Vapour Compression Systems, Refrigerants - MCQ Test 1


20 Questions MCQ Test Mock Test Series - Mechanical Engineering (ME) for GATE 2020 | Vapour Compression Systems, Refrigerants - MCQ Test 1


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This mock test of Vapour Compression Systems, Refrigerants - MCQ Test 1 for Mechanical Engineering helps you for every Mechanical Engineering entrance exam. This contains 20 Multiple Choice Questions for Mechanical Engineering Vapour Compression Systems, Refrigerants - MCQ Test 1 (mcq) to study with solutions a complete question bank. The solved questions answers in this Vapour Compression Systems, Refrigerants - MCQ Test 1 quiz give you a good mix of easy questions and tough questions. Mechanical Engineering students definitely take this Vapour Compression Systems, Refrigerants - MCQ Test 1 exercise for a better result in the exam. You can find other Vapour Compression Systems, Refrigerants - MCQ Test 1 extra questions, long questions & short questions for Mechanical Engineering on EduRev as well by searching above.
QUESTION: 1

The refrigerating efficiency of the plant is 0·8. What is the power required per kW of cooling to be produced? 

Solution:

h3 = h4 

Refrigerating effect (Qo)

 = (h1 – h4) ×  ɳ r

 = (350 – 225) × 0.8  
  = 100 kJ/kg  

Compressor work (W)  

= (h2 – h1)    

= 375 – 350  
  = 25 kJ/kg

The power required per kW of cooling  

QUESTION: 2

Consider the following statements regarding refrigerants: 

1. Refrigerant NH3 is used in reciprocating compressors.

2. Refrigerant CO2 is used in reciprocating compressors.

3. Refrigerant R-11 is used in centrifugal compressors.  

Which of these statements are correct?

Solution:
QUESTION: 3

For simple vapour compression cycle, enthalpy at suction = 1600 kJ/kg, enthalpy at discharge from the compressor = 1800 kJ/kg, enthalpy at exit from condenser = 600 kJ/kg.

What is the COP for this refrigeration cycle?

Solution:

COP of refrigeration cycle 

QUESTION: 4

Which one of the following is correct?

Environmental protection agencies advise against the use of chlorofluorocarbon refrigerants because these react with 

Solution:
QUESTION: 5

In a vapour compression refrigeration plant, the refrigerant leaves the evaporator at 195 kJ/kg and the condenser at 65 kJ/kg. For 1 kg/s of refrigerant, what is the refrigeration effect?

Solution:

QUESTION: 6

A standard vapour compression refrigeration cycle consists of the following 4 thermodynamic processes in sequence:

Solution:
QUESTION: 7

The enthalpies at the beginning of compression, at the end of compression and at the end of condensation are respectively 185 kJ/kg, 210 kJ/kg and 85 kJ/kg. The COP of the vapour compression refrigeration system is

Solution:
QUESTION: 8

The correct sequence of the given components of a vapour compression refrigerator is:

Solution:
QUESTION: 9

In conventional refrigerants what is the element responsible for ozone depletion?

Solution:

Ozone Depletion Potential (ODP): According to the Montreal protocol, the ODP of refrigerants should be zero, i.e., they should be non-ozone depleting substances. Refrigerants having non-zero ODP have either already been phased-out (e.g. R 11, R 12) or will be phased-out in near-future(e.g. R22). Since ODP depends mainly on the presence of chlorine or bromine in the molecules, refrigerants having either chlorine (i.e., CFCs and HCFCs) or bromine cannot be used under the new regulations.

QUESTION: 10

Consider the following statements:

1. Practically all common refrigerants have approximately the same COP and power requirement.

2. Ammonia mixes freely with lubricating oil and this helps lubrication of compressors.

3. Dielectric strength of refrigerants is an important property in hermetically sealed compressor units.

4. Leakage of ammonia can be detected by' halide torch method.  Of these statements:  

Solution:

Practically all refrigerants, except CO2 have fairly same COP and power requirements. Thus statement (a) is correct. Ammonia does not mix freely with lubricating oil. Therefore statement (b) is wrong. Dielectric strength of refrigerants is an important property in hermetically sealed compressor units. Leakage of ammonia is detected by its odour or sulphur candle with which ammonia forms white smoke like fumes. Thus statements 1 and 4 are correct and choice (d) is the right choice. 

QUESTION: 11

Match List-I with List-II and select the correct answer

Solution:
QUESTION: 12

Consider the following statements:  In the case of a vapour compression machine, if the condensing temperature of the refrigerant is closer to the critical temperature, then there will be:  

1.Excessive power consumption  

2.High compres sion

3.Large volume flow  

Of these statements:  

Solution:
QUESTION: 13

Assertion (A): In vapour compression refrigeration system throttle valve is used and not expansion cylinder.

Reason (R): Throttling is a constant enthalpy process. 

Solution:

A and R are true. But R is not right reasoning for A.  In vapour compression refrigeration system throttle valve is used and not expansion cylinder because the power produced by expansion cylinder is very low.  

QUESTION: 14

Sub-cooling with regenerative heat exchanger is used in a refrigeration cycle. The enthalpies at condenser outlet and evaporator outlet are 78 and 182 kJ/kg respectively. The enthalpy at outlet of isentropic compressor is 230 kJ/kg and enthalpy of subcooled liquid is 68 kJ/kg. The COP of the cycle is:

Solution:
QUESTION: 15

Assertion ( A): I n a practical vapour compression refrigerator, the vapour should leave the evaporator with a definite amount of superheat.

Reason (R): It reduces the work done by the compressor. 

Solution:
QUESTION: 16

Selection of a refrigerant for a vapour – compression system depends on which among the following?

Solution:
QUESTION: 17

Oil separator is NOT required in refrigeration system if:  

Solution:
QUESTION: 18

Consider the following statements:

Moisture should be removed from refrigerants to avoid 

1. Compressor seal failure

2. Freezing at the expansion valve  

3. Restriction to refrigerant flow

4. Corrosion of steel parts 

Of these statements: 

Solution:

All the statements about effect of moisture on refrigerant are correct. 

QUESTION: 19

Consider the following statements:

1.The work of compressor in vapour compression refrigeration system  increases with superheat of the suction vapour.  2.The work of compressor depends on the pressure difference rather than  the temperature difference of evaporator and condenser.  3.The coefficient of performance is within the range of 3 to 6 except at very  low temperature when it may be less than 1.  

Which of the statements given above are correct? 

Solution:
QUESTION: 20

In a vapour compression cycle, the refrigerant, immediately after expansion value is:

Solution:

In P-h diagram it is point 4' or 4 both are very wet vapour. 

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