Basic Fluid Mechanics - Week 1 Flashcards

1
Q

behaviour of plastics under stress

A

the shear stress must reach a minimum value berfore flow commences, thereafter shear stress increases with the rate of shear

  • curve with decreasing gradient the higher the rate (shear stress v rate of shear)
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2
Q

mass flow rate ṁ

A

= ρ A V

denisity (ρ)
cross-sectional area (A)
velocity (V)

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3
Q

behaviour of pseudo-plastics under stress

A

dynamic viscosity decreases as the rate of shear increases

  • curve with decreasing gradient the higher the rate (shear stress v rate of shear)
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4
Q

behaviour of thixotropic substances under stress

A

dynamic viscosity decreases with the time for which shearing forces are applied

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5
Q

behaviour of dilatant substances under stress

A

dynamic viscosity increases as the rate of shear increases

  • curve with increasing gradient the higher the rate (shear stress v rate of shear)
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6
Q

behaviour of rheopectic materials under stress

A

dynamic viscosity increases with the time for which shearing forces are applied

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7
Q

Poiseuille equation - pressure drop for laminar flow

A

∆𝑝 = 8𝜇𝐿𝑄 / 𝜋𝑟^4

dynamic viscosity (𝜇)
length of pipe (L)
volumetric flow rate (Q)

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8
Q

Converting absolute viscosity to kinematic viscosity

A

ν = μ/ρ
divide by density

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9
Q

Litres to m^3

A

Divide by 1000

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10
Q

Friction Factor in laminar flow

A

4f = 64/Re

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11
Q

How do you calculate pressure loss (Δp) and or head loss (h) for both laminar and turbulent flows

A

Using the Darcy equation
Δp = (4f) L/D ρū^2 / 2
h = Δp/ρg

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12
Q

Process of solving frictional problems

A
  • determine Re
  • if laminar 4f = 64/Re or could use Poiseuille equation (∆p)
  • if turbulent and Re < 100,000 or k/D < 0.001: 4f = 0.316/Re^0.25
  • otherwise read from moody chart
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13
Q

Work out power

A

P = Q∆p

flow rate (Q)
change in pressure (∆p)

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14
Q

What is head loss

A

measure of reduction in total head (elevation) loss, amount of PE converted to KE
h = p/ρg

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