Viscosity refers to the internal friction between molecules when the fluid is subjected to an external force. Dynamic viscosity is also referred to as absolute viscosity, simple viscosity, and dynamic viscosity. It refers to the ratio of stress to strain rate. When two plates with an area of 1 square meters and a distance of 1 m are immersed in a liquid, they move relative to each other at a speed of 1 m/s. The internal friction force generated by the interaction between the fluids, the unit is Newton second per square, and Pa·s Pa·s.
What is kinematic viscosity? Kinematic viscosity is also called kinematic viscosity, which refers to the ratio of hydrodynamic viscosity to fluid density ρ, in square meters/s. There are multiple unit expressions for kinematic viscosity, and the conversion unit is converted to: 1㎡/s=104St=106cSt. cSt is centistokes. The instrument for measuring kinematic viscosity is called a kinematic viscometer.
Kinematic viscosity xam cov mis:
The force exerted on the unit area of the liquid layer is called the shear stress τ (N/m2).
Shear rate (D) D=dv /dx (S-1)
Shear stress thiab shear rate yog ob qho piv txwv uas qhia txog cov khoom ntawm lub cev
Two parallel fluids with different planes have the same area "A", separated by a distance "dx", and flow in the same direction at different flow rates "V1" and "V2". Newton assumed that the force to maintain these different flow rates is proportional to the fluid's Relative velocity or velocity gradient, namely:
τ= ηdv/dx = ηD (Newton's formula) where η is the dynamic viscosity, which is related to the material properties.
Newtonian fluid: a fluid that conforms to Newton's formula. Viscosity is only related to temperature and has nothing to do with shear rate. τ is proportional to D.
Non-Newtonian fluid: does not conform to the Newtonian formula τ/D=f(D), and ηa represents the viscosity under a certain (τ/D), which is called the apparent viscosity.
Viscosity yog cov cuab yeej uas tsim kev sib txhuam sab hauv ntawm cov molecules hauv cov kua. Dynamic viscosity yog hais txog qhov sib piv ntawm cov kev sib txhuam sab hauv ib chav tsev tiv tauj cheeb tsam ntawm cov kua mus rau tus nqi ntawm qhov kev hloov pauv ntawm qhov khiav nrawm perpendicular mus rau kev taw qhia ntawm kev txav mus los. Kinematic viscosity yog hais txog dynamic viscosity ntawm tib qhov kub thiab txias. Qhov sib piv ntawm qhov ntom ntawm cov kua hauv qab siab. Viscosity feem ntau qhia los ntawm kinematic viscosity, thiab chav tsev yog mm2 / s.
Conversion ntawm dynamic viscosity unit:
1 poise (1P) =100 centipoise (100cP)
1 centipoise (1cP) = 1 mPa·s (1mPa·s)
1 mPa·s (1mPa·s)=1000 microPa·s (1000μPa·s)
Kev hloov pauv ntawm dynamic viscosity thiab kinematic viscosity
μ=ν·ρ
Where μ---dynamic viscosity of the sample (mPa·s)
ν－－- Kinematic viscosity of sample (mm2/s)
ρ－－- The density of the sample at the same temperature as the measured kinematic viscosity (g/cm3)
Viscosity muaj kev sib raug zoo nrog qhov kub thiab txias ntawm cov kua, tsis ntau nrog lub siab.
What does the higher the kinematic viscosity indicate? The greater the kinematic viscosity, the greater the viscosity value, and the greater the friction between the internal molecules. When the fluid moves under the action of external force, the energy consumed will be greater. If the external force acts on a certain situation, the distance of fluid circulation will be smaller. Falling ball viscometers, viscosity cups, and Ubbelohde viscometers are based on the characteristics of fluid kinematic viscosity, and use gravity as an external force to promote relative movement between fluids, which can be converted into fluid viscosity values by measuring time. Rotary viscometers and vibrating viscometers both use electrical energy to convert the friction between fluids into resistance or damping, and then convert them into viscosity values and display them on the display of the instrument. The greater the kinematic viscosity, the greater the displayed value, which represents the greater the viscosity of the fluid.