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In this article, the development of the energy separation for the vortex tube has been briefly reviewed. This review mainly focuses on three aspects, they are the energy separation principle, the design criteria of vortex tubes, and practical application. First, the research progress on the energy separation principle of the vortex tube from several aspects has been introduced, such as friction, pressure gradient, acoustic streaming, secondary circulation and multi-circulation theory. In addition, the control factors that affecting the performance of the vortex tube were summarized. Furthermore, due to its simple structure, safety and stability, the vortex tube is widely used in the field of refrigerating and heating, mixture separation. This survey, while extensive cannot cover all papers, some selection is necessary. The purpose of this review aims to summarize the important works of literature on the energy separation of vortex tube as well as identify limitations to existing studies and directions for future research.

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Pico-hydropower attracts much attention as a clean, reliable, and cost-efficient technology to generate electricity. Pico-hydropower systems are widely used in small rivers, aquacultures, irrigation systems, water supplies, and sewage systems. However, few studies have been conducted to investigate how to harness the excess energy in water supply systems (WSSs) in cities and towns. Previously, our research group developed several inline pico-hydropower systems for WSS which can supply power for monitoring sensor networks of water pipelines and maintenance services. In this paper, we have focused on the water turbine with a vertical 50% block water baffle for further analysis and optimization. We have carried out a combination of numerical and experimental investigations with the objective of improving the performance of this turbine at a velocity of 1.5 m/s–3.5 m/s and a rotational speed of 100 RPM–1000 RPM. The numerical results have been validated by the test results. A further optimization has been conducted through the numerical methods for the angle of water baffle and blade diameter. Also, we have presented the flow field in and around the water turbine to understand the power generation mechanism.

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