The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
Hongjie Wang - One of the best experts on this subject based on the ideXlab platform.
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numerical simulation of hysteresis characteristic in the hump region of a pump turbine model
Renewable Energy, 2018Co-Authors: Deyou Li, Hongjie WangAbstract:Abstract Pumped-storage technology is one of the cleanest methods of energy conversion. The stable and safe operation of pump-turbines as key parts of pumped-storage power plants are becoming more and more important with the rapid increase in the capacities, specific speeds and heads of pump-turbines. The hump characteristic is one of the unique unstable features that significantly influences the stability of pump-turbines. Recently, an interesting phenomenon hysteresis characteristic was found in the hump region, which enlarges the unstable region and results in a more unstable characteristic of the pump-turbine. In the present study, based on experimental validation, steady simulations were performed to predict the hump characteristic as well as the hysteresis phenomenon. An analysis of the Hydraulic Loss and flow field shows that the hump characteristic and the hysteresis phenomenon are caused by the decrease in the work of the runner and the increase in Hydraulic Loss, which are induced from vortices in the guide/stay vanes and backflow near the shroud at the runner inlet. For the same operating condition, owing to the difference in the input direction, the states of vortices and backflow are different, resulting in the hysteresis characteristic.
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entropy production analysis of hysteresis characteristic of a pump turbine model
Energy Conversion and Management, 2017Co-Authors: Deyou Li, Hongjie WangAbstract:Abstract The Hydraulic Loss due to friction and unstable flow patterns in hydro-turbines causes a drop in their efficiency. The traditional method for analyzing the Hydraulic Loss is by evaluating the pressure drop, which has certain limitations and cannot determine the exact locations at which the high Hydraulic Loss occurs. In this study, entropy production theory was adopted to obtain a detailed distribution of the Hydraulic Loss in a pump-turbine in the pump mode. In the past, the wall effects of entropy production were not considered, which caused larger errors as compared with the method of pressure difference. First, a wall equation was proposed to calculate the Hydraulic Loss in the wall region. The comparison of Hydraulic Loss calculated by entropy production and pressure difference revealed a better result. Then, through the use of the entropy production theory, the performance characteristics were determined for a pump-turbine with 19 mm guide vane opening, and the variation in the entropy production was obtained. Recently, an interesting phenomenon, i.e., a hysteresis characteristic, was observed in the hump region in pump-turbines. Research shows that the hysteresis characteristic is a result of the Euler momentum and Hydraulic Loss; the Hydraulic Loss accounts for a major portion of the hysteresis characteristic. Finally, the hysteresis characteristic in the hump region was analyzed in detail through the entropy production. The results showed that the hump characteristic and the accompanying hysteresis phenomenon are caused by backflow at the runner inlet and the presence of separation vortices close to the hub and the shroud in the stay/guide vanes, which is dependent on the direction of discharge.
Dexin Chen - One of the best experts on this subject based on the ideXlab platform.
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One effective measure to improve the efficiency of the super low specific speed turbine in cooling tower
2014 ISFMFE - 6th International Symposium on Fluid Machinery and Fluid Engineering, 2014Co-Authors: Di Zhao, Souqi Yuan, Dexin ChenAbstract:The Hydraulic Losses of Hydraulic turbine are mainly distributed in the volute, stay vane, runner and draft tube. The theories and practices show that the Hydraulic Loss of stay vane occupies a large proportion in total in low specific speed turbine and this problem is more serious in super low specific speed turbine. The super low specific speed Francis turbine, which has been widely used to drive the fan directly in cooling tower, has low height guide vane and small guide vane outlet angle. These cause great Hydraulic Loss of guide vane. Based on the CFD analysis, the Hydraulic Loss of the stay ring with guide vanes and that of the stay ring without guide vanes have been compared. It has been found that the Hydraulic Losses of the former can reach to 13.7% and the Hydraulic Losses of the latter can be reduced to 3.41%. That is to say, without stay vane, the total efficiency of the super low specific speed turbine can be improved nearly 10%. Lastly, the design principles of super low specific speed turbine without guide vanes have been proposed.
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Hydraulic Characteristic of Cooling Tower Francis Turbine with Different Spiral Casing and Stay Ring
Energy Procedia, 2012Co-Authors: Lanjin Zhang, Yan Ren, Dexin ChenAbstract:Abstract Cooling tower Francis turbine stands between heat exchanger and sprayer of cooling water system in cooling tower, so the level dimension of spiral casing is small and the flow rate coefficient is high to 1.42. Its flow rate limits to cooling water discharge, output to fan, and head to energy-saving of cooling water system, so its specific speed is very low, Hydraulic Loss of spiral casing and stay ring is high to reduce Hydraulic efficiency of water turbine. To increase the Hydraulic efficiency, a pump casing and stay ring with no stay vane is designed. Through CFD simulation and test, Hydraulic efficiency of water turbine with that spiral casing and stay ring is improved to 5%, Hydraulic Loss of casing and stay ring reduces from 13.7% to 3.41%, Hydraulic Loss of runner increases from 7.93% to 11.57%, and simulation result coincides with test. If that spiral casing and stay ring links to runner with no angle of blade attack, Hydraulic Loss of runner is about 7% and Hydraulic efficiency reaches to 82%.
Terumi Inagaki - One of the best experts on this subject based on the ideXlab platform.
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Loss analysis of gravitation vortex type water turbine and influence of flow rate on the turbine’s performance
Renewable Energy, 2020Co-Authors: Yasuyuki Nishi, Ryouta Suzuo, Daichi Sukemori, Terumi InagakiAbstract:A gravitation vortex type water turbine is a water turbine that uses gravitational vortices generated upon water draining from a tank bottom and can generate power at low head and low flow rate. In our case, given its operation in a free surface flow field, it is critical to quantitatively understand the performance and Hydraulic Loss at various flow rates for its design and operation. Accordingly, we investigated the influence of flow rates on the performance of the gravitation vortex type water turbine by conducting experiments and free surface flow analysis. Using the analysis results, we proposed a Loss analysis method and quantitatively evaluated the Hydraulic Loss. We found that the effective head and the turbine efficiency increased as the flow rate increased; hence, the turbine output increased at a rate greater than the increase rate of the flow rate. Our study revealed that among the Losses that occurred in the water turbine, the tank Loss and tank outlet Loss were the most dominant, followed by the friction Loss inside the tank, whereas the runner Loss and friction Loss in the runner were small.
Deyou Li - One of the best experts on this subject based on the ideXlab platform.
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numerical simulation of hysteresis characteristic in the hump region of a pump turbine model
Renewable Energy, 2018Co-Authors: Deyou Li, Hongjie WangAbstract:Abstract Pumped-storage technology is one of the cleanest methods of energy conversion. The stable and safe operation of pump-turbines as key parts of pumped-storage power plants are becoming more and more important with the rapid increase in the capacities, specific speeds and heads of pump-turbines. The hump characteristic is one of the unique unstable features that significantly influences the stability of pump-turbines. Recently, an interesting phenomenon hysteresis characteristic was found in the hump region, which enlarges the unstable region and results in a more unstable characteristic of the pump-turbine. In the present study, based on experimental validation, steady simulations were performed to predict the hump characteristic as well as the hysteresis phenomenon. An analysis of the Hydraulic Loss and flow field shows that the hump characteristic and the hysteresis phenomenon are caused by the decrease in the work of the runner and the increase in Hydraulic Loss, which are induced from vortices in the guide/stay vanes and backflow near the shroud at the runner inlet. For the same operating condition, owing to the difference in the input direction, the states of vortices and backflow are different, resulting in the hysteresis characteristic.
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entropy production analysis of hysteresis characteristic of a pump turbine model
Energy Conversion and Management, 2017Co-Authors: Deyou Li, Hongjie WangAbstract:Abstract The Hydraulic Loss due to friction and unstable flow patterns in hydro-turbines causes a drop in their efficiency. The traditional method for analyzing the Hydraulic Loss is by evaluating the pressure drop, which has certain limitations and cannot determine the exact locations at which the high Hydraulic Loss occurs. In this study, entropy production theory was adopted to obtain a detailed distribution of the Hydraulic Loss in a pump-turbine in the pump mode. In the past, the wall effects of entropy production were not considered, which caused larger errors as compared with the method of pressure difference. First, a wall equation was proposed to calculate the Hydraulic Loss in the wall region. The comparison of Hydraulic Loss calculated by entropy production and pressure difference revealed a better result. Then, through the use of the entropy production theory, the performance characteristics were determined for a pump-turbine with 19 mm guide vane opening, and the variation in the entropy production was obtained. Recently, an interesting phenomenon, i.e., a hysteresis characteristic, was observed in the hump region in pump-turbines. Research shows that the hysteresis characteristic is a result of the Euler momentum and Hydraulic Loss; the Hydraulic Loss accounts for a major portion of the hysteresis characteristic. Finally, the hysteresis characteristic in the hump region was analyzed in detail through the entropy production. The results showed that the hump characteristic and the accompanying hysteresis phenomenon are caused by backflow at the runner inlet and the presence of separation vortices close to the hub and the shroud in the stay/guide vanes, which is dependent on the direction of discharge.
Yasuyuki Nishi - One of the best experts on this subject based on the ideXlab platform.
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Loss analysis of gravitation vortex type water turbine and influence of flow rate on the turbine’s performance
Renewable Energy, 2020Co-Authors: Yasuyuki Nishi, Ryouta Suzuo, Daichi Sukemori, Terumi InagakiAbstract:A gravitation vortex type water turbine is a water turbine that uses gravitational vortices generated upon water draining from a tank bottom and can generate power at low head and low flow rate. In our case, given its operation in a free surface flow field, it is critical to quantitatively understand the performance and Hydraulic Loss at various flow rates for its design and operation. Accordingly, we investigated the influence of flow rates on the performance of the gravitation vortex type water turbine by conducting experiments and free surface flow analysis. Using the analysis results, we proposed a Loss analysis method and quantitatively evaluated the Hydraulic Loss. We found that the effective head and the turbine efficiency increased as the flow rate increased; hence, the turbine output increased at a rate greater than the increase rate of the flow rate. Our study revealed that among the Losses that occurred in the water turbine, the tank Loss and tank outlet Loss were the most dominant, followed by the friction Loss inside the tank, whereas the runner Loss and friction Loss in the runner were small.
