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Hubert Chanson - One of the best experts on this subject based on the ideXlab platform.
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estimate of void fraction and air entrainment flux in hydraulic jump using froude number
2018Co-Authors: Hang Wang, Hubert ChansonAbstract:Hydraulic jumps are induced in hydraulic facilities for the purposes of energy dissipation or flow Aeration. Presently there is no means for a simple estimate of void fraction distribution and air entrainment flux, without detailed physical modelling. This paper presents a semi-theoretical model to simulate the void fraction and velocity distributions in hydraulic jumps characterised by partially-developed inflow conditions. Relationships were established between the inflow Froude number, jump roller length and key parameters that determine the full expression of void fraction and velocity profiles. The proposed model enables accurate prediction of void fraction, longitudinal velocity and air flux using the inflow Froude number. The results indicated considerable air flux contribution of free-Surface Aeration, in addition to the singular air entrainment at the jump toe, for moderate to large Froude numbers. A Froude number between 8 and 9 tended to achieve highest Aeration rate with maximum total air flux...
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Self-Aeration in the rapidly- and gradually-varying flow regions of steep smooth and stepped spillways
2017Co-Authors: Gangfu Zhang, Hubert ChansonAbstract:In high-velocity chute flows, free-Surface Aeration is often observed. The phenomenon is called self-Aeration or white waters. When the turbulent shear stresses next to the free-Surface are large enough, air bubbles are entrained throughout the entire air–water column. A rapidly-varied flow region is observed immediately downstream of the inception point of free-Surface Aeration. An analytical solution of the air diffusion equation is proposed and the results compare well with new experimental data. Both experiments and theory indicate that the flow bulking spans over approximately 3–4 step cavities downstream of the inception point of free-Surface Aeration on a stepped chute. Further downstream the void fraction distributions follow closely earlier solutions of the air diffusion equation. The application of the diffusion equation solution to prototype and laboratory data shows air bubble diffusivities typically larger than the momentum transfer coefficient. The result highlights however a marked decrease in the ratio of air bubble diffusivity to eddy viscosity with increasing Reynolds number. The finding might indicate some limitation of laboratory investigations of air bubble diffusion process in self-aerated flows and of their extrapolation to full-scale prototype applications.
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interaction between free Surface Aeration and total pressure on a stepped chute
2016Co-Authors: Gangfu Zhang, Hubert ChansonAbstract:Abstract Stepped chutes have been used as flood release facilities for several centuries. Key features are the intense free-Surface Aeration of both prototype and laboratory systems and the macro-roughness caused by the stepped cavities. Herein the air bubble entrainment and turbulence were investigated in a stepped spillway model, to characterise the interplay between air bubble entrainment and turbulence, and the complicated interactions between mainstream flow and cavity recirculation motion. New experiments were conducted in a large steep stepped chute (θ = 45°, h = 0.10 m, W = 0.985 m). Detailed two-phase flow measurements were conducted for a range of discharges corresponding to Reynolds numbers between 2 × 105 and 9 × 105. The total pressure, air–water flow and turbulence properties were documented systematically in the mainstream and cavity flows. Energy calculations showed an overall energy dissipation of about 50% regardless of the discharge. Overall the data indicated that the bottom roughness (i.e. stepped profile) was a determining factor on the energy dissipation performance of the stepped structure, as well as on the longitudinal changes in air–water flow properties. Comparative results showed that the cavity aspect ratio, hence the slope, has a marked effect on the residual energy.
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hydraulics of the developing flow region of stepped spillways i physical modeling and boundary layer development
2016Co-Authors: Gangfu Zhang, Hubert ChansonAbstract:AbstractOn a stepped spillway, the steps act as macroroughness elements, contributing to enhanced energy dissipation and significant Aeration. In a skimming flow, the upstream flow motion is nonaerated, and the free Surface appears smooth and glossy up to the inception point of free-Surface Aeration. In this developing flow region, a turbulent boundary layer grows until the outer edge of the boundary layer interacts with the free Surface and air entrainment takes place. The flow properties in the developing flow region were documented carefully in a large stepped spillway model (1V:1H; h=0.10 m). The upstream flow was controlled by a broad-crested weir and critical flow conditions were observed along most of the weir crest, although the pressure distributions were not hydrostatic at the upstream and downstream ends. Downstream of the broad crest and upstream of the inception point, the free Surface was smooth, although some significant free-Surface curvature was observed for all discharges. The boundary ...
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free Surface Aeration in a steep stepped spillway
2016Co-Authors: Gangfu Zhang, Hubert ChansonAbstract:Self-Aeration has important civil and environmental applications in stepped chutes, ranging from cavitation protection to enhanced air-water mass transfer. Air bubble entrainment occurs when the turbulent stresses in the boundary layer exceed the combined effects of Surface tension and buoyancy. The governing equations for air diffusion in the rapidly-varied region next to and in the gradually-varied region away from the inception point of Aeration are introduced. New and existing solutions to these equations are discussed and compared with new experimental data. An analytical model for flow bulking is introduced. The concept of negative diffusivity is discussed.
Achanta Ramakrishna Rao - One of the best experts on this subject based on the ideXlab platform.
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performance comparison of batch and continuous flow Surface Aeration systems
2010Co-Authors: Bimlesh Kumar, Achanta Ramakrishna RaoAbstract:The oxygen transfer rate and the corresponding power requirement to operate the rotor are vital for design and scale-up of Surface aerators. The Aeration process can be analyzed in two ways such as batch and continuous systems. The process behaviors of batch and continuous flow systems are different from each other. The experimental and numerical results obtained through the batch systems cannot be relied on and applied for the designing of the continuous Aeration tank. Based on the experimentation on batch and continuous type systems, the present work compares the performance of both the batch and continuous Surface Aeration systems in terms of their oxygen transfer capacity and power consumption. A simulation equation developed through experimentation has shown that continuous flow Surface Aeration systems are taking more energy than the batch systems. It has been found that batch systems are economical and better for the field application but not feasible where large quantity of wastewater is produced.
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continuous flow Surface Aeration systems
2010Co-Authors: Bimlesh Kumar, Achanta Ramakrishna RaoAbstract:An Aeration process in ail activated sludge plant is a continuous-flow system. In this system, there is a steady input flow (flow from the primary clarifier or settling tank with some part from the secondary clarifier or secondary settling tank) and output flow connection to the secondary clarifier or settling tank. The experimental and numerical results obtained through batch systems can not be relied on and applied for the designing of a continuous Aeration tank. In order to scale up laboratory results for field application, it is imperative to know the geometric parameters of a continuous system. Geometric parameters have a greater influence on the mass transfer process of Surface Aeration systems. The present work establishes the optimal geometric configuration of a continuous-flow Surface Aeration system. It is found that the maintenance of these optimal geometric parameters systems result in maximum Aeration efficiency. By maintaining the obtained optimal geometric parameters, further experiments are conducted in continuous-flow Surface aerators with three different sizes in order to develop design curves correlating the oxygen transfer coefficient and power number with the rotor speed. The design methodology to implement the presently developed optimal geometric parameters and correlation equations for field application is discussed.
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oxygen transfer and energy dissipation rate in Surface aerator
2009Co-Authors: Bimlesh Kumar, Achanta Ramakrishna RaoAbstract:The dissipation rate of turbulent kinetic energy(e)is a key parameter for mixing in Surface aerators. In particular, determination e across the impeller stream, where the most intensive mixing takes place, is essential to ascertain that an appropriate degree of mixing is achieved. Present work by using commercial software VisiMix calculates the energy dissipation rate in geometrically similar unbaffled Surface Aeration systems in order to scale-up the oxygen transfer process. It is found that in geometrically similar system,oxygen transfer rate is uniquely correlated with dissipation rate of energy. Simulation or scale-up equation governing oxygen transfer rate and dissipation rate of energy has been developed in the present work.
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simulating Surface Aeration systems at different scale of mixing time
2009Co-Authors: Achanta Ramakrishna Rao, Bimlesh KumarAbstract:Abstract Macro and micromixing time represent two extreme mixing time scales, which governs the whole hydrodynamics characteristics of the Surface Aeration systems. With the help of experimental and numerical analysis, simulation equation governing those times scale has been presented in the present work.
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Oxygen transfer in circular Surface Aeration tanks
2009Co-Authors: Achanta Ramakrishna Rao, Ajey Kumar PatelAbstract:Surface Aeration systems employed in activated sludge plants are the most energy-intensive units of the plants and typically account for a higher percentage of the treatment facility's total energy use. The geometry of the Aeration tank imparts a major effect on the system efficiency. It is said that at optimal geometric conditions, systems exhibits the maximum efficiency. Thus the quantification of the optimal geometric conditions in Surface Aeration tanks is needed. Optimal geometric conditions are also needed to scale up the laboratory result to the field installation. In the present work, experimental studies have been carried out on baffled and unbaffled circular Surface Aeration tanks to ascertain the optimal geometric conditions. It is found that no optimal geometric conditions exist for the liquid/water depth in circular Surface Aeration tanks; however, for design purposes, a standard value has been assumed. Based on the optimal geometric conditions, a scale-up equation has been developed for the baffled circular Surface Aeration tanks.
Bimlesh Kumar - One of the best experts on this subject based on the ideXlab platform.
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performance comparison of batch and continuous flow Surface Aeration systems
2010Co-Authors: Bimlesh Kumar, Achanta Ramakrishna RaoAbstract:The oxygen transfer rate and the corresponding power requirement to operate the rotor are vital for design and scale-up of Surface aerators. The Aeration process can be analyzed in two ways such as batch and continuous systems. The process behaviors of batch and continuous flow systems are different from each other. The experimental and numerical results obtained through the batch systems cannot be relied on and applied for the designing of the continuous Aeration tank. Based on the experimentation on batch and continuous type systems, the present work compares the performance of both the batch and continuous Surface Aeration systems in terms of their oxygen transfer capacity and power consumption. A simulation equation developed through experimentation has shown that continuous flow Surface Aeration systems are taking more energy than the batch systems. It has been found that batch systems are economical and better for the field application but not feasible where large quantity of wastewater is produced.
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energy dissipation and shear rate with geometry of baffled Surface aerator
2010Co-Authors: Bimlesh KumarAbstract:The geometric parameters of Surface Aeration systems govern the process phenomena. The dissipation rate of turbulent kinetic energy (e) and shear rate (γ) are the key process parameters for mixing in Surface aerators. Present work by doing numerical computation by visimix® analyzes the effect of geometric parameters (impeller diameter, cross-sectional area of the tank, liquid height, width of the baffle, rotor blade length and immersion height) on e and γ. Analysis has been done by making the geometric parameters non-dimensionalized through rotor diameter. With an increase in liquid height and baffled width, there is an increase in the case of energy dissipation and shear rate values. In the case of tank area and blade length, it is vice versa. Energy dissipation and shear rate are not affected by the variation in immersion height of the impeller. Keywords: energy dissipation; mixing; shear rate; Surface aerator DOI = 10.3329/cerb.v14i2.4910 Chemical Engineering Research Bulletin 14 (2010) 92-96
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continuous flow Surface Aeration systems
2010Co-Authors: Bimlesh Kumar, Achanta Ramakrishna RaoAbstract:An Aeration process in ail activated sludge plant is a continuous-flow system. In this system, there is a steady input flow (flow from the primary clarifier or settling tank with some part from the secondary clarifier or secondary settling tank) and output flow connection to the secondary clarifier or settling tank. The experimental and numerical results obtained through batch systems can not be relied on and applied for the designing of a continuous Aeration tank. In order to scale up laboratory results for field application, it is imperative to know the geometric parameters of a continuous system. Geometric parameters have a greater influence on the mass transfer process of Surface Aeration systems. The present work establishes the optimal geometric configuration of a continuous-flow Surface Aeration system. It is found that the maintenance of these optimal geometric parameters systems result in maximum Aeration efficiency. By maintaining the obtained optimal geometric parameters, further experiments are conducted in continuous-flow Surface aerators with three different sizes in order to develop design curves correlating the oxygen transfer coefficient and power number with the rotor speed. The design methodology to implement the presently developed optimal geometric parameters and correlation equations for field application is discussed.
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Oxygen transfer and shear rate in Surface aerator
2009Co-Authors: Bimlesh KumarAbstract:Shear rate in a Surface Aeration system exerts a profound effect on its performance, affecting the mixing pattern, the power requirement and oxygen transfer process. Based on theoretical analysis, it is shown that the shear rate γ in the fluid is a function of the rotational speed N of the impeller in Surface Aeration systems. Analysis shows that the shear rate varies linearly with N in laminar flow and its behaviour is non‐linear in a turbulent flow regime. Experimental correlations of γ with N have been developed in the present study for different sized Surface aerators. Scale‐up or scale‐down criteria for oxygen transfer rate have been developed, which relate oxygen transfer rate to shear rate in Surface Aeration systems.
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oxygen transfer and energy dissipation rate in Surface aerator
2009Co-Authors: Bimlesh Kumar, Achanta Ramakrishna RaoAbstract:The dissipation rate of turbulent kinetic energy(e)is a key parameter for mixing in Surface aerators. In particular, determination e across the impeller stream, where the most intensive mixing takes place, is essential to ascertain that an appropriate degree of mixing is achieved. Present work by using commercial software VisiMix calculates the energy dissipation rate in geometrically similar unbaffled Surface Aeration systems in order to scale-up the oxygen transfer process. It is found that in geometrically similar system,oxygen transfer rate is uniquely correlated with dissipation rate of energy. Simulation or scale-up equation governing oxygen transfer rate and dissipation rate of energy has been developed in the present work.
Castillo Gálvez, Diego Heli Sebastián - One of the best experts on this subject based on the ideXlab platform.
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Aireador superficial de rotor con eje horizontal en aguas residuales industriales
2019Co-Authors: García Landa, Andrea Del Milagro, Castillo Gálvez, Diego Heli SebastiánAbstract:ABSTRACT The objective of this research work was to implement a rotor aerator with a horizontal axis to evaluate the oxygen transfer in industrial wastewater, determining its nominal Aeration oxygenation capacity and evaluating the oxygen transfer coefficient during the Surface Aeration time. The experimentation was carried out in the ZED wastewater treatment plant where the Aeration system was built with dimensions of 1,00 m long x 0,91 m wide and 0,42 m high, whose nominal capacity of the Surface aerator in the wastewater was 0,3177 kgO2/kWh. For the measurement of oxygen transfer, 3 sampling stations were carried out, in which they were located at the entrance, in the center and at the exit of the lagoon, with a total of 09 samples of 119,5 liters. The results that were obtained in the transfer coefficient with the highest value were in point 3, bottom level with 2,005 h-1 at 30 ° C, likewise 1,683 h-1 in the "INTERMEDIATE" level. The saturation factor α was 0,885, ratio between the coefficient of transfer of residual water with drinking water, and the saturation factor β was 0,844 corresponding to the pressure and temperature in both residual water and wate. Finally, it is concluded that a rotor Surface Aeration system with a horizontal axis was built, whose nominal capacity of the Surface aerator in the wastewater was 0,3177 kgO2/ kWh.TesisRESUMEN El presente trabajo de investigación tuvo por objetivos implementar un aireador de rotor con eje horizontal para evaluar la transferencia de oxígeno en aguas residuales industriales, determinando su capacidad nominal de oxigenación del aireador y evaluando el coeficiente de transferencia de oxígeno durante el tiempo de aireación superficial. La experimentación se realizó en la planta de tratamiento de aguas residuales de ZED donde se construyó el sistema de aireación con dimensiones de 1,00 m largo x 0,91 m ancho y 0,42 m de altura, cuya capacidad nominal del aireador superficial en las aguas residuales fue de 0,3177 kgO2/kWh. Para la medición de la transferencia de oxígeno se realizaron 3 estaciones de muestreo, en la que se ubicaron en la entrada, en el centro y a la salida de la laguna, siendo un total de 09 muestras de 119,5 litros. Los resultados que se obtuvieron en el coeficiente de transferencia con mayor valor fue en el punto 3, nivel fondo con 2,005 h-1 a 30°C, así mismo 1,683 h-1 en el nivel “INTERMEDIO”. El factor de saturación α fue de 0,885, relación entre el coeficiente de transferencia de agua residual con el agua potable, y el factor de saturación β fue de 0,844 correspondiente a la presión y temperatura tanto en agua residual con agua potable. Finalmente se concluye que se construyó un sistema de aireación superficial de rotor con eje horizontal, cuya capacidad nominal del aireador superficial en las aguas residuales fue de 0,3177 kgO2/kWh
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Aireador superficial de rotor con eje horizontal en aguas residuales industriales
2019Co-Authors: García Landa, Andrea Del Milagro, Castillo Gálvez, Diego Heli SebastiánAbstract:RESUMEN El presente trabajo de investigación tuvo por objetivos implementar un aireador de rotor con eje horizontal para evaluar la transferencia de oxígeno en aguas residuales industriales, determinando su capacidad nominal de oxigenación del aireador y evaluando el coeficiente de transferencia de oxígeno durante el tiempo de aireación superficial. La experimentación se realizó en la planta de tratamiento de aguas residuales de ZED donde se construyó el sistema de aireación con dimensiones de 1,00 m largo x 0,91 m ancho y 0,42 m de altura, cuya capacidad nominal del aireador superficial en las aguas residuales fue de 0,3177 kgO2/kWh. Para la medición de la transferencia de oxígeno se realizaron 3 estaciones de muestreo, en la que se ubicaron en la entrada, en el centro y a la salida de la laguna, siendo un total de 09 muestras de 119,5 litros. Los resultados que se obtuvieron en el coeficiente de transferencia con mayor valor fue en el punto 3, nivel fondo con 2,005 h-1 a 30°C, así mismo 1,683 h-1 en el nivel “INTERMEDIO”. El factor de saturación α fue de 0,885, relación entre el coeficiente de transferencia de agua residual con el agua potable, y el factor de saturación β fue de 0,844 correspondiente a la presión y temperatura tanto en agua residual con agua potable. Finalmente se concluye que se construyó un sistema de aireación superficial de rotor con eje horizontal, cuya capacidad nominal del aireador superficial en las aguas residuales fue de 0,3177 kgO2/kWh.ABSTRACT The objective of this research work was to implement a rotor aerator with a horizontal axis to evaluate the oxygen transfer in industrial wastewater, determining its nominal Aeration oxygenation capacity and evaluating the oxygen transfer coefficient during the Surface Aeration time. The experimentation was carried out in the ZED wastewater treatment plant where the Aeration system was built with dimensions of 1,00 m long x 0,91 m wide and 0,42 m high, whose nominal capacity of the Surface aerator in the wastewater was 0,3177 kgO2/kWh. For the measurement of oxygen transfer, 3 sampling stations were carried out, in which they were located at the entrance, in the center and at the exit of the lagoon, with a total of 09 samples of 119,5 liters. The results that were obtained in the transfer coefficient with the highest value were in point 3, bottom level with 2,005 h-1 at 30 ° C, likewise 1,683 h-1 in the "INTERMEDIATE" level. The saturation factor α was 0,885, ratio between the coefficient of transfer of residual water with drinking water, and the saturation factor β was 0,844 corresponding to the pressure and temperature in both residual water and wate. Finally, it is concluded that a rotor Surface Aeration system with a horizontal axis was built, whose nominal capacity of the Surface aerator in the wastewater was 0,3177 kgO2/ kWh
P A Tanguy - One of the best experts on this subject based on the ideXlab platform.
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retracted mass transfer characteristics by Surface Aeration of large paddle impeller application to a polymerization reactor with liquid level change
2008Co-Authors: Ryuichi Yatomi, Katsuhide Takenaka, Koji Takahashi, P A TanguyAbstract:The aim of this study is to investigate the mass-transfer characteristics of a large paddle impeller by comparing with those of the down-pumping pitched blade turbine and the Rushton turbine, and also to probe the application of Surface Aeration to batch hydrogenation in polymerization processes and the ethylene oxide additional reaction. Laboratory and industrial data were used for this purpose. As a result, it has been found that, with the large paddle impeller, large k L a values of Surface Aeration without sparging can be obtained continuously at any liquid level because of the combined effect of Surface breakage, bubble entrapment and efficient liquid circulation by axial pumping capacity of the impeller. Using these experimental k L aV data, the improvement in the operation time for a 12 m 3 alkoxylation reactor was estimated. The reactor was then retrofitted with a large paddle impeller, and the actual operation time of 17 h was found to be strictly identical to the estimation, that is 75% reduction of the usual 70 h. This result shows the advantage of large paddle impellers in industrial processes and the accuracy of the estimation procedure.
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mass transfer characteristics by Surface Aeration of large paddle impeller application to a polymerization reactor with liquid level change
2007Co-Authors: Ryuichi Yatomi, Katsuhide Takenaka, Koji Takahashi, P A TanguyAbstract:The aim of this study is to investigate the mass-transfer characteristics of a large paddle impeller by comparing with those of the down-pumping pitched blade turbine and the Rushton turbine, and also to probe the application of Surface Aeration to batch hydrogenation in polymerization processes and the ethylene oxide additional reaction. Laboratory and industrial data were used for this purpose. As a result, it has been found that, with the large paddle impeller, large kLa values of Surface Aeration without sparging can be obtained continuously at any liquid level because of the combined effect of Surface breakage, bubble entrapment and efficient liquid circulation by axial pumping capacity of the impeller. Using these experimental kLaV data, the improvement in the operation time for a 12 m3 alkoxylation reactor was estimated. The reactor was then retrofitted with a large paddle impeller, and the actual operation time of 17 h was found to be strictly identical to the estimation, that is 75% reduction of the usual 70 h. This result shows the advantage of large paddle impellers in industrial processes and the accuracy of the estimation procedure.
