42 research outputs found

    Development of a multi-functional ventilated façade with an integrated collector-storage: numerical model and experimental facility

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    The paper reports on physical modeling and experimental evaluation of glazed systems. A multi-functional ventilated façade with an integrated collector-storage is developed and mounted on a test cell facility under real weather conditions. The component uses solar radiation to produce solar heated water flow, which in turn can provide space heating or fulfill domestic hot water demands. Different operational modes of the ventilation channel are analyzed in order to improve the thermal performance of the buildings with glazed façades. The existing numerical platform for the prediction of the thermal performance of buildings and solar systems is used to implement a numerical model to address the multi-functional ventilated façade with integrated collector-storage element. The model uses the measured outdoor data as boundary conditions to obtain predictions by means of a general energy balance in the test room and the façade component. The model permits different levels of simulation depending on the desired precision in each element, applying a modular methodology. In this study, the convection heat transfer coefficient within the parallelepiped storage tank is obtained from a direct numerical simulation (DNS) of turbulent natural convection flow of water, while the remaining empirical information is obtained from the literature for similar geometries.Peer ReviewedPostprint (author’s final draft

    On the validity of the Boussinesq approximation in a tall differentially heated cavity with water

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    In the present work, the fluid flow and heat transfer inside an integrated solar collector installed on an advanced fac¬łade are investigated. According to Gray and Giorgini [1], the use of the Boussinesq approximation can be considered valid for variations of thermosphysical properties up to 10 % with respect to the mean value. In the configuration under study, there is a variation of about 20 % in the dynamic viscosity and 15 % in the thermal expansion coefficient. Thus, the main objective of this work is to analyse the validity of the Boussinesq approximation for the turbulent natural convection flow of water in a rectangular parallelepiped tank. The significance of the Boussinesq effects is studied comparatively by means of detailed DNS simulations.Peer ReviewedPostprint (author‚Äôs final draft

    Numerical Analysis of Viscoelastic Fluid Injection Processes

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    In this work, a numerical framework aimed at simulating high-viscous and viscoelastic liquid injection processes is presented. The study of fluid injection with viscoelastic properties, such as synthetic polymers, is of great importance in several industrial sectors, such as metallurgy, automotive, food and pharmaceutical products, ink jets and 3D printers. In this work, a Geometrical Volume-of-Fluid (VOF) method is used to represent the interface, while finite-volume discretizations of Navier-Stokes equations on collocated unstructured meshes are solved through a fractional step method. Viscoelastic constitutive models are used to resolve the non-Newtonian behaviours. The employed implementations allow integrating different types of constitutive equations and stabilization approaches. The test case proposed in the current work consist of the simulation of the discharge of a polymeric jet from an upper nozzle into an air-containing cavity with solid bottom. The behavior of the fluids under analysis is validated by observing the onset of fluid-buckling s tructures. This phenomenon consists in the appearance of toroidal oscillation (as coiling and folding patterns) after the jet hits the solid surface and begins to accumulate. First, low-Reynolds number (Re<1.0) Newtonian Jets are analyzed, with the objective of validating the appearance of buckling as a function of Re number, and comparing the results with reference works. Finally, the potentialities of the proposed numerical methods are shown by simulating buckling phenomena in viscoelastic Jets described with the Oldroyd-B constitutive model.This work was developed in the context of a research project (BASE3D 001-P-001646) co-financed by the European Union Regional Development Fund within the framework of the ERDF Operational Program of Catalonia 2014-2020 with a grant of 50% of total cost eligible. The work has also been financially supported by a competitive R+D project (ENE2017-88697-R) of the Spanish Research Agency. The author E.Schillaci acknowledges the financial support of the Programa Torres Quevedo (PTQ2018- 010060).Postprint (published version

    Non-Oberbeck-Boussinesq natural convection in a tall differentially heated cavity

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    Turbulent flow in a water-filled rectangular parallelepiped tank of an integrated solar collector is analyzed by means of a set of two and three dimensional simulations. The geometry and the working conditions of the prototype yield an aspect ratio of őď = 6:68, Rayleigh number of Ra = 2:2 x 10 11 and a Prandtl number of Pr = 3:42. Diff erent coarse DNS simulations and LES simulations using the dynamic Smagorinsky SGS and WALE model are presented. Validity of the Oberbeck-Boussinesq approximation is questioned. Heat transfer and first and second order statistics are studied.Peer ReviewedPostprint (published version

    Numerical simulation of the micro-extrusion process of printable biomaterials

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    This work aims to gain a better understanding of how the rheological properties of printable materials affect their processability, as well as the quality of the final product, which at the end can lead to reducing time and costs of the process and increase product development. As the first step, the proper rheological non-Newtonian models are extracted from experimental studies. Later, three-dimensional numerical simulation of extrusion process is performed in the context of Direct Numerical Simulation (DNS) of governing equations, where the whole physics of fluid motion is taken into account. A finite-volume fractional step approach is used to solve the Navier-Stocks equations on collocated arbitrary meshes. Geometrical volume-of-fluid (GVOF) interface capturing approach is used to resolve the topological changes of the moving interface. The governing equations are solved using High-Performance Computing (HPC) parallel approaches. Besides the contribution of this work to the advancement of numerical techniques applied to multiphase complex flows, obtained results will shed light on the nature of non-Newtonian extrusion process with vast applications in the 3D printer industrial sectors.This work was developed in the context of a research project (BASE3D 001-P-001646) co-financed by the European Union Regional Development Fund within the framework of the ERDF Operational Program of Catalonia 2014-2020 with a grant of 50% of total cost eligible.Postprint (published version

    Directive 86-5: Drop Shipments; Retailer Engaged in Business in Commonwealth; Massachusetts Consumer

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    The present work addresses a flat plate solar collector with transparent insulation material (TIM) and high temperature protection system. The design and optimization of the collector have been numerically carried out by means of a parallel object-oriented simulation tool which is capable of simulating all the entities constituting the system as a whole, using efficient coupling between the elements. Three variants of the design are chosen to first test them under laboratory conditions. These collectors then are mounted in the roof of a hospital building, where their performance are comparatively tested along with a conventional flat plate solar collector, under real meteorological conditions and during long periods of time. Thus, due to long term exposure of the collectors, aspects such as reliability, durability, energy performance, correct functioning of the protection system will be analyzed, with the objective of improving the detected shortcomings for the future generations of the present design.Peer ReviewedPostprint (published version

    Numerical simulation of the micro-extrusion process of printable biomaterials

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    This work aims to gain a better understanding of how the rheological properties of printable materials affect their processability, as well as the quality of the final product, which at the end can lead to reducing time and costs of the process and increase product development. As the first step, the proper rheological non-Newtonian models are extracted from experimental studies. Later, three-dimensional numerical simulation of extrusion process is performed in the context of Direct Numerical Simulation (DNS) of governing equations, where the whole physics of fluid motion is taken into account. A finite-volume fractional step approach is used to solve the Navier-Stocks equations on collocated arbitrary meshes. Geometrical volume-of-fluid (GVOF) interface capturing approach is used to resolve the topological changes of the moving interface. The governing equations are solved using High-Performance Computing (HPC) parallel approaches. Besides the contribution of this work to the advancement of numerical techniques applied to multiphase complex flows, obtained results will shed light on the nature of non-Newtonian extrusion process with vast applications in the 3D printer industrial sectors

    Thermal and fluid dynamic optimization of a CPV-T receiver for solar co-generation applications: numerical modelling and experimental validation

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    Solar co-generation, i.e., the generation of electricity and heat in a single device by concentrating the sunbeams, has the potential to significantly increase the overall system performance. The main challenge is related to the cooling of solar cells. In order to do so, it is essential to reduce the thermal resistance between the cell and heat transfer fluid. This paper features the optimization procedure of a low-cost custom concentrated photovoltaic thermal (CPV-T) receiver for a parabolic trough collector using silicon solar cells. A finite volume model for the thermal process has been developed. Hence, a fluid dynamic thermal simulation of the receiver is presented. The optimized heat sink tube geometries have been manufactured and tested in a lab environment, allowing for a comparison between modelling and experimental test results. Three possible heat sink geometries have been designed and compared regarding their overall heat transfer coefficient with respect to the non-dimensional pumping power, i.e. the ratio between the overall transferred heat and the energy required for pumping. The overall heat transfer coefficient for a finned heat sink has been increased up to 60% with respect to a baseline case without fins under similar conditions.This project has received funding from SOLAR-ERA.NET Cofund 2 joint call undertaking under the European Union‚Äôs Horizon 2020 research and innovation programme. This work has also been supported by Scientific and Technological Research Council of T√ľrkiye (T√úBńįTAK) under grant number 219M028. The authors acknowledge the Heat and Environment Laboratory, Mechanical Engineering Department, METU, and the help of Bulent G. Akinoglu and Elsen Aydin. D. Santos acknowledges FI AGAUR-Generalitat de Catalunya fellowship (2022FI_B2_00173).Peer ReviewedPostprint (published version

    Numerical study of the non-Oberbeck-Boussinesq effects in turbulent water-filled cavities

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    The work carried out in the framework of the present thesis aims at shedding light into the complex phenomena involved in turbulent water-filled cavities, questioning the validity of the well-established Oberbeck-Boussinesq effects, and determining the influence of these on the flow structure and heat transfer. First, the relevance of the variable thermophyical properties have been submitted to investigation by means of direct numerical simulations of a differentially heated cavity flow using the aspect ratio of a particular prototype. The simulations consider the so-called non-Oberbeck-Boussinesq effects, and study the temperature range for which these effects could be considered relevant. The work has been conducted employing a 2D flow assumption, estimating that this methodology -promoted by the necessity of a compromise between the accuracy and the cost of the simulations- would be valid to detect the non-Oberbeck-Boussinesq effects without the loss of generality, even though the actual flow structures of the flow are inherently 3D. The numerical results have revealed that up to the temperature difference of 30 ¬ļC, Oberbeck-Boussinesq solution can estimate the heat transfer within 1 % error, although the loss of symmetry is certified even for a temperature difference of 10 ¬ļC. Moreover, it has been observed that the boundary layers at hot and cold isothermal confining walls behave differently, such that the boundary layer instabilities and transition to turbulence location move downstream along the hot wall and upstream along the cold wall. As a consequence, the stratification region shifts upwards, giving rise to higher stratification numbers. Later, the non-Oberbeck-Boussinesq effects have been studied considering three-dimensional domain by means of direct numerical simulations, in the quest of analyzing their impact on the three-dimensional flow structure. The results have revealed delayed transition in the hot wall and earlier triggered transition in the cold wall boundary layers. This has been shown to be a consequence of the initial heating of the cavity due to favorable heat transfer properties in the hot wall boundary layer, which results in warmer upper cavity. As time advances, due to the influence of the stratified flow feeding the hot and cold boundary layers, the strength of the natural convection gradually decreases and increases in the hot and cold boundary layers, respectively. When a balance is attained between these two boundary layers, the cold wall boundary is found at a higher equivalent Rayleigh number, justifying its premature transition. Accordingly, the early transitioning cold wall boundary layer is thicker. This boundary layer interacts actively with the hot wall boundary layer, causing vertical oscillations in the transition to turbulent locations on both boundary layers. This interaction is also responsible for the degradation of the already shifted stratification zone. Besides the qualitative agreement in some aspects, this important effect is not captured by means of 2D simulations, which invalidates 2D flow hypothesis when it comes to describing the flow characteristics with non-Oberbeck-Boussinesq effects. As for the heat transfer, the Non-Oberbeck-Boussinesq effects do not necessarily enhance the heat transfer, as Oberbeck-Boussinesq solution is observed to overestimate the Nusselt number by about 3 %. Last but not the least, considering the huge computational resources required for simulating these turbulent natural convection flows with water, and bearing in mind the importance of an appropriate modeling of the present phenomena, different subgrid-scale models have been analyzed in order to predict the thermal and fluid dynamics of the flow within a turbulent water-filled cavity. It has been shown that the performance of the models is directly linked to the accurate prediction of the transition to turbulence, which is the main challenge in the proper modeling of this flow.El treball realitzat en el marc de la present tesi t√© com a objectiu analitzar els fen√≤mens complexos involucrats en la convecci√≥ natural en cavitats amb aigua en r√®gim turbulent, q√ľestionant la validesa de la ben establerta hip√≤tesi d'Oberbeck-Boussinesq. S'ha estudiat la influ√®ncia dels efectes Oberbeck-Boussinesq sobre l'estructura de flux i la transfer√®ncia de calor. En primer lloc, l'efecte de la depend√®ncia en la temperatura de les propietats termof√≠siques variables s'ha estudiat mitjan√ßant simulacions num√®riques directes del flux en una cavitat amb aigua escalfada diferencialment, emprant l'hipot√®si de flux 2D. Els resultats num√®rics han revelat que per difer√®ncies de temperatura fins a 30 ¬ļC, la soluci√≥ Oberbeck-Boussinesq pot estimar la transfer√®ncia de calor amb un error m√†xim d'1%, tot i que la p√®rdua de simetria est√† certificada fins i tot per una difer√®ncia de temperatura de 10 ¬ļC. D'altra banda, s'ha observat que les capes l√≠mit en les dues parets es comporten de manera diferent, de tal manera que les inestabilitats de la capa l√≠mit i el punt de transici√≥ es mouen aig√ľes avall en la paret calenta i aig√ľes amunt en la freda. Com a conseq√ľ√®ncia d'aix√≤, la regi√≥ d'estratificaci√≥ es despla√ßa cap amunt, donant lloc a un nombre d'estratificaci√≥ m√©s elevat. Tot seguit, els efectes Oberbeck-Boussinesq s'han estudiat tenint en compte el flux 3D per mitj√† de simulacions num√®riques directes, en la recerca d'analitzar el seu impacte en l'estructura del flux tridimensional. Els resultats han confirmat la transici√≥ retardada a la paret calenta i la transici√≥ provocada aig√ľes amunt a la paret freda. S'ha demostrat que aquest fet √©s una conseq√ľ√®ncia de l'escalfament inicial de la cavitat a causa de les propietats de transfer√®ncia de calor favorables a la capa l√≠mit de la paret calenta, el que resulta en un escalfament de la part superior de la cavitat. A mesura que avan√ßa el temps, a causa de la influ√®ncia del flux estratificat que alimenta les dues capes l√≠mit, la for√ßa de la convecci√≥ natural disminueix i augmenta gradualment en la capa l√≠mit de les parets calenta i freda, respectivament. Quan s'arriba a un equilibri entre aquestes dues capes l√≠mit, la capa l√≠mit de la paret freda es troba a un nombre de Rayleigh equivalent superior, justificant la seva transici√≥ prematura. En conseq√ľ√®ncia, la capa l√≠mit de la paret freda √©s m√©s gruixuda. Aquesta capa l√≠mit interactua activament amb la capa de la paret calenta, causant oscil¬∑lacions verticals en el punt de transici√≥ en les dues capes l√≠mit. Aquesta interacci√≥ tamb√© √©s responsable de la degradaci√≥ de la zona d'estratificaci√≥. Aquest important efecte no √©s capturat per mitj√† de simulacions 2D, el que invalida la hip√≤tesi de flux 2D quan es tracta de descriure les caracter√≠stiques de flux amb efectes no-Oberbeck-Boussinesq. Pel que fa a la transfer√®ncia de calor, els efectes no Oberbeck-Boussinesq no milloren necess√†riament la transfer√®ncia de calor, tal com s'observa a la soluci√≥ Oberbeck-Boussinesq al sobreestimar el nombre de Nusselt en un 3%. Finalment, tenint en compte els enormes recursos computacionals necessaris per a la simulaci√≥ d'aquestes cavitats en r√®gim turbulent amb aigua, i tenint en compte la import√†ncia d'una modelitzaci√≥ adequat dels fen√≤mens que s'hi troben, s'han analitzat els diferents models LES utilitzant un cas semblant, per√≤ sense efectes Boussinesq. S'ha demostrat que el rendiment dels models est√† directament relacionat amb la predicci√≥ precisa del punt de transici√≥, que √©s el principal repte en la modelitzaci√≥ adequada d'aquest flux.Postprint (published version

    Simulació numèrica de fenòmens de transferència de calor i dinàmics de fluids transitoris

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    The work carried out during the 4 year research activity can be barely classified in two main lines. On the one hand, a considerable effort is taken to address issues related with the verification of multi-dimensional and transient solutions that are obtained by numerical simulations. Within the studied cases, we can consider cases of piston-cylinder ows within geometries similar to those of hermetic reciprocating compressors.This issue is mentioned in Part I. On the other hand, numerical simulations of different phenomena have been performed. More emphasis has been given to the natural convection ow within enclosures. This is explained in Part II. The case extensively studied has been the natural convection ow. The natural convection ow within enclosures has attracted the attention of many researchers due to its potential to model numerous applications of engineering interest, such as cooling of electronic devices, air ow in buildings, heat transfer in solar collectors, among others. The natural convection studies corresponding to the parallelepipedic enclosures can be classified into two elementary classes: i) heating from a horizontal wall (heating from below); ii) heating from a vertical wall. The characteristic example of the former case is the Rayleigh-B_enard ow, however this research is on the cavities heated from the side. This configuration is referred commonly as the differentially heated cavity
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