Cavitation is one of the main causes of deteriorating stability of bulb turbines.To enhance their stability,this study examines the effects of runner cavitation on draft tube pressure fluctuation and vibration in bulb...Cavitation is one of the main causes of deteriorating stability of bulb turbines.To enhance their stability,this study examines the effects of runner cavitation on draft tube pressure fluctuation and vibration in bulb turbine through experimental methods.With varying cavitation coefficients,a synchronous test system,including a high-speed camera,vibration acceleration sensors and pressure pulsation sensors,is applied to obtain cavitation images of the runner,vibration and internal fluid pressure pulsation data of the draft tube.The results show that the correlated component of pressure pulsation signals during the cavitation process is the synchronous pressure pulsation of 16f_(n)With the development of cavitation,the amplitude of synchronous pressure pulsation increases first and then decreases.Cavitation enhances the high-frequency vibration on the wall of runner chamber.The root mean square(rms)of the vertical vibration component IMF3,the horizontal vibration components IMF2,IMF4 are linearly negatively correlated with the cavitation coefficient.The associated component between cavitation-induced vibration and pressure pulsation signal is 16f_(n)and its harmonics.In the process of cavitation,pressure pulsation plays a leading role in vibration.展开更多
Self-healing anticorrosive coatings in extreme environment have attracted considerable interest from researchers.In this work,4-tert-butylpyridine(TBP)was incorporated into brominated butyl rubber(BIIR)polymer network...Self-healing anticorrosive coatings in extreme environment have attracted considerable interest from researchers.In this work,4-tert-butylpyridine(TBP)was incorporated into brominated butyl rubber(BIIR)polymer networks to form a reversible ionic bond with the highly reactive bromine anion.Based on the low glass transition temperature of the BIIR polymer and the electrostatic effects,a robust self-healing anticorrosive coating of TBP-BIIR was prepared.TBP-BIIR coating showed a maximum protection efficiency(PE)of more than 94%(TBP-BIIR-acid,94.37%;TBP-BIIR-alkali,94.95%;TBP-BIIR-salt,95.49%)when treated with a strong acid(HNO_(3),pH=2),strong base(NaOH,pH=12)and high salt solution(3.5 wt%NaCl).In addition,the PE of coating repaired exceed 89%,and the maximum PE value was approximately 95%in different solutions,which demonstrated its extinguished self-healing abilities.These results indicated that the TBP-BIIR anticorrosive coating could provide excellent safety and durability in special environment,which would be extremely beneficial to improve the working life of metal parts used in aviation and shipping,oil and gas and related industries.展开更多
Aerogels are special porous materials with low thermal conductivity,light weight,high energy absorption rate and large surface area,which have been applied in many fields.However,controlling the aerogel microstructure...Aerogels are special porous materials with low thermal conductivity,light weight,high energy absorption rate and large surface area,which have been applied in many fields.However,controlling the aerogel microstructure remains an academic challenge.Herein,by employing graphene oxide(GO)as the aerogel skeleton and utilizing poly(vinyl alcohol)(PVA)to regulate the ice crystal growth,we elucidate the relationships between the physicochemical properties of GO/PVA aerogel precursors and the nucleation and growth of ice crystals by using an ice-templating method.We demonstrate that due to the hydrogen bond formed between PVA and water molecules,resulting in the initial crystallization temperature being reduced from-12.60℃(GO/PVA-0.01)to-16.21℃(GO/PVA-0.1).Meanwhile,the strong hydrogen bond between PVA and GO limits the diffusion of water molecules,thereby inhibiting the growth of ice crystals,decreasing the pore size of the GO/PVA aerogel from 9.96 nm(GO/PVA-0.01)to 7.19 nm(GO/PVA-0.3),and thus the compressive strength of the aerogel increases from 0.045 MPa to 0.13MPa.Overall,the finding of this study can be extended to other aerogel precursors,and exhibit important scientific value and practical significance for the preparation of aerogel materials with highly controllable structures and performances.展开更多
The tip leakage flow formed by the tip clearance of a semi-open centrifugal pump adversely affects the energy performance and the energy waste. A T-shaped blade is proposed to be used to improve the energy characteris...The tip leakage flow formed by the tip clearance of a semi-open centrifugal pump adversely affects the energy performance and the energy waste. A T-shaped blade is proposed to be used to improve the energy characteristics. The internal flow field is simulated via the shear stress transport turbulence model to analyze the influence of the T-shaped blade on the performance of a centrifugal pump. It is shown that with the T-shaped blade, the hydraulic loss can be reduced, the Euler head can be increased, and the external characteristics can be improved. The maximum head and efficiency improvements are 3% and 1.6%, respectively. The relative flow angle near the tip clearance of the T-shaped blade decreases, and the strength of the backflow region is remarkably weakened. The area of the high entropy production region decreases, and the trend of the upstream diffusion is restrained under the design condition. The T-shaped blade can help to inhibit the diffusion of the high entropy production region to the hub under the low flow rate condition, but the entropy production and the mixing losses at the tip clearance are slightly increased. This research provides a new method for improving the energy performance of the semi-open centrifugal pump.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.52079108)supported by the School-Enterprise Collaborative Innovation Fund for graduate students of Xi'an University of Technology.
文摘Cavitation is one of the main causes of deteriorating stability of bulb turbines.To enhance their stability,this study examines the effects of runner cavitation on draft tube pressure fluctuation and vibration in bulb turbine through experimental methods.With varying cavitation coefficients,a synchronous test system,including a high-speed camera,vibration acceleration sensors and pressure pulsation sensors,is applied to obtain cavitation images of the runner,vibration and internal fluid pressure pulsation data of the draft tube.The results show that the correlated component of pressure pulsation signals during the cavitation process is the synchronous pressure pulsation of 16f_(n)With the development of cavitation,the amplitude of synchronous pressure pulsation increases first and then decreases.Cavitation enhances the high-frequency vibration on the wall of runner chamber.The root mean square(rms)of the vertical vibration component IMF3,the horizontal vibration components IMF2,IMF4 are linearly negatively correlated with the cavitation coefficient.The associated component between cavitation-induced vibration and pressure pulsation signal is 16f_(n)and its harmonics.In the process of cavitation,pressure pulsation plays a leading role in vibration.
基金the National Natural Science Foundation of China(No.51873133)Material Corrosion and Protection Key Laboratory of Sichuan province(No.2022CL12).
文摘Self-healing anticorrosive coatings in extreme environment have attracted considerable interest from researchers.In this work,4-tert-butylpyridine(TBP)was incorporated into brominated butyl rubber(BIIR)polymer networks to form a reversible ionic bond with the highly reactive bromine anion.Based on the low glass transition temperature of the BIIR polymer and the electrostatic effects,a robust self-healing anticorrosive coating of TBP-BIIR was prepared.TBP-BIIR coating showed a maximum protection efficiency(PE)of more than 94%(TBP-BIIR-acid,94.37%;TBP-BIIR-alkali,94.95%;TBP-BIIR-salt,95.49%)when treated with a strong acid(HNO_(3),pH=2),strong base(NaOH,pH=12)and high salt solution(3.5 wt%NaCl).In addition,the PE of coating repaired exceed 89%,and the maximum PE value was approximately 95%in different solutions,which demonstrated its extinguished self-healing abilities.These results indicated that the TBP-BIIR anticorrosive coating could provide excellent safety and durability in special environment,which would be extremely beneficial to improve the working life of metal parts used in aviation and shipping,oil and gas and related industries.
基金financially supported by the National Natural Science Foundation of China(No.51873133)。
文摘Aerogels are special porous materials with low thermal conductivity,light weight,high energy absorption rate and large surface area,which have been applied in many fields.However,controlling the aerogel microstructure remains an academic challenge.Herein,by employing graphene oxide(GO)as the aerogel skeleton and utilizing poly(vinyl alcohol)(PVA)to regulate the ice crystal growth,we elucidate the relationships between the physicochemical properties of GO/PVA aerogel precursors and the nucleation and growth of ice crystals by using an ice-templating method.We demonstrate that due to the hydrogen bond formed between PVA and water molecules,resulting in the initial crystallization temperature being reduced from-12.60℃(GO/PVA-0.01)to-16.21℃(GO/PVA-0.1).Meanwhile,the strong hydrogen bond between PVA and GO limits the diffusion of water molecules,thereby inhibiting the growth of ice crystals,decreasing the pore size of the GO/PVA aerogel from 9.96 nm(GO/PVA-0.01)to 7.19 nm(GO/PVA-0.3),and thus the compressive strength of the aerogel increases from 0.045 MPa to 0.13MPa.Overall,the finding of this study can be extended to other aerogel precursors,and exhibit important scientific value and practical significance for the preparation of aerogel materials with highly controllable structures and performances.
基金Projects supported by the National Natural Science Foundation of China (Grant Nos.51879216, 52079108, 51679196 and 51839010).
文摘The tip leakage flow formed by the tip clearance of a semi-open centrifugal pump adversely affects the energy performance and the energy waste. A T-shaped blade is proposed to be used to improve the energy characteristics. The internal flow field is simulated via the shear stress transport turbulence model to analyze the influence of the T-shaped blade on the performance of a centrifugal pump. It is shown that with the T-shaped blade, the hydraulic loss can be reduced, the Euler head can be increased, and the external characteristics can be improved. The maximum head and efficiency improvements are 3% and 1.6%, respectively. The relative flow angle near the tip clearance of the T-shaped blade decreases, and the strength of the backflow region is remarkably weakened. The area of the high entropy production region decreases, and the trend of the upstream diffusion is restrained under the design condition. The T-shaped blade can help to inhibit the diffusion of the high entropy production region to the hub under the low flow rate condition, but the entropy production and the mixing losses at the tip clearance are slightly increased. This research provides a new method for improving the energy performance of the semi-open centrifugal pump.