Darcy (unit)

Permeability measures the ability of fluids to flow through rock (or other porous media). The darcy is defined using Darcy's law, which can be written as: :Q = \frac{A k\,\Delta P}{\mu\,\Delta x} where: : The darcy is referenced to a mixture of unit systems. A medium with a permeability of 1 darcy permits a flow of 1 cm3/s of a fluid with viscosity 1 cP (1 mPa·s) under a pressure gradient of 1 atm/cm acting across an area of 1 cm2. Typical values of permeability range as high as 100,000 darcys for gravel, to less than 0.01 microdarcy for granite. Sand has a permeability of approximately 1 darcy. Tissue permeability, whose measurement is still in its infancy, is somewhere in the range of 0.01 to 100 darcy. ==Origin==

The darcy is named after Henry Darcy. uses the following unit abbreviations and grammar in their publications: • darcy (plural darcys, not darcies): d • millidarcy (plural millidarcys, not millidarcies): md ==Conversions==

Converted to SI units, 1 darcy is equivalent to or 0.9869233 μm2. This conversion is usually approximated as 1 μm2. This is the reciprocal of 1.013250—the conversion factor from atmospheres to bars. Specifically in the hydrology domain, permeability of soil or rock may also be defined as the flux of water under hydrostatic pressure (≈ 0.1 bar/m) at a temperature of 20 °C. In this specific setup, 1 darcy is equivalent to 0.831 m/day. ==References==