9/13/2023 0 Comments Low viscous liquid![]() ![]() The Society of Automotive Engineers developed a viscosity index (VI), which is most often used for describing the viscosity of motor oils or other lubricants. The SI unit of viscosity is Newton-second per square meter, and the equivalent English unit is pound-seconds per square foot. Where μ is the coefficient of viscosity, A is the area over which the force is acting, and du/ dy is the velocity gradient in the direction perpendicular to the flow. The viscous force of a liquid is expressed by the following equation: ![]() The layers of a low viscosity liquid move easily because there is less friction between them. The viscosity of a liquid is related to how well its layers move in relation to each other. ![]() In terms of a more technical definition, low viscosity liquids have less resistance to flow when they are subject to shear stress. Often, the difference between water and honey is used to illustrate how the viscosity of a liquid can be visualized. Generally, the viscosity of a liquid can be associated with its “thickness”, with low viscosity liquids being less “thick”. Some examples of liquids with low viscosities are shown in the following table: Liquid Depending on the specific situation, how viscous a liquid is can play an important role in its application. Low viscosity liquids are liquids that flow freely. To apply low viscosity liquids in engineering, knowing how various liquids are used in specific applications, and how the conditions of use affect the viscosity of liquids are important things to consider. By understanding the viscosity of a liquid, what affects that viscosity, and whether the viscosity is considered low or high, it is possible to choose a liquid that is appropriate for a specific application. Also available in English translations.Although liquids and gases both have viscosity, it is liquids that are most commonly analyzed for their viscous properties. Zarzycki,J (1982): Les Verres et l'état vitreux.Götze,W (2009): Complex Dynamics of glass forming liquids.This theory describes a slowing down of structural relaxation on cooling towards a critical temperature Tc, typically located 20% above Tg. The microscopic dynamics at low to moderate viscosities is addressed by a mode-coupling theory, developed by Wolfgang Götze and collaborators since the 1980s. More recently, the fragility has been quantitatively related to the details of the interatomic or intermolecular potential, and it has been shown that steeper interatomic potentials lead to more fragile liquids. Materials with a higher enthalpy of configuron formation compared with their enthalpy of motion have a higher Doremus fragility ratio, conversely melts with a relatively lower enthalpy of configuron formation have a lower fragility. Bond breaking modifies the properties of an amorphous material so that the higher the concentration of broken bonds termed configurons the lower the viscosity. Fragility is related to materials bond breaking processes caused by thermal fluctuations. Strong melts are those with (R D-1) < 1, whereas fragile melts are those with (R D-1) ≥ 1. The fragility of amorphous materials is numerically characterized by the Doremus’ fragility ratio R D=Q H/Q L. Amorphous materials are classified accordingly to the deviation from Arrhenius type behaviour of their viscosities as either strong when Q H-Q L
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