http://hdl.handle.net/2117/213 Fri, 24 May 2013 14:37:54 GMT 2013-05-24T14:37:54Z 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 Andrés; 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 Andrés; 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/2117/19334 Title: Current control design for three-phase grid-connected inverters using a pole placement technique based on numerical models Authors: Citro, Costantino; Gavriluta, Catalin; Nizak Md, H. K.; Beltran, H. Abstract: This paper presents a design procedure for linear current controllers of three-phase grid-connected inverters. The proposed method consists in deriving a numerical model of the converter by using software simulations and applying the pole placement technique to design the controller with the desired performances. A clear example on how to apply the technique is provided. The effectiveness of the proposed design procedure has been verified through the experimental results obtained with a 10kW grid-connected three-phase inverter prototype. Fri, 17 May 2013 12:31:51 GMT http://hdl.handle.net/2117/19334 2013-05-17T12:31:51Z Citro, Costantino; Gavriluta, Catalin; Nizak Md, H. K.; Beltran, H. no This paper presents a design procedure for linear current controllers of three-phase grid-connected inverters. The proposed method consists in deriving a numerical model of the converter by using software simulations and applying the pole placement technique to design the controller with the desired performances. A clear example on how to apply the technique is provided. The effectiveness of the proposed design procedure has been verified through the experimental results obtained with a 10kW grid-connected three-phase inverter prototype. http://hdl.handle.net/2117/19294 Title: Resonance analysis of a wind power plant with modal approach Authors: Rauma, Kalle; Md. Hasan, Khairul Nisak; Gavriluta, Catalin; Citro, Costantino Abstract: A detailed harmonic resonance analysis of power systems is more and more important due to the increasing number of power electronic devices. The topic is especially wellgrounded in wind power plants that besides having several possible sources of harmonics have many inductive and capacitive elements. This combination forms a severe concern over harmonic resonance that composes a threat to the power quality and the function of wind power plants. This paper presents and applies the harmonic resonance mode analysis (HRMA) in a model of an off shore wind power plant with and without a passive filtering. The results of the harmonic resonance mode analysis are verified and compared with the results calculated with the frequency scan. Thu, 16 May 2013 12:36:35 GMT http://hdl.handle.net/2117/19294 2013-05-16T12:36:35Z Rauma, Kalle; Md. Hasan, Khairul Nisak; Gavriluta, Catalin; Citro, Costantino no A detailed harmonic resonance analysis of power systems is more and more important due to the increasing number of power electronic devices. The topic is especially wellgrounded in wind power plants that besides having several possible sources of harmonics have many inductive and capacitive elements. This combination forms a severe concern over harmonic resonance that composes a threat to the power quality and the function of wind power plants. This paper presents and applies the harmonic resonance mode analysis (HRMA) in a model of an off shore wind power plant with and without a passive filtering. The results of the harmonic resonance mode analysis are verified and compared with the results calculated with the frequency scan. http://hdl.handle.net/2117/19293 Title: A simple approach for fast controller prototyping for a three phase interleaved DC-DC converter Authors: Gavriluta, Catalin; Citro, Costantino; Nisak, Khairul; Beltrán San Segundo, Héctor Abstract: Initial control prototyping in power electronics is often a matter of trial and error because of the complicated mathematics involved in modeling systems based on their internal structure. Moreover, in practice, small changes as the introduction of a measurement filter or the change of the sensing system appear all the time. If the controller design method was based on the internal structure of the system, then these small changes would mean a re-iteration through all the cumbersome equations. This paper presents a simple methodology for fast control prototyping based on the approximation of the Bode plots. As prerequisites, a power electronics simulation software as PSIM is needed. The method is presented by taking as a study case the design of a current control loop of a 30kW three phase interleaved DC-DC converter. Simulations are presented for the different considered controllers, and finally the method is validated by experimental results. Thu, 16 May 2013 12:30:03 GMT http://hdl.handle.net/2117/19293 2013-05-16T12:30:03Z Gavriluta, Catalin; Citro, Costantino; Nisak, Khairul; Beltrán San Segundo, Héctor no Initial control prototyping in power electronics is often a matter of trial and error because of the complicated mathematics involved in modeling systems based on their internal structure. Moreover, in practice, small changes as the introduction of a measurement filter or the change of the sensing system appear all the time. If the controller design method was based on the internal structure of the system, then these small changes would mean a re-iteration through all the cumbersome equations. This paper presents a simple methodology for fast control prototyping based on the approximation of the Bode plots. As prerequisites, a power electronics simulation software as PSIM is needed. The method is presented by taking as a study case the design of a current control loop of a 30kW three phase interleaved DC-DC converter. Simulations are presented for the different considered controllers, and finally the method is validated by experimental results. http://hdl.handle.net/2117/19288 Title: Accurate Bearing Faults Classification based on Statistical-Time Features, Curvilinear Component Analysis and Neural Networks Authors: Delgado Prieto, Miquel; Cirrincione,, Giansalvo; García Espinosa, Antonio; Ortega Redondo, Juan Antonio; Henao, Humberto Abstract: Bearing faults are the commonest form of malfunction associated with electrical machines. So far, the research has been carried out mainly in the detection of localized faults, but the diagnosis of distributed faults is still under development. In this context, this work presents a new scheme for detecting and classifying both kinds of faults. This work deals with a new diagnosis monitoring scheme, which is based on statistical-time features calculated from vibration signal, curvilinear component analysis for compression and visualization of the features behavior and a hierarchical neural network structure for classification. The obtained results from different operation conditions validate the effectiveness and feasibility of the proposed methodology. Thu, 16 May 2013 11:46:14 GMT http://hdl.handle.net/2117/19288 2013-05-16T11:46:14Z Delgado Prieto, Miquel; Cirrincione,, Giansalvo; García Espinosa, Antonio; Ortega Redondo, Juan Antonio; Henao, Humberto no Bearing faults are the commonest form of malfunction associated with electrical machines. So far, the research has been carried out mainly in the detection of localized faults, but the diagnosis of distributed faults is still under development. In this context, this work presents a new scheme for detecting and classifying both kinds of faults. This work deals with a new diagnosis monitoring scheme, which is based on statistical-time features calculated from vibration signal, curvilinear component analysis for compression and visualization of the features behavior and a hierarchical neural network structure for classification. The obtained results from different operation conditions validate the effectiveness and feasibility of the proposed methodology. http://hdl.handle.net/2117/19280 Title: A novel condition monitoring scheme for bearing faults based on Curvilinear Component Analysis and hierarchical neural networks Authors: Delgado Prieto, Miquel; Cirrincione,, Giansalvo; García Espinosa, Antonio; Ortega Redondo, Juan Antonio; Henao, Humberto Abstract: Mostly the faults in electrical machines are related with the bearings. Thus, a reliable bearing condition monitoring scheme able to detect either local or distributed defects are mandatory to avoid a breakdown in the machine. So far, the research has been carried out mainly in the detection of local faults, such as balls and raceways faults, but surface roughness is not so reported. This paper deals with a novel and reliable scheme capable to detect any fault that may occur in a bearing, based on EXIN Curvilinear Component Analysis, CCA, and Neural Network. The EXIN CCA, which is an improvement of the Curvilinear Component Analysis, has been conceived for data visualization, interpretation and classification for real time industrial applications. The effectiveness of this condition monitoring scheme has been verified by experimental results obtained from different operation conditions. Thu, 16 May 2013 09:59:44 GMT http://hdl.handle.net/2117/19280 2013-05-16T09:59:44Z Delgado Prieto, Miquel; Cirrincione,, Giansalvo; García Espinosa, Antonio; Ortega Redondo, Juan Antonio; Henao, Humberto no Mostly the faults in electrical machines are related with the bearings. Thus, a reliable bearing condition monitoring scheme able to detect either local or distributed defects are mandatory to avoid a breakdown in the machine. So far, the research has been carried out mainly in the detection of local faults, such as balls and raceways faults, but surface roughness is not so reported. This paper deals with a novel and reliable scheme capable to detect any fault that may occur in a bearing, based on EXIN Curvilinear Component Analysis, CCA, and Neural Network. The EXIN CCA, which is an improvement of the Curvilinear Component Analysis, has been conceived for data visualization, interpretation and classification for real time industrial applications. The effectiveness of this condition monitoring scheme has been verified by experimental results obtained from different operation conditions. http://hdl.handle.net/2117/19262 Title: STLF in the user-side for an iEMS based on evolutionary training of adaptive networks Authors: Cárdenas Araújo, Juan José; Giacometto Torres, Francisco; García Espinosa, Antonio; Romeral Martínez, José Luis Abstract: It is a fact that the short-term load forecasting (STLF)in the user side is growing interest. Consequently, intelligent energy management systems (iEMSs) are including this capability in order to take autonomous decisions. In this context, this paper presents a new STLF scheme based on Adaptative Networks Fuzzy Inference Systems (ANFIS). This ANFIS has an exponential output membership functions (e-ANFIS) and has been trained by means of a novel evolutionary training algorithm (ETA). Due to the computational burden required by ETA, parallel computing was used to eliminate this problem especially for embedded applications. This new scheme has been tested with real data from an automotive factory and it shows better results in comparison with typical adaptative network structures (neural network and ANFIS). Wed, 15 May 2013 15:19:10 GMT http://hdl.handle.net/2117/19262 2013-05-15T15:19:10Z Cárdenas Araújo, Juan José; Giacometto Torres, Francisco; García Espinosa, Antonio; Romeral Martínez, José Luis no It is a fact that the short-term load forecasting (STLF)in the user side is growing interest. Consequently, intelligent energy management systems (iEMSs) are including this capability in order to take autonomous decisions. In this context, this paper presents a new STLF scheme based on Adaptative Networks Fuzzy Inference Systems (ANFIS). This ANFIS has an exponential output membership functions (e-ANFIS) and has been trained by means of a novel evolutionary training algorithm (ETA). Due to the computational burden required by ETA, parallel computing was used to eliminate this problem especially for embedded applications. This new scheme has been tested with real data from an automotive factory and it shows better results in comparison with typical adaptative network structures (neural network and ANFIS). http://hdl.handle.net/2117/19111 Title: Electric drives for light e-scooters Authors: Andrada Gascón, Pedro; Blanqué Molina, Balduino; Martínez Piera, Eusebio; Torrent Burgués, Marcel; Perat Benavides, Josep Ignasi; Sánchez López, José Antonio Abstract: In the next years is expected an important rise in sales of electrical scooters in the entire world but especially in China. In order to address this challenge the electric scooter industry has to be more competitive in the transportation market and therefore important improvements, in terms of energy density and costs, have to be done in the electric storage system and in the electric propulsion system. In this paper, an analytical and experimental comparison of two different drives for electric scooters is carried out. Both are permanent magnet synchronous outer rotor motor drives but one placed inside the rear wheel and the other connected to the wheel trough a mechanical transmission. Mon, 06 May 2013 17:52:03 GMT http://hdl.handle.net/2117/19111 2013-05-06T17:52:03Z Andrada Gascón, Pedro; Blanqué Molina, Balduino; Martínez Piera, Eusebio; Torrent Burgués, Marcel; Perat Benavides, Josep Ignasi; Sánchez López, José Antonio no In the next years is expected an important rise in sales of electrical scooters in the entire world but especially in China. In order to address this challenge the electric scooter industry has to be more competitive in the transportation market and therefore important improvements, in terms of energy density and costs, have to be done in the electric storage system and in the electric propulsion system. In this paper, an analytical and experimental comparison of two different drives for electric scooters is carried out. Both are permanent magnet synchronous outer rotor motor drives but one placed inside the rear wheel and the other connected to the wheel trough a mechanical transmission. http://hdl.handle.net/2117/19009 Title: Experimental analysis of a degraded open-cathode PEM fuel cell stack Authors: Strahl, Stephan; Gasamans Rodríguez, Noemí; Llorca Piqué, Jordi; Husar, Attila Peter Abstract: The well-known challenges to be overcome in PEM fuel cell research are their relatively low durability and high costs for the platinum catalysts. Thus, this work focuses on factors that impact durability and the links to the fuel cell performance. Therefore a degraded, open-cathode, 20-cell, PEM fuel cell stack, which was used in a laboratory test station for characterization experiments, was analyzed experimentally. Voltage transients during external perturbations, such as changing temperature, humidity and stoichiometries show that degradation affects individual cells quite differently throughout the lifetime of the stack. Electrochemical impedance spectroscopy (EIS) data presents non-reversible catalyst layer and membrane degradation of several cells. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) are in progress in order to validate the results of the electrical analysis and elucidate catalyst and membrane degradation. Fri, 26 Apr 2013 12:04:59 GMT http://hdl.handle.net/2117/19009 2013-04-26T12:04:59Z Strahl, Stephan; Gasamans Rodríguez, Noemí; Llorca Piqué, Jordi; Husar, Attila Peter no power generation control PEM fuel cell, operating conditions, degradation, EIS The well-known challenges to be overcome in PEM fuel cell research are their relatively low durability and high costs for the platinum catalysts. Thus, this work focuses on factors that impact durability and the links to the fuel cell performance. Therefore a degraded, open-cathode, 20-cell, PEM fuel cell stack, which was used in a laboratory test station for characterization experiments, was analyzed experimentally. Voltage transients during external perturbations, such as changing temperature, humidity and stoichiometries show that degradation affects individual cells quite differently throughout the lifetime of the stack. Electrochemical impedance spectroscopy (EIS) data presents non-reversible catalyst layer and membrane degradation of several cells. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) are in progress in order to validate the results of the electrical analysis and elucidate catalyst and membrane degradation. 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/2117/18780 Title: Numerical simulation of wind flow around a parabolic trough solar collector Authors: Amine Hachicha, Ahmed; Rodríguez Pérez, Ivette María; Castro González, Jesús; Oliva Llena, Asensio Abstract: The use of parabolic trough solar technology in solar power plants has been increased in recent years. Such devices are located in open terrain and can be the subject of strong winds. As a result, the stability of these devices to track accurately the sun and the convection heat transfer from the receiver tube could be affected. In this paper, a detailed numerical aerodynamic and heat transfer model based on Large Eddy Simulations (LES) modelling for these equipments is presented. First, the model is verified on a circular cylinder in a cross-flow. The drag forces and the heat transfer coefficients are then validated with available experimental measurements. After that, simulations are performed on an Eurotrough solar collector to study the fluid flow and heat transfer around the solar collector and its receiver. Computations are carried out for a Reynolds number of Re W = 3.6 x 10(5) (based on the aperture) and for various pitch angles (h=0,45,90, 135, 80, 270). The aerodynamic coefficients are calculated around the solar collector and validated with measurements performed in wind tunnel tests. Instantaneous velocity field is also studied and compared to aerodynamic coefficients for different pitch angles. The time-averaged flow is characterised by the formation of several recirculation regions around the solar collector and the receiver tube depending on the pitch angle. The study also presents a comparative study of the heat transfer coefficients around the heat collector element with the circular cylinder in a cross-flow and the effect of the pitch angle on the Nusselt number. Fri, 12 Apr 2013 13:17:16 GMT http://hdl.handle.net/2117/18780 2013-04-12T13:17:16Z Amine Hachicha, Ahmed; Rodríguez Pérez, Ivette María; Castro González, Jesús; Oliva Llena, Asensio no The use of parabolic trough solar technology in solar power plants has been increased in recent years. Such devices are located in open terrain and can be the subject of strong winds. As a result, the stability of these devices to track accurately the sun and the convection heat transfer from the receiver tube could be affected. In this paper, a detailed numerical aerodynamic and heat transfer model based on Large Eddy Simulations (LES) modelling for these equipments is presented. First, the model is verified on a circular cylinder in a cross-flow. The drag forces and the heat transfer coefficients are then validated with available experimental measurements. After that, simulations are performed on an Eurotrough solar collector to study the fluid flow and heat transfer around the solar collector and its receiver. Computations are carried out for a Reynolds number of Re W = 3.6 x 10(5) (based on the aperture) and for various pitch angles (h=0,45,90, 135, 80, 270). The aerodynamic coefficients are calculated around the solar collector and validated with measurements performed in wind tunnel tests. Instantaneous velocity field is also studied and compared to aerodynamic coefficients for different pitch angles. The time-averaged flow is characterised by the formation of several recirculation regions around the solar collector and the receiver tube depending on the pitch angle. The study also presents a comparative study of the heat transfer coefficients around the heat collector element with the circular cylinder in a cross-flow and the effect of the pitch angle on the Nusselt number. http://hdl.handle.net/2117/18731 Title: Autonomous photovoltaic lighting system Authors: Hafez, Ahmed A. A.; Montesinos Miracle, Daniel; Sudrià Andreu, Antoni Abstract: This paper introduces a comparison between the conventional and Photovoltaic (PV) lighting systems. A simple sizing procedure for a PV stand-alone system was advised. The paper also proposes a novel PV lighting system. The proposed system is simple, compact and reliable. The system operation was investigated by thoroughly mathematical and simulation work. Tue, 09 Apr 2013 11:31:27 GMT http://hdl.handle.net/2117/18731 2013-04-09T11:31:27Z Hafez, Ahmed A. A.; Montesinos Miracle, Daniel; Sudrià Andreu, Antoni no lighting, solar power This paper introduces a comparison between the conventional and Photovoltaic (PV) lighting systems. A simple sizing procedure for a PV stand-alone system was advised. The paper also proposes a novel PV lighting system. The proposed system is simple, compact and reliable. The system operation was investigated by thoroughly mathematical and simulation work.