Nesta pesquisa, desenvolveu-se uma solução analítica para previsão e análise do desempenho de injetores de fertilizantes. As equações de conservação de massa, quantidade de movimento e energia, foram aplicadas ao processo de mistura dos fluidos de sucção e motriz através de uma formulação adimensional. Injetores de alto desempenho foram avaliados experimentalmente, utilizando-se água, tanto como fluido motriz como de sucção, de forma que os coeficientes de perda de carga em cada componente desses equipamentos, fossem obtidos através de calibração. A formulação proposta apresentou estreita concordância com os dados experimentais e forneceu valores adequados para os coeficientes de perda de carga implícitos nas equações. Através de curvas teóricas de rendimento, geradas a partir dos coeficientes de perda de carga calibrados, constatou-se que, quanto maior é a densidade do fluido de sucção menores são as faixas de vazão de operação e os rendimentos alcançados.

Desenvolveu-se, nessa pesquisa, um programa computacional para previsão e análise do rendimento de ejetores para bombeamento de misturas de água com sólidos em suspensão, nas atividades de mineração. A estrutura do programa consiste na entrada de dados de curvas características obtidas com o ejetor operando com água, tanto como fluido motriz, como de sucção, fornecidas pelo fabricante, para calibração dos coeficientes de perda de carga e simulação do rendimento de tal equipamento para diferentes vazões, massas específicas e concentrações de sólidos no fluido de sucção, baseando-se nas equações de conservação de massa, quantidade de movimento e energia. Os resultados obtidos com o programa apresentaram adequada concordância com dados experimentais disponíveis na literatura.

Abstract: Field surveys and integral modelling were carried out to study the effect of bubble plumes on the flow hydrodynamics and the time-evolution of water temperature profiles in a shallow lake with maximum depth of about 4 m. Then, model simulations were performed to verify the feasibility of destratification of ten water-supply reservoirs with capacities of 10-2,000 hm3. Finally, hydrological modelling was conducted to assess the impact of destratification on evaporation suppression and its effects on reservoir yield. The results indicate that net temperature reductions of the order of 1.0°C can be obtained, which corresponds to evaporation suppressions of approximately 10%. In turn, this resulted in increases in the regulated flow of 2-12% that could be described by a general correlation. Lastly, a simplified feasibility analysis provided an operational cost of about 1.0 US$ per cubic meter of saved water, which suggests that artificial destratification cannot be discarded as an alternative for supplementing water supply in rural water-scarce regions.

ABSTRACT This paper presents an integral model to evaluate the impact of gas transfer on the hydrodynamics of bubble plumes. The model is based on the Gaussian type self-similarity and functional relationships for the entrainment coefficient and factor of momentum amplification due to turbulence. The impact of mass transfer on bubble plume hydrodynamics is investigated considering different bubble sizes, gas flow rates and water depths. The results revealed a relevant impact when fine bubbles are considered, even for moderate water depths. Additionally, model simulations indicate that for weak bubble plumes (i.e., with relatively low flow rates and large depths and slip velocities), both dissolution and turbulence can affect plume hydrodynamics, which demonstrates the importance of taking the momentum amplification factor relationship into account. For deeper water conditions, simulations of bubble dissolution/decompression using the present model and classical models available in the literature resulted in a very good agreement for both aeration and oxygenation processes. Sensitivity analysis showed that the water depth, followed by the bubble size and the flow rate are the most important parameters that affect plume hydrodynamics. Lastly, dimensionless correlations are proposed to assess the impact of mass transfer on plume hydrodynamics, including both the aeration and oxygenation modes.

Abstract This study investigated experimentally the air entrainment and pressure drop in low-cost ejectors composed of two pieces shaped from PVC bars inserted in a 25 mm T-junction of the same material. The hydraulic behavior was very similar for the different ejector designs, and linear relationships between the water and air flow rates were fitted. However, when a rotameter was installed at the air line, the head losses resulted in a pronounced decrease (3-fold) in the air entrainment rate. The maximum air-water entrainment ratios reached by the low-cost ejectors was 1.7, while the pressure drop was about 80% of the upstream pressure. The results suggest that these ejectors have a better benefit-cost ratio than conventional ones for applications such as aeration and mixing in reactors, tanks and water bodies. Comparing our results with those obtained previously by using water both as primary and suction fluids, it was shown that under gas-liquid flow conditions the entrainment ratio was about 2.5 times larger than that for the single-phase case, while the pressure drop was about 15% higher. This was attributed to the lower density of the air and the higher dissipation of turbulent kinetic energy due to bubble-liquid interactions in the two-phase flow case.

Abstract: This paper investigates phosphorus dynamics in a highly polluted system composed of a drainage channel followed by a shallow reservoir in the city of Fortaleza, Brazilian semiarid. During the dry season, significant non-point source loads of total phosphorus originated from residences unconnected to sewers were identified along the channel, resulting in an increasing flow rate of untreated sewage towards the reservoir. During the rainy season, as a consequence of dilution, phosphorus concentrations decreased by about 5-fold. The results also revealed that the reservoir was acting similarly to a waste stabilization pond, with phosphorus removal efficiency of about 33%. Assuming one-dimensional flow for the channel and complete mixing for the reservoir, it was possible to adjust phosphorus decay coefficients of kc = 2.2 day-1 and kr = 22.8 year-1, respectively, which were higher than their corresponding values available in the literature. This was attributed mainly to the relatively high temperatures and shallow water depths. The results also revealed an inverse dependence of kc and kr on water and wind velocity, with potential thresholds of respectively 0.3 and 5.0 m/s for resuspension of bed sediments and internal phosphorus loading.

This study investigates the relationships between yield and evaporation as a function of lake morphology in semi-arid Brazil. First, a new methodology was proposed to classify the morphology of 40 reservoirs in the Ceará State, with storage capacities ranging from approximately 5 to 4500 hm3. Then, Monte Carlo simulations were conducted to study the effect of reservoir morphology (including real and simplified conical forms) on the water storage process at different reliability levels. The reservoirs were categorized as convex (60.0%), slightly convex (27.5%) or linear (12.5%). When the conical approximation was used instead of the real lake form, a trade-off occurred between reservoir yield and evaporation losses, with different trends for the convex, slightly convex and linear reservoirs. Using the conical approximation, the water yield prediction errors reached approximately 5% of the mean annual inflow, which is negligible for large reservoirs. However, for smaller reservoirs, this error became important. Therefore, this paper presents a new procedure for correcting the yield-evaporation relationships that were obtained by assuming a conical approximation rather than the real reservoir morphology. The combination of this correction with the Regulation Triangle Diagram is useful for rapidly and objectively predicting reservoir yield and evaporation losses in semi-arid environments.