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Physics RCOA > Fluids & Pressure > Flashcards

Fluids & Pressure Flashcards

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1
Q

What is pressure?

A

Force applied per unit area

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2
Q

What is a fluid?

A

A substance that continually deforms under an applied shear stress

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3
Q

What is fluid pressure?

A

The pressure at some point in a fluid. Can be static (still) or dynamic (moving)

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4
Q

What is flow?

A

The quantity of fluid passing a point per unit time
Flow = Quantity/Time

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5
Q

What are the 2 types of flow?

A
  • LAMINAR: Molecules pass smoothly & steadily, parallel to walls of vessel
  • TURBULENT: Molecules swirl into eddies
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6
Q

What factors affect how a fluid flows?

A
  • Viscosity
  • Density
  • Pressure gradient
  • Tube features
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7
Q

What is viscosity?

A

Property of a fluid that causes resistance to flow
- Newtonian: Viscosity is constant
- Non-newtonian: Viscosity changes (blood)

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8
Q

What is density?

A

Mass of a substance per unit volume (kg/m3)

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9
Q

What is a pressure gradient?

A

The fall in pressure across the tube length/orifice

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10
Q

What equation can be used to describe Laminar flow?

A

Hagen- Poiseuille equation

Q = πPr^4 / 8ηl

Q = flow
P = pressure drop
n = viscosity
l = tube length

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11
Q

What does the Hagen - Poiseuille equation show?

A

Flow is proportional to:
- pressure gradient across a tube
- the radius to the power of 4
Flow is inversely proportional to:
- Viscosity
- Length of tube

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12
Q

What is the most important factor in turbulent flow?

A

Density
Flow is inversely proportional to the square root of density

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13
Q

Is heliox useful in bronchospasm?

A

No - similar viscosity to air, in bronchospasm flow is largely laminar

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14
Q

What does Reynold’s number tell you?

A

Whether flow is likely to be laminar or turbulent
< 2000 = laminar
> 2000 = turbulent

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15
Q

What is the equation for Reynold’s number?

A

Re = pvd / n

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16
Q

What is the equation for resistance?

A

R = P / Q
(Pressure gradient / flow)

17
Q

How is resistance linked to laminar flow?

A

On a pressure/flow graph resistance is the gradient of the line

18
Q

What is the equation for resistance in terms of turbulent flow?

A

R = P / Q2

19
Q

What is Bernoulli’s principle?

A

In a closed system the amount of energy remains constant. Therefore as flow/velocity increases pressure must decrease by an equal amount

20
Q

What does the Bernoulli principle give rise to?

A

Venturi effect

21
Q

What is the Venturi effect?

A

When a fluid flows through a constriction within a tube the velocity increases and drop in pressure. This drop in pressure allows a second fluid to be introduced.

22
Q

What is the equation for entrainment ratio?

A

ER = Entrained flow / driving flow

23
Q

What devices use Venturi effect?

A
  • Venturi O2 masks
  • Nebulisers
  • Sanders injector for ventilation
  • Suction
24
Q

What is the Coanda effect?

A

The tendency of a stream of fluid flowing close to a convex surface to follow the surface rather than its course.

25
Q

What can the Coanda effect explain?

A
  • Uneven ventilation at bronchiole
  • Myocardial ischaemia distal to CA branching
26
Q

How can gas flow be measured?

A
  • Vitalograph
  • Bell spirometer
  • Rotameter
  • Pneumotachographs
  • Vane meters
  • Mechanical flow transducers
  • USS flow meter
  • Hot wire anemometers
27
Q

How can liquid flow be measured?

A
  • Infusion pumps: Syringe drivers, peristaltic pumps
  • IV drip counters
28
Q

How does a rotameter work?

A
  • Valve opened allowing greater flow rate of gas
  • Bobbin rises in tube to position where force of gas pushing up is equal to gravity pushing down
29
Q

How do low & high flows affect a rotameter?

A

LOW: Bobbin at narrower end of tube. Gas flows across greater length than diameter - laminar flow
HIGH: Bobbin at wider ed of tube. Gas flows across greater diameter than length - turbulent flow

30
Q

What factors can affect a rotameters accuracy?

A
  • Warmer gasa have lower density - may over-read
  • Reduced atmospheric pressure reduces gas density- may over-read
31
Q
A

Physics RCOA (9 decks)

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