Abstract
During the design and optimization of hydraulic turbomachines, the experimental evaluation of hydraulic performances beyond the best efficiency point and for off-design conditions remains essential to validate the simulation process and to finalize the development. In this context, an alternative faster method to measure the efficiency of hydraulic turbomachines using a dynamic approach has been investigated. The so-called “sliding-gate” dynamic measurement method has been adapted and implemented on the hydraulic test rig of the HES-SO Valais//Wallis, Sion, Switzerland. This alternative approach, particularly gainful for small-hydro for which the investment devoted to development is limited, has been successfully assessed on two cases for drinking water networks energy recovery. A 2.65 kW double-regulated laboratory prototype of a tubular axial micro-turbine with two independent variable speed counter-rotating runners and a 11 kW multi-stage centrifugal pump-as-turbine (PAT) with variable speed have been selected. The hydraulic efficiency results obtained by dynamic measurements are compared to the ones obtained by the classical steady point-by-point method. This dynamic method, suitable not only for hydraulic machinery, allows: (i) reducing significantly (up to 10×) the time necessary to draw the complete efficiency characteristics of a hydraulic machine; (ii) rapidly detecting the hydrodynamic instabilities within the operating range of the machine.
Highlights
Hydropower, small and large, remains the most important source of renewable energy for electrical power production providing 16.4% of the world electricity mix in 2016 [1]
The hydraulic-to-electrical efficiency ηh-elec can be expressed as the product between the hydraulic-to-mechanical efficiency ηh-mec and the electrical efficiency of the generator ηelec : ηh−elec = ηh−mec × ηelec = ηh × ηm × ηelec = ηe × ηq × ηrm × ηm × ηelec [%]
Ηh-mec results from the product between the hydraulic ηh and the bearing efficiency ηm, with the hydraulic efficiency ηh including the efficiency of the disc friction ηrm, the energetic efficiency ηe as well as the volumetric efficiency ηq
Summary
Hydropower, small and large, remains the most important source of renewable energy for electrical power production providing 16.4% of the world electricity mix in 2016 [1]. In Switzerland, hydropower provides 56.7% of the electricity of the country, 5.7% coming from small-hydro (see [2]), considering plants with an “annual average used” capacity up to 10 MW [3]. In the post-Fukushima era, Switzerland has decided to renounce to its nuclear energy power stations and to accelerate the transition to a sustainable energy future based on carbon-free renewable electricity sources. To increase the small hydropower production while limiting the environmental impact, the primary sustainable solution would be to harness the energy of existing infrastructure, such as drinking water networks or wastewater networks
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