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The SI unit for permeability is the square metre (m 2). A practical unit for permeability is the darcy (d), or more commonly the millidarcy (md) (1 d ≈ 10 −12 m 2). The name honors the French Engineer Henry Darcy who first described the flow of water through sand filters for potable water supply. Permeability values for most materials ...
The darcy is referenced to a mixture of unit systems. A medium with a permeability of 1 darcy permits a flow of 1 cm 3 /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 cm 2. Typical values of permeability range as high as 100,000 darcys for gravel, to less than 0.01 microdarcy for ...
In physics and engineering, permeation (also called imbuing) is the penetration of a permeate (a fluid such as a liquid, gas, or vapor) through a solid.It is directly related to the concentration gradient of the permeate, a material's intrinsic permeability, and the materials' mass diffusivity. [1]
And finally, the centimetre and square centimetre are used in the normal way to measure thickness and area. The cm corresponds in the permeability equations to the thickness of the material whose permeability is being evaluated, the cm 3 STP cm −2 s −1 to the flux of gas through the material, and the cmHg to the pressure drop across the ...
Allen Hazen derived an empirical formula for approximating hydraulic conductivity from grain-size analyses: = where Hazen's empirical coefficient, which takes a value between 0.0 and 1.5 (depending on literature), with an average value of 1.0. A.F. Salarashayeri & M. Siosemarde indicate C is usually between 1.0 and 1.5, with D in mm and K in cm/s.
In SI units, permeability is measured in henries per meter (H/m), or equivalently in newtons per ampere squared (N/A 2). The permeability constant μ 0, also known as the magnetic constant or the permeability of free space, is the proportionality between magnetic induction and magnetizing force when forming a magnetic field in a classical vacuum.
The coefficient of permeability varies with the void ratio as e/sup>/(1+e). For a given soil, the greater the void ratio, the higher the value of the coefficient of permeability. Here 'e' is the void ratio. Based on other concepts it has been established that the permeability of a soil varies as e 2 or e 3 /(1+e). Whatever may be the exact ...
The absolute permeability number, which has no units, is determined by the rate of flow of air, under standard pressure, through a rammed cylindrical specimen. DIN standards define the specimen dimensions to be 50 mm in diameter and 50 mm tall, [ 2 ] while the American Foundry Society defines it to be two inches in diameter and two inches tall.