Compressible vs Incompressible Fluids
Fluids are either gases or liquids that take the shape of the container. In fluid dynamics, the compressibility of a fluid is a very important factor. In nature, all the fluids are compressible, but we define incompressible fluids for our convenience of study. The concepts of compressible and incompressible fluids play a major role in fields such as fluid dynamics, fluid statics, aviation and many other fields. It is vital to have a proper understanding in the concepts of compressibility of fluids in order to understand such fields. In this article, we are going to discuss what compressibility is, what compressible fluids and incompressible fluids are, their definitions, the similarities of compressible and incompressible fluids and finally the differences between compressible fluid and incompressible fluid.
What is Compressible Fluid?
Every fluid we encounter in our daily lives is compressible. To understand what compressible fluids is one must first understand what compressibility is. The compressibility of a fluid is the reduction of the volume of the fluid due to external pressures acting on it. A compressible fluid will reduce its volume in the presence of an external pressure. The quantitative measurement of the compressibility is taken as the relative volume change of the liquid in response for a pressure change. The compressibility is denoted with a β or a κ. The compressibility is defined mathematically as κ =(-1/v) ∂V/∂p, where V is the volume and p is the pressure. In reality, every gas is highly compressible, but liquids are not highly compressible. Compressibility is defined in two forms. The adiabatic compressibility describes the compressibility of the system when the temperature of the system is constant. This is denoted by βV. The isothermal compressibility refers to the compressibility measured under no energy transfer between the system and the surroundings. This is denoted by βS. Since an adiabatic process is also isentropic, this process is a constant entropy process.
What is Incompressible Fluid?
Incompressible fluids are a hypothetical type of fluids, which are introduced for the convenience of calculations. An incompressible fluid is a fluid that does not change the volume of the fluid due to external pressure. Most of the basic calculations done in fluid dynamics are done assuming the fluid is incompressible. The approximation of incompressibility is acceptable for most of the liquids as their compressibility is very low. However, the compressibility of gases is high, so gases cannot be approximated as incompressible fluids. The compressibility of an incompressible fluid is always zero.
What is the difference between Compressible Fluids and Incompressible Fluids?
• Compressible fluids are found in reality. In fact, all of the fluids found in nature are compressible. Incompressible fluids are a concept developed for ease of calculations.
• Compressible fluids reduce in volume when an external pressure is applied, but incompressible fluids do not change the volume.
• The fluid dynamic calculations for the incompressible fluids are very easy compared to the calculations involving compressible fluids.