Development of an Equation for the Volume of Flow Passing Through an Archimedes Screw Turbine

Archimedes Screw Turbines (ASTs) are a new form of hydraulic energy converter for small hydroelectric powerplants. ASTs can operate even with very low levels of water and are a safer solution for wildlife and especially fish. It is very important to have an estimation about the volume of water that can pass through the screw for designing AST hydropower plants, making operation plans and operation. However, developing a general relationship for the volume of flow entering an AST as a function of inlet water level and other variables for all screw sizes is challenging: In ASTs, water flows through a helical array of blades that are wrapped around a central cylinder while there is a small gap between the trough and screw which could be considered as free flow. Screw geometry and rotation speed are two other important factors that intensify the scaling difficulties. In this study, an equation is developed to estimate the volume flow rate that passes through an AST based on its inlet water level, rotation speed and pitch. The resulting relationship is validated using data from five lab-scale and one full-scale AST. Then it is optimized using Genetic Algorithms to produce a general equation for all screw sizes. Data analysis is completed to find and control effective parameters by using principal component analysis (PCA) techniques. Finally, the equation is modified to maximize accuracy. Results indicate that the proposed equation can estimate the volume flow rates of both lab-scale and full-scale studied screws with reasonable accuracy.