Compressibility Factor Charts

n-hexane

carbon dioxide

ethane

nitrogen

hydrogen

The compressibility factor chart plots the compressibility factor

Z

, equal to

PV

RT

, where

V

is the volume per mole, versus the reduced pressure

P

r

for several values of the reduced temperature

T

r

. The reduced pressure and temperature are defined by

P

r

=P/

P

c

and

T

r

=T/

T

c

, respectively, where

P

c

is the critical pressure and

T

c

is the critical temperature. Use buttons to select one of five molecules, and move the black dot to display the compressibility factor curve (blue) for any value of

T

r

between 1.0 and 1.8. The

Z

and

P

r

values for the location of the black dot are displayed on the chart. For an ideal gas,

Z=1

(green line).

Details

The Soave modification of the Redlich–Kwong (SRK) equation of state is used to calculate the compressibility factor:

P=

RT

V-b

-

aα

V(V+b)

.

This equation can be written in terms of the reduced temperature

T

r

=T/

T

c

:

P=

R

T

r

T

c

V-b

-

aα

V(V-b)

,

where

P

is pressure (bar),

R

is the ideal gas constant (

3

cm

bar/molK

),

T

is temperature (K),

T

c

is the critical temperature (K),

V

is volume (

3

cm

/mol

), and

a

,

b

and

α

are constants:

a=0.427

2

R

2

T

c

P

c

α

,

b=0.087

R

T

c

P

c

,

α=

2

(1+κ(1-

T

r

))

,

where

P

c

is the critical pressure

κ=0.48+1.574ω-0.176

2

ω

, and

ω

is the acentric factor.

The compressibility factor is defined by:

Z=

PV

RT

.

External Links

Compressibility Factors Using the Soave-Redlich-Kwong Equation of State

Permanent Citation

Rachael L. Baumann, John L. Falconer

"Compressibility Factor Charts"
http://demonstrations.wolfram.com/CompressibilityFactorCharts/
Wolfram Demonstrations Project
Published: May 17, 2017