Search

In this article, CFD simulations results are presented as a key tool to the comprehension of the target gas concentration evolution in a test chamber, at different working conditions. The simulation results are compared with the experimental data, which shows a qualitative good correlation with the evolution of the concentration gradient detected. The experiments were carried out using an aluminum gas test chamber, where a WO3 based conductometric sensor is introduced. The results demonstrate how the response time is dependent on the sensor working conditions. Analyzing the CFD and experimental results, some assumptions for this behavior are proposed. The WO3 sensor needs a Pt heating element, which is heated up to 300 °C. As the response is highly temperature-dependent, the temperature distribution on the sensor surface was measured by an IR thermographic camera. The simulation results show that the temperature distribution matches with those obtained experimentally. To validate the model, a mesh and time step convergence study was also implemented.

The paradigm of renewable energies brings a number of challenges to be solved in a short-term period. In the case of wind energy, it turns necessary to relocate onshore wind-farms in both offshore coastal regions and urban environments, so that visual and environmental impacts of current devices are reduced. This modifies the flow regime noticeably; indeed, turbulence and environmentally-induced roughness need to be accounted for, in addition to the scale-effect in case of urban wind turbines. The effects of such factors on the aerodynamic efficiency of a standard NACA0021 airfoil are tested via wind-tunnel measurements, showing the resultant decrease in aerodynamic efficiency when passing from ideal to real flow conditions. Such a decrease leads to concluding that aerodynamic tests should be undertaken with flow configurations that represent real operational conditions., Energia berriztagarrien paradigmak erronka ugari dakartza berorrekin, epe laburrean erantzun beharrekoak bederen. Energia eolikoaren kasuan, ustiapena ohiko haize-parkeetatik itsasalde edota hiriguneetara mugitzean datza, inpaktu bisuala nahiz ingurumen kalteak murrizteko asmoz. Horrek haizearen fluxu baldintzak nabarmen aldatzea dakar; bereziki, turbulentzia eta ingurumen-eragileek sorturiko gainazal-zimurtasuna hartu behar da kontuan eta, hiriguneetako kasuan, aerosorgailuen eskala aldaketa. Haize-tunel bidezko entseguak burutuz, faktore horiek NACA0021 geometriadun pala baten efizientzia aerodinamikoan duten eragina aztertu da, baldintza idealetatik errealetara igarotzean ematen den efizientzia galera ikusaraziz. Galera hori dela-eta, entsegu esperimentalak harik eta baldintza errealenetan egiteko beharra ondorioztatzen da.

An application-agnostic procedure is outlined for checking the validity of momentum-deficit-based drag measurements performed under different turbulent conditions in a wind tunnel. The approach defines a two-step methodology: the first stage characterizes the turbulent flowfield generated downstream a passive grid through a set of statistical parameters. Acceptable values for such parameters are determined by means of two criteria: compliance with the threshold value set by an analysis of the experimental uncertainties, and fulfilment of the isotropic condition for ensuring a well-established turbulent flowfield. Those two prerequisites define a set of turbulent configurations for which the momentum-deficit-based technique applies feasibly. The second stage of the procedure is configuration-specific, and undertakes drag measurements upon a NACA0021 airfoil subjected to a set of different turbulent configurations. It is shown that performing measurements under invalid turbulent conditions leads to inconsistent drag curves, which serves for defining a validity map based on the testable cases.

This paper presents numerical studies of thermophoresis approach for separation of nanoparticles in liquid media. We simulated the thermophoresis process to test it as a method of separation of particles in suspension. At the same time, the specific software was appraised to establish whether it would meet the computational challenge. Then, a microfluidic device designed to separate different species of nanoparticles using thermal gradients was conceptualised. We used a theoretical nanoparticle species with diameters ranging between 40 and 250 nm. Different geometrical models, temperature gradients and entry flows were simulated to analyse their effect on the separation of nanoparticle species. On the basis of our results, we formulated a proposal for construction of efficient nanoparticle separation device.

This paper describes a smart system to monitor high temperature in industrial applications. The solution includes a semipassive microchip which allows logging data and wireless reading. Protection for the electronics against high temperature environment is provided by a vacuum packaging. Thermal isolation at 150°C and 800°C ambient temperature allows the system to work properly during 14 and 2 minutes respectively.

Los sistemas microfluídicos han demostrado ser una alternativa prometedora ante procesos convencionales de separación y caracterización. Este trabajo muestra el estudio numérico del fenómeno de la termoforesis en un microdispositivo para la separación de diferentes poblaciones de exosomas (vesículas entre 40-250nm liberadas por la mayoría de las células) en base a su tamaño. Empleando el software ANSYS Fluent v.16.0 se han analizado diferentes modelos geométricos del microdispositivo, gradientes de temperatura entre la pared superior e inferior y flujos de entrada, con el fin de determinar la trayectoria de los exosomas a través del dispositivo microfluídico y extraer las diferentes poblaciones. En base a los resultados obtenidos se muestra el dispositivo propuesto para la fabricación de un dispositivo eficiente.

[EN] Therefore the understanding and proper evaluation of the flow and mixing behaviour at microscale becomes a very important issue. In this study, the diffusion behaviour of two reacting solutions of HCI and NaOH were directly observed in a glass/polydimethylsiloxane microfluidic device using adaptive coatings based on the conductive polymer polyaniline that are covalently attached to the microchannel walls. The two liquid streams were combined at the junction of a Y-shaped microchannel, and allowed to diffuse into each other and react. The results showed excellent correlation between optical observation of the diffusion process and the numerical results. A numerical model which is based on finite volume method (FVM) discretisation of steady Navier-Stokes (fluid flow) equations and mass transport equations without reactions was used to calculate the flow variables at discrete points in the finite volume mesh element. The high correlation between theory and practical data indicates the potential of such coatings to monitor diffusion processes and mixing behaviour inside microfluidic channels in a dye free environment.

Microfluidic devices are poised to dramatically influence the future of the process industry. Therefore the understanding and proper evaluation of the flow and mixing behaviour at microscale becomes a very important issue. In this study, the diffusion behaviour of two reacting solutions of HCl and NaOH were directly observed in a glass/polydimethylsiloxane microfluidic device using adaptive coatings based on the conductive polymer polyaniline that are covalently attached to the microchannel walls. The two liquid streams were combined at the junction of a Y-shaped microchannel, and allowed to diffuse into each other and react. The results showed excellent correlation between optical observation of the diffusion process and the numerical results. A numerical model which is based on finite volume method (FVM) discretization of steady Navier-Stokes (fluid flow) equations and mass transport equations without reactions was used to calculate the flow variables at discrete points in the finite volume mesh element. The high correlation between theory and practical data indicates the potential of such coatings to monitor diffusion processes and mixing behaviour inside microfluidic channels in a dye free environment.

The choice of substrate material in a chip that combines ultrasound with microfluidics for handling biological and synthetic microparticles can have a profound effect on the performance of the device. This is due to the high surface-to-volume ratio that exists within such small structures and acquires particular relevance in polymer-based resonators with 3D standing waves. This paper presents three chips developed to perform particle flow-through separation by ultrasound based on a polymeric SU-8 layer containing channelization over three different substrates: Polymethyl methacrylate (PMMA); Pyrex; and a cracked PMMA composite-like structure. Through direct observations of polystyrene microbeads inside the channel, the three checked chips exhibit their potential as disposable continuous concentration devices with different spatial pressure patterns at frequencies of resonance close to 1 Mhz. Chips with Pyrex and cracked PMMA substrates show restrictions on the number of pressure nodes established in the channel associated with the inhibition of 3D modes in the solid structure. The glass-substrate chip presents some advantages associated with lower energy requirements to collect particles. According to the results, the use of polymer-based chips with rigid substrates can be advantageous for applications that require short treatment times (clinical tests handling human samples) and low-cost fabrication.

The work of this doctoral thesis, has focused on the numerical, experimental analysis of the separation processes optimization in micro-nano-biotechnology interest fluids. Specifically, we have determined the thermophysical and transport properties of biological and nanofluidic mixtures. The results obtained have been used to optimize the separation process for extraction application of the DMSO employed as cryoprotectant from previously cryopreserved cells through the application of temperature gradients. On the other hand, a microdevice for selective extraction of peripheral blood surrounding tumor cells by means of ultrasonic technology it has developed. Using numerical analysis, the geometric parameters and the ideal boundary conditions to achieve a separation efficiency suitable for clinical application have been identified. Finally, we have designed, built and validated a new termogravitacional installation formed by a microcolumn with the aim of analyzing biological fluids. The analysis system developed, to determine the transport properties in the new microcolumn, has been purely optic., Doktoretza tesi honetan aurrera eramandako lana, interes mikro-nano-bioteknologikoa duten fluidoen banaketa prozesuaren analisi numeriko eta esperimentalean oinarritu da. Zehatzago azalduz, nahaste biologiko eta nanofluidikoen ezaugarri termofisikoak eta garraiagarritasuna zehaztu dira. Ikerketa honetatik lortutako emaitzak, aldez aurretik kriogenizatutako zelulen krioprotektore moduan erabilitako DMSOaren erauzketari dagokion banaketa prozesuaren optimizaziorako erabili dira, tenperatura gradienteak aplikatuz. Bestalde, teknologia ultrasonikoaz baliatuz, odol periferikoko zelula tumoral zirkundateen erauzketa selektiborako mikrodispositibo bat garatu da. Analisi numerikoaren bitartez, aplikazio klinikorako egokia den banaketa eraginkorra lortzeko parametro geometriko eta inguruneko baldintza aproposak identifikatu dira. Azkenik, mikrokolumna batez osatutako instalazio termograbitazional berri bat diseinatu, eraiki eta balioztatu da fluido biologikoak aztertzeko helburuarekin. Mikrokolumnan berrian garraiagarritasuna propietateak zehazteko sortutako analisi sistema, guztiz optikoa izan da., El trabajo de esta tesis doctoral, se ha centrado en el análisis numérico, experimental sobre la optimización de los procesos de separación en fluidos de interés micro-nano-biotecnológico. En concreto, se han determinado las propiedades termofísicas y de transporte en mezclas biológicas y nanofluídicas. Los resultados obtenidos han sido utilizados para optimizar el proceso de separación hacia la aplicación de la extracción del DMSO utilizado como crioprotector de células previamente criogenizadas, mediante la aplicación de gradientes de temperatura. Por otro lado, se ha desarrollado un microdispositivo para la extracción selectiva, mediante la tecnología ultrasónica de células tumorales circundantes en sangre periférica. El análisis numérico ha permitido identificar los parámetros geométricos y las condiciones de contorno idóneas para lograr una eficiencia de separación apta para la aplicación clínica. Finalmente, se ha diseñado, construido y validado una nueva instalación termogravitacional formada por una microcolumna con el fin de analizar fluidos biológicos. El sistema de análisis elaborado para determinar las propiedades de transporte en la nueva microcolumna, ha sido puramente óptico.