AskDefine | Define porosity

Dictionary Definition

porosity n : the property of being porous; being able to absorb fluids [syn: porousness] [ant: solidity]

User Contributed Dictionary

English

Noun

  1. The state of being porous
  2. A measure of how porous a material is; the ratio of the volume of pores to the total volume

Translations

Extensive Definition

Porosity is a measure of the void spaces in a material, and is measured as a fraction, between 0–1, or as a percentage between 0–100%. The term porosity is used in multiple fields including manufacturing, earth sciences and construction.

Porosity in earth sciences and construction

Used in geology, hydrogeology, soil science, and building science, the porosity of a porous medium (such as rock or sediment) describes the fraction of void space in the material, where the void may contain, for example, air or water. It is defined by the ratio:
\phi = \frac
where VV is the volume of void-space (such as fluids) and VT is the total or bulk volume of material, including the solid and void components. Both the mathematical symbols \phi and n are used to denote porosity.
Porosity is a fraction between 0 and 1, typically ranging from less than 0.01 for solid granite to more than 0.5 for peat and clay, although it may also be represented in percent terms by multiplying the fraction by 100.
The porosity of a rock, or sedimentary layer, is an important consideration when attempting to evaluate the potential volume of water or hydrocarbons it may contain. Sedimentary porosities are a complex function of many factors, including but not limited to: rate of burial, depth of burial, the nature of the connate fluids, the nature of overlying sediments (which may impede fluid expulsion). One commonly used relationship between porosity and depth is given by the Athy (1930) equation:
\phi(z) = \phi_0 e^\,
where \phi_0 is the surface porosity, k is the compaction coefficient (m−1) and z is depth (m).
A value for porosity can alternatively be calculated from the bulk density \rho_ and particle density \rho_:
\phi = 1-\frac
Normal particle density is assumed to be approximately 2.65 g/cm³, although a better estimation can be obtained by examining the lithology of the particles.

Porosity and hydraulic conductivity

Porosity is indirectly related to hydraulic conductivity; for two similar sandy aquifers, the one with a higher porosity will typically have a higher hydraulic conductivity (more open area for the flow of water), but there are many complications to this relationship. Clays, which typically have very low hydraulic conductivity also have very high porosities (due to the structured nature of clay minerals), which means clays can hold a large volume of water per volume of bulk material, but they do not release water very quickly.

Sorting and porosity

References

porosity in Catalan: Porositat
porosity in German: Porosität
porosity in Spanish: Porosidad
porosity in Persian: تخلخل
porosity in French: Porosité
porosity in Italian: Porosità
porosity in Lithuanian: Poringumas
porosity in Marathi: छिद्रता
porosity in Dutch: Porositeit
porosity in Polish: Porowatość skały
porosity in Portuguese: Porosidade
porosity in Russian: Пористость
porosity in Serbian: Порозност
porosity in Finnish: Huokoisuus
porosity in Ukrainian: Пористість
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