Design and prediction performance of Venturi injectors in drip irrigation

[EN] The design and prediction performance of four Venturi injector prototypes have been studied using Computational Fluid Dynamics (CFD) techniques. Results were compared with experimental tests carried out in the laboratory of the Universitat Politecnica de Valencia, Valencia, Spain. The analysed and selected geometries for each prototype were used to simulate the operation without nutrient injection (G1) and with nutrient injection (G2). In first case (G1), the results were presented in the form of pressure profile at the injector axe under different velocities and the pressure distribution in the whole geometry. Additionally, this paper analysed the evolution of pressures and head loss versus main water flow in the different prototypes. The relative error was estimated to compare CFD and experimental results. The second case (G2), the graphical representation for the relations between the nutrient aspiration flow and water main flow were obtained for numerical and experiment approaches. In conclusion, CFD techniques appear as a suitable tool for the analysis of the Venturi injector operation, but its validation with experimental data is recommended.[ES] En la Universitat Politècnica de València, Valencia, España, se ha estudiado el diseño y funcionamiento de cuatro prototipos del inyector Venturi con técnicas de Dinámica de Fluidos Computacional (CFD), comparándo las con ensayos en laboratorio. Para cada prototipo, las geometrías definidas y analizadas han permitido simular el funcionamiento sin (G1) y con inyección (G2) para quimigación. En el caso G1, se presentan los gráficos del perfil de presiones en el eje del inyector para diversas velocidades, así como la distribución del campo de presiones y de la evolución de las diferencias de presión y pérdidas de carga frente al caudal principal. Para comparar los resultados obtenidos con CFD frente al resultado experimental, se calculó el error relativo. En el caso G2, se obtuvo la representación gráfica del el caudal de inyección frente al caudal principal. Las técnicas CFD exigen un buen ajuste del modelo para dar un resultado aceptable. Son interesantes para comparar geometrías, analizar sus variantes, realizar prediseños y aproximar ordenes de magnitud, pero es recomendable su ensayo en laboratorio para validar los resultados.Manzano Juarez, J.; De Azevedo, BM.; Do Bomfim, GV.; Royuela, A.; Palau Estevan, CV.; Viana, TVDA. (2014). Diseño y predicción del funcionamiento de inyectores Venturi en riego localizado. 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Applications of computational fluid dynamics (CFD) in the modelling and design of ventilation systems in the agricultural industry: A review. Bioresource Technology, 98(12), 2386-2414. doi:10.1016/j.biortech.2006.11.025Palau-Salvador, G., Gonzalez Altozano, P., & Arviza-Valverde, J. (2007). Numerical modeling of cavitating flows for simple geometries using FLUENT V6.1. Spanish Journal of Agricultural Research, 5(4), 460. doi:10.5424/sjar/2007054-269Palau-Salvador, G., González-Altozano, P., & Arviza-Valverde, J. (2007). Three-Dimensional Modeling and Geometrical Influence on the Hydraulic Performance of a Control Valve. Journal of Fluids Engineering, 130(1). doi:10.1115/1.2813131Reader-Harris, M. ., Brunton, W. ., Gibson, J. ., Hodges, D., & Nicholson, I. . (2001). Discharge coefficients of Venturi tubes with standard and non-standard convergent angles. Flow Measurement and Instrumentation, 12(2), 135-145. doi:10.1016/s0955-5986(01)00007-3Singhal, A. K., Athavale, M. 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Enhanced electrochemical performance in lithium ion batteries of a hollow spherical lithium-rich cathode material synthesized by a molten salt method

A high voltage layered Li1.2Ni0.16Co0.08Mn0.56O2 cathode material with a hollow spherical structure has been synthesized by molten-salt method in a NaCl flux. Characterization by X-ray diffraction and scanning electron microscopy confirmed its structure and proved that the as-prepared powder is constituted of small, homogenously sized hollow spheres (1-1.5 μm). The material exhibited enhanced rate capability and high first cycle efficiency due to the good dispersion of secondary particles. Galvanostatic cycling at different temperatures (20, 40, and 60 °C) and a current rate of 2 C (500 mA·g-1) showed no significant capacity fade. [Figure not available: see fulltext.] © 2014 Tsinghua University Press and Springer-Verlag Berlin Heidelberg

The truth about the 1st cycle Coulombic efficiency of LiNi 1/3_{1/3} Co 1/3_{1/3} Mn 1/3_{1/3} O 2_{2} (NCM) cathodes

The 1st cycle Coulombic efficiency (CE) of LiNi1/3Co1/3Mn1/3O2 (NCM) at 4.6 V vs. Li/Li+ has been extensively investigated in NCM/Li half cells. It could be proven that the major part of the observed overall specific capacity loss (in total 36.3 mA h g−1) is reversible and induced by kinetic limitations, namely an impeded lithiation reaction during discharge. A measure facilitating the lithiation reaction, i.e. a constant potential (CP) step at the discharge cut-off potential, results in an increase in specific discharge capacity of 22.1 mA h g−1. This capacity increase during the CP step could be proven as a relithiation process by Li+ content determination in NCM via an ICP-OES measurement. In addition, a specific capacity loss of approx. 4.2 mA h g−1 could be determined as an intrinsic reaction to the NCM cathode material at room temperature (RT). In total, less than 10.0 mA h g−1 (=28% of the overall capacity loss) can be attributed to irreversible reactions, mainly to irreversible structural changes of NCM. Thus, the impact of parasitic reactions, such as oxidative electrolyte decomposition, on the irreversible capacity is negligible and could also be proven by on-line MS. As a consequence, the determination of the amount of extracted Li+ (“Li+ extraction ratio”) so far has been incorrect and must be calculated by the charge capacity (=delithiation amount) divided by the theoretical capacity. In a NCM/graphite full cell the relithiation amount during the constant voltage (CV) step is smaller than in the half cell, due to irreversible Li+ loss at graphite