With the development of large-capacity hydro turbines, the hydraulicinstability of hydro turbines has become one of the most important problems that affect the stableoperation of the hydro-electric units. The hydrauli...With the development of large-capacity hydro turbines, the hydraulicinstability of hydro turbines has become one of the most important problems that affect the stableoperation of the hydro-electric units. The hydraulic vibration and unstable operation of Francishydro turbines are primarily caused by the unsteady pressure pulsations inside draft tubes. Theforced rotating vortex core at the runner exit and the channel vortices inside Francis turbinerunners are origins of the unsteady pressure pulsations when operating at partial load. This paperbriefly analyzes the hydraulic instability of operation caused by the vortex core and channelvortices at partial load, then, presents a way to estimate the hydraulic stability by calculation ofthe flow behavior at the runner exit. The validity of estimation is examined by comparison withexperimental data. This will be helpful to evaluate the alternative design and predict the hydraulicstability for both the prototype and model hydro turbines.展开更多
The heat transfer and thermal hydraulic stability in a two-phase thermosyphon with coaxial riser and down-comer has been experimentally investigated and theoretically analyzed to facilitate its application in cold neu...The heat transfer and thermal hydraulic stability in a two-phase thermosyphon with coaxial riser and down-comer has been experimentally investigated and theoretically analyzed to facilitate its application in cold neutron source. The flow in a coaxial thermosyphon was studied experimentally for a variety of heat- ing rates, transfer tube lengths, charge capacities, and area ratios. A numerical analysis of the hydraulic balance between the driving pressure head and the resistance loss has also been performed. The results show that the presented coaxial thermosyphon has dynamic performance advantages relative to natural cir- culation in a boiling water reactor.展开更多
Variable air volume air-conditioning system(VAV system)has multiple control loops that interfered with each other,which has serious impacts on its actual operation effect.To solve this problem,the index of global hydr...Variable air volume air-conditioning system(VAV system)has multiple control loops that interfered with each other,which has serious impacts on its actual operation effect.To solve this problem,the index of global hydraulic stability,which takes the physical quantity of the pipe network pressure and the air flow rate as reference,is proposed based on Graph theory,and a pipe network model for the hydraulic calculation is built.Then,the simulation study based on the actual operation data is carried out in MATLAB.The distribution of the pressure and the air flow in the pipe network is obtained,and the action interferences among adjacent terminal boxes are analyzed based on global hydraulic stability under damper position regulation strategy(DP strategy)and fan frequency regulation strategy(FF strategy).Results indicate that the FF strategy can decrease the total change distance of the damper position compared with the DP strategy,and then the fluctuation of the pressure and the air flow can be reduced.The contribution of this study is to provide an evaluation index of global hydraulic stability,which can also be used in other air-conditioning systems with multiple terminals and multiple control loops.展开更多
文摘With the development of large-capacity hydro turbines, the hydraulicinstability of hydro turbines has become one of the most important problems that affect the stableoperation of the hydro-electric units. The hydraulic vibration and unstable operation of Francishydro turbines are primarily caused by the unsteady pressure pulsations inside draft tubes. Theforced rotating vortex core at the runner exit and the channel vortices inside Francis turbinerunners are origins of the unsteady pressure pulsations when operating at partial load. This paperbriefly analyzes the hydraulic instability of operation caused by the vortex core and channelvortices at partial load, then, presents a way to estimate the hydraulic stability by calculation ofthe flow behavior at the runner exit. The validity of estimation is examined by comparison withexperimental data. This will be helpful to evaluate the alternative design and predict the hydraulicstability for both the prototype and model hydro turbines.
文摘The heat transfer and thermal hydraulic stability in a two-phase thermosyphon with coaxial riser and down-comer has been experimentally investigated and theoretically analyzed to facilitate its application in cold neutron source. The flow in a coaxial thermosyphon was studied experimentally for a variety of heat- ing rates, transfer tube lengths, charge capacities, and area ratios. A numerical analysis of the hydraulic balance between the driving pressure head and the resistance loss has also been performed. The results show that the presented coaxial thermosyphon has dynamic performance advantages relative to natural cir- culation in a boiling water reactor.
基金supported by the National Natural Science Foundation of China (Grant No.52,078,096)the Fundamental Research Funds for the Central Universities (Grant No.DUT20JC47)the open Foun-dation of the Key lab of Anhui Province Key Laboratory of Intelligent Building&Building Energy Saving (Grant No.IBES2021KF03).
文摘Variable air volume air-conditioning system(VAV system)has multiple control loops that interfered with each other,which has serious impacts on its actual operation effect.To solve this problem,the index of global hydraulic stability,which takes the physical quantity of the pipe network pressure and the air flow rate as reference,is proposed based on Graph theory,and a pipe network model for the hydraulic calculation is built.Then,the simulation study based on the actual operation data is carried out in MATLAB.The distribution of the pressure and the air flow in the pipe network is obtained,and the action interferences among adjacent terminal boxes are analyzed based on global hydraulic stability under damper position regulation strategy(DP strategy)and fan frequency regulation strategy(FF strategy).Results indicate that the FF strategy can decrease the total change distance of the damper position compared with the DP strategy,and then the fluctuation of the pressure and the air flow can be reduced.The contribution of this study is to provide an evaluation index of global hydraulic stability,which can also be used in other air-conditioning systems with multiple terminals and multiple control loops.
