ES-DAF, a novel DAF with low cost, high reliability and easy controllability, was studied. Without a costly air saturator, ES-DAF consists of an ejector and a static mixer between the pressure side and suction side of...ES-DAF, a novel DAF with low cost, high reliability and easy controllability, was studied. Without a costly air saturator, ES-DAF consists of an ejector and a static mixer between the pressure side and suction side of the recycle rotary pump. The bubble size distribution in this novel unit was studied in detail by using a newly developed CCD imagination through a microscope. Compared with M-DAF under the same saturation pressure, ES-DAF can produce smaller bubble size and higher bubble volume concentration, especially in lower pressure. In addition, the bubble size decreases with the increase of reflux ratio or decrease of superficial air-water ratio. These results suggested that smaller bubbles will be formed when the initial number of nucleation sites increases by enhancing the turbulence intensity in the saturation system.展开更多
The primary purpose of this research is to evaluate the feasibility of dissolved air flotation(DAF) as pretreatment process for membrane modules in river water treatment.The performances of DAF in combination with an ...The primary purpose of this research is to evaluate the feasibility of dissolved air flotation(DAF) as pretreatment process for membrane modules in river water treatment.The performances of DAF in combination with an up-flow membrane biofilter(MBF) and a hollow-fiber ultrafiltration membrane(UFM) were investigated respectively.Removal efficiency of ultraviolet absorbance at 254 nm(UV254),ammonia nitrogen(NH3-N),particle counts and microbial index were measured for both systems.Results showed that DAF was a robust pretreatment process for floc particles separation despite of raw water quality fluctuations.For DAFUFM system,the monitoring data indicated bacteria breeding,nitrite accumulation in membrane vessel and the ammonia concentration of permeate water even exceeded regulatory limits.By contrast,DAF-MBF system was established via the introduction of multilayer filter media between DAF and curtain type ultrafiltration membrane.In MBF,the matured biological activated carbon(BAC) and zeolite particles guaranteed the efficient removal of both organic matters and ammonia.Moreover,the high dissolved oxygen levels in DAF effluent significantly improved bio-adsorption and degradation of pollutants in MBF.The retention of microorganisms by the membrane not only ensured a high concentration of biomass,but also eliminated the risk of microbes leaking out from MBF.In addition,compared with UFM,the curtain membrane exhibited obviously slower fouling development.These results suggested that the DAF-MBF system was more suitable for purifying raw waters seriously polluted by dissolved contaminants.展开更多
A new type of dissolved air released flotation column is developed to treat wastewater containing Cr（Ⅵ） based on advantages of both dissolved air floatation and column floatation. By using a column with a diameter ...A new type of dissolved air released flotation column is developed to treat wastewater containing Cr（Ⅵ） based on advantages of both dissolved air floatation and column floatation. By using a column with a diameter of 50 mm and a specially made dissolved air releaser, micro-bubbles inside the column can be formed. N2H4H2O was used as reductant, AlCl3 as flocculant, C12H25SO3Na（SDS） as surfactant in the experiment. The effects of pH of wastewater, pressure of dissolved air, ratio of return water, and concentration of flocculant and surfactant on the removal efficiency are studied. The results show that the efficiency of dissolved air released flotation column is much higher than that of other approaches after the operation parameters are optimized, with the reduction ratio of Cr（Ⅵ ） in wastewater reaching 98%. So this technique can be widely used in wastewater treatment展开更多
The aim of the present study was to implant an efficient strategy for controlling the level of the effluent-oily foam interface in a DAF （dissolved air flotation） chamber of a pilot-scale prototype. DAF has been suc...The aim of the present study was to implant an efficient strategy for controlling the level of the effluent-oily foam interface in a DAF （dissolved air flotation） chamber of a pilot-scale prototype. DAF has been successfully used in the treatment of oily water, which is one of the main environmental problems in different industrial facilities. Along with important operational parameters, such as microbubble size and flow rate, the control strategy for the automation of a DAF chamber may be an important tool for increasing efficiency. Controlling the level was the strategy chosen to enhance the separation efficiency in a pilot-scale DAF prototype, with monitoring performed using a computational program in LabVIEW （laboratory virtual instrument engineering workbench）. The findings demonstrate that it is possible to maintain the level of the fluid at a reference value established by the operator using the software program through the application of classic proportional integral derivative controllers. Using this control tool, the efficiency of water-oil separation in the pilot flotation chamber prototype was increased to nearly 98%.展开更多
It is a complicated dynamic phenomenon when a transient pressure pulse is triggered by two high-speed trains passing each other in a tunnel. The air pressure pulse is a transient excitation to side wall of the car bod...It is a complicated dynamic phenomenon when a transient pressure pulse is triggered by two high-speed trains passing each other in a tunnel. The air pressure pulse is a transient excitation to side wall of the car body. It can stimulate almost all vibration modes of the car body and the correlated assemblies, cause serious aerodynamic noise, and have important impacts on car body distortion, train noise, and operation safety. This article analyzes the time- frequency characteristics and main parameters of field-measured the air pressure wave, and its relationship with the train velocity as well as the vibration of the car body. Cepstrum analysis concludes that in the process of the meeting, the air pressure wave in tunnel crossing is a multiplying pressure wave instead of a superposed wave. The pressure pulse during the meeting is non-symmetrical one featured with a sharp front, large amplitude, fluctuating central sec- tion, and less sharp tail. The pulse width is inversely proportional to the train speed. As the speed increases, the impulse amplitude is amplified, and the speed of pulse front is advanced.展开更多
The treatment of typical north China water by dissolved air flotation(DAF)and sedimentation process was examined.A pilot plant with a water treatment capacity of 120 m^3/d constructed in the Jieyuan Water Treatment Pl...The treatment of typical north China water by dissolved air flotation(DAF)and sedimentation process was examined.A pilot plant with a water treatment capacity of 120 m^3/d constructed in the Jieyuan Water Treatment Plant(JWTP) of Tianjin,China,was utilized for the comparison of the two processes.The results show that during the pilot test,DAF process can remove particles and organic mater more efficiently than sedimentation process.The removal rate for turbidity by DAF process is 5.5% higher than that by sedimentation in normal turbidity period,and 40% higher in low turbidity period,it is 5%～10% higher for removals of algae,total organic carbon(TOC),trihalomethane formation potential(THMFP)and bacteria in all periods.The removal rates for turbidity,TOC,THMFP,algae and bacteria by DAF process can reach 95%,30%, 20%,94% and 97% respectively.From the results of the pilot test,it can be concluded that DAF is a feasible clarification process,especially for source water with low turbidity and high algal blooming.展开更多
In this paper, we build an air conveyor with newly developed vortex bearing elements, and study the flotation precision of the front-end of the substrate in quasi-static flotation transport. We experimentally discuss ...In this paper, we build an air conveyor with newly developed vortex bearing elements, and study the flotation precision of the front-end of the substrate in quasi-static flotation transport. We experimentally discuss the three influential factors: air supply pressure, thickness of the substrates and installing direction of the vortex bearing element. We find that during the process of transport the movement of the substrate leads to the variation of flotation height. The amplitude of variation (e.g. flotation precision) is dependent upon the bearing stiffness and the suction force of the vortex bearing elements. Increasing air supply pressure properly can improve the flotation precision, but an excess pressure can cause over-suction due to high negative pressure and result in a poor flotation precision. We also know that the flotation precision of thin and light substrates are easily affected by the suction force of vortex flow because they float with a high flotation height and are more susceptible to deformation. Finally, we investigate four installing directions of the vortex bearing element. Different installing direction can lead to different variation of flotation height.展开更多
The global concern over indoor air pollution in public vehicles has grown significantly.With a focus on enhancing passengers’comfort and health,this study endeavors to investigate the distribution characteristics of ...The global concern over indoor air pollution in public vehicles has grown significantly.With a focus on enhancing passengers’comfort and health,this study endeavors to investigate the distribution characteristics of formaldehyde within a high-speed train cabin by employing a computational fluid dynamics(CFD)model which is experimentally validated in a real cabin scenario.The research focuses on analyzing the impact of air supply modes,temperature,relative humidity,and fresh air change rate on the distribution and concentration of formaldehyde.The results demonstrate that the difference in average formaldehyde concentration between the two air supply modes is below 1.3%,but the top air supply mode leads to a higher accumulation of formaldehyde near the sidewalls,while the bottom air supply mode promotes a more uniform distribution of formaldehyde.Furthermore,the temperature,relative humidity,and fresh air change rate are the primary factors affecting formaldehyde concentration levels,but they have modest effects on formaldehyde’s distribution pattern within the cabin.As the temperature and relative humidity increase,the changes in formaldehyde concentrations in response to variations in these factors become more evident.Importantly,the formaldehyde concentration may surpass the standard limit of 0.10 mg/m^(3)if the fresh air change rate falls below 212 m^(3)/h.This research provides a systematic approach and referenceable results for exploring formaldehyde pollution in high-speed train cabins.展开更多
文摘ES-DAF, a novel DAF with low cost, high reliability and easy controllability, was studied. Without a costly air saturator, ES-DAF consists of an ejector and a static mixer between the pressure side and suction side of the recycle rotary pump. The bubble size distribution in this novel unit was studied in detail by using a newly developed CCD imagination through a microscope. Compared with M-DAF under the same saturation pressure, ES-DAF can produce smaller bubble size and higher bubble volume concentration, especially in lower pressure. In addition, the bubble size decreases with the increase of reflux ratio or decrease of superficial air-water ratio. These results suggested that smaller bubbles will be formed when the initial number of nucleation sites increases by enhancing the turbulence intensity in the saturation system.
基金Sponsored by the National High Technology Research and Development Program of China(Grant No.SS2012AA062902)the Science and Technology Department of Heilongjiang Province,China(Grant No.PS13H05)
文摘The primary purpose of this research is to evaluate the feasibility of dissolved air flotation(DAF) as pretreatment process for membrane modules in river water treatment.The performances of DAF in combination with an up-flow membrane biofilter(MBF) and a hollow-fiber ultrafiltration membrane(UFM) were investigated respectively.Removal efficiency of ultraviolet absorbance at 254 nm(UV254),ammonia nitrogen(NH3-N),particle counts and microbial index were measured for both systems.Results showed that DAF was a robust pretreatment process for floc particles separation despite of raw water quality fluctuations.For DAFUFM system,the monitoring data indicated bacteria breeding,nitrite accumulation in membrane vessel and the ammonia concentration of permeate water even exceeded regulatory limits.By contrast,DAF-MBF system was established via the introduction of multilayer filter media between DAF and curtain type ultrafiltration membrane.In MBF,the matured biological activated carbon(BAC) and zeolite particles guaranteed the efficient removal of both organic matters and ammonia.Moreover,the high dissolved oxygen levels in DAF effluent significantly improved bio-adsorption and degradation of pollutants in MBF.The retention of microorganisms by the membrane not only ensured a high concentration of biomass,but also eliminated the risk of microbes leaking out from MBF.In addition,compared with UFM,the curtain membrane exhibited obviously slower fouling development.These results suggested that the DAF-MBF system was more suitable for purifying raw waters seriously polluted by dissolved contaminants.
基金Projects 50425414 supported by National Fund for Distinguished Young Scholars and B200403 by Science and Technology Fund of China University ofMining &Technology
文摘A new type of dissolved air released flotation column is developed to treat wastewater containing Cr（Ⅵ） based on advantages of both dissolved air floatation and column floatation. By using a column with a diameter of 50 mm and a specially made dissolved air releaser, micro-bubbles inside the column can be formed. N2H4H2O was used as reductant, AlCl3 as flocculant, C12H25SO3Na（SDS） as surfactant in the experiment. The effects of pH of wastewater, pressure of dissolved air, ratio of return water, and concentration of flocculant and surfactant on the removal efficiency are studied. The results show that the efficiency of dissolved air released flotation column is much higher than that of other approaches after the operation parameters are optimized, with the reduction ratio of Cr（Ⅵ ） in wastewater reaching 98%. So this technique can be widely used in wastewater treatment
文摘The aim of the present study was to implant an efficient strategy for controlling the level of the effluent-oily foam interface in a DAF （dissolved air flotation） chamber of a pilot-scale prototype. DAF has been successfully used in the treatment of oily water, which is one of the main environmental problems in different industrial facilities. Along with important operational parameters, such as microbubble size and flow rate, the control strategy for the automation of a DAF chamber may be an important tool for increasing efficiency. Controlling the level was the strategy chosen to enhance the separation efficiency in a pilot-scale DAF prototype, with monitoring performed using a computational program in LabVIEW （laboratory virtual instrument engineering workbench）. The findings demonstrate that it is possible to maintain the level of the fluid at a reference value established by the operator using the software program through the application of classic proportional integral derivative controllers. Using this control tool, the efficiency of water-oil separation in the pilot flotation chamber prototype was increased to nearly 98%.
基金supported by the National Science and Technology Pillar Programs of China (No.2009BAG12A01-E02,No. 2009BAG12A01-E03 and No. 2009BAG12A01-E04)
文摘It is a complicated dynamic phenomenon when a transient pressure pulse is triggered by two high-speed trains passing each other in a tunnel. The air pressure pulse is a transient excitation to side wall of the car body. It can stimulate almost all vibration modes of the car body and the correlated assemblies, cause serious aerodynamic noise, and have important impacts on car body distortion, train noise, and operation safety. This article analyzes the time- frequency characteristics and main parameters of field-measured the air pressure wave, and its relationship with the train velocity as well as the vibration of the car body. Cepstrum analysis concludes that in the process of the meeting, the air pressure wave in tunnel crossing is a multiplying pressure wave instead of a superposed wave. The pressure pulse during the meeting is non-symmetrical one featured with a sharp front, large amplitude, fluctuating central sec- tion, and less sharp tail. The pulse width is inversely proportional to the train speed. As the speed increases, the impulse amplitude is amplified, and the speed of pulse front is advanced.
基金Supported by the National Hi-tech Research and Development Program (863 Program) of China (No.2002AA601140)
文摘The treatment of typical north China water by dissolved air flotation(DAF)and sedimentation process was examined.A pilot plant with a water treatment capacity of 120 m^3/d constructed in the Jieyuan Water Treatment Plant(JWTP) of Tianjin,China,was utilized for the comparison of the two processes.The results show that during the pilot test,DAF process can remove particles and organic mater more efficiently than sedimentation process.The removal rate for turbidity by DAF process is 5.5% higher than that by sedimentation in normal turbidity period,and 40% higher in low turbidity period,it is 5%～10% higher for removals of algae,total organic carbon(TOC),trihalomethane formation potential(THMFP)and bacteria in all periods.The removal rates for turbidity,TOC,THMFP,algae and bacteria by DAF process can reach 95%,30%, 20%,94% and 97% respectively.From the results of the pilot test,it can be concluded that DAF is a feasible clarification process,especially for source water with low turbidity and high algal blooming.
文摘In this paper, we build an air conveyor with newly developed vortex bearing elements, and study the flotation precision of the front-end of the substrate in quasi-static flotation transport. We experimentally discuss the three influential factors: air supply pressure, thickness of the substrates and installing direction of the vortex bearing element. We find that during the process of transport the movement of the substrate leads to the variation of flotation height. The amplitude of variation (e.g. flotation precision) is dependent upon the bearing stiffness and the suction force of the vortex bearing elements. Increasing air supply pressure properly can improve the flotation precision, but an excess pressure can cause over-suction due to high negative pressure and result in a poor flotation precision. We also know that the flotation precision of thin and light substrates are easily affected by the suction force of vortex flow because they float with a high flotation height and are more susceptible to deformation. Finally, we investigate four installing directions of the vortex bearing element. Different installing direction can lead to different variation of flotation height.
基金This work is supported by the National Natural Science Foundation of China(No.52072413)the graduate school of Central South University(No.1053320220012).The authors are grateful for resources from the High-Performance Computing Center of Central South University.
文摘The global concern over indoor air pollution in public vehicles has grown significantly.With a focus on enhancing passengers’comfort and health,this study endeavors to investigate the distribution characteristics of formaldehyde within a high-speed train cabin by employing a computational fluid dynamics(CFD)model which is experimentally validated in a real cabin scenario.The research focuses on analyzing the impact of air supply modes,temperature,relative humidity,and fresh air change rate on the distribution and concentration of formaldehyde.The results demonstrate that the difference in average formaldehyde concentration between the two air supply modes is below 1.3%,but the top air supply mode leads to a higher accumulation of formaldehyde near the sidewalls,while the bottom air supply mode promotes a more uniform distribution of formaldehyde.Furthermore,the temperature,relative humidity,and fresh air change rate are the primary factors affecting formaldehyde concentration levels,but they have modest effects on formaldehyde’s distribution pattern within the cabin.As the temperature and relative humidity increase,the changes in formaldehyde concentrations in response to variations in these factors become more evident.Importantly,the formaldehyde concentration may surpass the standard limit of 0.10 mg/m^(3)if the fresh air change rate falls below 212 m^(3)/h.This research provides a systematic approach and referenceable results for exploring formaldehyde pollution in high-speed train cabins.
