Question Set 107

1. Name the Cycles used in refrigeration systems .

Ans : Reversed Carnot Cycle .

Draw the P-V Diagram of Reversed Carnot Cycle .

p-v diagram for reverse carnot cycle

Ans :

2. Why Reversed Carnot Cycle is not possible practically ?

Ans : It is not because adiabatic processes are not possible to obtain due to losses in the pipes condensers, compressors and evaporator.

3. Which Cycle is used in Air – Refrigeration System ?

Ans : Bell – Coleman Cycle

4. In refrigeration system why heat rejected is more than heat absorbed ?

Ans: For cooling purpose it is necessary to reject more heat than the heat absorbed. Mathematically Heat Rejected = Heat absorbed + Work Done .

5. How Defrosting is done in a refrigerator ?

Ans : Defrosting is done by stopping the compressor for a short time.

6. Why Copper is not used in ammonia refrigeration system ? / Which metal is used in the pipelines when the refrigerant is ammonia ?

Ans . In ammonia refrigeration system Steel is used as the pipe line material because ammonia attacks copper.

7. What is the difference between heat pump and refrigerators ?

Ans : Heat pumps gives heat by taking work input on the other hand refrigerator ejects heat by taking heat input.

8. What is basis of Refrigeration System ? (Important mechanical engneerin)

Ans : Second Law of Thermodynamics .

9. Show the Practical Refrigeration Cycle With T-S and P-h diagram with Subcooling and Super Heating .

Ans : Please Follow This Link : T-S and P-h Diagram with Subcooling and Superheating for VC

10. Describe Dry and Wet Compression in Refrigeration System .

Ans : The starting point of compression in the T-S diagram determines the final state of vapor after compression. If the final state of vapor is dry and saturated then the compression is known as wet compression and if the final state of vapor is super heated then it is known as dry compression.

The refrigerant enters as a vapor in compressor from the evaporator. If the vapor draw into the compressor is drier than the initial condition on the same pressure range the vapor becomes superheated.

11. How to improve Refrigerating effect ?

Ans : By applying superheating and subcooling.

12. What is Undercooling or Subccooling is refrigeration system ? How Subcooling or undercooling is done ?

Ans: The COP can be improved by undercooling or pre-cooling. It is the process where the liquid refrigerant is allowed to cool below the saturation temperature. Subcooling is done by circulating greater amount of cooling agent i.e water through the condenser or by using water cooler than natural temperature water.

13. What is advantage of vapor compression refrigeration system ?

Ans: Smaller size for a given refrigeration effect , Higher COP, Lower power consumption, Less Complicated in design and operation.