ/kg

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