Gas expander is a power generating mechanical device that converts thermal energy into useful mechanical work. It does so by using an isentropic process. Gas expander is a centrifugal or axial flow turbine through which a high-pressure gas is expanded to produce work that is typically used to drive a compressor. Due to the reason that work is extracted from the expanding high-pressure gas, the expansion is isentropic and the low-pressure exhaust gas from the turbine is at a very low temperature, often as low as 200 K or less. Turbo expanders are very widely used as sources of refrigeration in industrial processes such as the extraction of ethane as well as natural gas liquids from natural gas, the liquefaction of gases and other low-temperature processes.