Page 38 - DJJ20063- Thermodynamics 1

DJJ20063- Thermodynamics 1

2.3.2 Draw and label the temperature-specific enthalpy diagram for

steam/water.

The T-s diagram for a steam

o
o
As mentioned earlier, the zero specific entropy is taken as 0.01 C for steam and 40 C for
refrigerants only. The T-s diagram for steam is considered here. The diagram for a

refrigerant is exactly similar to the T-s diagram for steam. However, the zero specific

entropy is different.

The T-s diagram for steam in Fig. shows:

❑ Three lines of constant pressure P1, P2 and P3 ( i.e. ABCD, EFGH and JKLM). The

pressure lines in the liquid region are practically coincident with the saturated liquid
line (i.e. AB, EF and JK), and the difference is usually neglected.

❑ The pressure remains constant with temperature when the latent heat is added,

hence the pressure lines are horizontal in the wet region (i.e. portions BC, FG and KL).

❑ The pressure lines curve upwards in the superheat region (i.e. portions CD, GH and
LM). Thus the temperature rises as heating continues at constant pressure.

❑ Two constant volume lines (v1 and v2 shown as chain-dotted) are also drawn in Fig.

2.2.2-1. The lines of constant volume are concaved down in the wet region and slope

up more steeply than pressure lines in the superheat region.

T

P3 P3 > P2 > P1
M

P2 v1 > v2
H
v2
K L v1 P1
D
J F G
E B C
A
273 K
s

Figure 2.3.2-1 Temperature-entropy diagram for liquid and steam

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