Other Definitions
darcy (enc)
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DarcyDarcy is the unit of the permeability of fluids in rocks and is named after Henry Darcy. Rock permeability is usually expressed in millidarcies which is equivalent to 0.001 Darcies. The physical definition of the Darcy comes from Darcy's Law which can be rearranged to: where, - is the permeability of a medium
- is the volumetric fluid flux through the medium
- is the dynamic viscosity of the fluid
- is the applied pressure difference
- is the thickness of the medium
Thus, 1 millidarcy (md) defined as the permeability of a medium 1 cm thick through which water at 20C flows at a velocity of 1 cm3/cm2.s under a 1 atm driving pressure. When converted to SI units, it can be shown that 1 md is equivalent to 0.98923 m2. This conversion is usually simplified to 1 m2. To convert square micrometres (m2) to millidarcies, multiply the permeability by 1.01325 (atmospheric pressure in bar).
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