Vapour Absorption refrigeration system || Chapter-3 || RAC || Rgpv Important Theory & Mcq Questions

(Rgpv online exam important questions & answers 2020 )|| Chp-2|| RAC )


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2. Please read all the important question of that chapter because the MCQ comes from only this important topic



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Vapour Absorption refrigeration system || Important Theory Questions




Q1. Simple Vapour absorption refrigeration cycle. Advantages & Disadvantages of VAR Over VCR?





Working of Simple Vapor absorption system: A Simple Vapor absorption system consists of evaporator, absorber, generator, condenser, expansion valve, pump & reducing valve. In this system ammonia is used as refrigerant and solution is used is aqua ammonia. Strong solution of aqua ammonia contains as much as ammonia as it can and weak solution contains less ammonia. The compressor of vapor compressor system is replaced by an absorber, generator, reducing valve and pump. The heat flow in the system at generator, and work is supplied to pump. Ammonia vapors coming out of evaporator are drawn in absorber. The weak solution containing very little ammonia is spread in absorber. The weak solution absorbs ammonia and gets converted into strong solution. This strong solution from absorber is pumped into generator. The addition of heat liberates ammonia vapor and solution gets converted into weak solution. The released vapor is passed to condenser and weak solution to absorber through a reducing valve. Thus, the function of a compressor is done by absorber, a generator, pump and reducing valve. The simple vapor compressor system is used where there is scarcity of Electricity and it is very useful at partial and full load.



Advantages & Disadvantages of VAR Over VCR?


  1. Advantages of using Vapor – Absorption Refrigeration System • As there is no moving part in the entire system, the operation is essentially quite and subjected to a very little wear. • The load variations does not effect the performance of a vapour absorption system. • Absorption system may be designed to use any readily available source of thermal energy such as process steam ,hot exhaust from furnaces and solar energy, therefore they can be used in places where electric power is hard to obtain or is very expensive. • In here pump is used for pumping refrigerant absorbant solution, which consumes less power. • Maintenance cost is low as because of absence of moving part. • In the absorption refrigeration system no refrigerant produces the greenhouse effect, so their use won’t be stopped in future.

  2. Advantages of using Vapor – Absorption Refrigeration System  No moving part except pump-motor, which is comparatively smaller than compressor system.  Quiet in operation, low maintenance cost.  Can work only with thermal energy as an input.  Can be built for huge working capacities. (even for above 1000 TR)  Can be operated at designed C.O.P’s or even at part loads by varying generator temperature.  Space and Auto. control requirements favor absorption system.  In ammonia-water absorption refrigeration system, ammonia is used as the refrigerant, which is easily and cheaply available. In lithium bromide system, water is used as the refrigerant, which is also available cheap.

  3. Disadvantages of using Vapor - Absorption Refrigeration System • Set up is too large as it consists of three more equipment those are absorber, generator ,and pump. • Initial cost is high. • Corrosive in nature. • Low working pressure. • Due to low working pressure the cop of vapour refrigeration is low, it is about 1.1 • High heat rejection system is required, as heat is being rejected from condenser, analyzer, rectifier and absorber.



Q2. Compare theoretical & practical VAR?





Q3.Expression of COP for VAR Over evaporator temp. , generator temp. , condenser temp. ?






Q4. Electrolux refrigeration system? or 3 fluid refrigeration?





Q5. Steam Jet refrigeration system ? Expression for mass of motive steam required ?










Q6. Lithium Bromide absorption refrigeration system?





Q7. Define refrigerants. Properties of refrigerants?


a refrigerant agent, as a drug. a liquid capable of vaporizing at a low temperature, as ammonia, used in mechanical refrigeration. a cooling substance, as ice or solid carbon dioxide, used in a refrigerator


Desirable Properties of Refrigerants


  • Low Freezing Point. Refrigerants should have low freezing point than the normal operating conditions. ...

  • Low Condensing Pressure. ...

  • High Evaporator Pressure. ...

  • High Critical Pressure. ...

  • High Vapor Density. ...

  • High Dielectric strength. ...

  • High Latent Heat of Vaporization. ...

  • High Heat Transfer Coefficient

The most common refrigerants include Chlorofluorocarbons (CFCs), Hydrochlorofluorocarbons (HCFCs), Hydrofluorocarbons (HFCs), and Natural Refrigerants. Freons or halocarbons are synthetically produced. The classification also depends on their chemical elements chlorine (Cl), hydrogen (H), carbon (C), and Florine (F)


In addition to fluorine and carbon, Freons often contain hydrogen, chlorine, or bromine. Thus, Freons are types of chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and related compounds. The name Freon is a trademark registered by E.I. du Pont de Nemours & Company.


R-11 is a colorless and odorless CFC refrigerant that was completely banned from production by 1996 under the Montreal Protocol for depleting the ozone. It is a low-pressure refrigerant that was commonly used in centrifugal chillers and before the 1970's it was used as a propellant for aerosols.


R134a is also known as Tetrafluoroethane (CF3CH2F) from the family of HFC refrigerant. ... It is now being used as a replacement for R-12 CFC refrigerant in the area of centrifugal, rotary screw, scroll and reciprocating compresssors. It is safe for normal handling as it is non-toxic, non-flammable and non-corrosive.


R744 (CO2) is refrigerant grade CO2, used as a replacement for R134a and R404A in ultra-low, low and medium temperature refrigeration applications. ... With an Ozone Depleting Potential (ODP) of 0 and a Global Warming Potential (GWP) of 1, R744 (CO2) is a natural refrigerant.


Even though water (R718) is one of the oldest refrigerants, state of the art technology is required to use water as a refrigerant in compression refrigeration plants with turbo compressors. ... Because the cycle works at very low pressure, the volumetric cooling capacity of water vapor is very low


Freon™ 124 (R-124) refrigerant is a hydrochlorofluorocarbon (HCFC) retrofit replacement for R-114 used in centrifugal chillers and high-ambient cooling applications, including overhead cranes.



MCQ important questions || Rgpv online Exams


Q1. The mechanical work required to run vapour absorption system


a. is more than the mechanical work required to run vapour compression system

b. is less than the mechanical work required to run vapour compression system

c. is similar to the mechanical work required to run vapour compression system

d. cannot say


View Answer / Hide Answer

ANSWER: b. is less than the mechanical work required to run vapour compression system


Q2. The compressor in the vapour compression system id replaced by


a. an absorber

b. a generator

c. an absorber-generator

d. none of the above


View Answer / Hide Answer

ANSWER: c. an absorber-generator


Q3. What is the condition of refrigerant at the exit of evaporator in aqua-ammonia absorption system?


a. low pressure ammonia vapour

b. high pressure ammonia vapour

c. low pressure strong vapour mixture of ammonia and water

d. high pressure strong vapour mixture of ammonia and water


View Answer / Hide Answer

ANSWER: a. low pressure ammonia vapour



Q4. What is the process carried out in generator of vapour absorption refrigeration cycle?


a. weak solution of ammonia in water is heated

b. strong solution of ammonia in water is heated

c. only water is heated and heat is given to the ammonia to form its vapour

d. none of the above


View Answer / Hide Answer

ANSWER: b. strong solution of ammonia in water is heated


Q5. In absorber of aqua-ammonia absorption refrigeration system


a. strong solution is taken in and weak solution is given out

b. weak solution is taken in and strong solution is given out

c. the ammonia vapour from strong solution is taken out and made it a weak solution

d. none of the above


View Answer / Hide Answer

ANSWER: b. weak solution is taken in and strong solution is given out



Q6. What is the purpose of analyser-rectifire in aqua-ammonia absorption system?


a. to absorb ammonia into the water

b. to remove water vapour out from ammonia after generator

c. to exchange heat between weak solution and strong solution

d. none of the above


View Answer / Hide Answer

ANSWER: b. to remove water vapour out from ammonia after generator


Q7. What is an advantage using analyser-rectifier in aqua-ammonia absorption system?


a. it makes ammonia-water solution strong

b. it prevents expansion valve from blocking due to ice formation

c. both a. and b.

d. none of the above


View Answer / Hide Answer

ANSWER: b. it prevents expansion valve from blocking due to ice formation



Q8. For a same pressure the saturation temperature of ammonia is


a. higher than the saturation temperature of water

b. lower than the saturation temperature of water

c. same as the saturation temperature of water

d. none of the above


View Answer / Hide Answer

ANSWER: b. lower than the saturation temperature of water


Q9. Which type of energy is required to expend in vapour absorption refrigeration system?


a. high-grade energy

b. low-grade energy

c. medium-grade energy

d. none of the above


View Answer / Hide Answer

ANSWER: b. low-grade energy



Q10. The vapour absorption refrigeration system is


a. more noisy than the vapour compression refrigeration system

b. more silent than the vapour compression refrigeration system

c. equally noisy as the vapour compression refrigeration system

d. it depends upon plant capacity


View Answer / Hide Answer

ANSWER: b. more silent than the vapour compression refrigeration system


Q11. For the same capacity of plant, the COP of the vapour absorption refrigeration system is


a. lower than the COP of the vapour compression refrigeration system

b. higher than the COP of the vapour compression refrigeration system

c. same as the COP of the vapour compression refrigeration system

d. cannot say


View Answer / Hide Answer

ANSWER: a. lower than the COP of the vapour compression refrigeration system



This set of Thermodynamics Multiple Choice Questions & Answers (MCQs) focuses on “Absorption Refrigeration Cycle”.

1. In absorption refrigeration cycle, which of the following is used? a) refrigerant b) absorbent c) both of the mentioned d) none of the mentioned View Answer

Answer: c Explanation: Both refrigerant and absorbent are used in absorption refrigeration cycle.


2. In absorption system, compressor in vapour compression cycle is replaced by absorber-generator assembly. a) true b) false View Answer

Answer: a Explanation: The absorber-generator assembly involves less mechanical work.



3. In the aqua-ammonia absorption system, a) water is the refrigerant and ammonia is the absorbent b) ammonia is the refrigerant and water is the absorbent c) both ammonia and water can be used as refrigerant or absorbent d) none of the mentioned View Answer

Answer: b Explanation: This is the basic absorption refrigeration cycle.


4. Which of the following statement is true? a) ammonia vapour is absorbed in water b) boiling point of ammonia is more than that of water c) both of the mentioned d) none of the mentioned View Answer

Answer: a Explanation: The boiling point of ammonia is less than that of water.


5. why is an analyser-rectifier combination is used in absorption refrigeration cycle? a) to increase the amount of water vapour in ammonia vapour b) to decrease the amount of water vapour in ammonia vapour c) to eliminate the water vapour from ammonia vapour d) all of the mentioned View Answer

Answer: c Explanation: This is done to prevent the blocking of expansion valve because of frozen ice.


6. Which of the following condenses first? a) ammonia vapour b) water vapour c) both condense at same temperature d) none of the mentioned View Answer

Answer: b Explanation: The saturation temperature of water is higher than ammonia at any given pressure.



7. The vapour going to condenser is ____ in temperature and ____ in ammonia. a) higher, less b) higher, richer c) lower, less d) lower, richer View Answer

Answer: d Explanation: When passing through analyser, the vapour is cooled and enriched by ammonia.


8. Lithium bromide-water vapour is another absorption refrigeration system. a) true b) false View Answer

Answer: a Explanation: In this, water is the refrigerant and solution of lithium bromide in water is the absorbent.


9. Water is used as a ____ in air conditioning units. a) absorbent b) refrigerant c) absorbent and refrigerant d) none of the mentioned View Answer

Answer: b Explanation: The reason is that water cannot be cooled below 0 degree Celsius.


10. The COP of absorption refrigeration system is a) low b) high c) equal to that of vapour compression refrigeration system d) none of the mentioned View Answer

Answer: a Explanation: The Cop of absorption refrigeration system is low


11.In a vapour absorption refrigeration system the power is required for vapour compressor as compared to that in vapour compression cycle is

[A].More[B].Less[C].Half[D].One forth[E].There is no such relation

Answer: Option E




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