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Anaesthetic FRCA Primary - eLFH Physics > eLFH - Density and Viscosity > Flashcards

eLFH - Density and Viscosity Flashcards

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1
Q

Density definition and equation

A

Mass per unit volume

Density = mass / volume

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2
Q

Effect of pressure on density / viscosity

A

Increased pressure increases density and viscosity

More particles in a smaller area

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3
Q

Effect of temperature on density / viscosity

A

Increased temperature reduces density and viscosity

Higher average kinetic energy of molecules within the gas so particles move further apart

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4
Q

Specific gravity of gases definition

A

Density of the gas divided by the density of air (1.2 kg/m^3)

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5
Q

Specific gravity of gases interpretation

A

Gases with specific gravity > 1 are more dense than air
< 1 less dense than air

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6
Q

Specific gravity of liquids and solids

A

Density is compared with density or water

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7
Q

Viscosity definition

A

Tendency of a fluid to resist flow
Denoted with Greek letter Eta (η) (or sometimes Mu)

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8
Q

Units of viscosity

A

Poise (P)

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9
Q

Newtonian fluid

A

Fluid where viscosity is unaffected by the shear or tangential stresses inflicted upon it

Viscosity solely dependent on temperature and pressure

Most gases are Newtonian fluids

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10
Q

Non-Newtonian fluid

A

Fluid which may deform when stirred or become less viscous

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11
Q

SI units of flow

A

kg/s

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12
Q

Types of flow

A

Laminar - streamlined flow in smooth layers

Turbulent - interrupted flow with swirls

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13
Q

Importance of viscosity vs density in laminar vs turbulent flow

A

Viscosity more important in laminar flow

Density more important in turbulent flow

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14
Q

Hagen-Poiseuille equation

A

Can be used for laminar flow only, not turbulent flow

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15
Q

Where does turbulent flow occur in a tube

A

At and orifice

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16
Q

Orifice definition

A

Tube in which diameter exceeds length

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17
Q

How to measure gas flow

A

Rotameter:
Uses bobbin of fixed size
Moves up and down as pressure from gas flow pushes bobbin up until gravitational force pushing down counteracts it and pressure across the bobbin is constant

Flow calculated from Poiseuille’s law and pressure to give flow

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18
Q

Which part of bobbin to read flow from

A

Top of a flat topped bobbin

Middle of a sphere bobbin

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19
Q

Colour of oxygen cylinder

A

Black with white collar

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20
Q

Atomic weight of oxygen

A

16

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21
Q

Molecular weight of oxygen

A

32
As is O2 molecule

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22
Q

How is oxygen produced for hospital use

A

Fractional distillation of air

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23
Q

Colour of nitrous oxide (N2O) cylinder

A

Completely blue

24
Q

How is nitrous oxide produced for medical use

A

Heating ammonium nitrate and extracting N2O from impurities

25
Q

Why can’t use nitrous oxide in pneumothorax or ophthalmic surgery

A

Nitrous oxide 40x more soluble than nitrogen

Diffuses into air filled cavities faster than nitrogen can diffuse out and therefore increases size if air filled cavities

26
Q

How is Entonox produced

A

Bubbling oxygen through liquid nitrous oxide
(Poynting effect)

50% N2O + 50% O2

27
Q

Colour of Entonox cylinder

A

Blue with blue and white collar

28
Q

Safety point for Entonox storage

A

Pseudocritical temperature -5.5 degrees Celsius at 117 bar and -7 degrees at 137 bar

Therefore cylinders must be kept above this temperature to prevent liquefaction and hence separation out of N2O which can lead to delivery of hypoxic mixture

29
Q

Colour of CO2 cylinder

A

Completely grey

30
Q

How is Carbon dioxide produced for medical use

A

heating calcium carbonate or magnesium carbonate

31
Q

Colour of helium cylinder

A

Completely brown

32
Q

Features / medical use of helium

A

Lower density but higher viscosity than nitrogen

Therefore in upper airway obstruction where turbulent flow is present, Helium-oxygen mixture will increase flow compared with nitrogen-oxygen mixture

33
Q

Heliox

A

Helium-oxygen mixture
79% helium
21% Oxygen

34
Q

Colour of Heliox cylinder

A

Black with Brown and White collar

35
Q

Boiling point of oxygen

A

-183 degrees Celsius

36
Q

Melting point of oxygen

A

-219 degrees Celsius

37
Q

Critical temperature of oxygen

A

-118 degrees Celsius

38
Q

Critical pressure of oxygen

A

50 Bar

39
Q

Saturated vapour pressure of oxygen at 20 degrees Celsius

A

1.4 Bar

40
Q

Boiling point of Nitrous oxide

A

-88 degrees Celsius

41
Q

Melting point of Nitrous oxide

A

-91 degrees Celsius

42
Q

Critical temperature of Nitrous oxide

A

36.5 degrees Celsius

43
Q

Critical pressure of Nitrous oxide

A

72 Bar

44
Q

Saturated vapour pressure of Nitrous oxide at 20 degrees Celsius

A

50.8 Bar

45
Q

Boiling point of CO2

A

-79 degrees Celsius

46
Q

Melting point of CO2

A

-57 degrees Celsius

47
Q

Critical temperature of CO2

A

30 degrees Celsius

48
Q

Critical pressure of CO2

A

73 Bar

49
Q

Saturated vapour pressure of CO2 at 20 degrees Celsius

A

57 Bar

50
Q

Boiling point of helium

A

-269 degrees Celsius

51
Q

Melting point of helium

A

-272 degrees Celsius

52
Q

Critical temperature of helium

A

-268 degrees Celsius

53
Q

Critical pressure of helium

A

2.3 Bar

54
Q

Saturated vapour pressure of helium at 20 degrees Celsius

A

N/A

55
Q

Reynold’s number definition

A

Dimensionless number which predicts likelihood of laminar or turbulent flow

Not absolute

56
Q

Reynold’s number equation

A

Reynold’s number = (Velocity of fluid x density of fluid x diameter of tube) / viscosity of fluid

57
Q

Reynold’s number interpretation

A

< 2000 predicts laminar flow

2000 - 4000 predicts transitional flow

> 4000 predicts turbulent flow

Anaesthetic FRCA Primary - eLFH Physics (33 decks)

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