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Some xerophytes have tiny hair on their surfaces to provide a wind break and reduce air flow, thereby reducing the rate of evaporation. When a plant surface is covered with tiny hair, it is called tomentose. Stomata is located in these hair or in pits to reduce their exposure to wind. This enables them to maintain a humid environment around them.
Permeability is a property of porous materials that is an indication of the ability for fluids (gas or liquid) to flow through them. Fluids can more easily flow through a material with high permeability than one with low permeability. [1] The permeability of a medium is related to the porosity, but also to the shapes of the pores in the medium ...
Volumetric flow rate [m 3 /s] Permeability of porous medium [m 2]. The permeability is a function of material type, and also varies with stress, temperature, etc. Fluid viscosity [Pa.s] Cross-sectional area of Porous medium [m 2] ()
Darcy's law is an equation that describes the flow of a fluid through a porous medium. 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. It is analogous to Ohm's law in electrostatics, linearly relating the volume ...
Permeation. 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]
The pressure drop across the sample and the flow rate are measured and permeability is calculated using Darcy's law. Normally, either nitrogen or brine can be used as a fluid. When high rates of flow can be maintained, the results are comparable. At low rates, air permeability will be higher than brine permeability. This is because gas does not ...
The air permeability specific surface of a powder material is a single-parameter measurement of the fineness of the powder. The specific surface is derived from the resistance to flow of air (or some other gas) through a porous bed of the powder. The SI units are m 2 ·kg −1 ("mass specific surface") or m 2 ·m −3 ("volume specific surface").
Relative permeability. 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.