Design of Zero Head Turbines for Power Generation

Failure analysis of the blades of a horizontal axis hydrokinetic turbine of 1 kW is presented. Analysis consisted of the determination of the pressure on the blade surface using Computational Fluid Dynamics, and the calculation of the stress distribution in the blade due to hydrodynamic, inertial and gravitational loads using the finite element methods. The results indicate that the blade undergoes significant vibration and deflection during the operation, and the centrifugal and hydrodynamic loads considerably affect the structural response of the blade; however, the stresses produced in all of the analysed models did not exceed the safe working stresses of the materials used to manufacture the blade. Modal analysis was conducted to calculate first significant natural frequencies. Results were studied in depth against operating frequency of the turbine. After carrying out the modal analysis, harmonic analysis was also done to see the response of the turbine under dynamic loading. It was observed that the turbine is safe in its entire operating range as far as phenomenon of resonance is concerned. Additionally, it was observed that maximum harmonic response of the turbine on the application of dynamic loading is far lesser than its failure limit within the specified operating range

Degradation of polycyclic aromatic hydrocarbons in water: Alternative treatments to conventional processes.

Nowadays, polycyclic aromatic hydrocarbons (PAHs) are a group of chemical substances that deserves a great attention. PAHs consist of two or more condensed benzene rings, bonded in linear, cluster or angular arrangements that are ubiquitous in the environment. Due to their low solubility and high affinity for particulate matter, PAHs are found in water in extreme low concentrations, in the range of ng L-1 or µg L-1. However, even at these ultra-trace or trace levels, they exhibit harmful effects on living beings and humans, especially when present as mixtures. That is the case of anthracene (AN), which has been reported as an acute phototoxic compound, and benzo[a]pyrene (BaP), which is a carcinogenic and mutagenic pollutant. Therefore, their presence in the environment and, specifically in aquatic resources must be monitored. For this purpose, the chromatographic behavior of AN and BaP was studied, and three models were found describing the identification of AN and BaP, the quantification of AN and that of BaP. The factors influencing each of the models or indexes were also optimized and a new and fast analytical method allowing the determination of the analytes of interest at ultra-trace concentrations in surface water samples was developed. In addition to monitor the target pollutants, they must be also eliminated from water because of the adverse health effects associated. However, conventional processes water treatment facilities are operating with are not efficient in tackling the problem of AN and BaP pollution in water. In this regard, the implementation of alternative treatments, including advanced oxidation processes (AOPs), provides a very attractive option. AOPs have demonstrated to be highly interesting technologies for water remediation, particularly the combination of ultraviolet radiation in the UV-C range (UV-C) and hydrogen peroxide (H2O2). This Thesis addresses the evaluation of the efficiency of the UV-C/H2O2 oxidation system to treat water sampled from a natural reservoir polluted with AN and BaP. For this purpose, initially, the removal profiles of AN and BaP were investigated, as well as the organic matter mineralization capacity of the oxidation system and the production of innocuous degradation by-products. The system allowed obtaining very positive results in terms of the degradation of the pollutants of interest and the organic matter mineralization, avoiding the production of dangerous reactive intermediates. Furthermore, after the application of this treatment process, a residual H2O2 was observed in the reaction solution, which can be used for additional microbial load removal. The residual H2O2 found within the bulk after the application of the oxidation treatment was analyzed using an analytical method proposed here. Moreover, the oxidation potential of the UV-C/H2O2 process was assessed for the inactivation of wild total coliforms naturally contained in the water of study and the results were compared with the findings obtained from other photochemical technologies based on sonochemical reactions. It was found that the technology achieving the highest microorganism elimination in the shortest time and with the lowest electrical costs results was the UV-C/H2O2 process. Nevertheless, in spite of that, it is worth noting that the implementation of the UV-C/H2O2 oxidation process still requires high electrical needs, which increases the operating costs of the process. Therefore, in order to reduce such as costs, a photovoltaic (PV) array was sized and installed for supplying the energy requirements of the selected water treatment system. The installed PV system allows for the use of renewable energy both in developing and non-developing countries. In this regard, the treatment of water to be drinkable was observed to be plausible in countries with lack of economical resources and in communities far from the electrical grid, which exist in a high number in countries such as Colombia. In the second stage of the research, and taking into account the necessity of having kinetic models for finding out the optimal operating conditions without the necessity of conducting extensive experimentation, a kinetic model for the performance of the UV-C/H2O2 oxidation process was constructed and validated using a model compound. The kinetic model allows calculating the optimal level of H2O2 for efficiently degrading the pollutant of interest, as well as the effective level of HO• to be maintained throughout the reaction time of the UV-C/H2O2 system for achieving an efficient pollutant degradation, contributing to save costs and time.Ingeniería, Industria y Construcció

Computational Fluid Dynamic Simulation of Vertical Axis Hydrokinetic Turbines

Hydrokinetic turbines are one of the technological alternatives to generate and supply electricity for rural communities isolated from the national electrical grid with almost zero emission. These technologies may appear suitable to convert kinetic energy of canal, river, tidal, or ocean water currents into electricity. Nevertheless, they are in an early stage of development; therefore, studying the hydrokinetic system is an active topic of academic research. In order to improve their efficiencies and understand their performance, several works focusing on both experimental and numerical studies have been reported. For the particular case of flow behavior simulation of hydrokinetic turbines with complex geometries, the use of computational fluids dynamics (CFD) nowadays is still suffering from a high computational cost and time; thus, in the first instance, the analysis of the problem is required for defining the computational domain, the mesh characteristics, and the model of turbulence to be used. In this chapter, CFD analysis of a H-Darrieus vertical axis hydrokinetic turbines is carried out for a rated power output of 0.5 kW at a designed water speed of 1.5 m/s, a tip speed ratio of 1.75, a chord length of 0.33 m, a swept area of 0.636 m2, 3 blades, and NACA 0025 hydrofoil profile

Kinetic Modeling of the UV/H2O2 Process: Determining the Effective Hydroxyl Radical Concentration

A kinetic model for pollutant degradation by the UV/H2O2 system was developed. The model includes the background matrix effect, the reaction intermediate action, and the pH change during time. It was validated for water containing phenol and three different ways of calculating HO° level time-evolution were assumed (non-pseudo-steady, pseudo-steady and simplified pseudo-steady state; denoted as kinetic models A, B and C, respectively). It was found that the kind of assumption considered was not significant for phenol degradation. On the other hand, taking into account the high levels of HO2° formed in the reaction solution compared to HO° concentration (~10–7 M >>>> ~10–14 M), HO2° action in transforming phenol was considered. For this purpose, phenol-HO2° reaction rate constant was calculated and estimated to be 1.6x103 M-1 s-1, resulting in the range of data reported from literature. It was observed that, although including HO2° action allowed slightly improving the kinetic model degree of fit, HO° developed the major role in phenol conversion, due to their high oxidation potential. In this sense, an effective level of HO° can be determined in order to be maintained throughout the UV/H2O2 system reaction time for achieving an efficient pollutant degradation

Analysis of biochars produced from the gasification of pinus patula pellets and chips as soil amendments

In this work, biochar (BC), a co-product of the fixed bed gasification process of Pinus patula wood pellets (PL) and chips (CH), was characterized as soil amendment. The physicochemical properties and the mineral content of the pellet’s biochar (PL-BC) and the chips biochar (CH-BC) were analyzed following the NTC5167 Colombian technical standard. The BET surface area values of the BCs were 367,33 m2/g and 233,56 m2/g for the PL-BC and the CH-BC, respectively, and the pore volume was 0,20 cm3/g for the PL-BC and 0,13 cm3/g for the CH-BC. These characteristics favor the increase of the BCs water-holding capacity (WHC). Properties such as the pH (8,8-9,0), the WHC (219 % - 186,4 %), the total organic carbon (33,8 % - 23,9 %), the metalloid presence (Ca, Mg, K, Mn, Al, Si, and Fe), and the ash (1,92 wt% - 2,74 wt%) and moisture contents (11,13 wt% - 11,63 wt%) for both BCs were found to be within the limits set by the NTC5167 standard. Furthermore, the presence of micro and macronutrients, such as Fe and phosphorus (P), and the alkaline pH, make possible the use of these BCs as amendments for acid soils

Otimização do processo sono-foto-Fenton para o tratamento de águas residuais usando um experimento composto central

Introducción. Debido al aumento de la toxicidad de las aguas residuales y a la limitada eficiencia de los sistemas convencionales, se hace necesaria la aplicación de procesos alternativos, entre los que destaca el sistema sono-foto-Fenton. Objetivo. Con este trabajo se busca optimizar las variables que afectan directamente el poder de oxidación del proceso sono-foto-Fenton, tales como el pH de la solución y la concentración de agente oxidante y promotor, para el tratamiento de un agua residual de origen petroquímico, con el fin de validar la conveniencia del uso de diseños de experimentos basados en un número reducido de corridas. Materiales y métodos. Para ello, se utilizó un diseño de experimentos central compuesto centrado en las caras, cuyo modelo de regresión de segundo orden obtenido fue validado. Los resultados alcanzados fueron comparados con los reportados en la literatura usando un mayor número de corridas experimentales. Resultados. Bajo condiciones de operación optimizadas (3 unidades de pH, 525 mg/L de H2O2 y 25,70 mg/L de Fe2+) se obtuvieron remociones de DQO > 70 %. Estos resultados fueron similares a las condiciones óptimas obtenidas e informadas previamente en la literatura utilizando un diseño de experimentos factorial completo. Conclusiones. Se demuestra, por tanto, la importancia de llevar a cabo diseños de experimentos que permitan optimizar sistemas de tratamiento de aguas usando un reducido número de corridas, lo cual se traduce en la reducción tanto de costos económicos como de tiempos de experimentación y análisis de la variable respuesta objeto de estudio. Palabras clave: diseño de experimentos, tratamiento del agua, proceso avanzado de oxidación, contaminante persistente, contaminación.Introduction. Due to the increased toxicity of wastewater and the limited efficiency of conventional systems, the application of alternative processes is required, among which the sono-photo-Fenton system is highlighted. Objective. This work aims at optimizing the variables that directly affect the oxidation power of the sono-photo-Fenton process, such as the pH of the solution and the concentration of the oxidizing and the promoting agents, for the treatment of a petrochemical wastewater, in order to validate the suitability of using designs of experiments based on a reduced number of runs. Materials and methods. For this purpose, a face-centered composite central experiment design was used, whose second-order regression model was validated. The results achieved were compared Conclusiones. Se demuestra, por tanto, la importancia de llevar a cabo diseños de experimentos que permitan optimizar sistemas de tratamiento de aguas usando un reducido número de corridas, lo cual se traduce en la reducción tanto de costos económicos como de tiempos de experimentación y análisis de la variable respuesta objeto de estudio. Palabras clave: diseño de experimentos, tratamiento del agua, proceso avanzado de oxidación, contaminante persistente, contaminación. Optimization of the sono-photo-Fenton process for wastewater treatment using a central composite design. ABSTRACT to those ones reported in the literature using a larger number of experimental runs. Results. Under optimized operating conditions (3 pH units, 525 mg/L H2O2 and 25,70 mg/L Fe2+), COD removals > 70 % were obtained. These results were similar to the optimal conditions previously obtained and informed in the literature by using a full factorial experiment design. Conclusions. Therefore, it is demonstrated the importance of conducting designs of experiments that allow optimizing water treatment systems using a reduced number of runs, which results in the reduction of both economic costs and times of experimentation and analysis of the response variable of interest. Keywords: design of experiments, water treatment, advanced oxidation process, persistent pollutant, pollution

Surrogate modelling for high-lift multi-element hydrofoil shape optimization of a hydrokinetic turbine blade

The hydrodynamic shape of a blade is one of the most important factors in the design process of a horizontal axis hydrokinetic turbine that influences its performance. The present work is focused on the design and hydrodynamic analysis of a high-lift system using the optimization method of surrogate models and computational fluid dynamics (CFD) analysis. The parameters that affect the amount of the lift and the drag force that a hydrofoil can generate are the gap, the overlap, the flap deflection angle (δ), the flap chord length (C2) and the angle of attack of the hydrofoil (α). These factors were varied to examine the turbine performance in terms of the ratio between the lift (CL) and the drag coefficient (CD), and the minimum negative pressure coefficient (min Cpre) in order to avoid the cavitation inception. For this propose, surrogate models were implemented to analyse the CFD results and find the optimal combination of the design parameters of the high-lift hydrofoil. The traditional Eppler 420 hydrofoil was utilized for the design of the multi-element profile, which was composed of a main element and a flap. The multi-element design selected as optimal had a gap of 2.825 %C1, an overlap of 8.52 %C1, a δ of 19.765˚, a C2 of 42.471 %C1 and a α of -4˚, where C1 refers to the chord length of the main element. In comparison with the traditional Eppler 420 hydrofoil, CL/CD ratio increases from 39.050 to 42.517. Key words. Horizontal axis hydrokinetic turbine, surrogate model, computational fluid dynamics, high-lift system, multielement hydrofoi

Kinetic model describing the UV/H2O2 Photodegradation of phenol From water

ABSTRACT: A kinetic model for phenol transformation through the UV/H2O2 system was developed and validated. The model includes the pollutant decomposition by direct photolysis and HO, HO2 and O2 - oxidation. HO scavenging effects of CO32-, HCO3-, SO42- and Cl- were also considered, as well as the pH changes as the process proceeds. Additionally, the detrimental action of the organic matter and reaction intermediates in shielding UV and quenching HO was incorporated. It was observed that the model can accurately predict phenol abatement using different H2O2/phenol mass ratios (495, 228 and 125), obtaining an optimal H2O2/phenol ratio of 125, leading to a phenol removal higher than 95% after 40 min of treatment, where the main oxidation species was HO. The developed model could be relevant for calculating the optimal level of H2O2 efficiently degrading the pollutant of interest, allowing saving in costs and time

Simulación numérica de una columna de agua oscilante para las condiciones de ola del océano Pacífico colombiano

Ocean wave energy is one of the least exploited sources in Colombia. The oscillating water column (OWC) can be a sustainable technology to generate electricity in hard-to-reach areas using the energy available in the Pacific Ocean. Currently, Colombia lacks the development of these devices; however, there are hopes focused on wave energy as a feasible alternative to provide renewable energy in non-interconnected zones (NIZ) in the country. In this work, it is intended to numerically simulate an OWC for the Colombian Pacific Ocean conditions, so computational fluid dynamics was used through ANSYS Fluent program to model an onshore OWC. This research reaches the numerical simulation stage, however, it can be taken to small-scale experimental studies. The maximum chamber efficiency and the media free surface velocity of the water column for the studied geometry were 66.81 % and 0.118 m/s, respectively. Sensitivity analysis of the geometrical factors describing the resonant chamber of the device against various sea conditions could be of crucial interest to improve its hydrodynamic efficiency.La energía de las olas es una de las fuentes menos explotadas en Colombia. La columna de agua oscilante (OWC, por siglas en inglés) puede ser una tecnología sostenible para generar electricidad en zonas de difícil acceso utilizando la energía disponible en el océano Pacífico. En la actualidad, Colombia carece del desarrollo de estos dispositivos; sin embargo, hay esperanzas centradas en la energía de las olas como alternativa factible para proporcionar energía renovable en las zonas no interconectadas (ZNI) del país. En este trabajo, se pretende simular numéricamente una OWC para las condiciones del océano Pacifico colombiano, por lo que se empleó la dinámica de fluidos computacional a través del programa ANSYS Fluent para modelar una OWC ubicada en la orilla. Esta investigación alcanza la etapa de simulación numérica; sin embargo, puede ser llevada a estudios experimentales a pequeña escala. La eficiencia máxima de la cámara resonante simulada y la velocidad media de la superficie libre de la columna de agua para la geometría estudiada fueron 66.81 % y 0.118 m/s, respectivamente. El análisis de sensibilidad de los factores geométricos que describen la cámara resonante del dispositivo frente a diversas condiciones de mar podría ser de crucial interés para mejorar su eficiencia hidrodinámica