An automatic pump is developed using low water-head hydropower. The energy conversion efficiency η of the gas-water energy conversion equipment is the focus. In this equipment, low-head water normally drains to the vertical downcomer. When water particles separate via gravity, a vacuum is generated, and air is mixed into the water spontaneously. High-pressure gas is ultimately produced at the end of the pipe. To discuss the effects of the air intake pipe diameter, river drop and water flow rate on η, a full-scale experiment is conducted, and an analytical solution based on the separation of water particles is derived. The air intake pipe diameter has almost no effect on η, but η changes dramatically as the water flow rate varies. Meanwhile, η initially increases and then decreases as the river drop increases. These findings enable the development of a method for low water-head hydropower utilization.
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Considering the new applications of high-pressure gas pumps in practical engineering, the gas-liquid two-phase flow in small-diameter vertical pipes of the system in this study was tested. The gas volumetric flow rate, water volumetric flow rate, and working efficiency at different submergence height, pressure, and head values were measured. The results revealed that the pressure of high-pressure gas determines the gas consumption of the device and that a linear relationship exists between them. The void fraction of the vertical pipe effectively reflects the mixing of gas and water and affects the pumping capacity of the system. The water volumetric flow rate and working efficiency of the system reach their maximum values simultaneously when the void fraction reaches β0, which is a fixed value. A smaller diameter of the gas inlet pipe d enables the pump water efficiency to reach its peak at a lower pressure. We also present an optimization scheme for the selection of the diameter of vertical pipe D. These findings help facilitate a better understanding of the mechanism of the phase distribution and the interaction of the gas-water phases with each other in small-diameter vertical pipes and provide the basis for experiments to further improve the device performance.
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