Fluid and Thermal Systems
Fluid is a general term used to represent a gas or a liquid. A fluid is said to be incompressible if its density does not change with pressure. All gases are considered compressible, whereas liquids can be considered incompressible. Although real liquids are actually compressible, the changes in their densities are insignificant when pressure is varied. Fluid systems can be divided into pneumatics and hydraulics. A pneumatic system is one in which the fluid is compressible, whereas a hydraulic system is one in which the fluid is incompressible. A general type of incompressible liquid systems is the liquid-level system. These systems are operated by adjusting the heights or levels of liquids in storage tanks.