Compression Basics

The basis of a positive displacement compressor is that pressure is related to volume with an exponential relationship:

formula_1

Or more simply:

formula_2
The work or energy required to compress a gas by a particular amount to a particular pressure can be calculated with the following integral:

formula_3

Graphically, the result of this integral is, in effect, the area under the Pressure versus Volume curve (PV Plot), shown in the figure below. The curves in a PV plot show how the pressure increases as volume decreases. For different compression processes, the curves vary, resulting in different amounts of work required to achieve a certain pressure.

pressure_chart1

As seen in the plot all compression processes fall between two extremes: adiabatic, where no heat is exchanged with the outside environment and the energy put into the system remains internal, and isothermal, where energy is removed from the system in the form of heat and the temperature of the gas remains constant. In practice, all compression processes fall somewhere between adiabatic and isothermal and are known as polytropic processes. To achieve a more efficient compression process, it is ideal to reduce the polytropic constant to as close to the isothermal process as possible, where the polytropic constant is 1. Our proprietary compressor design is able to achieve polytropic constants of 1.06 or lower, reducing the amount of work required to achieve a target pressure and improving efficiencies over conventional, adiabatic compressors by forty percent or more.