Vapour Compression Cycle Notes | Study Mechanical Engineering SSC JE (Technical) - Mechanical Engineering

Mechanical Engineering: Vapour Compression Cycle Notes | Study Mechanical Engineering SSC JE (Technical) - Mechanical Engineering

The document Vapour Compression Cycle Notes | Study Mechanical Engineering SSC JE (Technical) - Mechanical Engineering is a part of the Mechanical Engineering Course Mechanical Engineering SSC JE (Technical).
All you need of Mechanical Engineering at this link: Mechanical Engineering

VAPOUR COMPRESSION CYCLE
If in a Reversed Carnot Cycle

  •  Refrigerant is compressed from dry saturated condition.
  • Expander is replaced by a throttling device.

The modified cycle is vapour compression cycle with no draw back of reversed carnot cycle with vapour as refrigerant

Vapour Compression Cycle Notes | Study Mechanical Engineering SSC JE (Technical) - Mechanical Engineering
Vapour Compression Cycle Notes | Study Mechanical Engineering SSC JE (Technical) - Mechanical Engineering
Vapour Compression Cycle Notes | Study Mechanical Engineering SSC JE (Technical) - Mechanical Engineering
Vapour Compression Cycle Notes | Study Mechanical Engineering SSC JE (Technical) - Mechanical Engineering

  •  Refrigerant circulation rate

Vapour Compression Cycle Notes | Study Mechanical Engineering SSC JE (Technical) - Mechanical Engineering

  •  Volume of suction vapour = m& V1

V1 – Specific volume of the vapour at suction

  •  Actual piston displacement volume of compressor  Vapour Compression Cycle Notes | Study Mechanical Engineering SSC JE (Technical) - Mechanical Engineering h= volumetric efficiency of compressor
  •  Power consumption of compressor
    Vapour Compression Cycle Notes | Study Mechanical Engineering SSC JE (Technical) - Mechanical Engineering
  •  Heat rejected in the condenser
    Vapour Compression Cycle Notes | Study Mechanical Engineering SSC JE (Technical) - Mechanical Engineering
  •  The superheat discharge temperature is found by
    Vapour Compression Cycle Notes | Study Mechanical Engineering SSC JE (Technical) - Mechanical Engineering
  •  Refrigerating effect = Vapour Compression Cycle Notes | Study Mechanical Engineering SSC JE (Technical) - Mechanical Engineering(h1 - h4 ) = Q0
    •  In case of R - 11, R - 22 and Ammonia system, wet suction state leads to maximum COP, for all other refrigerants system. suction from super heated state gives maximum COP,

Actual vapour compression system has following deviation from simple VCC.
(i) Superheating of vapour in evaporator.
(ii) Heat gain and superheating of vapour in suction line.
(iii) Pressure drop in suction line
(iv) Polytropic compression instead of isentropic compression due to friction.
(v) Pressure drop at discharge valve.
(vi) pressure drop in condenser and evaporator.
(vii) Subcooling of liquid in condenser and heat gain in liquid line.

EFFECT OF OPERATING CONDITIONS ON COP OF PAOUR COMPRESSION CYCLE.

Effect of Decrease in Evaporator Pressure

Vapour Compression Cycle Notes | Study Mechanical Engineering SSC JE (Technical) - Mechanical Engineering

  • Decrease in refrigerating effect
  • Increases in specific volume of suction vapour
  • Decease in Volumetric efficiency of compressor due to increase in pressure ratio.
  • Increase in compressor work

Effect of Increase in Condenser Pressure
Vapour Compression Cycle Notes | Study Mechanical Engineering SSC JE (Technical) - Mechanical Engineering

 

  •  Deceases in Refrigerating effect
  •  Increase in compressor work
  •  Decrease in volumetric efficiency of compressor
  •  Increase in mass flow of refrigerant.
    • COP decreases with both decreasing evaporator pressure and increasing compressor pressure. Effect of decreasing evaporator pressure is more on hte decrease in COP than the effect of increase in condenser pressure by same account.

Effect of suction Vapour Superheat
Vapour Compression Cycle Notes | Study Mechanical Engineering SSC JE (Technical) - Mechanical Engineering

  •   Increase in Refrigerating effect
  •   Increase in specific volume of suction vapour
  •   Increase in compressor work.
  •  It ensures complete vaporization of liquid before entering compressor.
    •  For R - 12, suction vapour superheat increases the COP.
    •  For R-22 & ammonia system, suction vapour super heat decreases the COP.

Effect of Liquid subcooling
Vapour Compression Cycle Notes | Study Mechanical Engineering SSC JE (Technical) - Mechanical Engineering

  •  Increase in refrigerating effect
  •  Compressor work is same & COP in creases

If Energy Gained by Subcooling is Utilized in super Heating the Suction Vapour
Vapour Compression Cycle Notes | Study Mechanical Engineering SSC JE (Technical) - Mechanical Engineering

  •  For R-12, work per TR is decreased and COP increases.
  •  For R-22 Ammonia, work per TR increases & COP decreases.
    •  There is large pressure drop in evaporator and very less drop in condenser. So pressure drop in evaporator is very critical in design.
The document Vapour Compression Cycle Notes | Study Mechanical Engineering SSC JE (Technical) - Mechanical Engineering is a part of the Mechanical Engineering Course Mechanical Engineering SSC JE (Technical).
All you need of Mechanical Engineering at this link: Mechanical Engineering

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