Fluid Dynamics Flashcards

1
Q

ideal fluid

A
  • steady flow
  • incompressible and homogenous
  • 1-D velocity profile
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2
Q

velocity head

A

U^2 / 2g

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3
Q

pressure head

A

P / ρ g

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4
Q

Hydraulic grade

A

= pressure head + elevation

= P / ρg + z

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5
Q

Total Energy

A

= Hydraulic grade + velocity head

= P / ρg + z + U^2 / 2g

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6
Q

stagnation point

A

point of no flow

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7
Q

reservoir assumptions

A

fluid velocity inside a reservoir = 0

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8
Q

free jet assumptions

A

pressure within a free jet of water = 0

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9
Q

Energy at any point on flow cross section is the same provided:

A
  1. the flow velocity profile can be approximated as uniform

2. The only forces acting on the fluid are weight and pressure (hydrostatic pressure distribution)

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10
Q

Two main types of energy loss in pipes

A
h(f) = friction loss
h(m) = local losses (valves, constrictions)
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11
Q

friction loss

A

h(f) = fL/D * V^2/2g

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12
Q

f

A

friction factor - describing friction resistance of pipe

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13
Q

Re

A

Reynolds number = VD / ѵ

- Re

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14
Q

low Re

A

hydraulically SMOOTH

- roughness height has no effect

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15
Q

mid-range Re

A

Transition

- f varies with Re and roughness

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16
Q

high Re

A
hydraulically ROUGH (loose cell viscous sublayer)
- depends only on roughness
17
Q

f (Laminar flow)

A

f = 64 / Re

18
Q

f (turbulent flow)

A

Swarmee and Jain Equation

f = 1.325 /

19
Q

h(m)

A

local/minor losses

h(m) = k V^2 / 2g

20
Q

k (entry into pipe from reservoir - square entrance)

21
Q

k (exit into reservoir)

22
Q

Gate Valve

A
  • low head loss

- plate lifted away (small energy effect)

23
Q

Butterfly Valve

A
  • for shedding head

- plate rotated

24
Q

Problems with Negative Pressure

A
  • Blockage (0
25
System Curve
= Total Energy (B) - Total Energy (A) + h(f) + h(m)
26
Pump efficiency
``` e = Power (out) / Power (in) e = ɣQh(p) / Power (in) ```
27
Pump Selection Procedure
1. Find pump that intersects system curve at flow that client is happy with 2. Ensure pump is working at high efficiency 3. Ensure pump will not cavitate
28
NPSH
net positive suction head | - NPSHA upstream of pump > NPSHR
29
Pump Groups Steps
1. work out total Q and total h(p) relationships 2. combine all pumps into single pump curve 3. solve system like it is single pump using combined pump curve
30
Pumps in Series
Qtot = Q1 = Q2 | h(p) tot = h(p,1) + h(p,2)
31
Pumps in Parallel
Qtot = Q1 + Q2 | h(p) tot = h(p,1) = h(p,2)