Properties of Fluids
Mass Density
At a point:
For liquids
Varies very slightly with temperature (negligible in calculations).
Example: Water
- at - at
For gases
Highly dependent on pressure & temperature.
Specific Weight / Unit Weight
Relative Density / Specific Density
For solids and liquids, water is the standard substance.
Pressure
A force is exerted on all surfaces in contact with a fluid. A scalar.
Vapour Pressure
Vaporisation is when evaporation happens at the free surface of a liquid.
Vapour Pressure is the pressure due to liquid vapour just above the free surface of the liquid. Increases with temperature.
A liquid boils when:
Bulk Modulus
In terms of the density:
High bulk modulus means hard to compress.
Surface Tension
Negligible in many applications. Considered in small-scale applications. Causes capillary effect.
Viscosity
The force resisting the flow of a liquid.
In liquids, viscosity is mainly caused by inter-molecular attraction. Decreases slightly with temperature.
In gases, mainly due to momentum exchange between molecules. Increases with temperature.
Newton’s law of viscosity
In straight & parallel flow, the shear stress
As
Coefficient of dynamic viscosity
Above,
Fluids can be divided into 2 types:
is a constant: Newtonian fluid is not a constant: Non-newtonian fluid (not focused on for s1)