Investigating the potential for using a simple water reaction turbine for power production from low head hydro resources

Abstract

In this analysis the simple reaction water turbine known as Barker’s Mill is revisited. The major geometrical and operational parameters have been identified and, using principles of conservation of mass, momentum and energy, the governing equations have been developed for the ideal case of there being no frictional losses. The solutions of the resulting equations are offered in a non-dimensional form. It is shown that the maximum torque produced by the machine is developed when the turbine is stationary. At this point the net output power is zero. As the load torque is decreased the turbine rotates and power is produced. Furthermore, because of a centrifugal pumping effect, the mass flow rate of water through the turbine increases during acceleration. Further decrease in the load torque is accompanied by increases of speed, output power, water mass flow rate and efficiency. It is shown that when the load torque is reduced towards half the value of the torque at the stationary condition, water mass flow rate, rotational speed and output power tend towards infinity. Under this condition the efficiency of the machine approaches unity. The non-dimensional characteristics of the idealized turbine are used to investigate the general characteristics of the machine and to explore its application for production of power from water reservoirs with low heads. Theoretical analysis of a simple reaction turbine is presented including consideration of the fluid frictional losses for a practical situation. A practical turbine will never run away towards infinite speed and the maximum power and efficiency of such a turbine will depend on the fluid frictional losses. Here a new factor is defined, representing the overall fluid frictional losses within the turbine. Finally this paper presents briefly the experimental performance results for two simple reaction water turbine prototypes. The two turbine prototypes under investigation have rotor diameters Ø0.24m and Ø0.12m respectively. The two turbine models were tested under supply heads ranging from 1m to 4m. The simple reaction water turbine can operate under very low hydro-static head with high energy conversion efficiency. This type of turbine exhibits prominent self-pumping ability at high rotational speeds. Under low head to achieve high rotational speeds the turbine diameter should be very small and this limits the volumetric capacity and hence the power generation capacity of such a turbine. Consequently the practical applications of this turbine would be limited to micro-hydro power generation. The split pipe design of the reaction turbine tested is easy to manufacture and it has been shown to have overall energy conversion efficiency of approximately 50% even under low heads.