If the fluid quality of a change in the status process is not in heat exchange with the outside world, the process is called adiabatic process. Orifice by cutting expenditure when measuring gas flow, fluid flow orifice flow holiday when the state changes, May be similar to that of a thermal insulation process. In order to measure the gas expansion coefficient can be calculated, measured on the need to know characterization of the process gas for insulation insulation index. If the gas can be considered to be ideal gas, its insulation K index is set Heat and pressure than the specific heat capacity ratio, that is,

KCp / Cv 125

The actual gas, thermal insulation and gas index of the types, the pressure and temperature. Generally speaking, single-atom gases insulation for the K index 1.66, diatomic gas insulation K index was 1.41. Table l-5 Given the various gas insulation index more accurate values.