The Effect of the Ratio of Wheel Tangential Velocity and Upstream Water Velocity on the Performance of Undershot Waterwheels

Abstract

Pico hydro type undershot waterwheels are one of solutions to overcome energy crises in remote areas. The geometry of the wheels is based on the Betz limit concept: a wheel tangential velocity of one-third of the upstream water velocity. Although this concept has long been proposed, it has never been empirically demonstrated. The aim of this study was to identify the optimal ratio between the wheel tangential velocity (U) of undershot water wheels and the average upstream water velocity (V). The experimental work was done in a run of river conditions (irrigation) in remote areas with a discharge of 0.105 m3/s. Two instruments measured power output: a tachometer (used to measure wheel rotational speed) and a force meter (used to measure torque) with accuracies of 0.05% and 0.1 kg, respectively. Testing variation was done 29 times by loading masses ranging from 0–56 kg. A peak efficiency of 24.31% was achieved with a mechanical power of 10.55 W, a wheel rotation of 2.26 rpm and a torque of 29.01 N·m. This peak efficiency occurred at a U/V ratio of 0.39 if using the Gaussian fit approach of 0.41. Thus, the recommended ???? value for designing the undershot waterwheel is 0.4????. Furthermore, in the application of undershot waterwheels in independent power plants with a run of river conditions in remote areas, the installation of filter bars prior to the wheels is needed.