Viscosity and Momentum transport

Question 1

Newtons Law of viscosity

Answer 1

τ_{xy} = -μ * dv_{x}/dy : Shearing force pr. unit area (Shear stress) is proportional to the negative velocity gradient

Question 2

How does viscosity depend on density and temperature for Gas and Liquid fluids?

Answer 2

GAS: Density= Low ; Temp=Increasing ; Viscosity=Increasing
LIQUID: Density= Low ; Temp= Increasing ; Viscosity= Decreasing

Question 3

How can the term τ_{ij} be interpreted?

Answer 3

The force in j-direction on unit area perpendicular to i-direction

Question 4

How to know what sign the viscous stress should have

Answer 4

If force is acting inward –> viscous stress (-) sign

If force is acting outward –> viscous stress (+) sign