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Measurement of fill level and effects of overflow in power-generating Archimedes screws

ABSTRACT Archimedes screw generators are an increasingly popular form of small-scale hydropower generation. The power output of an Archimedes screw depends on water fill level within the rotating screw, which is difficult to directly observe. Fill level in a very small screw with a transparent plastic trough has been successfully measured photographically, but this is not practical in larger screws. An alternative, non-optical method was developed using a static pressure sensor in the screw trough to measure fill height during screw operation, which is a new capability. Non-dimensional fill height was measured with an uncertainty of ± 0.072. This method was then used to experimentally investigate overflow in operating screws as a function of fill height. Existing overflow models are based on fill height, screw geometry and inclination angle assuming static water conditions. Results of these experiments showed that overflow in laboratory-scale screws is also dependent on rotational speed.