The West number is an empirical parameter used to characterize the performance of Stirling engines and other Stirling systems.
The West number is often used to approximate of the power output of a Stirling engine.
The average value is (0.25) for a wide variety of engines, although it may range up to (0.35),[1] particularly for engines operating with a high temperature differential.
To estimate the power output of a new engine design, nominal values are assumed for the West number, pressure, swept volume and frequency, and the power is calculated as follows:[2] For example, with an absolute temperature ratio of 2, the portion of the equation representing temperature correction equals 1/3.
This factor accounts for the difference between the West equation, and the Beale equation in which this temperature term is taken as a constant.