http://hdl.handle.net/2117/3252 2013-05-23T22:42:42Z http://hdl.handle.net/2117/18433 Title: Experimental investigation of added mass effects on a hydrofoil under cavitation conditions Authors: Torre Rodríguez, Óscar de la; Escaler Puigoriol, Francesc Xavier; Egusquiza Estévez, Eduard; Farhat, Mohamed Abstract: The influence of leading edge sheet cavitation and supercavitation on the added mass effects experienced by a 2-D NACA0009 truncated hydrofoil has been experimentally investigated in a hydrodynamic tunnel. A non-intrusive excitation and measuring system based on piezoelectric patches mounted on the hydrofoil surface was used to determine the natural frequencies of the fluid–structure system. The appropriate hydrodynamic conditions were selected to generate a range of stable partial cavities of various sizes and also to minimize the effects of other sources of flow noise and vibrations. The main tests were performed for different sigma values under a constant flow velocity of 14 m/s and for incident angles of both 1° and 2°. Additionally, a series of experiments in which the hydrofoil was submerged in air, partially and completely submerged in still water and without cavitation at 7 and 14 m/s were also performed. The maximum added mass effect occurs with still water. When cavitation appears, the added mass decreases because the cavity length is increased, and the added mass is minimum for supercavitation. A linear correlation is found between the added mass coefficients and the entrained mass that accounts for the mean density of the cavity, its dimensions and its location relative to the specific mode shape deformation. 2013-03-20T11:33:13Z http://hdl.handle.net/2117/17901 Title: Numerical and experimental analysis of the dynamic response of large submerged trash-racks Authors: Huang, Xingxing; Valero Ferrando, M.del Carmen; Egusquiza Estévez, Eduard; Presas Batlló, Alexandre; Guardo Zabaleta, Alfredo de Jesús Abstract: This paper investigates the effect of water in the dynamic response of large trash-racks used in hydropower plants. These are large structures that are fully submerged in water and located in the hydraulic circuits to prevent debris and large bodies from entering the turbine. These structures are prone to suffering fatigue damage. Broken bars are rather common, which can produce damage in the turbine and other hydraulic components. To avoid fatigue problems, the trash-racks must be designed to avoid coincidence between the excitation frequencies of vortex shedding and the natural frequencies of the trash rack. Therefore, it is of paramount importance to know which are the natural frequencies and the associated mode-shapes, so as to avoid fluid–structure coupling (lock-in), which can lead to high vibration levels. Finite element models, including the surrounding mass of water, are used for this study. The methodology is applied to two existing trash-racks by calculating the modal parameters and using the numerical finite element model. An experimental investigation is also carried out in one of the trash-racks by impacting the underwater grille and measuring the response using submergible accelerometers. Experimental modal analysis is utilized to extract the modal characteristics of the actual trash rack. There is a good agreement between the numerical and the experimental results. With the validated model, the effects of fluid added mass and damping on the dynamic response of both trash-racks are evaluated and discussed in order to extract some common conclusions. 2013-02-21T08:58:02Z http://hdl.handle.net/2117/17766 Title: Numerical and experimental analysis of the dynamic response of large submerged trash-racks Authors: Huang, Xingxing; Valero Ferrando, M.del Carmen; Egusquiza Estévez, Eduard; Presas Batlló, Alexandre; Guardo Zabaleta, Alfredo de Jesús Abstract: This paper investigates the effect of water in the dynamic response of large trash-racks used in hydropower plants. These are large structures that are fully submerged in water and located in the hydraulic circuits to prevent debris and large bodies from entering the turbine. These structures are prone to suffering fatigue damage. Broken bars are rather common, which can produce damage in the turbine and other hydraulic components. To avoid fatigue problems, the trash-racks must be designed to avoid coincidence between the excitation frequencies of vortex shedding and the natural frequencies of the trash rack. Therefore, it is of paramount importance to know which are the natural frequencies and the associated mode-shapes, so as to avoid fluid–structure coupling (lock-in), which can lead to high vibration levels. Finite element models, including the surrounding mass of water, are used for this study. The methodology is applied to two existing trash-racks by calculating the modal parameters and using the numerical finite element model. An experimental investigation is also carried out in one of the trash-racks by impacting the underwater grille and measuring the response using submergible accelerometers. Experimental modal analysis is utilized to extract the modal characteristics of the actual trash rack. There is a good agreement between the numerical and the experimental results. With the validated model, the effects of fluid added mass and damping on the dynamic response of both trash-racks are evaluated and discussed in order to extract some common conclusions. 2013-02-14T13:58:52Z http://hdl.handle.net/2117/17764 Title: Capability of structural-acoustical FSI numerical model to predict natural frequencies of submerged structures with nearby rigid surfaces Authors: Rodríguez, Cristian; Flores, P.; Pierart, F.G.; Contzen, L.R.; Egusquiza Estévez, Eduard Abstract: Structural–acoustical model is used in industry to determine natural frequencies of runners and impellers in hydraulic turbomachinery in the stage of design. In these calculations the fluid domain is considered with comparable large distances to stationary parts while there are parts of the submerged structure (runner or impeller) that are extremely close (in relation to its thickness) to a rigid surface (hydraulic seals). These seals are not considered in the numerical model because it is assumed that structural– acoustical model is not capable to predict natural frequencies with nearby rigid surfaces. The present work builds a fluid structure interaction numerical model based on structural–acoustic coupling, checks the numerical model’s accuracy, and determines its capability to predict natural frequencies reduction due to nearby rigid surfaces comparing this model against experimental data of submerged cantilever plates. It is found that the structural–acoustical model can accurately predict the natural frequencies for submerged structures with nearby rigid surfaces with averaged absolute errors of 2.5%. This is an interesting result because it suggests that simulation of runners and impellers can be carried out considering the effect of hydraulic seals, therefore, obtaining natural frequencies that are closer to those found under operation. 2013-02-14T13:08:40Z http://hdl.handle.net/2117/17729 Title: Failure investigation of a large pump-turbine runner Authors: Egusquiza Estévez, Eduard; Valero Ferrando, M.del Carmen; Huang, Xingxing; Guardo Zabaleta, Alfredo de Jesús; Jou Santacreu, Esteban; Rodríguez, Cristian 2013-02-13T15:03:40Z http://hdl.handle.net/2117/17056 Title: Optimización de un banco de ensayos de cavitación mediante fluidodinámica computacional Authors: Moll, Flavio; Manuele, Diego; Coussirat Núñez, Miguel Gustavo; Cappa, E. Franco; Gandolfo, Ernesto; Guardo Zabaleta, Alfredo de Jesús; Fontanals García, Alfred Abstract: Los flujos cavitantes se corresponden a una estructura bifásica (líquido-vapor) cuando la presión del líquido disminuye hasta su presión de vapor, pv. La aparición y el posterior colapso de cavidades de vapor cerca de paredes sólidas, generan pulsos de presión de alta frecuencia que ocasionan la falla por fatiga del material sólido, y pérdida de rendimiento y daño mecánico en turbomáquinas. Experimentos que identifican el patrón de flujos cavitantes muestran que el estado de cavitación desarrollada puede tener diferentes estructuras no estacionarias, en algunos casos del tipo periódica. Éstas dependen de su estado fluidodinámico, siendo algunas de ellas más agresivas desde el punto de vista del daño por cavitación. Relacionados con el daño por cavitación en materiales, existen montajes experimentales orientados a estudios que implican la búsqueda y/o desarrollo de materiales resistentes al daño por cavitación. Debido al alto costo de los experimentos en bancos hidrodinámicos, es de interés evaluar las condiciones óptimas de cavitación que maximicen el daño en probetas de materiales resistentes a este fenómeno. Esto puede hacerse mediante modelado numérico (CFD), ya que es posible caracterizar el tipo de estructura que posee la zona de vaporización/colapso de las burbujas en estos dispositivos de ensayo, aunque este tipo de flujo muestra una gran complejidad en su modelado, debido a que se debe tener en cuenta el estado bifásico y turbulento del flujo. El objetivo de este trabajo ha sido contribuir mediante el uso de CFD a la optimización del diseño de un banco de ensayos hidrodinámico actualmente en construcción, para el ensayo de probetas de diversos aleaciones de materiales que se usarán para recargue de álabes de turbinas. Se necesita garantizar que existan mecanismos de cavitación lo más agresivos posibles en el dispositivo de ensayo en donde se insertarán las probetas de cara a minimizar los tiempos de ensayo, que son del orden de 150 horas. El estudio mediante CFD se ha hecho aplicando diferentes modelos para la cavitación y para la turbulencia, utilizando los estudios de validación y de sensibilidad a parámetros de los submodelos ya realizados en un trabajo previo al presente trabajo. 2012-11-30T12:27:19Z http://hdl.handle.net/2117/16505 Title: Continuous production of biodiesel from vegetable oil using supercritical ethanol/carbon dioxide mixtures Authors: Santana Scotelari de Souza, Aline; Maçaira, José; Larrayoz Iriarte, María Angeles Abstract: Biodiesel production is worthy of continued study and optimization of production procedures because of its environmentally beneficial attributes and its renewable nature. Transesterification of triglycerides using supercritical ethanol on ion-exchange resin catalyst was investigated to study the ethyl ester conversion process. The reaction parameters investigated were the reaction time, pressure, temperature and molar ratio (alcohol to triglycerides), and their effect on the biodiesel formation. Addition of a co-solvent, supercritical carbon dioxide (critical point at 31 °C and 7.3 MPa), decreased the operating conditions maintaining a high reaction rate. The mixture ethanol/carbon dioxide used in this work was 1:3 molar ratio. The experiments were conducted at temperatures of 150–200 °C, pressure from 150 to 250 bar and reaction times from 2 to 10 min, and molar ratios of ethanol to vegetable oil from 20 to 45. The evolution of the process was followed by gas chromatography, determining the concentration of the ethyl esters at different reaction times. Results showed that ethyl esters obtained in the continuous fixed bed reactor under supercritical conditions can achieve 80% yield of biodiesel at reaction time of 4 min. 2012-09-17T09:59:42Z http://hdl.handle.net/2117/16497 Title: Crystallization of microparticulate pure polymorphs of active pharmaceutical ingredients using CO 2-expanded solvents Authors: Veciana, J.; Sala, S.; Córdoba, A.; Moreno Calvo, E.; Elizondo, E.; Muntó, M.; Rojas, P.E.; Larrayoz Iriarte, María Angeles; Ventosa, N. Abstract: The feasibility of the Depressurization of an Expanded Liquid Organic Solution (DELOS) method to process different active pharmaceutical ingredients (APIs) as finely divided powders with narrow particle size distribution, high crystallinity degree, high polymorphic purity, and free from residual solvent has been demonstrated. Cholesterol, acetylsalicylic acid (aspirin), naproxen, acetaminophen, and ibuprofen were chosen as model drugs. It has been demonstrated that the supersaturation ratio attained during crystallization from CO2-expanded solvents can be modulated through appropriate variations of process parameters  CO2 content and concentration of the initial solution. In view of the potential application that compressed fluidsbased technologies have in the pharmaceutical industry, a preliminary scalability study of the process in compliance with the constraints imposed by the Good Manufacturing Practices (GMP) specifications is presented herein 2012-09-14T11:32:10Z http://hdl.handle.net/2117/16356 Title: Analysis of chatter marks damage on the Yankee dryer surface of a tissue machine Authors: Escaler Puigoriol, Francesc Xavier; Torre Rodríguez, Óscar de la; Egusquiza Estévez, Eduard Abstract: A tissue machine suffering from Yankee chatter marks has been experimentally investigated. A series of vibration measurements during normal operation at various Yankee speeds on both the creping and the cleaning blade holders have been carried out. The analysis in a frequency range up to 20 kHz has permitted to identify speed dependent frequency peaks and broadband high frequency vibration content on the creping zone. Hence, an experimental modal analysis of the creping blade and holder has been carried out with the machine stopped to identify its natural frequencies. As a result, resonance conditions have been identified due to the gearbox excitation originated by the meshing process. The study of the corresponding mode shapes has permitted to understand the vibration behavior and its relationship with the damage. To solve the problem, the creping blade holder structure has been redesigned to detune the resonances. Since this overhaul, comparable measurements have confirmed a significant reduction of vibrations and high frequency noise. The appearance of chatter marks has been minimized. 2012-07-27T10:43:23Z http://hdl.handle.net/2117/15083 Title: Fatty oil hydrogenation in supercritical solvents: process design and safety issues Authors: Ramírez Rangel, Eliana; Mayorga Cárdenas, Miguel Yuri; Cuevas, Daniel; Recasens Baxarías, Francisco Javier Abstract: A simulation study of a SCF process is carried out using Aspen™ with previously available catalytic kinetics for the simulation of the reactor. Two supported catalysts were considered: a standard Pd/carbon, and an egg-shell Pd/alumina, in a vapour-phase process that uses propane as solvent. Best reactor–catalyst combination was selected using optimization. Optimal reactor–catalyst conditions were: Pd (0.5 wt%) on alumina catalyst in tubes, shell cooling, inlet temperature 170 °C, space-time 100 s, 4 mol% of H2 in the feed, oil feed 1 mol%, propane 95 mol%, with pressure up to 20 MPa. Three SC solvents, were considered in the simulation. These were (i) SC propane, (ii) a cosolvent case with hexane-modified CO2, and (iii) a case with pure liquid hexane. In plant simulation, three recycle streams (H2, CO2 and cosolvent) complicate the separations. In order to assess the safety differences between these options, a study was done using the Dow Fire and Explosion Index to roughly figure out process safety. It is shown that plant complexity increases with cosolvent use, but the hazard index is sensibly reduced, from F&EI = 150 (pure propane) to a low value (F&EI = 60) for a plant with CO2 with 40 mol% of hexane as cosolvent. 2012-02-13T10:48:44Z http://hdl.handle.net/2117/15082 Title: Effect of reactor type on trans fatty acid and stearate formation in fat hydrogenation in SCF solvent Authors: Mayorga, M. J.; Ahrweiller, Chloé; Cuevas, Daniel; Recasens Baxarías, Francisco Javier Abstract: Hydrogenation of vegetable fats is an important biomolecule modification process, traditionally carried out in a slurry reactor at low pressure (2–6 bar). Here, the hydrogenation of sunflower oil in supercritical propane and dimethyl ether catalysed by Pd (supported on activated carbon or alumina) is studied. One-dimensional simulation models for plug flow and mixed flow reactors, as well as two-dimensional dispersed plug flow reactor models, were developed for the case of isothermal and adiabatic operation. The hydrogenation of sunflower oil is considered as a reaction network based on linoleate, oleate (cis C18:1), elaidate (trans C18:1) and stearate triesters. Since trans fatty C18:1 ester and stearate formation is not desired, the question arises as to which reactor type is best to achieve a low elaidate content. Depending on the final allowed stearate content, different mixed and plug flow reactor models can be applied. However, for a fixed stearate formation rate, the mixed reactor gives a lower trans content than the plug flow reactor in most cases. Also, low temperature operation results in better oleate/stearate selectivity. Two-dimensional tubular reactor dispersed simulation does not give further insight into the problem. The use of Multiphysics (finite element method) for solving the dispersed plug flow model provides a way to simulate CSTR reactor behaviour. In our case, both heat and mass Péclet numbers of 10−4 or less are sufficient to describe well-mixed reactor behaviour using the 2D mass and heat transfer pseudo-homogeneous model with radial and axial effects, with parameter values available for SCF. The models can be used for planning reaction operations in SCF as solvents intended for low trans fatty acid. 2012-02-13T10:22:28Z http://hdl.handle.net/2117/14738 Title: Caracterización del tipo de cavitación mediante dinámica computacional de fluidos para posteriores aplicaciones al estudio experimental del daño por cavitación Authors: Moll, Flavio; Manuele, Diego; Coussirat Núñez, Miguel Gustavo; Guardo Zabaleta, Alfredo de Jesús; Fontanals García, Alfred Abstract: La cavitación se corresponde a una estructura bifásica (líquido-vapor) cuando la presión del líquido disminuye hasta su presión de vapor, pv. Esta disminución de pv puede deberse a diversos factores relacionados con la hidrodinámica del flujo y las propiedades físicas del fluido, pudiendo presentar diferentes características. En la cavitación hidrodinámica, pueden distinguirse efectos que pueden producir un acoplamiento fluido-estructura (lock-in) que puede favorecen la falla del material, sólido que confina al fluido, lo que conduce a la pérdida de rendimiento y daño mecánico en turbomáquinas. Los ensayos experimentales muestran que el estado de cavitación desarrollada puede tener diferentes estructuras, (e.g. de burbujas, de lámina, supercavitación, etc.), siendo algunas de ellas de tipo periódica. Estas estructuras dependen del estado fluidodinámico del flujo, siendo algunas de ellas más agresivas desde el punto de vista del daño por cavitación. Debido al costo de los experimentos, es de interés evaluar si mediante dinámica computacional de fluidos (CFD) se puede caracterizar el tipo de estructura que posee la zona de vaporización/colapso de las burbujas en diferentes dispositivos hidrodinámicos. Este tipo de flujo muestra una gran complejidad ya que deben tenerse en cuenta el estado bifásico y turbulento del flujo El objetivo de este trabajo es demostrar si es posible caracterizar mediante CFD el tipo de estructura que se presenta cuando hay cavitación desarrollada, utilizando datos experimentales para una configuración de flujo sobre un escalón, probándose primero las aproximaciones que se obtienen mediante CFD. Se estudia la validación y la sensibilidad a parámetros de modelado con el objetivo de aplicar el conocimiento adquirido a la optimización del diseño de probetas que se insertarán en un banco de ensayos hidrodinámico para la comprobación de la resistencia al daño por cavitación de distintos materiales. Se identifican parámetros que permitan reproducir las condiciones de cavitación más agresiva con el objeto de reducir los tiempos de ensayo. 2012-01-23T12:46:00Z http://hdl.handle.net/2117/14267 Title: Biodiesel production using supercritical methanol/carbon dioxide mixtures in a continuous reactor Authors: Maçaira, José; Santana Scotelari de Souza, Aline; Recasens Baxarías, Francisco Javier; Larrayoz Iriarte, María Angeles Abstract: Fatty acid methyl esters (biodiesel) were produced by the transesterification of triglycerides with compressed methanol (critical point at 240 C and 81 bar) in the presence of solid acids as heterogeneous catalyst (SAC-13). Addition of a co-solvent, supercritical carbon dioxide (critical point at 31 C and 73 bar), increased the rate of the supercritical alcohols transesterification, making it possible to obtain high biodiesel yields at mild temperature conditions. Experiments were carried out in a fixed bed reactor, and reactions were studied at 150–205 C, mass flow rate 6–24 ml/min at a pressure of 250 bar. The molar ratio of methanol to oil, and catalyst amount were kept constant (9 g). The reaction temperature and space time were investigated to determine the best way for producing biodiesel. The results obtained show that the observed reaction rate is 20 time faster than conventional biodiesel production processes. The temperature of 200 C with a reaction time of 2 min were found to be optimal for the maximum (88%) conversion to methyl ester and the free glycerol content was found below the specification limits. 2011-12-19T11:18:14Z http://hdl.handle.net/2117/13535 Title: Glycerol desorption from ion exchange and adsorbent resin using supercritical fluid technology: An optimization study Authors: Costa, A. E.; Santana Scotelari de Souza, Aline; Quadri, M.B; Machado, R.A.F; Recasens Baxarías, Francisco Javier; Larrayoz Iriarte, María Angeles Abstract: In this study, glycerol desorption from Purolite® PD206 resin was investigated using conventional and supercritical fluids (SCF) techniques. Untreated biodiesel was purified by dry washing using the resin and, after purification, the glycerol desorption was carried out using absolute ethanol under atmospheric conditions at different mass flows (10–30 g/min) or using ethanol-modified supercritical CO2 (1:3 molar ratio of ethanol:CO2), under a pressure of 140 bar, within a temperature range of 106–134ºC and with mass flow rates of 6–34 g/min. The results showed that ethanol is an efficient solvent for this process and that the supercritical desorption is much faster than conventional desorption process. Employing the Response Surface Methodology (RSM) it was found that temperature has the greatest effect on the resin regeneration time using supercritical fluids. Optimum conditions obtained were 106.1ºC and 21.9 g/min, in which the resin was regenerated in only 4.17 min. 2011-10-17T12:52:29Z http://hdl.handle.net/2117/7680 Title: Dynamic analysis of Francis Runners-Experiment and numerical simulation Authors: Lais, Stefan; Qwenguei, Liang; Henggeler, Urs; Weiss, Thomas; Escaler Puigoriol, Francesc Xavier; Egusquiza Estévez, Eduard 2010-06-16T09:44:56Z