Fluids Basics Flashcards
What is viscosity (m)?
Property of a fluid, due to cohesion and interaction between molecules, which offers resistance to shear deformation.
Different fluid …. at different rates under the same….
…. deform…. shear stress
Fluids with…. viscosity such as syrup, deform more …. than fluids with…. viscosity such as water.
…. high…. slowly…. low….
Formula for shear stress
τ=μdV/dy
μ is coefficient of dynamic viscosity
dV/dy is velocity gradient or rate of shear strain
Coefficient of dynamic viscosity
μ=(τ)/(dV/dy)=(force/area)/(velocity/distance)=(force×time)/(area)=(mass)/(length×time)
Kinematic viscosity equation
ν=μ/ρ
Pascal’s law
Pressure at a point in a fluid at rest or in motion, is independent of direction as long as there are no shearing stresses present.
pz=py=ps
In a fluid under gravity, pressure…. with depth
…. increases….
P=Patm+ρgh
Pressure guage
Pressure measured with respect to atmospheric pressure.
pguage=ρgh=γh
Pressure head formula
h=pguage/ρg
Formula for force on a submerged plane surface
FR=γhcA
γ=specific weight of fluid
hc=depth to centroid of object
A=cross sectional area of object
Formula for distance to FR from x-axis along y-axis
yR=(Ixc/ycA)+yc
Ixc=second moment of area of the object around an axis praying through the centroid, parallel to x-axis
yc=orthogonal distance to centroid from the x-axis
Resultant force formula
FR=√(FH²+FV²)
Angle of inclination of FR to horizontal
Φ=tan⁻¹(FV/FH)
dV/dt=
Av
Continuity equation
A₁v₁=A₂v₂
Bernoulli’s equation
P+ρgh+0.5ρv²=constant
PV (pressure times volume)
W (work done)
Force on a vertical wall
F=Pave×A
Pave=vertical pressure half way down the pool
A=area of wall
(Works on angles if use length of hypotenuse)
Resultant force on a curved submerged surface
R=√(F²+W²)
F=horizontal force
W=weight of fluid directly above curve
Laminar flow
Motion is particles very orderly work all particles moving in a strait line parallel to the pipe
Transitional flow
Short burst of turbulence embedded in laminar flow
Turbulent flow
Eddying or mixing action. Fluid particle’s motion is complex and involves fluctuations in velocity and direction.
Reynolds number formula
Re=ρVL/μ=VL/ν V=velocity L=representative length μ=absolute viscosity ν=kinematic viscosity
Reynolds number boundaries
Re<2000 - laminar flow
2000
