Design considerations for an Archimedean screw hydro turbine

Archimedean screws have been used for centuries, but only for pumping water. In the last decades, a growing interest appeared to also use them as hydro turbines for electricity generation. While Archimedean screws are already well optimized for working as pumps, studies are still carried out to identify those parameters that assure the best performances when they operate as turbines. This paper proposes a simple yet efficient procedure for the design of an Archimedean screw operating as a turbine. The most important formulas proposed in the paper are those for calculating the outer diameter and the rotational speed of the screw. The condition imposed for finding the diameter is the maximization of the torque produced. The calculation of the diameter requires to estimate the volume of the water buckets that form between the blades of the screw. It is practically impossible to find an analytical formula for this volume, but a rough estimate can be found easily. This rough estimate is corrected afterwards based on regression of data available for turbines that already operate with good efficiencies. The rotational speed is then determined based on the condition that the rated discharge can run through the turbine operating at the rated speed.