Working fluid

Some hydraulic and passive heat-transfer systems are open to the water supply and/or atmosphere, sometimes through breather filters.

The working fluid's properties are essential for the full description of thermodynamic systems.

Pressure, temperature, enthalpy, entropy, specific volume, and internal energy are the most common.

This issue does not really affect thermodynamic analysis since in most cases it is the end states of a process which are sought after.

Also, in thermodynamic cycles energy may be input to the working fluid by means of a compressor.

In a thermodynamic cycle it may be the case that the working fluid changes state from gas to liquid or vice versa.

The physical and chemical properties of the working fluid are extremely important when designing thermodynamic systems.

Compared with water (which can also be used as a refrigerant), ammonia makes use of relatively high pressures requiring more robust and expensive equipment.

In the open cycle gas turbine, air enters a compressor where its pressure is increased.

The fluid is then transferred to a combustion chamber where this time heat energy is input by means of the burning of a fuel.