Advancing Domestic Freezers With Phase Change Materials: Experimental Study Towards Commercialization Daniel Marques, Vitor Silva, Nelson Martins, Fernando Neto Heat Transfer, 2025 The urgency for more efficient and sustainable domestic refrigeration systems (DRSs) is intensifying due to climate change events like more frequent heat waves. Such challenges impose reducing greenhouse gas emissions, increasing renewable energy storage rates, meeting the perishable food needs for cooling, and mitigating food wastage through power outages. While previous investigations contributed to these goals by studying the potential benefits of adding phase change materials (PCMs) to DRSs, our study extends their application to chest freezers: a type of system still underexplored. Additionally, it seeks to enhance industrialization and design decision‐making towards tailoring different solutions to distinct markets. Namely, by adopting test procedures closely adhering to the European Standard EN 62552:2013 for experimentally testing four prototypes. The analysis of the novel systems' performance focuses on two metrics internationally recognized but scientifically overlooked by previous peer research: the temperature rise time and the daily energy consumption. A novel approach for filling the top‐mounted door with PCMs and an industrialization technique for simultaneous wrapping PCM bags and evaporator tubes around the freezer compartment are introduced to incorporate PCMs, with melting temperatures (Tm) of −21°C and −12°C. Our findings reveal the potential to extend blackout autonomy by 7%–40% and to reduce daily energy consumption by 13%. Furthermore, the results demonstrate that higher Tm values enhance the commercial attractiveness of DRSs in regions with unstable electricity grids where significant autonomy gains are appreciated, while lower Tm values suit sophisticated markets where extended energy storage capacity and compressor lifetime can be prioritized.
Residential Buildings at Climate Crossroads: Insights from Portugal for South European Energy Performance Alexandre Castro, Sandra Sorte, Vera Rodrigues, Nelson Martins Energies, 2025 This study evaluates the impact of climate change on the energy performance of residential buildings across Portugal’s diverse climatic regions, providing a representative reference for Southern European contexts. Dynamic energy simulations using EnergyPlus were conducted for standardised residential building models in five cities: Bragança, Porto, Lisbon, Évora, and Faro. Three climate scenarios were analysed: present-day conditions (TMY2021), the current regulatory scenario (LNEG-EPW), and a projected mid-century scenario (CCW-EPW). Results indicate substantial regional variations, with significant increases in cooling demands and corresponding reductions in heating needs, exposing limitations in the regulatory climate files currently used in energy certification processes. These findings emphasise the critical need to incorporate predictive climatic scenarios into building design standards and energy policies. Adopting such an approach will enhance residential building resilience, ensure thermal comfort, reduce energy consumption, and contribute to sustainable development goals. These insights offer practical guidance for policymakers, urban planners, architects, and engineers aiming to effectively adapt residential buildings to anticipated climatic shifts, facilitating proactive and informed decision-making to address future energy challenges.
Advancing Power Transformer Cooling: The Role of Fluids and Nanofluids—A Comprehensive Review Sandra Sorte, Alexandre Salgado, André Ferreira Monteiro, Diogo Ventura, Nelson Martins, et al. Materials, 2025 The ongoing pursuit of enhanced efficiency and sustainability in power transformer cooling systems has spurred extensive research into the properties and performance of insulating fluids. This review explores the evolution of transformer cooling technologies, focusing on traditional mineral oils and the emerging roles of alternative fluids, such as natural and synthetic esters, and nanofluids. Mineral oils, though widely used, degrade over time, leading to a reduction in breakdown voltage (BDV) from 46 kV to 30 kV, exhibiting low fire resistance. Natural and synthetic esters provide improved biodegradability, fire safety but have higher viscosities—potentially limiting convective cooling. Nanofluids, have demonstrated BDV enhancements of up to 47.8%, reaching 88.7 kV in optimised formulations, alongside increases in partial discharge inception voltage (PDIV) of 20–23%. Additionally, thermal conductivity improvements of 5–20% contribute to enhanced heat dissipation. Moreover, it addresses challenges such as nanoparticle agglomeration, sedimentation, ageing, and compatibility with transformer materials. The analysis provides critical insights into the trade-offs between technical performance and economic feasibility. Concluding with an outlook on future research directions, the review identifies key parameters across various categories, establishing a roadmap for nanofluid integration with existing transformer systems.
Power Transformers Cooling Design: A Comprehensive Review Sandra Sorte, André Ferreira Monteiro, Diogo Ventura, Alexandre Salgado, Mónica S. A. Oliveira, et al. Energies, 2025 Efficient cooling technologies for power transformers are critical to modern power systems, ensuring reliability, performance, and AN extended lifespan. This review systematically analyses advancements, challenges, and opportunities in cooling systems for power transformers. Oil-immersed transformers, widely used due to their superior insulation and effective cooling, require efficient thermal management to prevent overheating and ensure operational stability. This review evaluates key cooling strategies across oil-natural air-natural (ONAN), oil-natural air-forced (ONAF), oil-directed air-forced (ODAF), and oil-forced air-forced (OFAF) systems. It highlights innovations in radiator design, such as top-mounted radiators and chimney caps, and explores sustainable alternatives, including biodegradable esters, nanofluids, and hybrid ventilation methods. Advanced computational tools like Computational Fluid Dynamics (CFD) and artificial intelligence (AI), particularly neural networks, are identified as transformative for optimising cooling performance, predicting thermal behaviour, and enabling real-time monitoring. Despite progresses, challenges persist in radiator optimisation, airflow dynamics, and scalability of innovative cooling methods. By offering a comprehensive review and identifying critical areas for improvement, this study provides a foundation for developing cost-effective, reliable, and environmentally sustainable cooling systems, aligning with the growing demand for efficient energy infrastructure.
Geometry Optimisation of a Wave Energy Converter Susana Costa, Jorge Ferreira, Nelson Martins Energies, 2025 The geometry optimisation of a point-absorber wave energy converter, focusing on the increase in energy absorption derived from heave forces, was performed. The proposed procedure starts by developing an initial geometry, which is later evaluated in terms of hydrodynamics and optimised through an optimisation algorithm to tune the shape parameters that influence energy absorption, intending to obtain the optimal geometry. A deployment site on the Portuguese coast was defined to obtain information on the predominant waves to assess several sea states. NEMOH and WEC-Sim (both open-source software packages) were used to evaluate the interaction between the structure and the imposed wave conditions. The results extracted and analysed from this software included forces in the six degrees of freedom. Under extreme wave conditions, the highest increase in the relative capture width between the initial and final shapes was around 0.2, corresponding to an increase from 0.36 to 0.54, while under average wave conditions, the increase only reached a value of around 0.02, corresponding to an increase from 0.22 to 0.24, as calculated through the relative capture width values.
Hydrogen production from salinity gradients Eduardo Durana, Francisco José Almeida Loureiro, Nelson Martins, Duncan P. Fagg Hydrogen Technology Fundamentals and Applications, 2024
