TITLE.PM5

72 ENGINEERING THERMODYNAMICS

Dharm

\M-therm/th3-1.p65

Ts = Saturation temperature in K,

Tsup = Temperature of superheated steam in K, and

vsup = Volume of 1 kg of superheated steam at pressure p,

Then,

pv

T

pv

T

g

s

= sup

sup

or, v

vT

T

g

sup s

= sup ...(3.6)

3.9. Thermodynamic Properties of Steam and Steam Tables

In engineering problem, for any fluid which is used as working fluid, the six basic thermo-
dynamic properties required are : p (pressure), T (temperature), v (volume), u (internal energy), h
(enthalpy) and s (entropy). These properties must be known at different pressure for analysing the
thermodynamic cycles used for work producing devices. The values of these properties are deter-
mined theoretically or experimentally and are tabulated in the form of tables which are known as
‘Steam Tables’. The properties of wet steam are then computed from such tabulated data. Tabu-
lated values are also available for superheated steam. It may be noted that steam has only one
saturation temperature at each pressure.
Following are the thermodynamic properties of steam which are tabulated in the form of
table :
p = Absolute pressure (bar or kPa) ;
ts = Saturation temperature (°C) ;
hf = Enthalpy of saturated liquid (kJ/kg) ;
hfg= Enthalpy or latent heat of vapourisation (kJ/kg) ;
hg= Enthalpy of saturated vapour (steam) (kJ/kg) ;
sf = Entropy of saturated liquid (kJ/kg K) ;
sfg= Entropy of vapourisation (kJ/kg K) ;
sg = Entropy of saturated vapour (steam) (kJ/kg K) ;
vf = Specific volume of saturated liquid (m^3 /kg) ;
vg = Specific volume of saturated vapour (steam) (m^3 /kg).
Also, hfg = hg – hf ...... Change of enthalpy during evaporation
sfg = sg – sf ...... Change of entropy during evaporation
vfg = vg – vf ...... Change of volume during evaporation.
The above mentioned properties at different pressures are tabulated in the form of tables as
under :
The internal energy of steam (u = h – pv) is also tabulated in some steam tables.
STEAM TABLES
Absolute Temperature Specific enthalpy Specific entropy Specific volume
pressure °C kJ/kg kJ/kg K m^3 /kg
bar, p ts hf hfg hg sf sfg sg vf vg

1.0 99.6 417.5 2257.9 2675.4 1.3027 6.0571 7.3598 0.001043 1.6934

50.0 263.9 1154.9 1639.7 2794.2 2.9206 3.0529 5.9735 0.001286 0.00394

100.0 311.1 1408.0 1319.7 2727.7 3.3605 2.2593 5.6198 0.001452 0.01811