Q. Determine the viscosity of a liquid having kinematic viscosity 6 stokes and specific gravity 1.9.
SOLUTION:
Kinematic viscosity u = 6 stokes
= 6cm²/ s = 6 * 10-⁴m²/ s
Sp. Gravity of liquid = Density of liquid/Density of water
1.9=Density of liquid/ 1000
Density of liquid= 1000×1.9=1900kg / (m³) .
Using the relations v = μ/p we get
6 * 10-⁴ = μ/1900
μ = 6 * 10-⁴ * 1900 = 1.14Ns / (m ^ 2)
= 1.14 * 10 = 11.4 poise. Ans.
Q. The velocity distribution for flow over a flat plate is given by u = 3/4 * y – y² in which u is the velocity in meter per second at a distance y metre above the plate. Determine the shear stress at y = 0.15m Take dynamic viscosity of fluid is 8.6 poise.
SOLUTION:
Given:
u = 3/4 * y – y²
du/dy = 3/4 – 2y
At y = 0.15 , du/dy = 3/4 – 2 * 0.15 = 0.75 – 0.3 = 0.45
Viscosity μ = 8.5 poise
= 8.5/10 Ns / m² (:: 10 poise = 1 Ns/m²]
Using equation τ = μ * du/dy = 8.5/10 * 0.45N /m²
= 0.3825N /m² Ans.
