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.
Kinematisk viskositetsberegningsformel:
The force exerted on the unit area of the liquid layer is called the shear stress τ (N/m2).
Forskydningshastighed (D) D=dv /dx (S-1)
Forskydningsspænding og forskydningshastighed er to grundlæggende parametre, der karakteriserer systemets rheologiske egenskaber
To parallelle væsker med forskellige planer har det samme område "A", adskilt af en afstand "dx", og strømmer i samme retning ved forskellige strømningshastigheder "V1" og "V2". Newton antog, at kraften til at opretholde disse forskellige strømningshastigheder er proportional med væskens relative hastighed eller hastighedsgradient, nemlig:
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.
Viskositet er den egenskab, der genererer intern friktion mellem molekyler inde i væsken. Dynamisk viskositet refererer til forholdet mellem den indre friktionskraft pr. enheds kontaktareal af væsken og hastigheden for ændring af strømningshastigheden vinkelret på bevægelsesretningen. Kinematisk viskositet refererer til den dynamiske viskositet ved samme temperatur. Forholdet mellem densiteten af væsken under tryk. Viskositet udtrykkes normalt ved kinematisk viskositet, og enheden er mm2/s.
Konvertering af dynamisk viskositetsenhed:
1 poise (1P)=100 centipoise (100cP)
1 centipoise (1cP) = 1 mPa·s (1mPa·s)
1 mPa·s (1mPa·s)=1000 microPa·s (1000μPa·s)
Konvertering af dynamisk viskositet og kinematisk viskositet
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)
Viskositet har et godt forhold til væskens temperatur, ikke meget med trykket.
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.