Acentric factor
The acentric factor is a conceptual number introduced by Kenneth Pitzer in 1955, proven to be very useful in the description of matter.[1] It has become a standard for the phase characterization of single & pure components. The other state description parameters are molecular weight, critical temperature, critical pressure, and critical volume.The acentric factor is said to be a measure of the non-sphericity (centricity) of molecules.[2]
It is defined as:
.
where
is the reduced temperature,
is the reduced pressure saturation of vapors.
For many monatomic fluids
,
is close to 0.1, therefore . In many cases,
lies above the boiling temperature of gases at atmosphere pressure.
Values of can be determined for any fluid from
, and a vapor measurement from
, and for many liquid state matter is tabulated into many thermodynamical tables.
The definition of gives zero-value for the noble gases argon, krypton, and xenon.
is almost exactly zero for other spherical molecules.[2]
Experimental data yields compressibility factors for all fluids that are correlated by the same curves when
(compressibility factor) is represented as a function of
and
. This is the basis premises of three-parameter theorem of corresponding states:
All fluids at any -value, in
conditions, have about the same
-value, and same degree of convergence.
Values of some common gases
Molecule | Acentric Factor[3] |
Acetylene | 0.187 |
Ammonia | 0.253 |
Argon | 0.000 |
Carbon Dioxide | 0.228 |
Decane | 0.484 |
Helium | -0.390 |
Hydrogen | -0.220 |
Krypton | 0.000 |
Neon | 0.000 |
Nitrogen | 0.040 |
Nitrous Oxide | 0.142 |
Oxygen | 0.022 |
Xenon | 0.000 |
See also
- Equation of state
- Reduced pressure
- Reduced temperature
References
- ↑ Adewumi, Michael. "Acentric Factor and Corresponding States". Pennsylvania State University. Retrieved 2013-11-06.
- ↑ 2.0 2.1 Saville, G. (2006). "ACENTRIC FACTOR". A-to-Z Guide to Thermodynamics, Heat and Mass Transfer, and Fluids Engineering. doi:10.1615/AtoZ.a.acentric_factor.
- ↑ Yaws, Carl L. (2001). Matheson Gas Data Book. McGraw-Hill.