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734 ENGINEERING THERMODYNAMICS

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Liquid

line

dg f

s (Entropy)

Saturation

line

Rn

T 2 a

b

12

e

Evaporation

Compression

W

Expansion

T (Temp.)

T 1

43 Condensation

Fig. 14.12. T-s diagram.

14.3.5. Pressure-enthalpy (p-h) chart

The diagram commonly used in the analysis of the refrigeration cycle are :
(i) Pressure-enthalpy (p-h) chart (ii) Temperature-entropy (T-s) chart.
Of the two, the pressure-enthalpy diagram seems to be the more useful.
The condition of the refrigerant in any thermodynamic state can be represented as a point
on the p-h chart. The point on the p-h chart that represents the condition of the refrigerant in any
one particular thermodynamic state may be located if any two properties of the refrigerant for that
state are known, the other properties of the refrigerant for that state can be determined directly
from the chart for studying the performance of the machines.

Constant

pressure line

Constant

pressure line

Constant enthalpy lineConstant enthalpy line

Enthalpy

Pressure

Constant temp. line

Sub-cooled liquid region

Co

ns

tan

td

ryn

es

s

fra

ct

ion

lin

e

Co

ns

tan

td

ryn

es

s

fra

ct

ion

lin

e Constant temperature lineConstant temperature line

Dry saturated vapour line

Constant entropy

line

Constant entropy

line

Specific

volume

line

Specific volume

line

Specific volume

line

Two phase

region or

wet region

Saturated liquid line

Fig. 14.13. Pressure enthalpy (p-h) chart.