Author: Du, Jiyun
Title: Development of micro inline cross-flow turbine for energy harvesting from urban water mains
Advisors: Yang, Hongxing (BSE)
Degree: Ph.D.
Year: 2018
Subject: Hong Kong Polytechnic University -- Dissertations
Water leakage -- Management
Department: Department of Building Services Engineering
Pages: xxvi, 176 pages : color illustrations
Language: English
Abstract: Water supply is of vital importance for urban development and the subsistence of urban residents. Due to continually increasing populations and urban development, many cities around the world are facing great challenges in securing a reliable water supply. However, fresh water is often wasted in the delivery process due to leakage or pipe bursting. It is estimated that more than 32 billion m³ of water from water mains is wasted every year worldwide. In Hong Kong, for instance, nearly 1200 Mm3 of water is delivered through water pipes to residents annually, and the amount will grow to 1315 Mm3 in 2030. However, nearly 15% of fresh water was wasted in 2016 due to pipe leakage. Therefore, many kinds of water monitoring sensors, including water flow sensors, pressure sensors, and acoustic leakage sensors, are used along urban water mains for timely detection of water leakage. However, most of the monitoring devices are powered by chemical batteries which need to be replaced frequently. The main objective of this thesis is to develop a micro inline hydropower technology to provide constant and reliable power for the water monitoring system. Numerical simulations and experimental methods were first used to develop a novel inline cross-flow turbine. In the design scheme of the inline turbine, a DN100 T-joint is integrated to a part of water main, then a cross-flow runner, which connects a generator via a shaft, is inserted in the pipe through the T-joint to harvest hydropower and transmit power to the generator. Two blocks that are fixed on the pipe inner wall are used to let more water flow through the runner, increasing the velocity of water that passes through the runner and reducing the resistance of water on the returning blades. A prototype with self-adjustable vane was developed by Computational Fluid Dynamics (CFD) method. Relevant lab tests were conducted to study the turbine performance. The test results could not only prove feasibility of the proposed design scheme, but also provide validation for the CFD simulation results. The prototype test results showed that the turbine output power at the design point was 69.1W with 2.62m water head reduced. Besides, over a flow velocity range varying from 1.2m/s to 2.2m/s, the water head loss was always below 5m, so the normal water supply would not be affected.
A novel mathematic design method for the block design was then developed and a theoretical analysis on the working mechanism of the cross-flow runner was performed. The mathematic design method and theoretical analysis could not only provide an understanding of working principle of the inline cross-flow turbine, but also show the effects of different geometrical parameters on turbine performance, which provides inspirations for performance improvement of the inline cross-flow turbine. Furthermore, numerical studies were conducted to investigate the effects of block geometries on turbine performance. Several turbine models with different block designs were established and simulated. Then output power and water head loss were recorded to compare the performance of different turbine models. After that, analysis of flow velocity and pressure distribution was performed to study the block's effects on flow inlet angle, flow separation in the blades passages and water head loss through the runner. The analysis could offer an in-depth understanding about the influencing mechanism of blocks on turbine performance and provide guidance for the determination of the optimal block shape in this research. Moreover, the effects of runner geometries on turbine performance were studied by CFD simulations. In this research, several turbine models with different runner geometries were built and simulated to analyze the output power, water head loss and flow characteristics. Therefore, the optimal runner geometrical parameters (i.e. runner inlet arc angle, blades outer angle, diameter ratio and blades number) of the inline cross-flow turbine can be obtained. Based on the research results, the maximum turbine efficiency could reach 50.9% after block and runner optimization. Finally, a bidirectional inline cross-flow turbine was newly designed and relevant lab tests were performed to study its performance. The experimental results indicated that when runner rotation speed was 600rpm, the bidirectional turbine reached its best efficiency 17.4% with 190W output power and 4.7m water head reduction, which could meet the design requirement in this case study. The case study indicated that the research presented in this thesis could provide an effective method for the design of inline cross-flow turbine design under different working conditions.
Rights: All rights reserved
Access: open access

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