The world is now facing a serious energy problem. Mass consumption of fossils fuels such as oil and coal cause global warming and other environmental problems due to acid rain. To deal with this problem, hydropower should be the focus of the electric power generation systems, as clean and cool energy sources with the highest energy density. However, as any suitable type of turbine has not been determined yet for the range of small hydropower at this stage, we shall need further study of the most effective turbine type.
According to the recent study results related to the small hydropower development, wasted energy by pressure reducing valve at the end of the pipeline can be extracted by a small hydropower turbine.
The main concept of using the small hydropower turbine is based on using the different water pressure levels in pipe lines. A propeller type hydropower turbine, which is called as tubular turbine, has been used in order to use this renewable differential pressure energy.
Conventionally, tubular turbines have been used in the range of relatively low head of below 20m. However, in order to widen the operating range of the turbine, the present study is focused on the developing a new design of tubular turbine which can be used in the head range of 1.5m~20m.
Moreover, this study aims to propose the optimum design of the tubular turbines using differential pressure in marine small hydro power plants, water supply systems, and wastewater hydro power plants. The reliability of the proposed design method can be acquired by theoretical analysis, CFD analysis and experimenting with tubular turbine models.
According to the present study, the results are obtained as follows.
(1) Operational range of tubular turbine head using differential pressure in the water supply system can be extended to over 10m by the adoption of variable vane angle and number of turbine runners.
(2) An optimum design method for the best turbine efficiency by changing an opening angle of the runner vane is inconsistent with those of CFD analysis for the tubular turbine efficiency.
(3) Under 10m of the hydraulic head range, the optimum operational condition can be obtained by using 4 pieces of runner vane according to the present design method, and more than 10m of the hydraulic head range, using 5 pieces of runner vane is more efficient.
(4) Application of servo motors for the variation of runner vane opening angle allows extension operational condition of the tubular turbine for the expected small hydropower resources.
(5) It is found that a tubular turbine can be used for a low head under 1.5m as operating marine small hydro power plant. The tubular turbine efficiency under the hydraulic head of 19.5m from a wastewater hydro power plant is also verified.
(6) This study shows that a tubular turbine can be used under the head from 1.5m to 20m and at 2.5m3/sec. Five types of the tubular turbines can be standardized for all conditions. If necessary, an operational range of tubular turbines can be extended by parallel-serial conversion.