VAPOR ABSORPTION REFRIGERATION QUESTIONS ANSWERS

VAPOR ABSORPTION REFRIGERATION

 QUESTIONS ANSWERS

 

Vapor absorption system can operate

without the use of electricity. The heat

energy operates the system. Obtain heat

 by burning of fuel or wood & solar

energy. Use of solar energy makes it

eco-friendly. It resembles very much with a

vapor compression system. It uses

different means of compression. As

an absorbent absorbs refrigerant vapors,

700 cc of vapor becomes 1 cc of

liquid. Vapor absorption refrigeration is a

simple method. It is an economical

method for producing refrigeration.

1. What is the principle of operation of vapor absorption system?

There are many combinations of refrigerant and absorbents. The most common refrigerant-absorbent combinations are ammonia and water & water and lithium bromide . Their boiling points differ greatly. The affinity high  for each other. A small amount of absorbent can absorb large quantity of the refrigerant. On absorption, the heats released are latent heat of vaporization and the heat of mixing.  Their boiling points are widely different. Refrigerant separates easily from the mixture.

2. Name the various types of vapor absorption refrigeration systems.

Mainly two types

•  Ammonia – water system–most popular- Ammonia is refrigerant and water is Absorbent.

•  Water and lithium bromide system- Water is refrigerant and lithium bromide is absorbent

  3. What are the main components of a vapor absorption unit?

  

• Figure : Line Diagram of a Vapor Absorption Refrigeration Cycle 

1. 1. Condenser

   2. Receiver

   3. Expansion valve

   4. Evaporator

   5. Absorber

   6. Aqua pump

   7. Aqua heat exchanger

   8. Generator

   9. Analyzer

   10. Rectifier

   11. Heat source

   12. Cooling arrangement in condenser

   13. Arrangement of cooling in absorber

   14. Cooling  in rectifier

   15. Second expansion valve

4. Give two examples of commonly used refrigerant-absorbent combinations.

Refrigerant                  Absorbent                  Practical Application

  Ammonia                   water                                         Used in industry

Water                           lithium bromide                       Used in Air Conditioning

5. Name the gases used in vapor absorption refrigeration system.

•  Small unit( Electrolux refrigerators) use ammonia and hydrogen gases.

•  Large cooling plants use  only ammonia gas.

       6.Why is ammonia water system common?

1.  Ammonia and water are cheap & easily available in abundance.

2. Ammonia has a very large latent heat and small amount produces large cooling effect.

3. Water and ammonia are cheap.

4. Small amount of water can absorb large quantity of ammonia.

5. Water boiling point is 100⁰ C. The boiling point of ammonia is –33.5⁰ C.  These differs by a huge value.  Ammonia separates from water on heating. There are remote chances of water going with ammonia.

7. Name the gas which reduces the pressure of ammonia in the evaporator. What increases the rate of evaporation in the evaporator of the Electrolux system?

 Hydrogen gas decreases the pressure in the evaporator. Pressure reduction is nearly 9/10 of the total pressure in the evaporator.

8. Purpose of water in the ammonia absorption system.

Water has high affinity for ammonia. It absorbs large amount of vapors. It reduces the pressure in the evaporator. This increases the rate of evaporation.  The cooling effect increases.

9. Which energy does vapor absorption system uses?

It is cheapest and easily available heat energy which operates the vapor absorption refrigeration system.

10. Piping material of vapor absorption system?

Use steel pipes. Ammonia is highly corrosive to copper pipes.

11. How is temperature and pressure rise in the vapor absorption system?

The pump and the generator does it in large cooling plants.  The generator does it in the Electrolux system.

12. Where does  ammonia separate from water?

It is the generator and in the rectifier.

13. In which part water absorbs ammonia?

It is in the absorber.

14. Under what conditions, an absorption machine give less cooling effect?

1. If heating in the generator is not proper.

2. Insufficient cooling in the condenser.

3.  Cooling in the absorber is insufficient.

4. Cooling cabinet has leakage.

5. Refrigerant is in less quantity.

6. Condenser and evaporator coils are dirty

15. Numerate the practical applications of vapor refrigeration system.

• On a small scale, there is Electrolux refrigerator

• Used in plants having high cooling requirements

Q. An ideal vapor absorption refrigeration system is a combined system of Carnot heat engine and Carnot refrigerator. Prove this statement.

There are three temperatures in an ideal vapor absorption system. These are

(i) Generator temperature

(ii) Condenser temperature (ambient temperature)

(iii) Absorber temperature (Ambient temperature)]

(iv) Evaporator temperature

HEAT ENGINE

 Supply heat in the generator. Condenser loses the heat to low temperature ambient air. Hence it becomes an heat engine.

Carnot refrigerator

Evaporation in the evaporator causes cooling. Boiler heating does the compressor function. Condenser loses the heat. Therefore, it becomes a Carnot refrigerator.

Enumerate distinctions between the vapor compression and vapor absorption refrigeration system.

Differences between Vapor Compression and Vapor Absorption Refrigeration

Sr. No.	Item	Vapor Compression	Vapor Absorption
1.	Low tons of cooling	Cheap	Costly
2.	50 Tons of Refrigeration	Same cost	Same cost
3.	> 50 Tons	Costly	Cheap
4.	Eco friendly	no,  uses Freon’s	yes as no GWP and no ODP
5.	A single unit capacity	200 TR	7000 TR or even Higher
6.	Effect of decrease of evaporator temp	Ton of refrigeration decreases	TR can be same  by controlling the heating rate in the generator
7.	Equipment	Compressor	Absorber, pump, Heat Exchanger, Generator, Analyzer, rectifier and second expansion Valve replaces a Single compressor
8.	Liquid from evaporator	Will break mechanically the compressor	No bad effect
9.	COP	High	Low
10.	Type of energy used	High grade  electrical energy	Low grade heat energy
11.	Pipe material	Copper pipe	Steel pipe
12.	Moving parts	Compressor with wear, tear & noise	Moving part is only aqua pump. Therefore less noise, wear and tear.
13.	Servicing requirement	yes	Almost nil
14.	Space requirements	Compact requires less space	Requires more space
15	Noisy	Noisy	Quiet

7. Why is a refrigerator working on vapor absorption system has limited use?

1. Its COP is less.

2. Layout of the refrigeration cycle is complex.

3. It uses three fluids. In the event of leakage, it is difficult to know which gas has leaked.  In what proportion has it  leaked.

4. It is slow in producing certain amount of cooling.

5. Charging of hydrogen and ammonia is difficult & cumbersome.

https://www.mesubjects.net/wp-admin/post.php?post=4188&action=edit         MCQ Vapor Absorption refrigeration

https://www.mesubjects.net/wp-admin/post.php?post=940&action=edit                Absorption refrigeration