Numerical investigation of different cooling technologies during heatwaves in Catalan Mediterranean buildings

The Mediterranean area is particularly affected by heatwaves, which are extremely critical for health and productivity of people inside the dwellings as well as for energy consumptions related to cooling demand. This study numerically investigated the resilience of different cooling technologies in the most common construction in Catalan building stock during present and future climatic conditions, heatwaves. The studied technologies include green roof, blinds, advanced windows, air conditioning and their combinations. Meteorological data of heatwaves for Barcelona city have been created for three time periods, Present, Mid Future and Long Future. They have been modelled using dynamical downscaled Regional Climate Models, climate projections based on IPCC scenarios. Resilience was assessed using indicators that consider the linear correlation between the grade of overheating inside a dwelling and the severity of outdoor conditions. Thermal comfort and survivability have been also investigated, evaluating sensations of building's occupants related to indoor air temperature and relative humidity. The original building presented acceptable levels of resilience with a resilience index a below 1, while thermal comfort conditions resulted poor, especially during heatwaves, being for more than 60% of the time in Extreme Caution conditions or worst. The application of the different cooling technologies significantly helped in the improvement of resilience and survivability inside the dwelling. However, their performances reduced in the future scenarios, reaching more than 90% of the time under Extreme Caution conditions or worst. Air conditioning resulted the best solution for avoiding overheating, especially in heatwaves constraining it to a maximum of 1.8°C. Combinations of several passive measures resulted necessary for maintaining suitable conditions.Peer ReviewedPostprint (published version

Investigating the capabilities of CFD-based data-driven models for indoor environmental design and control

In this work, we study the accuracy of CFD-based data-driven models, which predict comfort-related flow parameters in a ventilated cavity with a heated floor. We compare the computational cost and accuracy of three different models, namely artificial neural network, support vector regression, and gradient boosting regression. The tested scenarios include short and long cavities with different inlet velocities. Among the studied frameworks, the artificial neural network provides the most accurate predictions for most of the tested flow configurations. However, test configurations with jet separation and a secondary vortex are more difficult to predict correctly; thus more high-fidelity data is required in order to construct a more robust and reliable model.This work is supported by the Ministerio de Economía y Competitividad, Spain [ENE2017-88697-R]. N. Morozova is supported by the by the Ministerio de Economía y Competitividad, Spain [FPU16/06333 predoctoral contract]. Part of the calculations was performed on the MareNostrum 4 supercomputer at the Barcelona Supercomputing Center [RES project IM-2021-1-0015]. The authors thankfully acknowledge these institutions.Postprint (published version

Modelling thermal dynamics in intermittent operation of a PEMEL for green hydrogen production

Green hydrogen plays a pivotal role in the imminent energy transition, addressing energy storage and electricity generation decarbonization. The European Commission's hydrogen strategy underscores the goal to install at least 40 GW of green hydrogen electrolysers by 2023. Despite various electrolyser technologies, efficiency improvement and durability enhancement remain challenges, especially considering voltage intermittencies from renewable energy sources. This study emphasizes the impact of thermal gradients within electrolysers due to voltage interruptions, affecting membrane operation and causing premature wear. The study explores methods to minimize thermal gradients, revealing trade-offs between efficiency and durability. A lumped-parameter numerical model is developed and experimentally adjusted to simulate electrochemical and energy transport phenomena. Experimental and numerical results are compared, highlighting the need for a comprehensive thermal management code for effective electrolyser performance. The study addresses the importance of accurately modelling transient thermal responses for both proton exchange membrane electrolysis (PEMEL) and solid oxide electrolysis (SOEL) designs, providing insights for future advancements in thermal management strategies.Postprint (published version

Numerical simulation of heat transfer and fluid flow in a flat plate solar collector with TIM and ventilation channel

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.Peer ReviewedPostprint (published version

On the feasibility of affordable high-fidelity CFD simulations for indoor environment design and control

Computational fluid dynamics (CFD) is a reliable tool for indoor environmental applications. However, accurate CFD simulations require large computational resources, whereas significant cost reduction can lead to unreliable results. The high cost prevents CFD from becoming the primary tool for indoor environmental simulations. Nonetheless, the growth in computational power and advances in numerical algorithms provide an opportunity to use accurate and yet affordable CFD. The objective of this study is to analyze the feasibility of fast, affordable, and high-fidelity CFD simulations for indoor environment design and control using ordinary office computers. We analyze two representative test cases, which imitate common indoor airflow configurations, on a wide range of different turbulence models and discretizations methods, to meet the requirements for the computational cost, run-time, and accuracy. We consider statistically steady-state simulations for indoor environment design and transient simulations for control. Among studied turbulence models, the no-model and large-eddy simulation with staggered discretizations show the best performance. We conclude that high-fidelity CFD simulations on office computers are too slow to be used as a primary tool for indoor environment design and control. Taking into account different laws of computer growth prediction, we estimate the feasibility of high-fidelity CFD on office computers for these applications for the next decadesThis work is supported by the Ministerio de Economía y Competitividad, Spain [ENE2017-88697-R]. N. Morozova is supported by the by the Ministerio de Economía y Competitividad, Spain [FPU16/06333 predoctoral contract]. Part of the calculations was performed on the MareNostrum 4 supercomputer at the Barcelona Supercomputing Center [RES project I-2019-2-0021]. The authors thankfully acknowledge these institutions. The authors would also like to thank our colleague MSc Xavier Álvarez Farré for the productive discussions.Peer ReviewedPostprint (author's final draft

Estrategias de monitorización de la electrólisis de hidrógeno en electrolizadores PEM

Postprint (published version

CFD studies and experimental validation of the convective heat transfer coefficient in non-fully developed flows applied to conventional geometries used in particle accelerators

In the field of Particle Accelerators engineering, the design of the cooling channels of its components has been extensively based on experimental correlations for the calculation of convective heat transfer coefficients. In this scenario, this work is focused on studying whether the experimental correlations are conservative when the flow is turbulent in fully developed and non-fully developed regions. For this research, simulation models have been developed for turbulent flows in fully developed and non-fully developed regions, all of them for cooling channels with a 10 mm inner diameter. In the first case, for a circular channel, turbulence models have been studied, and comparative studies with respect to experimental correlations and previous studies performed at ALBA have been carried out. Simulation models based on the coefficients obtained from experimentally observed correlations, CFD models and an experimental validation of a mirror with inside cooling, have been performed in the second case.Postprint (published version

Exploring convective heat transfer coefficients in fully developed flows: a combined CFD analysis and experimental validation for common geometries in particle accelerators

Within the field of Particle Accelerators engineering, the design of cooling channels for its components has heavily relied on experimental correlations to compute convective heat transfer coefficients. These coefficients are believed to have a conservative factor which end up in oversized designs. The following study assesses this conservative factor for fully developed flows, in the laminar, turbulent and transition regimes. It will also focus on different geometries to do so. With this objective in mind, simulation models have been developed and correlated with experiments carried out at ALBA synchrotron. In the course of this research, various turbulence models and meshes have been examined for the development of the simulations. Heat transfer coefficients were derived from the Computational Fluid Dynamics (CFD) simulations and juxtaposed with empirical correlations. The specific geometries under investigation encompass a circular channel with a 10mm inner diameter, a rectangular section channel, and a pinhole geometry, the latter being frequently employed in accelerator technologyPostprint (published version

Formularis

2023/202

Col·lecció d'exàmens de mètodes numèrics: enunciat-resultat-resolució

2023/202