Viscosity Types - Dynamic Viscosity, Motion Viscosity, Relative Viscosity and Apparent Viscosity

dynamic viscosity

The Greek symbol η (η) denotes dynamic viscosity. To obtain dynamic viscosity (also sometimes called shear viscosity), Newton's laws need to be reformulated:

$$ \tta \{\eta}{\cdot} \dot{\gamma} \rightarrow{\eta} = {\tau \over \dot {\gamma}} [Pa \cdot{s}] = \left [ {Pa \ over {1 \ over s}} \ right] $$

Equation 4: Newton's Laws. How to derive dynamic viscosity.

SI (International System of Units [6] ) units: 

• [Pa.s.] Pascal seconds or [mPa.s] MilliPascal seconds. 1 Pa.s = 1000 mPa.s

Other commonly used units:

• [P]Poise or [cP] centipoise (named after Jean Poiseuille [7] ): 1 P = 100 cP

• Relationship between units: 1 cP = 1 mPa.s

Dynamic viscosity is preferred for life science and research applications.

kinematic viscosity

Kinematic viscosity ν(ny) reflects the effect of gravity on the flow of matter. Dynamic viscosity divided by density ρ (ρ) gives kinematic viscosity. Since density is defined as mass per volume, gravity enters the equation through the mass.

$$\nu={{eta}\over\rho}\left[{m^{2}}\over s\right]\:\:\rho={m\over V}\left[{kg}\ In {cubic meters{3}}\right]$$

Equation 5. Kinematic viscosity is dynamic viscosity divided by density. The influence of gravity is introduced through the mass contained in the density.

SI unit:

• [ms 2 / s] square meter per second or [mm 2 / s] square millimeter per second

• 1m 2 /s = 1 000 000mm 2 /s

$$ \ left [{m ^ {2}} \ over s \ right] = \ left [{Pa \ cdot s} \ over {kg \ over {m ^ {3}}} \ right] = \ left [{ N \ over {m ^ {2}} \ cdot s} \ over {kg \ over {m ^ {3}}} \ right] $$

$$ [N] = \ left {{kg \ cd m} \ over {s ^ {2}} \ right] $$

$$ \ left {{m ^ {2}} \ over {s} \ right] = \ left {{kg \ cdot m} \ over {{s ^ {2}} \ cdot {m ^ {2}} }} \ cdot s \ cdot {{m ^ {3}} \ over kg} \ right] $$

公式6.通过重新形成的牛顿定律推导运动粘度的SI单位。

其他常用单位：

• [St] stokes或[cSt] centistokes（以George G. Stokes [8]命名）。

• 1 St = 100 cSt

• 1cSt = 1mm 2 / s

运动粘度广泛用于所有石油化工流体，如燃料或润滑油。

相对粘度

测量溶解聚合物时，相对粘度是一个重要参数[9]。

聚合物的质量与其摩尔质量密切相关。大多数聚合物显示摩尔质量和粘度之间的明显关系。因此，为了确定摩尔质量，可以测量粘度。通常，聚合物溶液的粘度随着摩尔质量的增加而增加。事实上，大多数聚合物溶液都是剪切相关的（即非牛顿流体）。

However, in a sufficiently low range of shear rates, their behavior is Newtonian. The viscosity of the polymer solution (η) is divided by the viscosity of the pure solvent (η0) to obtain the relative viscosity in dimensionless units [1] .

The relative viscosity ηr is the basis for calculating other parameters relevant to polymer quality control:

$${\eta_{r}} = {{eta} \over {\eta_{0}}} \left[1\right]$$

Equation 7: Relative viscosity is the viscosity of the polymer solution divided by the viscosity of the pure solvent.

• Logarithmic Viscosity (also known as Intrinsic Viscosity)

• Specific viscosity (also known as relative viscosity gain)

• Decreased viscosity (also known as viscosity number (VN) or Staudinger function)

• Intrinsic Viscosity (also known as Intrinsic Viscosity Number (LVN) or Staudinger Index)

• K value

• Molar mass (molar mass is given in most cases in grams/mole, which is defined as the mass of a substance divided by the amount of the substance).

apparent viscosity

A satisfactory viscous or Newtonian fluid has a constant viscosity for all values ​​of shear rate. On the other hand, for shear-dependent fluids, the viscosity also changes. Therefore, you need to specify the shear rate at which the viscosity value is determined. This is "apparent viscosity" or "apparent shear viscosity". Each apparent value is a point of the viscosity function (η versus shear rate).

example:

$${\eta}(\dot{\gamma}=60{s^{-1}})=398\:mPa\cdot s$$