eLFH - Density and Viscosity Flashcards
Density definition and equation
Mass per unit volume
Density = mass / volume
Effect of pressure on density / viscosity
Increased pressure increases density and viscosity
More particles in a smaller area
Effect of temperature on density / viscosity
Increased temperature reduces density and viscosity
Higher average kinetic energy of molecules within the gas so particles move further apart
Specific gravity of gases definition
Density of the gas divided by the density of air (1.2 kg/m^3)
Specific gravity of gases interpretation
Gases with specific gravity > 1 are more dense than air
< 1 less dense than air
Specific gravity of liquids and solids
Density is compared with density or water
Viscosity definition
Tendency of a fluid to resist flow
Denoted with Greek letter Eta (η) (or sometimes Mu)
Units of viscosity
Poise (P)
Newtonian fluid
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
Non-Newtonian fluid
Fluid which may deform when stirred or become less viscous
SI units of flow
kg/s
Types of flow
Laminar - streamlined flow in smooth layers
Turbulent - interrupted flow with swirls
Importance of viscosity vs density in laminar vs turbulent flow
Viscosity more important in laminar flow
Density more important in turbulent flow
Hagen-Poiseuille equation
Can be used for laminar flow only, not turbulent flow
Where does turbulent flow occur in a tube
At and orifice
Orifice definition
Tube in which diameter exceeds length
How to measure gas flow
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
Which part of bobbin to read flow from
Top of a flat topped bobbin
Middle of a sphere bobbin
Colour of oxygen cylinder
Black with white collar
Atomic weight of oxygen
16
Molecular weight of oxygen
32
As is O2 molecule
How is oxygen produced for hospital use
Fractional distillation of air
Colour of nitrous oxide (N2O) cylinder
Completely blue
How is nitrous oxide produced for medical use
Heating ammonium nitrate and extracting N2O from impurities
Why can’t use nitrous oxide in pneumothorax or ophthalmic surgery
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
How is Entonox produced
Bubbling oxygen through liquid nitrous oxide
(Poynting effect)
50% N2O + 50% O2
Colour of Entonox cylinder
Blue with blue and white collar
Safety point for Entonox storage
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
Colour of CO2 cylinder
Completely grey
How is Carbon dioxide produced for medical use
heating calcium carbonate or magnesium carbonate
Colour of helium cylinder
Completely brown
Features / medical use of helium
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
Heliox
Helium-oxygen mixture
79% helium
21% Oxygen
Colour of Heliox cylinder
Black with Brown and White collar
Boiling point of oxygen
-183 degrees Celsius
Melting point of oxygen
-219 degrees Celsius
Critical temperature of oxygen
-118 degrees Celsius
Critical pressure of oxygen
50 Bar
Saturated vapour pressure of oxygen at 20 degrees Celsius
1.4 Bar
Boiling point of Nitrous oxide
-88 degrees Celsius
Melting point of Nitrous oxide
-91 degrees Celsius
Critical temperature of Nitrous oxide
36.5 degrees Celsius
Critical pressure of Nitrous oxide
72 Bar
Saturated vapour pressure of Nitrous oxide at 20 degrees Celsius
50.8 Bar
Boiling point of CO2
-79 degrees Celsius
Melting point of CO2
-57 degrees Celsius
Critical temperature of CO2
30 degrees Celsius
Critical pressure of CO2
73 Bar
Saturated vapour pressure of CO2 at 20 degrees Celsius
57 Bar
Boiling point of helium
-269 degrees Celsius
Melting point of helium
-272 degrees Celsius
Critical temperature of helium
-268 degrees Celsius
Critical pressure of helium
2.3 Bar
Saturated vapour pressure of helium at 20 degrees Celsius
N/A
Reynold’s number definition
Dimensionless number which predicts likelihood of laminar or turbulent flow
Not absolute
Reynold’s number equation
Reynold’s number = (Velocity of fluid x density of fluid x diameter of tube) / viscosity of fluid
Reynold’s number interpretation
< 2000 predicts laminar flow
2000 - 4000 predicts transitional flow
> 4000 predicts turbulent flow
