Simplified theory of Archimedean screws

Abstract

The Archimedean screw pump is one of the oldest hydraulic machines. Today, it is employed in pumping as well as - operating in reverse - in an energy conversion role. Despite its age, no consistent theory links the screw's geometry with its mechanical efficiency. Based on geometrical parameters and an idealised energy conversion process for one turn of the helix, a theoretical model is developed and compared with experimental results. Theoretical maximum efficiencies were found to be a function of the screw's geometry and matched reported experimental results well. The statement that the efficiency of a screw is a function of losses only could not be confirmed.