Hydrodynamic Screws: From Archimedes to Electricity

Hydrodynamic Screws: From Archimedes to Electricity

By Emanuele Quaranta

Birth of the Hydrodynamic Screw

The Hydrodynamic Screw is one of the oldest hydraulic machines still in use today. One theory regarding its creation supposes that the King of Egypt asked Archimedes to design a machine to remove water from his ships. A second theory suggests that the device was created hundreds of years prior to the birth of Archimedes and he adapted it to make it popular around the known world. Hence, this machine is also called Archimedes screw.

Further Development

The hydrodynamic screw was initially used for pumping water from one location to another, of higher altitude. Hence, it can be used as fish ladder to provide a method to allow fish to pass over a potential danger or obstruction, such as a dam or a turbine. In 2001, John Burland used the Archimedes screw to stabilize the leaning tower of Pisa: using an Archimedes screw, soil was removed from the foundations without any damage and reduced the inclination angle of the tower by approximately 0.5°. The screw was also used in the Netherlands to create polders (reclaimed land that is under sea level), where excess water is pumped from the area of interest towards the sea.

Furthermore, the Archimedes screw is employed during injection molding to deliver the compound material to the mold. The technology of this screw has been also used in the medical field in over 20,000 patients in need of a heart transplant, keeping them alive until a donor heart can be found, with the aim of replacing the left ventricle.

The Hydrodynamic Screw for Electricity Generation

At the end of the 20th century, the hydrodynamic screw started to operate as turbine, thus in the reversed way with respect to the pump principle. The first hydrodynamic screw turbines were installed in Europe in 1994. The torque is created by the hydrostatic force of water in the buckets, which makes the screw rotate around an inclined axis, typically 22°-35° on the horizontal. They can be used up to a hydraulic head of 8 meters and at maximum flow rates of 6 cubic meters per second.

Archimedes screws exhibit maximum hydraulic efficiency of 80-85%, constant over a wide range of flow rates. Therefore, like water wheels, Archimedes screws can represent an interesting technology in the micro-mini hydropower field. The only drawback is that they need a gearbox to match the electric grid frequency, since they generally turn at less than 50 revolutions per minute.

Future Prospects: More Than Just a Hydropower Converter!

The tidal barrage in the Severn Estuary is the most discussed tidal range project in the UK; it was suggested almost 100 years ago. However, each time that it was discussed, it was dismissed due to the very high initial costs and adverse environmental effects. The Archimedes screw turbine can also operate in this way, and thanks to his simple design the initial costs can be reduced. They can also be used with a horizontal rotation axle as tidal stream turbines, in series across a waterway.

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