Uncategorized - Laboratory for refrigeration and district energy

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

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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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A completed research secondment at the Bundesanstalt für Materialforschung und -prüfung (BAM)

admin — Tue, 13 Jan 2026 11:16:20 +0000

Our PhD student Kamyar Dobakhti recently completed a research secondment at the Bundesanstalt für Materialforschung und -prüfung (BAM). This secondment provided valuable hands-on experience in X-ray tomography and Life Cycle Assessment (LCA) methodologies relevant to thermomagnetic heat exchanger development.

During his stay at BAM, Kamyar visited several X-ray tomography facilities and a mechanical testing setup, gaining in-depth insight into tomography procedures for structural characterization and defect analysis. Close collaboration with experts in the field enabled a detailed understanding of how these techniques can be applied to optimize manufacturing parameters and material design.

Furthermore, precise geometrical parameters extracted from the X-ray tomography data were directly incorporated into numerical simulations. The primary focus of the secondment was the development of a numerical model to evaluate the heat transfer characteristics of different heat exchanger geometries, supporting the optimization of thermomagnetic heat exchanger performance.

A heartfelt thank you to Dr.-Ing. Anja Waske, Heike Q. and Savvina Papaioannou from BAM for their warm welcome and support. I also want to express my gratitude to our group leaders, the Laboratory for Refrigeration and District Energy, and the entire team for providing me with this incredible opportunity.

The post A completed research secondment at the Bundesanstalt für Materialforschung und -prüfung (BAM) first appeared on Laboratory for refrigeration and district energy.

Ultra-high-temperature electrocaloric heat pump

admin — Mon, 05 Jan 2026 09:01:01 +0000

Researchers from the Laboratory for Refrigeration and District Energy (LAHDE) have published first study on high-temperature electrocaloric heat pump in Journal of Energy conversion and management, one of the world’s leading scientific journal in the field of energy.

Nearly a quarter of waste heat is generated at temperatures exceeding 300 °C, yet conventional heat pump technologies remain inefficient in recovering and utilizing heat from such high temperature sources. In this study, we introduce a novel electrocaloric heat pump designed to operate with heat sources and sinks at ultra-high temperatures. The proposed heat pump system incorporates an active electrocaloric regenerator featuring PbZr_0.52Ti_0.48O₃ (PZT) epitaxial thin-film multilayers, which exhibit a superior electrocaloric adiabatic temperature change of 11.03 K at 402 °C (675 K), and pressurized helium gas as the working fluid. We conducted a parametric analysis to simulate the performance of the ultra-high-temperature electrocaloric heat pump and identified the optimal conditions for single- and multi-stage configurations. The single-stage setup achieved a maximum heating COP of 7.8 at a 30 K temperature span across the regenerator at a heat source temperature of 660 K. In comparison, the multi-stage configuration yielded the highest heating power 113.3 W/kg_EC and a max. COP 2.7 between 630 and 690 K. This study established a foundation for notable advancements in ultra-high-temperature heat pumps by employing electrocaloric energy conversion.

Link: https://www.sciencedirect.com/science/article/pii/S019689042501338X

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