Search results
Results from the WOW.Com Content Network
Packaging: The permeability of the package (materials, seals, closures, etc.) needs to be matched with the sensitivity of the package contents and the specified shelf life. Some packages must have nearly hermetic seals while others can (and sometimes must) be selectively permeable. Knowledge about the exact permeation rates is therefore essential.
Permeability is typically determined in the lab by application of Darcy's law under steady state conditions or, more generally, by application of various solutions to the diffusion equation for unsteady flow conditions. [8] Permeability needs to be measured, either directly (using Darcy's law), or through estimation using empirically derived ...
Measurement consists of packing the powder into a cylindrical "bed" having a known porosity (i.e. volume of air-space between particles divided by total bed volume). A pressure drop is set up along the length of the bed cylinder. The resulting flow-rate of air through the bed yields the specific surface by the Kozeny–Carman equation: [1]
Darcy's law is an equation that describes the flow of a fluid through a porous medium and through a Hele-Shaw cell.The law was formulated by Henry Darcy based on results of experiments [1] on the flow of water through beds of sand, forming the basis of hydrogeology, a branch of earth sciences.
The movement of a fluid through porous media is described by the combination of Darcy's law with the principle of conservation of mass in order to express the capillary force or fluid velocity as a function of various other parameters including the effective pore radius, liquid viscosity or permeability. [3]
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 material. That is, it measures the rate of fluid flow passing through an area of material with a thickness ...
Typical rates in aluminium foil laminates may be as low as 0.001 g/m 2 /day, whereas the rate in fabrics can measure up to several thousand g/m 2 /day. [citation needed] Often, barrier testing is conducted on a sheet of material. Calculations based on that can be useful when designing completed structures, clothing, and packages.
In multiphase flow in porous media, the relative permeability of a phase is a dimensionless measure of the effective permeability of that phase. It is the ratio of the effective permeability of that phase to the absolute permeability. It can be viewed as an adaptation of Darcy's law to multiphase flow.