Experimental determination of the efficiency of an air injection device in flowing water

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In North America, for ecological as well as economical reasons, fish-friendly hydroelectric equipment is preferred. In particular, the question of how much oxygen is contained in released waters from hydroelectric plants has been raised since it conditions the presence and health of fishes downstream of these structures. This, indeed, has an immediate effect on the river fish industry and biodiversity. More specifically, released waters are meant to meet standards on surface waters dissolved oxygen rates which must not fall beyond a prescribed threshold. On average, a minimum of 5 mg/l is required. For several locations, depending on seasons, oxygen depleted water is released by dams (natural dissolved oxygen gradient, leaf decomposition). Governments stiffen their legislations such that surface water dissolved oxygen standards are more and more enforced by the law. Hydroelectric turbine manufacturers need to re-oxygen water before release. In order to improve efficiently the oxygen content, they need to inject small air bubbles. The specific problem that Alstom faces is how to design and assemble air injection devices such that they generate bubbles of very small diameters that will be distributed uniformly downstream of the turbine. To fulfill the needs of Alstom, injection devices must be designed and tested for varying air and water flow rates. In particular the apertures that constitute the interface between water and air to be injected are a critical aspect of the injection device. As such, size and shape of various apertures will be tested for air injection. The experiments will be monitored to precisely measure air and water flow rates and pressures at inlet. Pressure transducers and optical probes will be used to this aim. Based on experimental results, correlations will be identified that will serve selecting best sizes and shapes. These correlations will serve to deduce partial similitude laws that will help devising injection apertures at real scale.