Vapour compression Cycle important Theory & Mcq || RGPV Online exam 2020 || Chapter-2 || RAC

(Rgpv online exam important questions & answers 2020 )|| Chp-1 || RAC )

Instruction To Prepare this chapter


1. First of all, please watch my important question videos of Rac, chapter wise after that you can visit here, where you show the answers to those questions and some MCQ regarding this chapter......


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



For Notes of this chapter:- https://www.4bengineers.com/payment-page

For Videos Of this Chapter:- https://www.youtube.com/watch?v=g754W6-_Zk0&list=PLelAq9xzEDXCZwXnq6z6f04dEhRqEWSmZ

Important Questions Chapter wise All subject playlist:- https://www.youtube.com/watch?v=MiT_RQoOxdY&list=PLelAq9xzEDXA5Bo_JAq4fz5KuSBlyCd06


Theory Important questions from this chapter




Q1. Factor affecting the performance of VCR?






Q2. Why the throttling process is prefered over the isentropic expansion process in a VCR?



Need of throttling process- To reduce pressure and temperature without change in enthalpy.


How it works : Energy equation for refrigerant

(h + KE +PE )of inlet + Q - W = (h +KE +PE)of outlet


KE= Kinetic energy 

PE=Potential energy

h=enthalpy

Q=heat transfer 

W=work transfer


Throttling process can be done by capillary tube.Working fluid is flow through capillary tube.

- capillary tube is isolated .so Q =0

 - Work transfer W=0

 - ∆KE= 0 ( velocity will change but it is negligible)

 -∆PE=0


So we can say 

(h)inlet =(h)outlet

h1=h2


Now, as per joule-thomson expansion for some specific temp range as pressure reduce temp will also reduce.


How pressure reduce ?

As fluid flow through capillary its velocity increase as per continuity eqation (AV=const).hence conversion of pressure energy into kinetic energy takes place. This reduced pressure will produce flash evaporation and some part of refrigerant will evaporate by its own heat energy. This will reduce its temperature.


Whereas icentropic expansion is also called Adiabatic expansion.


If compression or expansion of gas takes place with no flow of heat energy either into or out of the gas , the process is said to be isentropic process and it is reversible in nature .


So, During the throttling process, heat absorption capacity at a cons. pressure of a unit mass of refrigerant remains the same, ie,

                                             h1=h2.

hence it is preferred over icentropic expansion.



Q3. Three-stage Compression & Their P-V & T-S Diagram







Q4. What do you mean by dry ice? Explain with diagram & their manufacturing process?





Q5. Cascade Refrigeration System?







Q6.Linde- Hampson cycle of air liquefication?






Q7. Why compounding is good ? Describe the use of flash chamber and intercooling in two stage VCR?



1. The work done per kg of refrigerant is reduced in compound compression with intercooler as compared to single stage compression for the same delivery pressure.

2. It improves the volumetric efficiency for the given pressure ratio..


A flash chamber is a device which separates liquid from vapors. Only liquid is then passed to evaporator and the vapors will be passed to the compressor directly. This flash chamber between the condenser and evaporator is known as flash intercooling.



Q8. Two stage VCR with flash chamber gas removal?




Q9. Two stage VCR with intercooling & subcooling ?




Q10. Derive expression for volumetric efficiency of VCR ?







Q11.Simple VCR Merit & Demerits?


Advantages

  1. It has smaller size for the given capacity of refrigeration.

  2. It has less running cost.

  3. It can be employed over a large range of temperatures.

  4. The coefficient of performance is quite high.

Disadvantages

  1. The initial cost is high.

  2. The prevention of leakage of the refrigerant is the major problem in vapour compression system.

Q12. Numericals Based Topics

1. 2 stage vcr

2. simple vcr



MCQ Questions for RGPV Online exam 2020


Q1. Which device is used for the expansion of refrigerant in vapour compression refrigeration cycle?


a. throttling valve

b. capillary tube

c. either throttling valve or capillary tube

d. none of the above

ANSWER: c. either throttling valve or capillary tube


Q2. Wet compression is ______.


a. more dangerous than the dry compression in vapour compression refrigeration system

b. less dangerous than the dry compression in vapour compression refrigeration system

c. equally preferable in vapour compression refrigeration system

d. cannot say

ANSWER: a. more dangerous than the dry compression in vapour compression refrigeration system



Q3. How is the condensation process in vapour compression refrigeration cycle carried out?


a. at constant volume

b. at constant pressure

c. at constant enthalpy

d. all of the above

ANSWER: b. at constant pressure


Q4. What is flash gas fraction?


a. the mass fraction of liquid in liquid-vapour mixture of refrigerant at inlet to the evaporator


b. the mass fraction of vapour in liquid-vapour mixture of refrigerant at inlet to the evaporator


c. the mass of vapour actually compressed to the mass of vapour should have compressed ideally


d. none of the above

ANSWER: b. the mass fraction of vapour in liquid-vapour mixture of refrigerant at inlet to the evaporator



Q5. In evaporation process of vapour compression refrigeration system


a. heat is rejected from refrigerant to surroundings

b. heat is rejected from surroundings to refrigerant

c. only pressure change takes place

d. none of the above

ANSWER: b. heat is rejected from surroundings to refrigerant


Q6. The heat required to melt 1 tonne of ice in 12 hours is equivalent to


a. one tonne of refrigeration

b. two tonne of refrigeration

c. half tonne of refrigeration

d. four tonne of refrigeration

ANSWER: b. two tonne of refrigeration



Q8. What is the main reason behind subcooling of liquid refrigerant at the condenser outlet in vapour compression refrigeration system?


a. to increase the refrigerating effect

b. to reduce the mass of vapour formed during expansion process

c. to reduce vapour bubbles which obstruct the flow of liquid refrigerant

d. all of the above

ANSWER: d. all of the above


Q9. What is the result of superheating of vapour at the evaporator outlet?


a. no liquid droplets will travel to the compressor

b. the compressor discharge temperature increases

c. both a. and b.

d. none of the above

ANSWER: c. both a. and b.


Q10. Which expansion device is capable of regulating the flow of refrigerant according to the load on the evaporator?


a. capillary tube

b. throttle valve

c. both a. and b.

d. none of the above ANSWER: b. throttle valve



Q12. As the evaporator temperature lowers down, the required compression ratio


a. becomes lower for a given condensation temperature

b. becomes higher for a given condensation temperature

c. becomes steady for a given condensation temperature

d. cannot say

ANSWER: b. becomes higher for a given condensation temperature


Q13. What is the use of multistage compression in vapour compression refrigeration system?


a. to increase volumetric efficiency of of compressor

b. to allow the system to operate between higher pressures

c. to reduce risk of damage to refrigerant

d. all of the above

ANSWER: d. all of the above



Q14. What is used as an intercooler in multistage compression of vapour compression refrigeration system?


a. water

b. air

c. refrigerant itself

d. none of the above

ANSWER: c. refrigerant itself


Q15. Which of the following statement is true for a condenser? a) it can be air-cooled or water-cooled b) small self-contained units use water-cooled condenser c) large installations use air-cooled condenser d) all of the mentioned View Answer

Answer: a Explanation: We use air-cooled condenser for small self-contained units and water-cooled condenser for large installations.


Q16.For an expansion device, which of the following is true? a) it increases the pressure of refrigerant b) it regulates the flow of refrigerant to evaporator c) both of the mentioned d) none of the mentioned View Answer

Answer: b Explanation: The expansion device reduces the pressure of refrigerant.



Q17. Which of the following is a type of expansion device? a) capillary tubes b) throttle valves c) both of the mentioned d) none of the mentioned View Answer

Answer: c Explanation: These are the two types of expansion devices.


Q18. Throttle valves are used in ____ a) small units b) larger units c) both of the mentioned d) none of the mentioned View Answer

Answer: b Explanation: They regulate the flow of refrigerant according to load on evaporator.


Q19.The clearance volumetric efficiency is equal to a) 1 + C + C(p2/p1)^(1/n) b) 1 – C – C(p2/p1)^(1/n) c) 1 – C + C(p2/p1)^(1/n) d) 1 + C – C(p2/p1)^(1/n) View Answer

Answer: d Explanation: Here C is the clearance and p1,p2 are pressures.



Q20.Why is multistage compression with intercooling adopted? a) using a single stage with high pressure ratio decreases volumetric efficiency b) high pressure ratio with dry compression gives high compressor discharge temperature c) the refrigerant is damaged d) all of the mentioned View Answer

Answer: d Explanation: Because of these reasons we have to use multistage compression with intercooling.


Q21.The intercooler pressure is given by a) p1*p2 b) sqrt(p1*p2) c) (p1*p2)/(p1+p2) d) (p1+p2)/2 View Answer

Answer: b Explanation: Here p1 is the evaporator pressure and p2 is the condenser pressure.


Q22.The most widely used refrigerants are a) freon b) genetron c) arcton d) all of the mentioned View Answer

Answer: d Explanation: These are a group of halogenated hydrocarbons.



Q23.1. During a refrigeration cycle, heat is rejected by the refrigerant in a

  • Compressor

  • Condenser

  • Evaporator

  • Expansion valve

2. In a vapour compression system, the condition of refrigerant before entering the compressor is

  • Saturated liquid

  • Wet vapour

  • Dry saturated liquid

  • Superheated vapour

3. The highest temperature during the cycle, in a vapour compression system, occurs after

  • Compression

  • Condensation

  • Expansion

  • Evaporation

4. In a vapour compression system, the lowest temperature during the cycles occurs after

  • Compression

  • Condensation

  • Expansion

  • Evaporation

5. The sub-cooling in a refrigeration cycle

  • Does not alter C.O.P

  • Increases C.O.P

  • Decreases C.O.P

6. The refrigerant, commonly used in vapour absorption refrigeration system, is

  • Sulphur dioxide

  • Ammonia

  • Freon

  • Aqua-ammonia


7. In ammonia-hydrogen refrigerator


  • Ammonia is absorbed in hydrogen

  • Ammonia is absorbed in water

  • Ammonia evaporates in hydrogen

  • Hydrogen evaporates in ammonia



8. Which of the following refrigerants has the lowest boiling point?


  • Ammonia

  • Carbon dioxide

  • Sulphur dioxide

  • Freon-12

9. Which of the following refrigerant is highly toxic and flammable?


  • Ammonia

  • Carbon dioxide

  • Sulphur dioxide

  • Freon-12

Q24. The purpose of installing a flash chamber in the refrigeration circuit is to (A) improve overall heat transfer coefficient (B) reduce pressure losses through the evaporator (C) reduce the size of the evaporator by avoiding vapours going to the evaporator (D) all of the above

Answer (D)


Q25.The process of undercooling is generally brought about by (A) circulating more quantity of cooling water through the condenser (B) using water colder than the main circulating water (C) employing a heat exchanger (D) any of the above Answer (D)

Chapter-3 Vapour Absorption Refrigeration system (Coming Soon )


SSC-JE & RRB-JE(Mechanical) Full syllabus free video lectures:- https://www.4bengineers.com/post/ssc-je-rrb-je-free-full-video-lectures-mechanical-engineering

*******************************************************************

For College Info:-https://www.4bengineers.com/4bjobalert/categories/college-counselor

******************************************************************

FOR NOTES AND STUFFS (Our Website):- https://www.4bengineers.com/

*******************************************************************

My Amazon Store for You:- https://www.amazon.in/shop/4bengineers?isVisitor=true

*************************************************************************

Telegram channel link:-https://t.me/ashish4Bengineers

**********************************************************************

For Job Updates :- https://www.4bengineers.com/4bjobalert

*************************************************************

Instagram:- https://www.instagram.com/4bengineers/?hl=en

*************************************************************

Facebook:- https://www.facebook.com/4bengineers

***************************************************************

Gmail:- ashish4bengineers@gmail.com

737 views0 comments

Recent Posts

See All

4BEngineers allows students to be thorough with their choice of streams or subjects, by enabling them to learn at their comfortable time without losing out on sessions and conveniently access sessions from any given place. With the help of 4BEngineers, students can avail online coaching through video lecture at an unimaginably affordable cost, access the coaching content from renowned teaching experts, and be one on one with their personal favorite coach.

© Copyright ® 2020 by 4B Engineers
  • Instagram
  • Twitter Social Icon
  • LinkedIn Social Icon
  • Facebook Social Icon
  • YouTube Social  Icon