Volumetric Properties of Pure Fluids

Advanced Thermodynamics


Volumetric Properties of Pure Fluids

, A pressure-temperature diagram
• the sublimation curve
• the fusion curve
• the vaporization curve
• the triple point
• the critical point




Fig 3.1

, A pressure-volume diagram
• The isotherms
– the subcooled-liquid and the
superheated-vapor regions
– isotherms in the subcooled-
liquid regions are steep
because liquid volumes change
little with large change in
pressure
• The two-phase coexist region
• The triple point is the
horizontal line
• The critical point
Fig 3.2

, • An equation of state exists relating pressure, molar or specific volume, and
temperature for any pure homogeneous fluid in equilibrium states.
• An equation of state may be solved for any one of the three quantities P, V, or T as a
function of the other two.
• Example:



 V   V 
dV   dT    dP
 T P  P T
1 both
– For incompressible fluid, Vβ andκ are zero. 1  V 
Volume expansivity:    Isothermal compressibility:
 water    
– For liquids β is almostV
necessarily positive.
 T  P
positive (liquid V  P  T
between 0°C and 4°C is an exception), and κ is

dVcritical point, β andκ can be assumed constant:
– At conditions not close to the
 dT  dP
V




V2
ln  (T2  T1 )   ( P2  P1 )
V1