Permeability

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Description

The ability of a material to permit the flow of a gas, vapor, or liquid through its pore spaces without any chemical reaction. Permeability is measured as a rate of diffusion and is a function of the pressure differential on each side of the material. The permeability of gases (air, oxygen, nitrogen, etc.) is primarily dependent on the porosity of a substance, while water vapor transmission is dependent on the absorption of water into the material. Standard units for gas permeability is usually given in the units of milliliters per square meter per day (ml/m2.d). This indicates the volume of gas that will pass through a square meter of the test material in one day. The thickness of the test material must be specified. A typical test thickness is 1 mil (1 thousandths of an inch thick). Water vapor permeability is given as grams per square meter per day. The permeability of a rock is its ability to conduct liquid or gas. It is measured as the proportionality constant, k, between flow velocity, v, and the hydraulic gradient, i; v=ki.

See also gas permeability, and vapor permeability.

Synonyms and Related Terms

Permeabilität (Deut.); perméabilité (Fr.); permeabilidade (Port.); Examples: gas permeability; vapor permeability

Sources Checked for Data in Record

  • Submitted information Comment: José Delgado Rodrigues, LNEC, 2009.
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  • The American Heritage Dictionary or Encarta, via Microsoft Bookshelf 98, Microsoft Corp., 1998
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