What is the Difference Between Compressible and Incompressible Fluids?

The main difference between compressible and incompressible fluids lies in their response to external pressure and density changes. Here are the key differences between the two:

1. Volume change: Compressible fluids change their volume when subjected to external pressure, while incompressible fluids maintain a constant volume, regardless of the applied pressure.
2. Density change: Compressible fluids can experience density changes during flow, whereas incompressible fluids do not change their density.
3. Flow dynamics: Compressible flow is a flow that changes in density under pressure, whereas incompressible flow does not.
4. Mathematical models: Incompressible flow greatly simplifies the Navier-Stokes equations, which are used to describe fluid dynamics, making it easier to analyze and solve. Compressible flow is more complex, requiring a pair of equations to determine the flow velocity field as well as the density.

In reality, all fluids are compressible to some extent, but many fluids can be considered incompressible for practical purposes because their density changes are negligible. For example, air is considered an incompressible fluid when its flow velocity is 100 m/s or less, and a compressible fluid when the velocity is greater than 100 m/s. Water is often considered an incompressible fluid in fluid dynamics, even though it is technically compressible.

Comparative Table: Compressible vs Incompressible Fluids

The main difference between compressible and incompressible fluids lies in their density changes under pressure and temperature variations. Here is a table summarizing the differences between compressible and incompressible fluids:

In reality, all fluids are compressible to some extent, but incompressible fluids are a concept developed for the ease of calculations and to simplify fluid dynamics analysis.