AskDefine | Define porousness

Dictionary Definition

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

User Contributed Dictionary

English

Noun

  1. The quality of being porous; porosity

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

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