Emphasis on soil conservation in recent times has been brought about by the degradation of soils due to intensive tillage operations. A relatively new tillage philosophy, coined conservation tillage, has opened up a new realm of tillage equipment design. The Rotary Tine Aerator (RTA) is new tillage tool that is starting to see commercial applications within the agriculture industry.<p> Being a new tillage tool, very little information has been gathered about the RTA and especially the variables that affect tool loading. For the purpose of improving the design of the soil engaging components of the RTA, an experiment was carried out investigating the effect various settings have on tool loading. A factorial experiment was set up with three factors and two levels. The variables examined were depth, velocity of the tool carriage and tine, and the tine gang angle, with soil density and moisture content maintained constant.<p> Draft and vertical forces on the frame were seen to increase with depth. Side loading on the bearing mounts was seen to be primarily affected by the angle of the tine gang, increasing as the gang angle increased. Tool shape was seen to affect the side loading of the bearing mounts causing the force to change directions when the tool was working and 20 cm depth and the tine gang was set a 0º. Forward velocity was not seen to be a significant factor affecting forces on the frame.<p> The loading in the X, Y and Z direction on the tine increased as depth increased from 10cm to 20 cm. A decrease in force on the tine in the X, Y and Z direction was seen with increasing tine velocity. It is suggested that an overlap in soil failure zones could be the cause of this relationship. Opening the gang angle from 0º to 10º increased the force in the Z direction and decreased the force in the X direction. Tool shape was also seen to affect the direction of the load on the tine in the Z direction when the tine was tilling at a depth 20cm with a tine gang of 0º.<p> From the information gathered in this experiment, statistical models were developed for the loading on the tine and frame. The all possible regressors approach was used to formulate the statistical models. As each regressor was added, the new equations fit was assessed using the coefficient of determination (R2 ) and the sum of squared error (SSE). If there was a discrepancy as to whether an added regressor significantly contributed to the fit of the equation, a hypothesis test using the F-statistic was used to justify the regressors addition or removal. The models were then compared against the original data.<p> The models developed for the tine loading showed sufficient accuracy. The models for side loading of the bearing mounts and draft loading of the tool frame contained only one significant regressor. The lowest coefficient of correlation was R=0.63 for the model of side loading of the bearing mount. The statistical model for the vertical loading correlated well with the test data with a coefficient of correlation of R=0.95.

Emphasis on soil conservation in recent times has been brought about by the degradation of soils due to intensive tillage operations. A relatively new tillage philosophy, coined conservation tillage, has opened up a new realm of tillage equipment design. The Rotary Tine Aerator (RTA) is new tillage tool that is starting to see commercial applications within the agriculture industry.<p> Being a new tillage tool, very little information has been gathered about the RTA and especially the variables that affect tool loading. For the purpose of improving the design of the soil engaging components of the RTA, an experiment was carried out investigating the effect various settings have on tool loading. A factorial experiment was set up with three factors and two levels. The variables examined were depth, velocity of the tool carriage and tine, and the tine gang angle, with soil density and moisture content maintained constant.<p> Draft and vertical forces on the frame were seen to increase with depth. Side loading on the bearing mounts was seen to be primarily affected by the angle of the tine gang, increasing as the gang angle increased. Tool shape was seen to affect the side loading of the bearing mounts causing the force to change directions when the tool was working and 20 cm depth and the tine gang was set a 0º. Forward velocity was not seen to be a significant factor affecting forces on the frame.<p> The loading in the X, Y and Z direction on the tine increased as depth increased from 10cm to 20 cm. A decrease in force on the tine in the X, Y and Z direction was seen with increasing tine velocity. It is suggested that an overlap in soil failure zones could be the cause of this relationship. Opening the gang angle from 0º to 10º increased the force in the Z direction and decreased the force in the X direction. Tool shape was also seen to affect the direction of the load on the tine in the Z direction when the tine was tilling at a depth 20cm with a tine gang of 0º.<p> From the information gathered in this experiment, statistical models were developed for the loading on the tine and frame. The all possible regressors approach was used to formulate the statistical models. As each regressor was added, the new equations fit was assessed using the coefficient of determination (R2 ) and the sum of squared error (SSE). If there was a discrepancy as to whether an added regressor significantly contributed to the fit of the equation, a hypothesis test using the F-statistic was used to justify the regressors addition or removal. The models were then compared against the original data.<p> The models developed for the tine loading showed sufficient accuracy. The models for side loading of the bearing mounts and draft loading of the tool frame contained only one significant regressor. The lowest coefficient of correlation was R=0.63 for the model of side loading of the bearing mount. The statistical model for the vertical loading correlated well with the test data with a coefficient of correlation of R=0.95.

When evaluating the performance of horizontal rotor mechanical surface aeration equipment in accordance with the ASCE Standard for Measurement of Oxygen Transfer in Clean Water, several factors should be considered with regard to their impact on the reported performance. These include basin geometry and testing volume, source water quality, dissolved oxygen measurement location, and external environmental factors including air temperature and humidity. Each of these factors may influence the reported performance of mechanical surface aeration equipment, specifically horizontal rotor aeration devices, resulting in an inaccurate estimation of the true equipment performance that should be expected in practical applications.

The objective of this research was to characterize the performance of hypolimnetic aerators with respect to oxygen transfer and water flow rate to allow the development of two comprehensive process models. The oxygen transfer model is the first model that applies discrete-bubble principles to a hypolimnetic aerator, and the water flow rate model is the first that applies an energy balance to this particular type of lake aeration device. Both models use fundamental principles to predict hypolimnetic aerator performance, as opposed to empirical correlations. The models were verified with data collected from a full-scale hypolimnetic aerator installed in Lake Prince, which is a water supply reservoir for the City of Norfolk, Virginia. Water flow rate, gas-phase holdup and dissolved oxygen profiles were measured as a function of air flow rate. The initial bubble size was calculated by the oxygen transfer model using field data. The range of bubble diameters obtained using the model was 2.3-3.1 mm. The Sauter mean diameters of bubbles measured in a laboratory system ranged from 2.7-3.9 mm. The riser and downcomer DO profiles and gas holdups predicted by the model are in close agreement with experimental results. The water flow rate model was fitted to the experimental water velocity by varying the frictional loss coefficient for the air-water separator. An empirical correlation that predicts the loss coefficient as a function of superficial water velocity was obtained. The results of the correlation were similar to those predicted by literature equations developed for external airlift bioreactors. / Master of Science

The aeration potential of a low profile cascade aerator was studied under varying operational conditions in accordance with the ASCE Standard for Measurement of Oxygen Transfer in Clean Water [ASCE 2-06, 2007]. Operational parameters delved into included the channel slope (2.50, 4.50 and 6.50); water flow rate (465.75 L/min.m (37.5 gpm/ft), 931.45 L/min.m (75 gpm/ft) and 1397.20 L/min.m (112.5 gpm/ft)); and weir geometry (rectangular-shaped, inverted T-shaped, W-shaped and inverted Cross shaped weir). The oxygen transfer coefficient, KLa, was derived by use of a FORTRAN-based nonlinear regression analysis computer program and served to assess the effectiveness of various combinations of operational parameters. Statistical tests (ANOVA analysis and main plot, interactive plot) were performed on the results to determine the optimal operating conditions. It was discovered that the combination of the inverted Cross shaped weir and flow rates of 1397.20 L/min.m (112.5 gpm/ft) produced the highest reaeration rates for all slope considered. On the other hand, the W-shaped weir produced better reaeration values at lower flows of 465.75 L/min.m (37.5 gpm/ft) and 931.45 L/min.m (75 gpm/ft) for the range of channel slopes examined. These effects can be respectively attributed to the strong turbulent mixing generated by the plunging nappe flow and recirculating air vortices, which apparently led to substantial air entrainment in the water mass.

Baigiamajame magistro darbe nagrinėjamos pneumatinių bei mechaninių aeravimo sistemų problemos, jų konstrukcijos. Taip pat išnagrinėti veiksniai įtakojantys aeratorių efektyvumą. Išnagrinėjus konstrukcijas pasirinkti 3 aeratoriai su kuriais atlikti eksperimentai bei įvertintas jų efektyvumas. Darbą sudaro 8 dalys: įvadas, tyrimo objektas ir problemos aprašymas, tiriamųjų aeravimo sistemų apžvalga bei konstrukcijų analizė, mechaninių ir pneumatinių aeravimo sistemų efektyvumo analizė, tyrimo metodika bei eksperimentinis stendas, tyrimo rezultatai, išvados, literatūros sąrašas. / The following masters work consists of the analyse of the pneumatic and mechanical aeration systems, these problems and construction. Also explored factors who does influence for the efficiency of the aerators. When the constructions were explored, 3 aerators were selected, the experiments was made and valuated the efficiency. There are 8 chapters: introduction, the object of the analys and description of the problem, review of the explored aeration systems and analys of the constructions, efficiency analysis of mechanical and pneumatic aeration systems, methodology of the analysis and case of the experiment, results of the analysis, conclusions and suggestions, the list of the literature.

Major cavitation damages can seriously endanger the stability of hydraulic structures, in worst case lead to dam failure. To remedy the effect of cavitation on spillway chutes the most common method today is aeration of the flow. Aerators introduce air to the bottom layers of the flow, enough to prevent damages to occur in the concrete lining. The design of an aerator system is of a complex manner due to the many involving parameters such as the channel slope, ramp angle, Froude number, flow velocity. In this report the susceptibility of the Höljes Dam to cavitate has been outlined with the result that this would occur at an extreme and most unlikely situation and remedial measures have been proposed. The design of an aerator system has been proposed as the result from theoretical research. A physical hydraulic model to assess the efficiency of a proposed aerator design is highly recommended. Alternative causes to the damages observed in the spillway chute are discussed.

Due to the high-speed flow in a chute spillway, cavitation damages often occur. This undesired phenomenon threatens the safety of the structure. For the purpose of eliminating the damages, an aerator is often installed in the spillway. To understand its characteristics, physical model tests are a popular method. To complement the model tests, computation fluid dynamics (CFD) simulations are used to study aerator flows. To represent the two-phase flows, multiphase models should be employed. This thesis examines two of them, namely, the Volume-Of-Fluid model (VOF) and Two-Fluid model. Based on the background of the Bergeforsen dam, the aerator flow is modelled by means of the VOF model. The simulated spillway discharge capacity is in accordance with the experimental data. Compared with the results, empirical formulas fail to evaluate the air supply capacity of aerator as it is wider than the conventional width. A hypothetical vent modification is proposed. For the original and proposed layouts, the study illustrates the difference in the air-flow conditions. The results show that a larger vent area is, for a large-width aerator, preferable in the middle of the chute. To study the flip bucket-shaped aerators in the Gallejaur dam, physical model tests and prototype observations are conducted. The results lead to contradicting conclusions in terms of jet breakup and air entrainment. A CFD model is, as an option, employed to explain the reason of the discrepancy. The numerical results coincide with the prototype observations. The jet breakup and air entrainment are evaluated from air cavity profiles; the air-pressure drops are small in the cavity. The discrepancy is due to overestimation of the surface-tension effect in the physical model tests. Based on the experimental data of an aerator rig at the Laboratory of Hydraulics, Hydrology and Glaciology (VAW), ETH Zurich, the Two-Fluid model is used to predict air concentration distributions in the aerated flow. The model includes relevant forces governing the motion of bubbles and considers the effects of air bubble size. The numerical results are conformable to the experiments in the air cavity zone. Downstream of the cavity, the air concentration near the chute bottom is higher, which is presumably caused by the fact that the interfacial forces in the Two-Fluid model are underestimated. / <p>QC 20170224</p>

Made available in DSpace on 2017-07-10T17:37:04Z (GMT). No. of bitstreams: 1 Adriane Assenheimer.pdf: 1563722 bytes, checksum: 86dc567faf8f5b3b7b7c293078fb7abb (MD5) Previous issue date: 2007-03-29 / This work had as objective to evaluate the acting of an aeration equipment adopted in the treatment of dejections of bovine confined in the system ?free stall?, with the recycling of the diluted effluent in the cleaning of the facilities and subsequent use in the areas of cultivation of forages. A reactor was used, operated by the process of mud activated by ?boat-load? (LAB), with system of lingering and intermittent aeration, dimensioned for a time of hydraulic retention of 24 days, with dilution of the dejections in water in the proportion of volume 1:1. Samplings were accomplished in the entrance and inside the aeration tanks, in the exit of the irrigation tubulation and of the pure dejections of the animals. The following parameters were determined: pH, temperature, total Biochemical Oxygen Demand (BOD), total Chemical Oxygen Demand (COD), organic matter, total solids, total fixed solids, total solids suspended, solids suspended fixed, solids suspended volatile, total nitrogen, nitrogen amoniacal, potassium, phosphorus, total carbon, calcium and magnesium. High reductions of BOD (59,05%) and COD (48,16%) were reached for the irrigation effluent. Related to the stabilization of the organic matter, the relationship C/N of the irrigation effluent was of 13,9, indicating that the effluent was stabilized. Through the obtained results, it was found that the aeration system was efficient to reduce and to stabilize the organic matter of the liquid effluent, making possible the recycling in the cleaning of the facilities, providing considerable economy of water, with subsequent release of that treated effluent in the cultivation areas, improving the physical, chemical and biological characteristics of the soil / Este trabalho teve como objetivo avaliar o desempenho de um equipamento de aeração adotado no tratamento de dejetos de bovinos confinados em sistema free stall , com reciclagem do efluente diluído na limpeza das instalações e posterior utilização nas áreas de cultivo de forragens. Utilizou-se um reator, operado pelo processo de lodo ativado por batelada (LAB), com sistema de aeração prolongada e intermitente, dimensionado para um tempo de retenção hidráulica de 24 dias, com diluição dos dejetos em água na proporção de volume 1:1. Foram realizadas amostragens na entrada e no interior dos tanques de aeração, na saída da tubulação de irrigação e dos dejetos puros dos animais. Foram determinados os seguintes parâmetros: pH, temperatura, demanda bioquímica de oxigênio (DBO) e demanda química de oxigênio (DQO) totais, matéria orgânica, sólidos totais, sólidos voláteis totais, sólidos fixos totais, sólidos suspensos totais, sólidos suspensos fixos, sólidos suspensos voláteis, nitrogênio total, nitrogênio amoniacal, potássio, fósforo, carbono total, cálcio e magnésio. Altas reduções de DBO (59,05%) e DQO (48,16%) foram alcançadas para o efluente de irrigação. Com relação à estabilização da matéria orgânica, a relação C/N do efluente de irrigação foi de 13,9, indicando que o efluente foi estabilizado. Através dos resultados obtidos, conclui-se que o sistema de aeração foi eficiente para reduzir e estabilizar a matéria orgânica do efluente líquido, tornando possível a sua reciclagem na limpeza das instalações, proporcionando economia considerável de água, com posterior lançamento desse efluente tratado nas áreas de cultivo, melhorando as características físicas, químicas e biológicas do solo

Dissolved oxygen refers to the mass of oxygen that is contained in water. The concentration of dissolved oxygen is an important indicator of the environments water quality. The presence of oxygen in water is desirable therefore it is a positive sign; whereas the absence of oxygen is a sign of severe pollution. An adequate supply of dissolved oxygen is important for waste water treatment processes. Many naturally occurring biological and chemical processes use oxygen, thereby diminishing the dissolved oxygen concentration in the water. The physical process of oxygen transfer or oxygen absorption from the atmosphere acts to replenish the used oxygen. This process has been termed aeration. Aeration is the primary requirement of the biological treatment of water and wastewater treatment. As reported in the literature, the aeration process consumes as much as 60-80% of total power requirements in wastewater treatment plants. Therefore, it is necessary that the design and operation of aeration process should be economized in terms of their energy efficiency. The performance of surface aeration systems is rated in terms of their oxygen transfer rate; hence the choice of a particular surface aeration system depends on its performance and efficiency of oxygen transfer rates. Oxygen transfer rate and the corresponding power requirement to rotate the rotor are very vital parameters for the design and scale-up of surface aerators. Basically two types of operation are in use for surface aeration systems – batch operation and continuous operation. Batch operation involves a single vessel which is filled, aerated then completely emptied. Continuous operation method of operating a biological treatment plant is characterized by a steady input stream (in terms of chemical and biological composition and flow rate, when flow and concentration equalization is practiced), steady process conditions during the treatment steps and by a fairly consistent flow of treated material with only little variation in its composition. The work presented in this thesis consists of two parts. The first one deals with the experimental investigations on the three types of batch surface aeration tanks. A comprehensive design analysis has been worked out and presented on these types of surface aeration systems. In the second category, experimental investigations have been carried out extensively on continuous flow surface aeration systems of different sizes. Analysis has led to the formulation of optimal geometric dimension and the simulation criteria for the design purposes. As far as the first category of investigations is concerned, a substantial work has been reported on batch surface aerators on various issues, during the past several years. Still, a general methodology to scale up or scale down the process phenomena is lacking. In the present work, experiments were done on different shaped batch surface aeration system for generalizing or devising the scale up and scale down criteria for oxygen transfer coefficient and power consumption. Present work through experimental observations established that unbaffled circular tanks are more energy efficient than baffled when used as surface aerator. Power consumption in surface aeration systems is characterized by a fundamental non-dimensional parameter named power number. This number relates drag force to the inertial force in fluid flow system. Power number scaling up of unbaffled surface aerators of square, circular and rectangular shaped tanks is one of the most important contributions of the present work. Design charts have been developed for all the three shape of tanks for the installation as the batch surface aeration systems. Based on the experimental analyses in the present work, it was found that circular shape is the most efficient than any other shape and it is also established that generally a number of smaller sized tanks were more economic and efficient than using a single big tank while aerating the same volume of water. Based on the energy economy analysis, present work suggests the optimal speed range of batch systems of different shaped surface aeration tanks. Different sized rectangular aeration tanks with different aspect ratios (that is length to width ratio) were tested along with a series of square and circular tanks for comparing their relative performances. Present work by doing experiments answered this fact and found that square tank (aspect ratio =1) was more efficient than any other aspect ratio rectangular tanks. Vortexes are inherently present in any type of unbaffled tanks. Present work analyzed the vortex behavior of unbaffled surface aeration systems to determine the critical impeller speed in unbaffled batch surface aeration systems at which oxygen transfer rates are more. The second part of the present work establishes the optimal geometrical parameters of a continuous flow surface aeration systems. These types of operations were found to be least reported in the available literature and there appears to be of no report in the literature on optimal geometrical parameters. Extensive experimental work is reported in the present thesis on the establishment of the optimal geometrical parameters of continuous flow surface aeration systems. From there, simulation criteria are established by maintaining optimal geometrical similarity in different sized continuous flow surface aeration tanks; so that the scale up or scale down criteria can be applied to predict oxygen transfer rates and power number.