The hump characteristic is one of the main problems for the stable operation of pump turbines in pump mode.However,traditional methods cannot reflect directly the energy dissipation in the hump region.In this paper,3D...The hump characteristic is one of the main problems for the stable operation of pump turbines in pump mode.However,traditional methods cannot reflect directly the energy dissipation in the hump region.In this paper,3D simulations are carried out using the SST k-ω turbulence model in pump mode under different guide vane openings.The numerical results agree with the experimental data.The entropy production theory is introduced to determine the flow losses in the whole passage,based on the numerical simulation.The variation of entropy production under different guide vane openings is presented.The results show that entropy production appears to be a wave,with peaks under different guide vane openings,which correspond to wave troughs in the external characteristic curves.Entropy production mainly happens in the runner,guide vanes and stay vanes for a pump turbine in pump mode.Finally,entropy production rate distribution in the runner,guide vanes and stay vanes is analyzed for four points under the 18 mm guide vane opening in the hump region.The analysis indicates that the losses of the runner and guide vanes lead to hump characteristics.In addition,the losses mainly occur in the runner inlet near the band and on the suction surface of the blades.In the guide vanes and stay vanes,the losses come from pressure surface of the guide vanes and the wake effects of the vanes.A new insight-entropy production analysis is carried out in this paper in order to find the causes of hump characteristics in a pump turbine,and it could provide some basic theoretical guidance for the loss analysis of hydraulic machinery.展开更多
In 2007, the export of textile machinery products continued to keep a rapidly increasing trend. In accordance with the statistics from the custom, as of December this year, the value of exported textile machinery prod...In 2007, the export of textile machinery products continued to keep a rapidly increasing trend. In accordance with the statistics from the custom, as of December this year, the value of exported textile machinery products was USD1.528 billion, increased by 23.54% over the previous year. Except that the export of nonwoven cloth machinery products reduced to a certain degree compared with that in 2006, the export of other varieties of products increased greatly. The export of textile machinery products had been remaining relatively rapid growth since 2000. During this period, the structure of exported products has changed continuously, so do export enterprises. There are still many problems in export of textile machinery products, and manufacturers of textile machinery products should improve and advance continuously. However, on the whole, the integrated and international competitiveness of textile machinery products is enhanced, so is the internationalization level of manufacturers of textile machinery products.展开更多
With the development of mechanization popularity in rural area, agricultural machinery product not only needs to meet the production goals, and also requires the simple operation and human-centered. Human-centered des...With the development of mechanization popularity in rural area, agricultural machinery product not only needs to meet the production goals, and also requires the simple operation and human-centered. Human-centered design is always, on the basis of the user＇ s requirement and usage, to think over the issues by regarding operator as the center, and to design the products by emphasizing the ease of use and understandability during design and manufacture. In this study, Stubble-Mulch Rotocultivator for Boat Tractor （SMRBT） is chosen as the design object. The coordination approach of the user, machine and environment is discussed by deeply investigating their relationship, which is an empirical study of the human-centered technology of agricultural machinery.展开更多
基金Supported by National Key Technology R&G Program(Grant No.2012BAF03B01-X)Innovative Research Groups of National Natural Science Foundation of China(Grant No.51121004)
文摘The hump characteristic is one of the main problems for the stable operation of pump turbines in pump mode.However,traditional methods cannot reflect directly the energy dissipation in the hump region.In this paper,3D simulations are carried out using the SST k-ω turbulence model in pump mode under different guide vane openings.The numerical results agree with the experimental data.The entropy production theory is introduced to determine the flow losses in the whole passage,based on the numerical simulation.The variation of entropy production under different guide vane openings is presented.The results show that entropy production appears to be a wave,with peaks under different guide vane openings,which correspond to wave troughs in the external characteristic curves.Entropy production mainly happens in the runner,guide vanes and stay vanes for a pump turbine in pump mode.Finally,entropy production rate distribution in the runner,guide vanes and stay vanes is analyzed for four points under the 18 mm guide vane opening in the hump region.The analysis indicates that the losses of the runner and guide vanes lead to hump characteristics.In addition,the losses mainly occur in the runner inlet near the band and on the suction surface of the blades.In the guide vanes and stay vanes,the losses come from pressure surface of the guide vanes and the wake effects of the vanes.A new insight-entropy production analysis is carried out in this paper in order to find the causes of hump characteristics in a pump turbine,and it could provide some basic theoretical guidance for the loss analysis of hydraulic machinery.
文摘In 2007, the export of textile machinery products continued to keep a rapidly increasing trend. In accordance with the statistics from the custom, as of December this year, the value of exported textile machinery products was USD1.528 billion, increased by 23.54% over the previous year. Except that the export of nonwoven cloth machinery products reduced to a certain degree compared with that in 2006, the export of other varieties of products increased greatly. The export of textile machinery products had been remaining relatively rapid growth since 2000. During this period, the structure of exported products has changed continuously, so do export enterprises. There are still many problems in export of textile machinery products, and manufacturers of textile machinery products should improve and advance continuously. However, on the whole, the integrated and international competitiveness of textile machinery products is enhanced, so is the internationalization level of manufacturers of textile machinery products.
文摘With the development of mechanization popularity in rural area, agricultural machinery product not only needs to meet the production goals, and also requires the simple operation and human-centered. Human-centered design is always, on the basis of the user＇ s requirement and usage, to think over the issues by regarding operator as the center, and to design the products by emphasizing the ease of use and understandability during design and manufacture. In this study, Stubble-Mulch Rotocultivator for Boat Tractor （SMRBT） is chosen as the design object. The coordination approach of the user, machine and environment is discussed by deeply investigating their relationship, which is an empirical study of the human-centered technology of agricultural machinery.
