“viscosity”的概念、定义、翻译、参考文献-科学参考

viscosity

Physics

A measure of the resistance to flow that a fluid offers when it is subjected to shear stress. For a Newtonian fluid, the force, F, needed to maintain a velocity gradient, dv/dx, between adjacent planes of a fluid of area A is given by: F=η‎A(dv/dx), where η‎ is a constant, the coefficient of viscosity. In SI units it has the unit pascal second (in the c.g.s. system it is measured in poise). Non-Newtonian fluids, such as clays, do not conform to this simple model. See also kinematic viscosity.

http://www.kayelaby.npl.co.uk/general_physics/2_2/2_2_3.html Values of viscosities of liquids at the NPL website

Chemistry

A measure of the resistance to flow that a fluid offers when it is subjected to shear stress. For a Newtonian fluid, the force, F, needed to maintain a velocity gradient, dv/dx, between adjacent planes of a fluid of area A is given by: F = η‎A(dv/dx), where η‎ is a constant, called the coefficient of viscosity. In SI units it has the unit pascal second (in the c.g.s. system it was measured in poise). Non-Newtonian fluids, such as clays, do not conform to this simple model. See also kinematic viscosity.

Chemical Engineering

A measure of the flow transport behaviour of a fluid. It is the phenomenon in which a fluid will withstand a slight amount of molecular tension between particles, which will cause an apparent shear resistance between two adjacent layers. The term ‘viscosity’ is used to describe the fact that certain fluids flow easily, such as gases, water, and mercury, while others do not, such as tar, treacle, and glycerine. These fluids are broadly classified as thin and thick fluids. Sir Isaac Newton (1642–1727) proposed that the shear stress is proportional to the velocity gradient or shear rate. By considering a fluid sandwiched between two parallel plates set at a distance dz apart in which the upper plate moves with some small velocity dv in comparison with the lower plate, there will be a small resisting force over the plate area due to viscous frictional effects in the fluid. This force per unit area of plate (F/A) is known as the shear stress, τ. Newton’s law of viscosity is therefore given as:
$τ = μ \frac{d v_{X}}{d z} which is sometimes written as τ = μ \dot{γ}$

The proportionality constant, μ, is known as the coefficient of dynamic viscosity and is also known as the absolute or dynamic viscosity of the fluid; it is influenced by process conditions such as temperature. In the case of Newtonian fluids, μ is a constant. Examples of Newtonian fluids include water, ethanol, and benzene. The viscosity of a fluid may, however, not always be constant for certain fluids for different applied shear stresses. These fluids are known collectively as non-Newtonian fluids. In such cases, the term ‘apparent viscosity’ is conveniently used. Examples of non-Newtonian fluids include paint, polymers, most slurries, and many foodstuffs. The calculation remains the same and is the ratio of shear stress to shear rate. In SI units, it has examples of non-Newtonian fluids include paint, polymers, most slurries, and many foodstuffs. the units kgm^–1s^–1 or using derived SI units Nsm^–2 or Pa.s. In the c.g.s. system it is measured in poise (P) or centipoise (cP), where 1 cP is equivalent to 10^–3 Nsm^–2. The viscosities of gases are significantly less than for liquids. Oils, such as olive oil, are an order of magnitude higher than liquids such as water. In general, high-viscosity fluids can be considered in the order of 10 Nsm^–2 and above. See kinematic viscosity.

Geology and Earth Sciences

The internal resistance of a substance to flow when a shear stress is applied. Quantitatively defined, it is the ratio of the shear stress to the strain rate, in units of pascal seconds (1 Pas = 10 poise). Resistance to flow is caused essentially by molecular or ionic cohesion. In magmas, molecular cohesion can be very high, especially if the silica content is high as in rhyolite magmas, and a yield strength must be overcome before the magma can flow. The presence of solid crystals increases the effective internal cohesion, and dissolved gas reduces it. In general, basaltic magmas have lower viscosities than rhyolite magmas.

Geography

The resistance to flow exhibited by a material; the parameter describing the flow characteristics of a fluid. Easy flows result from low viscosity.

单词	viscosity
释义	viscosity Physics A measure of the resistance to flow that a fluid offers when it is subjected to shear stress. For a Newtonian fluid, the force, F, needed to maintain a velocity gradient, dv/dx, between adjacent planes of a fluid of area A is given by: F=η‎A(dv/dx), where η‎ is a constant, the coefficient of viscosity. In SI units it has the unit pascal second (in the c.g.s. system it is measured in poise). Non-Newtonian fluids, such as clays, do not conform to this simple model. See also kinematic viscosity. http://www.kayelaby.npl.co.uk/general_physics/2_2/2_2_3.html Values of viscosities of liquids at the NPL website Chemistry A measure of the resistance to flow that a fluid offers when it is subjected to shear stress. For a Newtonian fluid, the force, F, needed to maintain a velocity gradient, dv/dx, between adjacent planes of a fluid of area A is given by: F = η‎A(dv/dx), where η‎ is a constant, called the coefficient of viscosity. In SI units it has the unit pascal second (in the c.g.s. system it was measured in poise). Non-Newtonian fluids, such as clays, do not conform to this simple model. See also kinematic viscosity. Chemical Engineering A measure of the flow transport behaviour of a fluid. It is the phenomenon in which a fluid will withstand a slight amount of molecular tension between particles, which will cause an apparent shear resistance between two adjacent layers. The term ‘viscosity’ is used to describe the fact that certain fluids flow easily, such as gases, water, and mercury, while others do not, such as tar, treacle, and glycerine. These fluids are broadly classified as thin and thick fluids. Sir Isaac Newton (1642–1727) proposed that the shear stress is proportional to the velocity gradient or shear rate. By considering a fluid sandwiched between two parallel plates set at a distance dz apart in which the upper plate moves with some small velocity dv in comparison with the lower plate, there will be a small resisting force over the plate area due to viscous frictional effects in the fluid. This force per unit area of plate (F/A) is known as the shear stress, τ. Newton’s law of viscosity is therefore given as: $τ = μ \frac{d v_{X}}{d z} which is sometimes written as τ = μ \dot{γ}$ The proportionality constant, μ, is known as the coefficient of dynamic viscosity and is also known as the absolute or dynamic viscosity of the fluid; it is influenced by process conditions such as temperature. In the case of Newtonian fluids, μ is a constant. Examples of Newtonian fluids include water, ethanol, and benzene. The viscosity of a fluid may, however, not always be constant for certain fluids for different applied shear stresses. These fluids are known collectively as non-Newtonian fluids. In such cases, the term ‘apparent viscosity’ is conveniently used. Examples of non-Newtonian fluids include paint, polymers, most slurries, and many foodstuffs. The calculation remains the same and is the ratio of shear stress to shear rate. In SI units, it has examples of non-Newtonian fluids include paint, polymers, most slurries, and many foodstuffs. the units kgm^–1s^–1 or using derived SI units Nsm^–2 or Pa.s. In the c.g.s. system it is measured in poise (P) or centipoise (cP), where 1 cP is equivalent to 10^–3 Nsm^–2. The viscosities of gases are significantly less than for liquids. Oils, such as olive oil, are an order of magnitude higher than liquids such as water. In general, high-viscosity fluids can be considered in the order of 10 Nsm^–2 and above. See kinematic viscosity. Geology and Earth Sciences The internal resistance of a substance to flow when a shear stress is applied. Quantitatively defined, it is the ratio of the shear stress to the strain rate, in units of pascal seconds (1 Pas = 10 poise). Resistance to flow is caused essentially by molecular or ionic cohesion. In magmas, molecular cohesion can be very high, especially if the silica content is high as in rhyolite magmas, and a yield strength must be overcome before the magma can flow. The presence of solid crystals increases the effective internal cohesion, and dissolved gas reduces it. In general, basaltic magmas have lower viscosities than rhyolite magmas. Geography The resistance to flow exhibited by a material; the parameter describing the flow characteristics of a fluid. Easy flows result from low viscosity.
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