Barrer

Barrer is a non-SI unit of gas permeability (specifically, gas permeability) used in the membrane technology and contact lens industry. It is named after Richard Barrer.

Definition

${\rm {{1}\ barrer={10^{-10}}{\frac {cm_{STP}^{3}\cdot cm}{cm^{2}\cdot s\cdot cmHg}}}}$

Here the 'cm³_STP' is standard cubic centimeter, which is a unit of amount of gas rather than a unit of volume. It represents the amount of gas molecules or moles that would occupy one cubic centimeter at standard temperature and pressure, as calculated via the ideal gas law.
The cm corresponds in the permeability equations to the thickness of the material whose permeability is being evaluated, the cm³_STPcm⁻²s⁻¹ to the flux of gas through the material, and the cmHg to the pressure drop across the material. That is, it measures the rate of fluid flow passing through an area of material with a thickness driven by a given pressure. See Darcy's Law.
In SI unit Barrer can be expressed as:
${\rm {{1}\ barrer={3.35\times 10^{-16}}{\frac {mol\cdot m}{m^{2}\cdot s\cdot Pa}}}}$

To convert to CGS permeability unit, one must use the following:^[1]

${\rm {{1}\ barrer={M\ \times }\ {3.35\times 10^{-13}}\ {\frac {g\cdot cm}{s\cdot cm^{2}\cdot bar}}}}$

Where M is the molecular weight of the penetrant gas (g/mol).

Another commonly expressed unit is Gas Permeance Unit (GPU). It is used in the measurement of gas permeance. Permeance can be expressed as the ratio of the permeability with the thickness of membrane.^[2]

${\rm {{1}\ GPU=10^{-6}\ {\frac {cm_{STP}^{3}}{cm^{2}\cdot s\cdot cmHg}}=7.501\ \times \ 10^{-12}\ {\frac {m_{STP}^{3}}{m^{2}\cdot s\cdot Pa}}}}$

Or in SI units: ${\rm {{1}\ GPU=3.35\ \times \ 10^{-10}\ {\frac {mol}{m^{2}\cdot s\cdot Pa}}}}$

References

^ Stern, S. A. (1968-11-01). "The "barrer" permeability unit". Journal of Polymer Science Part A-2: Polymer Physics. 6 (11): 1933–1934. doi:10.1002/pol.1968.160061108. ISSN 1542-9377.
^ Lin, Haiqing; He, Zhenjie; Sun, Zhen; Vu, Jimmy; Ng, Alvin; Mohammed, Moyeen; Kniep, Jay; Merkel, Timothy C.; Wu, Tony; Lambrecht, Robert C. (2014-05-01). "CO2-selective membranes for hydrogen production and CO2 capture – Part I: Membrane development". Journal of Membrane Science. 457: 149–161. doi:10.1016/j.memsci.2014.01.020. ISSN 0376-7388.

[1] Stern, S. A. (1968-11-01). "The "barrer" permeability unit". Journal of Polymer Science Part A-2: Polymer Physics. 6 (11): 1933–1934. doi:10.1002/pol.1968.160061108. ISSN 1542-9377.

[2] Lin, Haiqing; He, Zhenjie; Sun, Zhen; Vu, Jimmy; Ng, Alvin; Mohammed, Moyeen; Kniep, Jay; Merkel, Timothy C.; Wu, Tony; Lambrecht, Robert C. (2014-05-01). "CO2-selective membranes for hydrogen production and CO2 capture – Part I: Membrane development". Journal of Membrane Science. 457: 149–161. doi:10.1016/j.memsci.2014.01.020. ISSN 0376-7388.

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