Frost formation: optimizing solutions under a finite volume approach

Published under licence in Journal of Physics: Conference Series by IOP Publishing Ltd. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.A three-dimensional transient formulation of the frost formation process is developed by means of a finite volume approach. Emphasis is put on the frost surface boundary condition as well as the wide range of empirical correlations related to the thermophysical and transport properties of frost. A study of the numerical solution is made, establishing the parameters that ensure grid independence. Attention is given to the algorithm, the discretised equations and the code optimization through dynamic relaxation techniques. A critical analysis of four cases is carried out by comparing solutions of several empirical models against tested experiments. As a result, a discussion on the performance of such parameters is started and a proposal of the most suitable models is presented.Peer ReviewedPostprint (published version

Optimized battery sizing for merchant solar PV capacity firming in different electricity markets

Comunicació presentada a IECON 2019 - 45th Annual Conference of the IEEE Industrial Electronics Society (Lisbon, Portugal 14-17 Oct. 2019)This work analyses the minimum energy capacity requirements to be demanded to battery energy storage systems used in megawatt-range merchant solar PV plants to grant capacity firming. The operation of such a plant is simulated (with a 2-minute time step, at three different locations of the Iberian Peninsula, and for different battery sizes) after solving a quadratic programming optimization problem. The control algorithm takes into account the irradiance forecast and the intraday electricity market configuration, which presents certain peculiarities in the Iberian region with regard to other European markets. The analysis has been performed in an annual basis and current irradiance measured values have been used

Estudio constructivo, propuesta de rehabilitación y cambio de uso de la antigua leprosería de Barcelona Can Masdeu

Can Masdeu, antigua leprosería de Barcelona. Desde su origen hasta la actualidad, ha sufrido una serie de cambios provocados por las necesidades funcionales en cada momento. La información más antigua obtenida de esta masía consta del 1901, cuando fue abjudicada por subasta al Hospital de la Santa Cruz hasta el 1977 que finalmente cerró durante más de 25 años, mostrando en la actualidad un avanzado estado de degradación constructiva con el agotamiento de sus elementos estructurales y constructivos. En el 2001 fue ocupada y rehabilitada como vivienda y centro social. El proyecto se centra en la masía de Can Masdeu, conocida como la antigua leproseria del Hospital de Sant Pau, ubicada en uno de los valles no urbanizados del Parque de Collserola, en Barcelona. Por estos motivos el edificio presenta cierta dificultad a la hora de estudiarlo, las ampliaciones y pequeñas intervenciones que se han ido realizando a lo largo de todos estos años nos han creado muchos conflictos para establecer la tipología constructiva correspondiente a cada época. Los objetivos de nuestro proyecto serán: - Un estudio histórico de la evolución de Can Masdeu. - Un levantamiento gráfico. - Un estudio de los elementos constructivos. - Un análisis de las lesiones existentes con sus propuestas de actuación. - Una propuesta de intervención del edificio

Heat and moisture insulation by means of air curtains: application to refrigerated chambers

The present study is devoted to the determination of the efficiency of air curtain units (ACUs) applied to heat and moisture insulation of refrigerated chambers. A detailed study of the fluid dynamics and heat and mass transfer of the ACU in the refrigerated space and the external ambient is carried out by means of large eddy simulations (LES). The heat and moisture entrainment through the doorway and their transport inside the inner space are fully described. Three different configurations are studied: non-recirculating, recirculating and twin-jet air curtains. The condensation produced in the cool walls of the refrigerated space is evaluated considering the warm humid air from the ambient which penetrates inside the chamber through the doorway. The influence of both the discharge velocities and the discharge angles on the sealing capabilities of the three different tested ACU configurations is determined.Peer ReviewedPostprint (author's final draft

A new statistical model for subgrid dispersion in large eddy simulations of particle-laden flows

This article is published under a CC BY licence. The Version of Record is available online at: http.//dx.doi.org/10.1088/1742-6596/745/3/032115Dispersed multiphase turbulent flows are present in many industrial and commercial applications like internal combustion engines, turbofans, dispersion of contaminants, steam turbines, etc. Therefore, there is a clear interest in the development of models and numerical tools capable of performing detailed and reliable simulations about these kind of flows. Large Eddy Simulations offer good accuracy and reliable results together with reasonable computational requirements, making it a really interesting method to develop numerical tools for particle-laden turbulent flows. Nonetheless, in multiphase dispersed flows additional difficulties arises in LES, since the effect of the unresolved scales of the continuous phase over the dispersed phase is lost due to the filtering procedure. In order to solve this issue a model able to reconstruct the subgrid velocity seen by the particles is required. In this work a new model for the reconstruction of the subgrid scale effects over the dispersed phase is presented and assessed. This innovative methodology is based in the reconstruction of statistics via Probability Density Functions (PDFs).Peer ReviewedPostprint (published version

Multi-layered solid-PCM thermocline thermal storage concept for CSP plants. Numerical analysis and perspectives

Thermocline storage concept has been considered for more than a decade as a possible solution to reduce the huge cost of the storage system in concentrated solar power (CSP) plants. However, one of the drawbacks of this concept is the decrease in its performance throughout the time. The objective of this paper is to present a new thermocline-like storage concept, which aims at circumventing this issue. The proposed concept consists of a storage tank filled with a combination of solid material and encapsulated PCMs, forming a multi-layered packed bed, with molten salt as the heat transfer fluid. The performance evaluation of each of the prototypes proposed is virtually tested by means of a detailed numerical methodology which considers the heat transfer and fluid dynamics phenomena present in these devices. The virtual tests carried out are designed so as to take into account several charging and discharging cycles until periodic state is achieved, i.e. when the same amount of energy is stored/released in consecutive charging/discharging cycles. As a result, the dependence of the storage capacity on the PCMs temperatures, the total energy and exergy stored/released, as well as the efficiencies of the storing process are compared for the different thermocline, single PCM, cascaded PCM and the proposed multi-layered solid-PCM (MLSPCM) configurations. The analysis shows that the multi-layered solid-PCM concept is a promising alternative for thermal storage in CSP plants.Peer ReviewedPostprint (author’s final draft

Numerical dynamic analysis of reciprocating compressor mechanism. Parametric studies for optimization purposes

© 2016. This version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/A complete numerical dynamic analysis of reciprocating compressor mechanism is presented, coupling the instantaneous pressure in the compression chamber, the electric motor torque and the hydrodynamic reactions, which arise from the piston and crankshaft secondary movements. Additionally, non-constant crankshaft angular velocity and the piston and crankshaft misalignment torques have also been considered. Two sensitivity analyses have been carried out to prove that neither the inertial forces in the directions of the secondary movements, nor the oscillations of the angular velocity produce significant differences in the compressor behaviour. Finally, a set of parametric studies has been developed to evaluate the influence of geometrical parameters in the stability of the secondary movements, the friction power losses and the compressor consumptionPeer ReviewedPostprint (author's final draft

Techno-economic performance evaluation of solar tower plants with integrated multilayered PCM thermocline thermal energy storage: a comparative study to conventional two-tank storage systems

Copyright 2016 AIP Publishing. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing.Solar Tower Power Plants with thermal energy storage are a promising technology for dispatchable renewable energy in the near future. Storage integration makes possible to shift the electricity production to more profitable peak hours. Usually two tanks are used to store cold and hot fluids, but this means both higher investment costs and difficulties during the operation of the variable volume tanks. Instead, another solution can be a single tank thermocline storage in a multi-layered configuration. In such tank both latent and sensible fillers are employed to decrease the related cost up to 30% and maintain high efficiencies. This paper analyses a multi-layered solid PCM storage tank concept for solar tower applications, and describes a comprehensive methodology to determine under which market structures such devices can outperform the more conventional two tank storage systems. A detail model of the tank has been developed and introduced in an existing techno-economic tool developed by the authors (DYESOPT). The results show that under current cost estimates and technical limitations the multi-layered solid PCM storage concept is a better solution when peaking operating strategies are desired, as it is the case for the two-tier South African tariff scheme.Peer ReviewedPostprint (published version

On the properties of discrete spatial filters for CFD

© 2016. This version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/The spatial filtering of variables in the context of Computational Fluid Dynamics (CFD) is a common practice. Most of the discrete filters used in CFD simulations are locally accurate models of continuous operators. However, when filters are adaptative, i.e. the filter width is not constant, or meshes are irregular, discrete filters sometimes break relevant global properties of the continuous models they are based on. For example, the principle of maxima and minima reduction or conservation are eventually infringed. In this paper, we analyze the properties of analytic continuous convolution filters and extract those we consider to define filtering. Then, we impose the accomplishment of these properties on explicit discrete filters by means of constraints. Three filters satisfying the derived conditions are deduced and compared to common differential discrete CFD filters on synthetic fields. Tests on the developed discrete filters show the fulfillment of the imposed properties. In particular, the problem of maxima and minima generation is resolved for physically relevant cases. The tests are conducted on the basis of the eigenvectors of graph Laplacian matrices of meshes. Thus, insight into the relations between filtering and oscillation growth on general meshes is provided. Further tests on singularity fields and on isentropic vortices have also been conducted to evaluate the performance of filters on basic CFD fields. Results confirm that imposing the proposed conditions makes discrete filters properties consistent with those of the continuous ones.Peer ReviewedPostprint (author's final draft

THE CYCAD SCALE, AULACASPIS YASUMATSUI TAKAGI (HOMOPTERA: DIASPIDIDAE): A NEW INVASIVE PEST TO PUERTO RICO

THE CYCAD SCALE, AULACASPIS YASUMATSUI TAKAGI (HOMOPTERA: DIASPIDIDAE): A NEW INVASIVE PEST TO PUERTO RIC