Vapor compression refrigeration cycle p-h and T-s

Explain the working of simple vapor compression refrigeration cycle with corresponding processes in p-h and T-s diagrams.

The simple vapour compression cycle is the most common refrigeration cycle (domestic refrigerators, air conditioners). A refrigerant (R-134a, ammonia) circulates through the system: it absorbs heat in the evaporator and rejects it in the condenser, while a compressor supplies work.

              Condenser (Q_H out)
         2 +-------------------+ 3
           |                   |
      Compressor          Expansion valve
           |                   |
         1 +-------------------+ 4
              Evaporator (Q_L in)

Processes

1-2: Isentropic compression. Saturated (or slightly superheated) vapour is compressed in the compressor to high pressure and temperature. Work W is supplied.
2-3: Constant-pressure heat rejection. The hot vapour first de-superheats, then condenses to saturated liquid in the condenser, rejecting Q_H to the surroundings.
3-4: Throttling (isenthalpic expansion). The liquid expands through the expansion valve or capillary tube to the low pressure, with h₃ = h₄. Its temperature falls and part of it flashes to vapour.
4-1: Constant-pressure heat absorption. The cold wet mixture evaporates in the evaporator, absorbing Q_L from the refrigerated space, and leaves as saturated vapour.

Diagrams

 p-h diagram
 p
 |              .-'''-.
 |            .'       '.
 |         3 /___________\_______ 2
 |          /|            \      /
 |         / |             \    /
 |        /  |              \  /
 |       /   |               \/
 |      /    4 _______________1
 |     /                       \
 +---------------------------------> h

 T-s diagram
 T
 |                     2
 |                   .'|
 |        .-'''-.  .'  |
 |      .'       '.'   |
 |  3  /__________2'   |
 |    /:           \   |
 |   / :            \  |
 |  /   :            \ |
 | /     4 ___________\1
 |/                    \
 +-------------------------> s

 1-2 isentropic compression    2-2'-3 condensation (2' = saturated vapour)
 3-4 throttling                4-1 evaporation
 (3-4 is vertical on p-h, and dotted on T-s because it is irreversible)

Performance

Refrigeration effect: q_L = h₁ − h₄
Compressor work: w = h₂ − h₁
Heat rejected: q_H = h₂ − h₃

COP = q_L/w = (h₁ − h₄)/(h₂ − h₁)

✓ Answer checked by Claude Opus 5.5 (high effort)

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Vapor compression refrigeration cycle p-h and T-s

Processes

Diagrams

Performance

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