Refrigeration and Air-conditioning: Assignment 2

1 point

1. In Bootstrap air refrigeration system

 The expansion of air takes place in two stages

 

The ambient air temperature is reduced by expansion for the cooling purpose

 The pressure of air is increased with a secondary Compressor

 The air from evaporator cools the air coming from condenser through a heat exchanger

Ans: c

1 point

2. In a vapor compression cycle the refrigerant immediately after expansion valve is

 Liquid

 Sub-cooled liquid

 Saturated liquid

 Subcooled liquid or wet vapor

Ans: d

1 point

3. A refrigerator working on Bell-Coleman cycle operates between pressure limits of 1.05 bar and 8.5 bar. Air is drawn from the cold chamber at 10°C. Air coming out of compressor is cooled to 30°C before entering the expansion cylinder. The expansion and compression follow the law of = constant. Heat extracted from the cold chamber per kg of air

 150.41 KJ/kg

 107.25 KJ/kg

 115.53 KJ/kg

 96.36 KJ/kg

Ans: b

1 point

4. The function of a ...... is to remove the vapour from the evaporator and to raise its temperature and

pressure to a point such that it (vapour) can be condensed with normally available condensing media.

 Evaporator

 Expansion valve

 Compressor

 Condenser

Ans: c

1 point

5. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P

 

More

 Less

 Equally

 Unpredictable

Ans: a

1 point

6. With reciprocating compressor in vapour compression refrigeration system, wet compression is not desirable because

 liquid trapped up in the head of cylinder may damage the compressor valves

 COP of the cycle decreases

 volumetric efficiency of compressor decreases

 mass flow rate per ton of refrigerant increases

Ans: b

1 point

7. In a vapor compression refrigeration plant, the refrigerant leaves the evaporator at 195 KJ/kg and the condenser at 65 KJ/kg. For every kg of refrigerant, the plant can supply per second, a cooling load of

 70 KW

 100 KW

 130 KW

 160 KW

Ans: b

1 point

Read the following and answer question 8-10.

8. In an ideal vapor compression refrigeration cycle, the specific enthalpy of refrigerant (in KJ/kg) at the following states is given as:

 

Inlet of condenser: 312

Exit of condenser: 124
Exit of evaporator: 268

8. The COP of this cycle is

 2.27

 2.75

 3.27

 3.75

Ans: c

1 point

9. Heat rejected from the refrigerant and absorbed by the refrigerant are (in KJ/kg)

 188 & 51

 188 & 144

 144 & 188

 51 & 144

Ans: b

1 point

10. Refrigeration effect in ton of refrigeration if the mass flow rate of refrigerant in the cycle is 0.2 kg/s

 6.8

 9.4

 7.4

 8.2

Ans: d