IntermediateTopic 45 of 105Thermodynamics & Fluids
Fluid properties
Density, viscosity, surface tension and compressibility characterise fluids.
In depth
Density ρ, specific weight γ=ρg, specific gravity, viscosity, surface tension, vapour pressure, bulk modulus K (compressibility). Liquids are nearly incompressible; gases change density with pressure and temperature. Properties depend on temperature strongly.
Key points
- Water 1000 kg/m³
- Air 1.2 kg/m³
- Capillary rise h=2σcosθ/(ρgr)
ExampleWater's bulk modulus is 2.2 GPa, so sound travels at about 1480 m/s.
Fluid properties such as density and viscosity decide how a fluid behaves in pipes, pumps and tanks, so they appear in nearly every fluid calculation.
What is Fluid properties?
Density, viscosity, surface tension and compressibility characterise fluids.
Why is it important to understand fluid properties?
Fluid properties such as density and viscosity decide how a fluid behaves in pipes, pumps and tanks, so they appear in nearly every fluid calculation.
What is viscosity?
The resistance of a fluid to shear deformation, which governs how easily it flows and how much force is needed to move it.
Why does viscosity matter for pumping?
Higher viscosity increases the pressure drop and power needed to move the fluid through pipes and components.
How is Fluid properties used in practice?
Typical applications include choosing a fluid for a hydraulic system based on viscosity at operating temperature, estimating the pressure needed to pump oil through a pipe and selecting a lubricant that keeps a bearing film at the right thickness.
What should I learn before Fluid properties?
Study "Thermodynamic relations" first (topic 44 of 105 in Thermodynamics & Fluids). It covers the groundwork this topic builds on.
What are the key points of Fluid properties?
Water 1000 kg/m³. Air 1.2 kg/m³. Capillary rise h=2σcosθ/(ρgr).
Can you give an example of Fluid properties?
Water's bulk modulus is 2.2 GPa, so sound travels at about 1480 m/s.
What comes after Fluid properties?
The next topic is "Viscosity", which builds directly on this one.
How difficult is Fluid properties?
It is classed as Intermediate in Thermodynamics & Fluids (topic 45 of 105). It is an intermediate topic. Work through the beginner topics in Thermodynamics & Fluids first.