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