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.
Bulk Modulus
In terms of the density:
High bulk modulus means hard to compress.
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: vapour pressures = external pressure on the liquid
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 between adjacent layers is proportional to the velocity gradient perpendicular to the layers.
Here,
Finally we will get Newton’s law of viscosity as
Coefficient of dynamic viscosity
Above,
Fluids can be divided into 2 parts:
is a constant: Newtonian fluid is not a constant: Non-newtonian fluid
Only Newtonian fluids are focused on for s1.
Coefficient of kinematic viscosity
Pressure
A force is exerted on all surfaces in contact with a fluid. A scalar.