http://hdl.handle.net/2117/3992 Fri, 24 May 2013 03:22:40 GMT 2013-05-24T03:22:40Z webmaster.bupc@upc.edu Universitat Politècnica de Catalunya. Servei de Biblioteques i Documentació no http://hdl.handle.net/2117/19374 Title: Numerical simulations of energy storage with encapsulated phase change materials. Special emphasis on solid-liquid phase change CFD modelling Authors: Galione Klot, Pedro Andres; Lehmkuhl Barba, Oriol; Rigola Serrano, Joaquim; Oliva Llena, Asensio; Rodríguez Pérez, Ivette María Wed, 22 May 2013 12:51:06 GMT http://hdl.handle.net/2117/19374 2013-05-22T12:51:06Z Galione Klot, Pedro Andres; Lehmkuhl Barba, Oriol; Rigola Serrano, Joaquim; Oliva Llena, Asensio; Rodríguez Pérez, Ivette María no http://hdl.handle.net/2117/19357 Title: Use of a Low-Mach model on a CFD&HT solver for the elements of an object oriented program to numerically simulate hermetic refrigeration compressors Authors: López Mas, Joan; Lehmkuhl Barba, Oriol; Rigola Serrano, Joaquim; Pérez Segarra, Carlos David Abstract: A powerful object oriented approach for the simulation of generic thermal systems (Damle et al., 2008) is used as a framework to numerically simulate the thermal and fluid behavior of hermetic reciprocating compressors. A physical abstraction of the compressor system provides a vertex-edge graph, defining the elements and the neighborhood relations of the system to be solved. Each one of these resulting elements is modeled in order to be solved by itself by giving their respective boundary conditions. Since each element provides its own solver tool, the coupled system can be solved in an integrated form. Into previous works, an unstructured and parallel object oriented Computational Fluid Dynamics and Heat Transfer code (from now on CFD&HT) for accurate and reliable solving of turbulent industrial flow, called TermoFluids (Lehmkuhl et al., 2007), was used to provide with CFD&HT capability the system elements (López et al., 2010). In this work, a Low-Mach based CFD&HT module (Chiva et al., 2011) implemented within the TermoFluids software has been used solve the fluid domain existing inside the shell of a reciprocating compressor, which is identified as one of the compressor elements in the abstraction stage. This improvement allows us to numerically simulate the recirculation flow inside the shell of a reciprocating compressor, providing detailed information about suction area of the compressor and allowing study of new geometric configurations of such part. Furthermore, in comparison with previously tested CFD&HT modules, the Low-Mach model allows better treatment of the compressibility effects generated at the inner elements of the compressor such as chambers, tubes and undoubtedly the compression chamber. Mon, 20 May 2013 15:15:42 GMT http://hdl.handle.net/2117/19357 2013-05-20T15:15:42Z López Mas, Joan; Lehmkuhl Barba, Oriol; Rigola Serrano, Joaquim; Pérez Segarra, Carlos David no A powerful object oriented approach for the simulation of generic thermal systems (Damle et al., 2008) is used as a framework to numerically simulate the thermal and fluid behavior of hermetic reciprocating compressors. A physical abstraction of the compressor system provides a vertex-edge graph, defining the elements and the neighborhood relations of the system to be solved. Each one of these resulting elements is modeled in order to be solved by itself by giving their respective boundary conditions. Since each element provides its own solver tool, the coupled system can be solved in an integrated form. Into previous works, an unstructured and parallel object oriented Computational Fluid Dynamics and Heat Transfer code (from now on CFD&HT) for accurate and reliable solving of turbulent industrial flow, called TermoFluids (Lehmkuhl et al., 2007), was used to provide with CFD&HT capability the system elements (López et al., 2010). In this work, a Low-Mach based CFD&HT module (Chiva et al., 2011) implemented within the TermoFluids software has been used solve the fluid domain existing inside the shell of a reciprocating compressor, which is identified as one of the compressor elements in the abstraction stage. This improvement allows us to numerically simulate the recirculation flow inside the shell of a reciprocating compressor, providing detailed information about suction area of the compressor and allowing study of new geometric configurations of such part. Furthermore, in comparison with previously tested CFD&HT modules, the Low-Mach model allows better treatment of the compressibility effects generated at the inner elements of the compressor such as chambers, tubes and undoubtedly the compression chamber. http://hdl.handle.net/2117/18870 Title: Numerical simulation of wrap scroll temperature for refrigeration and air conditioning compressors Authors: Rovira Casals, Jordi; Rigola Serrano, Joaquim; Pérez Segarra, Carlos David; Oliva Llena, Asensio Abstract: Being part of a model which simulates the whole consecutive overall compression process in a scroll compressor by solving equations of mass, momentum and energy balance for fluid refrigerant (Rovira et al. ,2006), an updated version is presented. In this new model, an energy balance over the scroll wraps is implemented; where temperatures and heat fluxes are obtain ed dividing the wall into 36 parts (slices) each turn. The scroll wrap is divided into different solid slices; energy balance is carried out, taking into account: i) conduction along the scroll wrap; ii) convection heat transfer between each slice and each fluid chamber, with special attention on solid slice - fluid chamber contact at each time step. The numerical model shows the one dimensional and transient temperature, pressure and mass flow rate, at each fluid chamber along the scroll compressor, among detailed solid wrap temperature distribution. The whole numerical model has been experimentally validated against experimental data from technical literature (Halm,1997)(Chen et al.,2004a)(Chen et al.,2004b), comparing mass flow rate, discharge temperature, compression work and power consumption. Finally, the influence of wall temperatures and wall heat fluxes on the compressor performance and other output variables is analyzed. Thu, 18 Apr 2013 13:51:51 GMT http://hdl.handle.net/2117/18870 2013-04-18T13:51:51Z Rovira Casals, Jordi; Rigola Serrano, Joaquim; Pérez Segarra, Carlos David; Oliva Llena, Asensio no Being part of a model which simulates the whole consecutive overall compression process in a scroll compressor by solving equations of mass, momentum and energy balance for fluid refrigerant (Rovira et al. ,2006), an updated version is presented. In this new model, an energy balance over the scroll wraps is implemented; where temperatures and heat fluxes are obtain ed dividing the wall into 36 parts (slices) each turn. The scroll wrap is divided into different solid slices; energy balance is carried out, taking into account: i) conduction along the scroll wrap; ii) convection heat transfer between each slice and each fluid chamber, with special attention on solid slice - fluid chamber contact at each time step. The numerical model shows the one dimensional and transient temperature, pressure and mass flow rate, at each fluid chamber along the scroll compressor, among detailed solid wrap temperature distribution. The whole numerical model has been experimentally validated against experimental data from technical literature (Halm,1997)(Chen et al.,2004a)(Chen et al.,2004b), comparing mass flow rate, discharge temperature, compression work and power consumption. Finally, the influence of wall temperatures and wall heat fluxes on the compressor performance and other output variables is analyzed. http://hdl.handle.net/2117/18868 Title: Numerical simulation of the turbulent fluid flow through valves based on low mach models Authors: Rigola Serrano, Joaquim; Lehmkuhl Barba, Oriol; Ventosa, Jordi; Pérez Segarra, Carlos David; Oliva Llena, Asensio Abstract: The aim of the present paper is to carry out a group of numerical experiments over the fluid flow through the valve reed, using the CFD&HT code TermoFluids, an unstructure d and parallel object-oriented CFD code for accurate and reliable solving of industrial flows (Lehmkuhl, O. et al. 2007 ) with special attention on incompressible hypothesis against low Mach compressible flow modeling, as a critic al numerical aspect depending on Reynolds number and gap thickness conditions. In all studied cases a multi-dimensional explicit finite volume fractional-step based algorithm extended to simulate low Mach fluxes using a Runge-Kutta/Crank-Nicholson time integration scheme, with a symmetry preserving discretization has been used. When turbulence modeling is needed, an extension of the WALE (Wall Adapting Local Eddy-viscosity) (Nicoud, F. and Ducros, F., 1999) model to non-structured meshes is applied. The pressure equation is solved by means of parallel Fourier Schur decomposition solver which is an efficient direct solver for loosely coupled PC clusters (Borrell, R. et al. 2011). In a two dimensional periodic way the fluid flow is approach ed by two parallel phenomena (an entrance flow through a channel and a free jet through a surface). In that sense, the present paper is focused on the numeri cal simulation model of the fluid flow through the valve reeds, considering a simplified geometry of an axial hole plus a radial diffuser. The numerical results presented are based on a specific geome try – valve diameter D is 3 times orifice diameter d, while s/d ratio is 0.6 – considering high Reynolds number at the entrance as boundary condition. The studied cases show the influence from laminar to turbulent flow from incompressible assumption to lower subsonic conditions and/or chocked flow. Thu, 18 Apr 2013 13:32:40 GMT http://hdl.handle.net/2117/18868 2013-04-18T13:32:40Z Rigola Serrano, Joaquim; Lehmkuhl Barba, Oriol; Ventosa, Jordi; Pérez Segarra, Carlos David; Oliva Llena, Asensio no The aim of the present paper is to carry out a group of numerical experiments over the fluid flow through the valve reed, using the CFD&HT code TermoFluids, an unstructure d and parallel object-oriented CFD code for accurate and reliable solving of industrial flows (Lehmkuhl, O. et al. 2007 ) with special attention on incompressible hypothesis against low Mach compressible flow modeling, as a critic al numerical aspect depending on Reynolds number and gap thickness conditions. In all studied cases a multi-dimensional explicit finite volume fractional-step based algorithm extended to simulate low Mach fluxes using a Runge-Kutta/Crank-Nicholson time integration scheme, with a symmetry preserving discretization has been used. When turbulence modeling is needed, an extension of the WALE (Wall Adapting Local Eddy-viscosity) (Nicoud, F. and Ducros, F., 1999) model to non-structured meshes is applied. The pressure equation is solved by means of parallel Fourier Schur decomposition solver which is an efficient direct solver for loosely coupled PC clusters (Borrell, R. et al. 2011). In a two dimensional periodic way the fluid flow is approach ed by two parallel phenomena (an entrance flow through a channel and a free jet through a surface). In that sense, the present paper is focused on the numeri cal simulation model of the fluid flow through the valve reeds, considering a simplified geometry of an axial hole plus a radial diffuser. The numerical results presented are based on a specific geome try – valve diameter D is 3 times orifice diameter d, while s/d ratio is 0.6 – considering high Reynolds number at the entrance as boundary condition. The studied cases show the influence from laminar to turbulent flow from incompressible assumption to lower subsonic conditions and/or chocked flow. http://hdl.handle.net/2117/18866 Title: Modular simulation of vapour compression systems with an object oriented tool Authors: Ablanque Mejía, Nicolás; Oliet Casasayas, Carles; Rigola Serrano, Joaquim; Lehmkuhl Barba, Oriol; Pérez Segarra, Carlos David Abstract: The objective of this work is to simulate vapour compression refrigeration systems through a modular approach by means of an object - oriented numerical tool called NEST. For this purpose, the global system is modeled as a collection of different elements which are linked between them. Each element represents a specific part of the system (e.g. heat exchanger, compressor, expansion device, tube, cavity, wall, etc.) and can be independently solved for given boundary conditions. The global resolution procedure is carried out by solving all the elements iteratively, transferring information between them, until a converged solution is reached. The system is easily modified by adding, subtracting or substituting any of its elements. This feature gives great flexibility to the model, not only because the configuration of the system can be clearly altered, but also because the numerical model of any element can be easily replaced allowing different levels of simulation. In this work the object - oriented methodology together with the elements description and their resolution procedures are presented. The model is validated against experimental data obtained from a refrigeration cycle working with isobutane. In addition to this, an illustrative case is presented in order to show the system capabilities. Thu, 18 Apr 2013 13:12:59 GMT http://hdl.handle.net/2117/18866 2013-04-18T13:12:59Z Ablanque Mejía, Nicolás; Oliet Casasayas, Carles; Rigola Serrano, Joaquim; Lehmkuhl Barba, Oriol; Pérez Segarra, Carlos David no The objective of this work is to simulate vapour compression refrigeration systems through a modular approach by means of an object - oriented numerical tool called NEST. For this purpose, the global system is modeled as a collection of different elements which are linked between them. Each element represents a specific part of the system (e.g. heat exchanger, compressor, expansion device, tube, cavity, wall, etc.) and can be independently solved for given boundary conditions. The global resolution procedure is carried out by solving all the elements iteratively, transferring information between them, until a converged solution is reached. The system is easily modified by adding, subtracting or substituting any of its elements. This feature gives great flexibility to the model, not only because the configuration of the system can be clearly altered, but also because the numerical model of any element can be easily replaced allowing different levels of simulation. In this work the object - oriented methodology together with the elements description and their resolution procedures are presented. The model is validated against experimental data obtained from a refrigeration cycle working with isobutane. In addition to this, an illustrative case is presented in order to show the system capabilities. http://hdl.handle.net/2117/18233 Title: Parallelization of the coupling between CFD models for airflow and building energy simulation with an object-oriented infrastructure Authors: Damle, Rashmin; Lehmkuhl Barba, Oriol; López Mas, Joan; Rigola Serrano, Joaquim; Oliva Llena, Asensio Abstract: Integrating CFD & HT models with the general building program raises the computational time of building simulations as these simulations are usually performed over a period of one year. Within this context, our aim is to couple a object-oriented modular building program with CFD & HT for airflow and parallelize the simulation with numerous processors for reducing computational time. Also the modular nature of the code will allow to resolve selective critical zones with CFD & HT models while employing simple models for airflow in less critical zones. Thus, there are different levels of modelling different rooms/elements of the building system depending on the requirements of a specific case. Tue, 12 Mar 2013 16:34:32 GMT http://hdl.handle.net/2117/18233 2013-03-12T16:34:32Z Damle, Rashmin; Lehmkuhl Barba, Oriol; López Mas, Joan; Rigola Serrano, Joaquim; Oliva Llena, Asensio no Integrating CFD & HT models with the general building program raises the computational time of building simulations as these simulations are usually performed over a period of one year. Within this context, our aim is to couple a object-oriented modular building program with CFD & HT for airflow and parallelize the simulation with numerous processors for reducing computational time. Also the modular nature of the code will allow to resolve selective critical zones with CFD & HT models while employing simple models for airflow in less critical zones. Thus, there are different levels of modelling different rooms/elements of the building system depending on the requirements of a specific case. http://hdl.handle.net/2117/18220 Title: Combined heat and moisture transfer in buildings systems Authors: Damle, Rashmin; Lehmkuhl Barba, Oriol; Rigola Serrano, Joaquim; Oliva Llena, Asensio Abstract: Temperature and humidity are the two main parameters indicating the comfort level of the building occupants. Although the effect of temperature is taken into account in thermal simulation of buildings, the moisture transfer through the rooms and porous building walls is sometimes neglected. The level of humidity can give different sensations of thermal comfort. It is necessary to take into account both heat and moisture transport in and around buildings to predict the hygrothermal behavior of rooms and building walls so as to calculate the energy demands correctly. In this work some benchmark exercises are worked out to see the performance of the heat and moisture transfer model implemented for rooms and porous walls. Finally, numerical results are compared with the measured data for a room exposed to varying outdoor conditions. Tue, 12 Mar 2013 15:10:08 GMT http://hdl.handle.net/2117/18220 2013-03-12T15:10:08Z Damle, Rashmin; Lehmkuhl Barba, Oriol; Rigola Serrano, Joaquim; Oliva Llena, Asensio no Temperature and humidity are the two main parameters indicating the comfort level of the building occupants. Although the effect of temperature is taken into account in thermal simulation of buildings, the moisture transfer through the rooms and porous building walls is sometimes neglected. The level of humidity can give different sensations of thermal comfort. It is necessary to take into account both heat and moisture transport in and around buildings to predict the hygrothermal behavior of rooms and building walls so as to calculate the energy demands correctly. In this work some benchmark exercises are worked out to see the performance of the heat and moisture transfer model implemented for rooms and porous walls. Finally, numerical results are compared with the measured data for a room exposed to varying outdoor conditions. http://hdl.handle.net/2117/18215 Title: Chicken feathers based composites: a life cycle assessment Authors: Molins Durán, Gemma; Álvarez del Castillo, María Dolores; Garrido Soriano, Núria; Macanàs de Benito, Jorge; Carrillo Navarrete, Fernando Abstract: Chicken feathers (CFs) are a waste material generated from poultry industry in large quantities. A composite material constituted of poly lactide and CFs is proposed in order to prepare a biodegradable composite with low environmental impact. In order to evaluate its environmental impact, a Life Cycle Assessment (LCA) is performed. The results show that, from the environmental point of view, the more chicken feathers in the material, the greater is its impact. This is mainly due to the non - inclusion of the impact data regarding CFs current waste management treatments required in accordance with the European Directive CE 1069/2009 (in study) and to the high energy consumption of the pre - treatment stages (cleaning and sanitizing) required to transform CFs waste into a CFs technical material that can be used for the preparation of CFs/PLA composites material, which needs to be optimized. Tue, 12 Mar 2013 14:31:40 GMT http://hdl.handle.net/2117/18215 2013-03-12T14:31:40Z Molins Durán, Gemma; Álvarez del Castillo, María Dolores; Garrido Soriano, Núria; Macanàs de Benito, Jorge; Carrillo Navarrete, Fernando no Chicken feathers (CFs) are a waste material generated from poultry industry in large quantities. A composite material constituted of poly lactide and CFs is proposed in order to prepare a biodegradable composite with low environmental impact. In order to evaluate its environmental impact, a Life Cycle Assessment (LCA) is performed. The results show that, from the environmental point of view, the more chicken feathers in the material, the greater is its impact. This is mainly due to the non - inclusion of the impact data regarding CFs current waste management treatments required in accordance with the European Directive CE 1069/2009 (in study) and to the high energy consumption of the pre - treatment stages (cleaning and sanitizing) required to transform CFs waste into a CFs technical material that can be used for the preparation of CFs/PLA composites material, which needs to be optimized. http://hdl.handle.net/2117/18205 Title: Diseño conceptual e ingenieria de detalle de un lazo experimental dual Pb15.7Li/ He (proyecto BCN_LOOP®): una propuesta de proyecto de I+D+i industrial para desarrollos clave en tecnologia nuclear de fusion Authors: Batet Miracle, Lluís; Reventós Puigjaner, Francesc Josep; Mas de les Valls Ortiz, Elisabet; Fernández, Iván; Veredas, G.; Abellà, Jordi; Sempere Cebrían, Julià; Sanmartí, Manel; Linares, José Ignacio; Sedano, L.A. Tue, 12 Mar 2013 12:24:21 GMT http://hdl.handle.net/2117/18205 2013-03-12T12:24:21Z Batet Miracle, Lluís; Reventós Puigjaner, Francesc Josep; Mas de les Valls Ortiz, Elisabet; Fernández, Iván; Veredas, G.; Abellà, Jordi; Sempere Cebrían, Julià; Sanmartí, Manel; Linares, José Ignacio; Sedano, L.A. no http://hdl.handle.net/2117/18170 Title: Análisis de la permeación de tritio en los canales de metal líquido de las envolturas regeneradoras de un reactor de fusión en presencia de burbujas de helio Authors: Batet Miracle, Lluís; Mas de les Valls Ortiz, Elisabet; Sedano, L.A. Abstract: En el interior de los canales de metal l quido de las envolturas regeneradoras de un reactor de fusi on, la posibilidad de existencia de burbujas de helio nucleado no es remota. El helio se forma junto al tritio en la reacci on de los neutrones escapados del plasma con el litio. La acumulaci on de helio en las super cies de contacto entre la estructura y el ML conllevar a una reducci on de la transferencia de calor, al mismo tiempo que una reducci on en la permeaci on de tritio. La coexistencia de tres fases en contacto: metal l quido, helio y material estructural, convierte al transporte de calor y tritio en fen omenos complejos. Para enriquecer estudios de transporte de tritio realizados en el pasado, se plantea ahora un an alisis de detalle del entorno de una burbuja de helio adherida a la pared de un canal de ML de una envoltura regeneradora. Para el estudio se ha utilizado una herramienta CFD desarrollada sobre el c odigo libre OpenFOAM. El transporte de tritio a trav es de las tres fases y a trav es de cada interfase se ha analizado de forma detallada mediante simulaci on CFD. El modelo incluye los distintos mecanismos de transporte: difusi on en ML y gas; recombinaci on y disociaci on en las interfases. Los resultados obtenidos deben permitir re nar los modelos simpli cados ya utilizados en el c alculo de transporte de tritio en canales de ML en presencia de helio nucleado en las paredes Mon, 11 Mar 2013 11:45:59 GMT http://hdl.handle.net/2117/18170 2013-03-11T11:45:59Z Batet Miracle, Lluís; Mas de les Valls Ortiz, Elisabet; Sedano, L.A. no En el interior de los canales de metal l quido de las envolturas regeneradoras de un reactor de fusi on, la posibilidad de existencia de burbujas de helio nucleado no es remota. El helio se forma junto al tritio en la reacci on de los neutrones escapados del plasma con el litio. La acumulaci on de helio en las super cies de contacto entre la estructura y el ML conllevar a una reducci on de la transferencia de calor, al mismo tiempo que una reducci on en la permeaci on de tritio. La coexistencia de tres fases en contacto: metal l quido, helio y material estructural, convierte al transporte de calor y tritio en fen omenos complejos. Para enriquecer estudios de transporte de tritio realizados en el pasado, se plantea ahora un an alisis de detalle del entorno de una burbuja de helio adherida a la pared de un canal de ML de una envoltura regeneradora. Para el estudio se ha utilizado una herramienta CFD desarrollada sobre el c odigo libre OpenFOAM. El transporte de tritio a trav es de las tres fases y a trav es de cada interfase se ha analizado de forma detallada mediante simulaci on CFD. El modelo incluye los distintos mecanismos de transporte: difusi on en ML y gas; recombinaci on y disociaci on en las interfases. Los resultados obtenidos deben permitir re nar los modelos simpli cados ya utilizados en el c alculo de transporte de tritio en canales de ML en presencia de helio nucleado en las paredes http://hdl.handle.net/2117/18018 Title: Building optisim, optimizador NZEB Authors: Fonseca Casas, Pau; Colls, Màxim; Casanovas Garcia, Josep; Fonseca Casas, Antoni; Garrido Soriano, Núria Abstract: La simulación de la demanda energética de un edificio es una tarea compleja debido principalmente a dos factores clave. En primer lugar, es necesario definir la física y las complejas relaciones entre todos los elementos que pertenecen al modelo. En segundo lugar, es necesario entender estas relaciones por un equipo que normalmente está compuesto por personal con experiencia y formación diferente. En este trabajo, proponemos el uso de un lenguaje formal para representar el comportamiento dinámico de un modelo que representa todo el ciclo de vida de un edificio (diseño, construcción, uso‐mantenimiento y deconstrucción), y técnicas de co‐simulación para combinar motores de simulación diferentes y obtener lo mejor de cada uno. Se presenta un modelo de sostenibilidad, Building OptiSim, de tal manera que permite obtener una solución óptima. El edificio que utilizamos para realizar la simulación es la construcción LOW 3, proyecto presentado en el concurso Solar Decathlon 2010, por la ETSAV (UPC). Thu, 28 Feb 2013 11:46:56 GMT http://hdl.handle.net/2117/18018 2013-02-28T11:46:56Z Fonseca Casas, Pau; Colls, Màxim; Casanovas Garcia, Josep; Fonseca Casas, Antoni; Garrido Soriano, Núria no La simulación de la demanda energética de un edificio es una tarea compleja debido principalmente a dos factores clave. En primer lugar, es necesario definir la física y las complejas relaciones entre todos los elementos que pertenecen al modelo. En segundo lugar, es necesario entender estas relaciones por un equipo que normalmente está compuesto por personal con experiencia y formación diferente. En este trabajo, proponemos el uso de un lenguaje formal para representar el comportamiento dinámico de un modelo que representa todo el ciclo de vida de un edificio (diseño, construcción, uso‐mantenimiento y deconstrucción), y técnicas de co‐simulación para combinar motores de simulación diferentes y obtener lo mejor de cada uno. Se presenta un modelo de sostenibilidad, Building OptiSim, de tal manera que permite obtener una solución óptima. El edificio que utilizamos para realizar la simulación es la construcción LOW 3, proyecto presentado en el concurso Solar Decathlon 2010, por la ETSAV (UPC). http://hdl.handle.net/2117/18010 Title: Modelling of absorption of H2O vapor in falling film of lbr aqueous solution in vertical tubes with presence of non-condensables Authors: García-Rivera, Eduardo; Castro González, Jesús; Farnós Baulenas, Joan; Oliva Llena, Asensio Abstract: One of the main reasons of the discrepancies between theoretical predictions made by models of absorbers of H2O-LiBr absorption chillers when they are compared with experimental results under real conditions is the presence of non-condensables gases. These non-condensables gases are inside the shell of the absorption chiller mainly for two reasons: i) air leakages (Oxygen-Nitrogen); ii) gases produced by corrosion (Hydrogen). A mathematical model of falling film absorption of H2O by LiBr aqueous solutions which considers the influence of non-condensable gases has been implemented. The model is semi-empirical, based on Navier Stokes equations together with energy and mass species simplified under the boundary layer hypotheses. Under such conditions, the differential system of equations in partial derivatives, becomes parabolic and could be solved by means of finite difference method in a step by step procedure. Detailed heat and mass transfer balances are applied at the interface to specify the boundary conditions between liquid and gas phases. In order to calculate gradient of air at the interface, the penetration theory is applied in order to avoid a detailed calculation of the gas phase. Numerically the presence of air in the interface results in a pressure drop and consequently in a reduction in heat and mass transfer rates. Wed, 27 Feb 2013 16:26:57 GMT http://hdl.handle.net/2117/18010 2013-02-27T16:26:57Z García-Rivera, Eduardo; Castro González, Jesús; Farnós Baulenas, Joan; Oliva Llena, Asensio no One of the main reasons of the discrepancies between theoretical predictions made by models of absorbers of H2O-LiBr absorption chillers when they are compared with experimental results under real conditions is the presence of non-condensables gases. These non-condensables gases are inside the shell of the absorption chiller mainly for two reasons: i) air leakages (Oxygen-Nitrogen); ii) gases produced by corrosion (Hydrogen). A mathematical model of falling film absorption of H2O by LiBr aqueous solutions which considers the influence of non-condensable gases has been implemented. The model is semi-empirical, based on Navier Stokes equations together with energy and mass species simplified under the boundary layer hypotheses. Under such conditions, the differential system of equations in partial derivatives, becomes parabolic and could be solved by means of finite difference method in a step by step procedure. Detailed heat and mass transfer balances are applied at the interface to specify the boundary conditions between liquid and gas phases. In order to calculate gradient of air at the interface, the penetration theory is applied in order to avoid a detailed calculation of the gas phase. Numerically the presence of air in the interface results in a pressure drop and consequently in a reduction in heat and mass transfer rates. http://hdl.handle.net/2117/17948 Title: Spectrally-consistent regularization modeling of wind farm boundary layers Authors: Trias Miquel, Francesc Xavier; Folch, David; Gorobets, Andrei; Oliva Llena, Asensio Abstract: The incompressible Navier-Stokes equations constitute an excellent mathematical modelization of turbulence. Unfortunately, attempts at performing direct simulations are limited to relatively low-Reynolds numbers because of the almost numberless small scales produced by the non-linear convective term. Alternatively, a dynamically less complex formulation is proposed here. Namely, regularizations of the Navier-Stokes equations that preserve the symmetry and conservation properties exactly. To do so, both convective and diffusive term are altered in the same vein. In this way, the convective production of small scales is effectively restrained whereas the modified diffusive term introduces a hyperviscosity effect and consequently enhances the destruction of small scales. In practise, the only additional ingredient is a self-adjoint linear filter whose local filter length is determined from the requirement that vortex-stretching must stop at the smallest grid scale. In the present work, the performance of the above-mentioned recent improvements is assessed through application to homogeneous isotropic turbulence, a turbulent channel flow and a turbulent boundary layer. As a final application, regularization modelling will be applied for large-scale numerical simulation of the atmospheric boundary layer through wind farms. Fri, 22 Feb 2013 15:08:48 GMT http://hdl.handle.net/2117/17948 2013-02-22T15:08:48Z Trias Miquel, Francesc Xavier; Folch, David; Gorobets, Andrei; Oliva Llena, Asensio no The incompressible Navier-Stokes equations constitute an excellent mathematical modelization of turbulence. Unfortunately, attempts at performing direct simulations are limited to relatively low-Reynolds numbers because of the almost numberless small scales produced by the non-linear convective term. Alternatively, a dynamically less complex formulation is proposed here. Namely, regularizations of the Navier-Stokes equations that preserve the symmetry and conservation properties exactly. To do so, both convective and diffusive term are altered in the same vein. In this way, the convective production of small scales is effectively restrained whereas the modified diffusive term introduces a hyperviscosity effect and consequently enhances the destruction of small scales. In practise, the only additional ingredient is a self-adjoint linear filter whose local filter length is determined from the requirement that vortex-stretching must stop at the smallest grid scale. In the present work, the performance of the above-mentioned recent improvements is assessed through application to homogeneous isotropic turbulence, a turbulent channel flow and a turbulent boundary layer. As a final application, regularization modelling will be applied for large-scale numerical simulation of the atmospheric boundary layer through wind farms. http://hdl.handle.net/2117/17885 Title: Numerical simulation of heat transfer and fluid flow in a flat plate solar collector with TIM and ventilation channel Authors: Kessentini, Hamdi; Capdevila Paramio, Roser; Lehmkuhl Barba, Oriol; Castro González, Jesús; Oliva Llena, Asensio Abstract: Flat plate solar collector with plastic transparent insulation materials and ventilation channel as overheating protection system inserted between the absorber and the back insulation has been studied numerically. First, a general object-oriented unsteady model of this solar collector is developed and presented. It allows solving, in parallel way, every component separately and interacting with its neighbors to set the boundary conditions in every time step of the simulation. Every component can be simulated using its own mesh and the number of CPUs necessary (depending on the simulation level needed). Second, the numerical simulations of the fluid flow and heat transfer by natural convection in the bottom part (ventilation channel) and the upper part (air gap + TIM) of the collector are done separately. The simulation has taken into account the different operation modes of the channel (opened at high operation temperatures and closed in normal operations). A three dimensional parallel turbulent CFD model based on Large Eddy Simulation is used in the simulations. The obtained numerical results are validated with experimental and benchmark results found in the literature. Tue, 19 Feb 2013 15:02:35 GMT http://hdl.handle.net/2117/17885 2013-02-19T15:02:35Z Kessentini, Hamdi; Capdevila Paramio, Roser; Lehmkuhl Barba, Oriol; Castro González, Jesús; Oliva Llena, Asensio no Flat plate solar collector with plastic transparent insulation materials and ventilation channel as overheating protection system inserted between the absorber and the back insulation has been studied numerically. First, a general object-oriented unsteady model of this solar collector is developed and presented. It allows solving, in parallel way, every component separately and interacting with its neighbors to set the boundary conditions in every time step of the simulation. Every component can be simulated using its own mesh and the number of CPUs necessary (depending on the simulation level needed). Second, the numerical simulations of the fluid flow and heat transfer by natural convection in the bottom part (ventilation channel) and the upper part (air gap + TIM) of the collector are done separately. The simulation has taken into account the different operation modes of the channel (opened at high operation temperatures and closed in normal operations). A three dimensional parallel turbulent CFD model based on Large Eddy Simulation is used in the simulations. The obtained numerical results are validated with experimental and benchmark results found in the literature. http://hdl.handle.net/2117/17884 Title: Numerical study of the incompressible Richtmyer-Meshkov instability. Interface tracking methods on general meshes Authors: Jofre Cruanyes, Lluís; Balcázar Arciniega, Néstor; Lehmkuhl Barba, Oriol; Castro González, Jesús; Oliva Llena, Asensio Abstract: The numerical simulation of interfacial and free surface flows is a vast and interesting topic in the areas of engineering and fundamental physics, such as the study of liquid-gas interfaces, formation of droplets, bubbles and sprays, combustion problems with liquid and gas reagents, study of wave motion and others. Many different methods for interface tracking exist, but Volume-of-Fluid and Level-Set methods are two of the most important. The Volume-of-Fluid preserves mass in a natural way but requires large computational resources. On the other hand, the Level-Set is not as accurate and mass conservative as the Volume-of-Fluid but is a faster way to track interfaces, representing them by the middle contour of a signed distance function. The objective of this work is to analyze the advantatges and drawbacks of the Volume-of-Fluid and Level-Set methods by solving the incompressible two-liquid Richtmyer-Meshkov instability and to compare the results to experimental data. Tue, 19 Feb 2013 14:33:54 GMT http://hdl.handle.net/2117/17884 2013-02-19T14:33:54Z Jofre Cruanyes, Lluís; Balcázar Arciniega, Néstor; Lehmkuhl Barba, Oriol; Castro González, Jesús; Oliva Llena, Asensio no The numerical simulation of interfacial and free surface flows is a vast and interesting topic in the areas of engineering and fundamental physics, such as the study of liquid-gas interfaces, formation of droplets, bubbles and sprays, combustion problems with liquid and gas reagents, study of wave motion and others. Many different methods for interface tracking exist, but Volume-of-Fluid and Level-Set methods are two of the most important. The Volume-of-Fluid preserves mass in a natural way but requires large computational resources. On the other hand, the Level-Set is not as accurate and mass conservative as the Volume-of-Fluid but is a faster way to track interfaces, representing them by the middle contour of a signed distance function. The objective of this work is to analyze the advantatges and drawbacks of the Volume-of-Fluid and Level-Set methods by solving the incompressible two-liquid Richtmyer-Meshkov instability and to compare the results to experimental data.