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

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

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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



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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