Compressible and Incompressible Fluids
A compressible fluid is a fluid whose density changes noticeably when pressure or temperature changes. Gases and vapours usually fall under this category because the distance between their molecules is relatively large, so even a small change in pressure or temperature can cause a significant change in density.
An incompressible fluid is a fluid whose density remains nearly constant even when pressure or temperature changes. Most liquids are treated as incompressible because their density variation is very small under normal engineering conditions.
In practical fluid mechanics, gases may sometimes be treated as incompressible when the pressure and temperature changes are very small. However, in applications involving pressure waves, high-speed flow, or strong pressure variations, compressibility becomes important.
The study of compressible and incompressible fluids is important in the design and operation of pumps, compressors, pipelines, turbines, and other fluid machinery.
Quick Summary
- Compressible fluid: Density changes significantly with pressure or temperature.
- Incompressible fluid: Density changes very little with pressure or temperature.
- Gases and vapours: Usually compressible.
- Liquids: Usually incompressible.