Permeability Definition
Permeability of the substance will affect the flow of liquid through them. Substances with high permeability allow for a more rapid flow of fluids through the fluids.
What is Permeability?
Permeability in reference to earth science refers to the porous structure of any substance such that it allows gases or fluids to pass through it. This ability is governed by the size and shape of porous and the porosity of the material. The permeability is also affected by the brittleness of rocks and the pressure in rocks.
Substances or rocks that have low permeability are fractured or acidized that leads to an increase in their permeability allowing free flow of fluids. Hence, the physical factors that influence permeability in rocks include the difference in applied pressure, the fluid viscosity, and the thickness of the medium.
Permeability units vary in accordance with what permeability we are measuring. For instance, in the case of rocks the permeability measuring unit is Darcy. This measuring unit measures the velocity of fluids through the pores in the rock. But in electromagnetism, newtons per ampere or Henries per meter is the magnetic permeability unit.
Permeability in general accounts for the ability of liquids to pass through a substance without hindrance through pores. Permeability depends on various factors like the number of pores, their interconnections, and size.
Permeability refers to how easily a fluid could pass through a material or substance. For instance, even though the rock is extremely porous it could still have low permeability if these pores are unconnected. But if a rock has only a few pores but if they are connected, then fluids can easily pass through.
Permeability Examples
Permeability has 3 types and they include effective, relative, and absolute permeabilities. Effective permeability pertains to the ease of flow of a particular fluid through membrane or pores when other fluids are present in the medium.
Absolute permeability accounts for the permeability measured when the medium comprises only one fluid that it is saturated with. Relative permeability is the ability of a given material to freely allow for the flow of a particular fluid. Hence, the relative permeability value changes when either the fluid or the rock is changed.
It can also be expressed as the ratio between the permeability of a given medium to the permeability of air (relative permeability of air is 1). Relative permeability ranges from 0-1 or can be expressed as a percentage and it does not have any unit. By using this permeability measure we can compare the permeability of 2 substances. The magnetic permeability in the case of water is close to that of a vacuum.
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Permeability generally speaking is a very broad term that refers to the easy passage and includes various types like rocks permeability, magnetic permeability, and membrane permeability. The common point is that all these kinds refer to the easy passage of liquids or gases through pores.
Permeability in geology can refer to the permeability of rocks to gases and fluids that pass through pores whereas, in the case of soil, permeability refers to the ability of soil particles to allow the passage of air and water.
Soil permeability influences various other soil properties and is considered a significant criterion when selecting the cultivation land area. The soil consists of several layers that have different properties and vary considerably from each other.
Permeability in the case of soil is a crucial factor as it determines the flow rate of water through the soil. Porous soil also allows for easy passage of air that makes it well oxygenated that helps in the respiration of bacteria and other microbes, organisms, and roots of the plant. This also helps in temperature regulation in the soil as oxygen regulates it.
Permeability is accounted for by the number and size of pores that can be studied from the soil texture. If impurities are present then it may decrease soil permeability. Magnetic permeability refers to the ratio of magnetic induction to magnet intensity. This helps to calculate the penetrance power of a magnetic field and the resistance of substances to magnetic fields.
If the magnetic permeability of a substance is high then there is greater conductivity of force of magnetic lines. It is influenced by factors like temperature, humidity, frequency of applying the force, the nature of the material, and the position of the magnet in the medium. This continuously changes with positional changes and varies with magnetic fields.
In the case of biology, permeability pertains to the ability of biological membranes to regulate the passage of molecules by different mechanisms like active transport or passive diffusion. The membrane permeability is indicated by the rate of diffusion and depends on the molar mass of the molecules, their polarity, and their electrical charge.
Cell membranes are comprised of bi-lipid layers and are thus hydrophobic in nature. Therefore, it is easier for small neutral molecules to pass through the membrane by direct diffusion. While charged large molecules may need carriers or channels. The membrane is permeable to small fluids and gases.
Permeability Citations
- Drug-permeability and transporter assays in Caco-2 and MDCK cell lines. Future Med Chem . 2011 Dec;3(16):2063-77.
- All disease begins in the (leaky) gut: role of zonulin-mediated gut permeability in the pathogenesis of some chronic inflammatory diseases. F1000Res . 2020 Jan 31;9:F1000 Faculty Rev-69.
