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.
Formula za izračunavanje kinematske viskoznosti:
The force exerted on the unit area of the liquid layer is called the shear stress τ (N/m2).
Brzina smicanja (D) D=dv /dx (S-1)
Posmično naprezanje i brzina smicanja dva su osnovna parametra koja karakteriziraju reološka svojstva sustava
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.
Viskoznost je svojstvo koje stvara unutarnje trenje između molekula unutar tekućine. Dinamička viskoznost odnosi se na omjer sile unutarnjeg trenja po jedinici kontaktne površine tekućine i brzine promjene brzine strujanja okomito na smjer kretanja. Kinematička viskoznost se odnosi na dinamičku viskoznost pri istoj temperaturi. Omjer gustoće tekućine pod tlakom. Viskoznost se obično izražava kinematičkom viskoznošću, a jedinica je mm2/s.
Pretvorba jedinice dinamičke viskoznosti:
1 pois (1P)=100 centipoise (100cP)
1 centipoise (1cP) = 1 mPa·s (1mPa·s)
1 mPa·s (1mPa·s)=1000 microPa·s (1000μPa·s)
Pretvorba dinamičke viskoznosti i kinematičke viskoznosti
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)
Viskoznost ima odličan odnos s temperaturom tekućine, a ne s tlakom.
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.