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Thermomagnetic conversion of low-grade waste heat: the role of permanent magnet selection

admin — Mon, 31 Aug 2026 08:39:29 +0000

A substantial amount of energy used in industrial and other thermal processes is ultimately released into the environment as low-grade waste heat. Recovering even a fraction of this energy and converting it into useful electricity could contribute to improved overall energy efficiency and a more sustainable use of energy resources. However, efficient conversion of heat available at relatively low temperatures remains a significant technological challenge.

Thermomagnetic energy conversion offers an alternative approach for harvesting low-grade waste heat. It exploits the strong temperature dependence of the magnetic properties of thermomagnetic materials. By cyclically heating and cooling the material around its magnetic transition temperature, changes in magnetization can be used to induce variations in magnetic flux and ultimately generate electrical power.

In our new study, published in iScience (Cell Press), we investigate an important component of a thermomagnetic generator (TMG) that has received comparatively little attention: the permanent magnets used as the magnetic-field source. Their properties directly influence the magnetic field available to the thermomagnetic material and therefore the performance of the complete energy-conversion system. At the same time, permanent-magnet selection also involves important considerations related to material availability, cost, thermal stability, and the use of critical raw materials.

A numerical model of the thermomagnetic generator was used to systematically compare configurations employing three technologically relevant permanent-magnet materials: neodymium-iron-boron (NdFeB), Alnico, and Ferrite. The analysis considers the interaction between the magnetic field source and the thermomagnetic material and evaluates the resulting electrical response of the generator, including output power, voltage, and current during cyclic operation.

The results demonstrate how strongly the choice of permanent magnet can influence the performance of a thermomagnetic generator. While high-performance permanent magnets can provide stronger magnetic fields and consequently higher electrical output, rare-earth-free alternatives such as Alnico and Ferrite offer different combinations of magnetic properties, temperature stability, material availability, and cost. The comparison therefore highlights that the optimal magnetic-field source cannot be selected solely on the basis of magnetic strength, but should be considered as part of the overall thermomagnetic-generator design.

The study contributes to the development of more efficient and practically viable thermomagnetic energy-harvesting systems and provides guidelines for selecting permanent magnets according to the requirements of a specific application. In the longer term, such systems could provide an additional pathway for converting currently unused low-temperature waste heat into electricity, particularly in applications where conventional heat-to-power technologies are difficult to implement.

The article is available in iScience: link to article.

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Phase change materials for more efficient household refrigeration

admin — Tue, 18 Aug 2026 08:27:13 +0000

A new review paper, Phase Change Materials for Performance Enhancement in Household Refrigeration: A Review, has been published in Strojniški vestnik – Journal of Mechanical Engineering. The paper explores the use of phase change materials (PCMs) to improve the performance of household refrigeration systems.

PCMs can store and release thermal energy during a phase transition, thereby increasing the thermal inertia of a refrigeration system. When properly selected and integrated, they can contribute to more stable temperatures, improved system efficiency, reduced peak loads, and longer preservation of suitable temperatures during power outages.

The paper presents key criteria for PCM selection and reviews different integration strategies, including PCM placement at the evaporator, condenser, inside the refrigerated compartment, and in combined configurations. The review also shows that commercially available PCMs already cover temperature ranges relevant to household refrigeration. Achieving the desired benefits, however, strongly depends on selecting an appropriate phase-change temperature and integrating the material correctly into the refrigeration system.

The work was carried out within the GreenTech project and is the result of collaboration between researchers from the Faculty of Mechanical Engineering, University of Ljubljana, and Gorenje, Hisense Europe.

The paper was authored by Urban Tomc, Katja Klinar, Luka Porenta, Marko Kralj, Tomaž Bregar and Andrej Kitanovski.

Paper: Phase Change Materials for Performance Enhancement in Household Refrigeration: A Review
DOI: 10.5545/sv-jme.2026.1670

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Our Young Researchers Present at the International Conference of PhD Students in Mechanical Engineering

admin — Tue, 21 Jul 2026 11:31:05 +0000

Last week, our young researchers participated in the International Conference of PhD Students in Mechanical Engineering, which brought together doctoral researchers from the Universities of Ljubljana, Maribor, and Zagreb.

Hosted by the Faculty of Mechanical Engineering, University of Ljubljana (UL FS), the conference provides a platform for presenting current research, exchanging ideas, and strengthening collaboration among doctoral students from the three partner universities.

Our laboratory was represented by:

Kamyar Dobakhti, who presented Validation of the Numerical Simulation of a High-Frequency Regenerative Thermomagnetic Generator: HYPEREG.

Matija Kalin, who presented A Generalized Numerical Framework for Active Electrocaloric Regenerators.

Participation in the conference provided an excellent opportunity to showcase ongoing research, receive valuable feedback from the scientific community, and foster collaboration with fellow researchers working in related fields.

We congratulate both researchers on their successful presentations and wish them continued success in their research.

Photo: UL Faculty of Mechanical Engineering

The post Our Young Researchers Present at the International Conference of PhD Students in Mechanical Engineering first appeared on Laboratory for refrigeration and district energy.

Comprehensive thermodynamic screening of low-GWP refrigerant mixtures for micro-scale vapour compression refrigerators and heat pumps

admin — Tue, 14 Jul 2026 18:19:52 +0000

As the demand for high-performance micro and power electronics grows, micro-scale vapour compression refrigeration (VCR) systems and heat pumps (VCHP) have emerged as critical technologies for active heating and cooling. However, the progressive phase-down of hydrofluorocarbon refrigerants under international environmental regulations, necessitates the identification of low-global warming potential alternatives specifically optimized for the unique constraints of small-scale hardware, such as limited compressor displacement and low refrigerant charge.

This study presents a comprehensive and systematic thermodynamic screening of approximately 30,000 refrigerant compositions, including pure fluids, binary, and ternary mixtures, specifically aimed at three key application scenarios: domestic and commercial micro-appliances, personal cooling systems for hostile environments, and reversible heat pumps for electric vehicle cabin and battery management. Using a multi-criteria decision-making approach based on the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) method to maximize simultaneously coefficient of performance and volumetric heating and cooling capacity, optimal candidates were identified across four practical scenarios: high-performance, safety-critical – low-flammability (A1), low-pressure, and a combined low-pressure/non-flammable scenario.

Findings demonstrate that added complexity in ternary mixtures offer no significant thermodynamic advantage over simpler binary blends for micro-scale applications. Final recommendations for next-generation micro-VCR/VCHP systems include: R1270 and R290/RE170 (60/40)% for maximum performance; R1234yf/R1224yd(Z) (72/28)% for safety-critical (A1) applications; RE170/R600 (65/35)% and R600/R1270 (28/72)% for natural, low-pressure operation; and R1234ze(E)/R1233zd(E) (72/28)% or R1234ze(E)/R1224yd(Z) (68/32)% for combined constraints. This study establishes a structured roadmap to navigate the complex landscape of sustainable refrigerant selection in the micro-VCR/VCHP domain.

Link: https://doi.org/10.1016/j.applthermaleng.2026.132282

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Direct Characterization of Electrocaloric and Magnetocaloric Responses in Multicaloric Composite Films

admin — Wed, 01 Jul 2026 05:57:47 +0000

Researchers from the Jožef Stefan Institute, the University of Ljubljana, the University of Barcelona, IFW-Dresden and collaborating institutions have published the article Direct observation of room-temperature electrocaloric and magnetocaloric responses in multicaloric composite films.

The study combines the electrocaloric ceramic PMN-10PT with the magnetocaloric La-Fe-Si-Co (LFSC) alloy. Using Powder Aerosol Deposition (PAD), the team fabricated dense multicaloric composite films approximately 5 μm thick. PAD enables the fabrication of functional thick films entirely at room temperature and offers an attractive route for integrating advanced caloric materials into future cooling devices.
A key achievement of the work is the direct characterization of both electrocaloric and magnetocaloric responses in the same multicaloric composite film at room temperature. The composite films exhibited an approximately 32 % higher electrocaloric temperature change compared to pure PMN-10PT films. The enhancement is attributed to Maxwell–Wagner polarization effects induced by the embedded magnetocaloric particles.
In addition, the magnetocaloric response was directly measured in the same composite films, experimentally confirming their multicaloric functionality and demonstrating the feasibility of combining electrocaloric and magnetocaloric effects within a single aerosol-deposited structure.
The results provide new insights into the development of multifunctional caloric materials and demonstrate the potential of multicaloric composite films for future solid-state cooling and micro-cooling technologies targeting electronics, sensors, and other miniaturized systems.

Link: https://www.sciencedirect.com/science/article/pii/S0955221926004607

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Thermag XI 2026: A successful gathering of the solid-state thermal community

admin — Tue, 16 Jun 2026 06:01:05 +0000

The 11th IIR Conference on Solid-State Cooling, Heating and Energy Harvesting – Thermag XI, held from 7-11 June in Ljubljana, Slovenia, has concluded successfully.

This milestone event brought together researchers, engineers, and industry experts from around the world to exchange the latest advances in solid-state cooling, heating, and energy harvesting. Thermag XI provided a unique forum for sharing cutting-edge research on functional materials, emerging concepts, and their integration into next-generation energy systems.

The presentations reflected a wide range of research activities, from fundamental studies and materials development to device prototyping, modelling, and practical applications that contribute to more sustainable energy technologies. The conference proceedings will be published soon on the IIR website: https://iifiir.org/en/conference-proceedings.

We sincerely thank all authors for their submissions and the reviewers for their valuable contributions. Special appreciation goes to the keynote speakers, session chairs, scientific committee, and organizing team whose efforts made the event possible. We also gratefully acknowledge the support of the International Institute of Refrigeration (IIR), the Slovenian Energy Association (SZE), the Chinese Association of Refrigeration (CAR), the Faculty of Mechanical Engineering at the University of Ljubljana, and all sponsors and partners.

The following topics were presented:

THE CONVENTIONAL AND ROTATING MAGNETOCALORIC EFFECT OF A GADOLINIUM PARALLEL PLATE MAGNETIC REGENERATOR – INFLUENCE OF GEOMETRY (Rafael Almeida, Rodrigo Kiefe, Darja Gačnik, Ricardo M. C. Pinto, João O. Silva, Katja Klinar, Henrique Souza, Gonçalo Oliveira, João S. Amaral, Andrej Kitanovski, João H. Belo)

IMPLEMENTATION AND VALIDATION OF AN ACTIVE ELECTROCALORIC REGENERATOR COMPONENT IN TCC BUILDER (Grega Belšak, Izak Oberčkal Pluško, Katja Vozel, Andrej Kitanovski, Markys Cain, Katja Klinar)

NUMERICAL STUDY ON THE FREQUENCY DEPENDENCE OF THE DIRECT MAGNETOCALORIC EFFECT OF GADOLINIUM FILM (Zhonghao Chang, Jorge Revuelta-Losada, Erika Fontana, Nora Dempsey, Katja Klinar, Andrej Kitanovski, Jia Yan Law, Victorino Franco)

VALIDATION OF THE NUMERICAL SIMULATION OF A HIGH-FREQUENCY REGENERATIVE THERMOMAGNETIC GENERATOR HYPEREG (Kamyar Dobakhti, Katja Klinar, Urban Tomc, Jure Javornik, Andrej Kitanovski)

FINITE ELEMENT MODELING AND OPTIMIZATION OF A MAGNETIC FIELD SOURCE FOR THERMOMAGNETIC GENERATION (Radel Gimaev, Katja Klinar, Andrej Kitanovski)

NUMERICAL MODELING OF AN ACTIVE MAGNETIC REGENERATOR BASED ON THE ROTATIONAL MAGNETOCALORIC EFFECT (Radel Gimaev, Darja Gačnika, Urban Tomc, Rafael Almeida, Rodrigo Kiefe, João H. Belo, João S. Amaral, Katja Klinar, Andrej Kitanovski)

PHASE-CHANGE MATERIAL THERMAL DIODES FOR CALORIC REFRIGERATOR (Karl Joulain, Katja Klinar, Katja Vozel, Andrej Kitanovski, Younès Ezzahri)

A GENERALIZED MODELLING APPROACH FOR ACTIVE ELECTROCALORIC REGENERATORS (Matija Kalin, Darja Gačnik, Katja Klinar, Andrej Kitanovski)

HYPEREG: HIGH-FREQUENCY MAGNETOCALORIC REGENERATOR (Andrej Kitanovski, Katja Klinar, Jure Javornik, Simon Nosan, Jakob Perne, Simon Bogić, Blaž Jagodic, Urban Tomc)

THE PERSPECTIVES OF ULTRA-HIGH-TEMPERATURE SOLID-STATE HEAT PUMPS (Katja Klinar, Darja Gačnik, Radel Gimaev, Andrej Kitanovski)

BRIDGING THE THERMAL GAP: THE ROLE OF FLUIDIC AND MECHANICAL THERMAL CONTROL DEVICES IN ADVANCING CALORIC TECHNOLOGIES (Katja Klinar, Urban Tomc, Katja Vozel, Andrej Kitanovski)

THERMAL CONDUCTIVITY OF CELLULOSE-BASED COMPOSITE FILMS (Vanja Kokol, Vera Vivod, Katja Klinar)

MODELING OF THERMOACOUSTIC GENERATOR IN TCCBUILDER (Izak Oberčkal Pluško, Harini Nivetha Raja, Grega Belšak, Jingyuan Xu, Katja Vozel, Andrej Kitanovski, Katja Klinar)

EVALUATION OF CURIE TEMPERATURE EFFECTS IN THE PERFORMANCE OF ACTIVE MAGNETIC REGENERATORS – PART I: SECOND ORDER PHASE TRANSITION (Urban Tomc, Guilherme F. Peixer, Chistian R. H. Bahl, Kaspar K. Nielsen, Jaime A. Lozano, Jader R. Barbosa Jr., Andrej Kitanovski)

DIGITAL MICROFLUIDIC THERMAL SWITCH CAPACITORS FOR MAGNETOCALORIC COOLING (Blaž Velkavrh, Hana Uršič, Urška Erjavec Nagode, Andrej Kitanovski, Lukas Beyer, Jens Freudenberger, Klara Lünser, Enric Stern-Taulats, Lluis Mañosa, Urban Tomc)

ENHANCING SOLID-STATE THERMAL RECTIFICATION VIA TEMPERATURE-DEPENDENT THERMAL CONTACT RESISTANCE (Katja Vozel, Andrej Kitanovski)

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New article: Roadmap for electrocaloric films characterization

admin — Thu, 28 May 2026 08:06:32 +0000

The article Roadmap for electrocaloric films characterization, published in iScience (Cell Press), presents a numerical investigation of substrate and infrared (IR) coating effects on the characterization of electrocaloric thick-film structures for future cooling applications.

Researchers from the Laboratory for Refrigeration and District Energy at the Faculty of Mechanical Engineering, University of Ljubljana, in collaboration with the Jožef Stefan Institute, investigated how substrate thermal properties and high-emissivity black coating thickness influence the accuracy of infrared temperature measurements of electrocaloric materials. The aim of the study was to establish guidelines for optimized characterization of electrocaloric structures at the micro- and nano-scale.

Using numerical simulations, the researchers demonstrated that substrates with low thermal effusivity and low thermal conductivity significantly reduce heat losses during measurements, enabling more accurate determination of the electrocaloric response. In addition, the influence of electrocaloric film thickness and black coating thickness on the IR correction factor was systematically analyzed. The results show that low single-digit correction factors can be achieved when the electrocaloric layer is thicker than the coating.

The study provides important guidelines for reliable electrocaloric material characterization and offers a roadmap for the design of future micro-scale caloric cooling systems..

Link: https://www.cell.com/iscience/fulltext/S2589-0042(26)01340-4

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World Energy Day 2026

admin — Tue, 10 Feb 2026 13:41:58 +0000

On February 14, we mark World Energy Day, a moment to reflect on how deeply energy shapes our daily lives and how critical it is to use it responsibly. From lighting our homes and powering transport to enabling food production and economic growth, energy supports modern society and quality of life worldwide.

At the same time, the global energy system faces a defining challenge. Scientific consensus is clear that emissions must be reduced significantly by 2030 and reach net zero by 2050 to limit the worst impacts of climate change. While renewable sources such as wind and solar continue to grow rapidly and are becoming dominant in electricity generation, fossil fuels still account for a large share of global energy supply.

World Energy Day is therefore not just a celebration, but a call to action to improve energy efficiency, accelerate the transition to renewables, and rethink how we produce and consume energy. A sustainable energy future is not just an option: it is essential.

The post World Energy Day 2026 first appeared on Laboratory for refrigeration and district energy.

Cool BatMan featured as M-ERA.NET Success Story

admin — Tue, 10 Feb 2026 13:40:49 +0000

The Cool BatMan project has been recognized as a Success Story by M-ERA.NET.

The project aimed to build a fundamental understanding of the dynamic thermal behavior of a compact cooling concept. It combines magnetocaloric materials, exploiting the magnetocaloric effect, with electrowetting-on-dielectric (EWOD) digital microfluidics. The work included advanced microfabrication and new characterization approaches.

A key outcome is the demonstration that digital microfluidics, widely used in bioanalytical lab-on-a-chip systems, also has strong potential for thermal management at the mini- and microscale.

We thank our consortium partners: Jožef Stefan Institute, Leibniz Institute for Solid State and Materials Research Dresden, and the University of Barcelona. We also thank M-ERA.NET for the recognition.

Read the full success story here:
https://www.m-era.net/news/successtory_coolbatman

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High-temperature electrocaloric heat pump presented at the High-temperature heat pump symposium

admin — Fri, 23 Jan 2026 09:56:23 +0000

Researchers from the Laboratory for Refrigeration and District Energy (LAHDE) have visited High-temperature heat pump symposium in Copenhagen, Danmark. The event offered an excellent overview of the latest research and industrial developments in high-temperature heat pumps, with many insightful discussions and opportunities to exchange perspectives with experts from industry and academia.

We were pleased to present our work on solid-state electrocaloric heat pump in the poster session and to receive valuable feedback that will support our ongoing research. Many thanks to the organizers for a well-structured and high-quality symposium, and to all colleagues for the engaging discussions.

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