Maximum Efficiency and Minimum Ecological Impact Water Wheel

Abstract

There are three types of water wheels: overshot wheel, breast wheel, and undershot wheel. Undershot wheels only exploit the kinetic energy (speed) of the water and have a theoretical maximum efficiency of 50%. The efficiency of overshot wheels depends substantially on the shape of the blades, which must not allow the water to flow out of the wheel at too high a level, thus reducing efficiency. In addition, its maximum unit flow rate is the lowest of all types of wheels. The largest variety of water wheels is represented by breast shot (side) wheels. Wheels of this type have blades designed in such a way that hydraulic losses are minimal when water enters the wheel (Sagebien), or when the wheel leaves the water (Zuppinger). Hydraulic wheels usually exploit small water falls (0.5m-4m) on rivers where relatively high water flows are usually available (lower courses). The research on which this article is based aims to develop types of hydraulic wheels that minimize hydraulic losses and allow the transit of high water flows. The type of wheel that meets these two conditions is the Sagebien wheel. In this wheel, hydraulic losses are minimal at the water inlet, and the unit flow rate is the highest. There are physical limits (water speed and depth, blade configuration, etc) that condition the wheel's efficiency. This article describes these limits and the need for experiments to quantify them.