Lab

Laboratory for refrigeration and district energy

About the lab

The Laboratory for Refrigeration and District Energy is active in scientific research and the educational process at the Faculty of Mechanical Engineering, University of Ljubljana, while also being closely tied to the professional and industrial field. All these activities are complemented because we are aware that research is crucial for the quality of educational and professional work.

Our areas of expertise are the fields of Heat and Mass Transfer, Refrigeration, Alternative refrigeration, Heat pumps and District energy systems.

In addition to educational activities we are involved with research and development in the field of energy and environmental technology.

Featured projects (1)

Project
This work presents the design and analysis of the two main parts of the magnetocaloric refrigeration device: an active magnetocaloric regenerator and a magnetic field source, respectively. For the purpose of the analysis, the active magnetocaloric regenerator was designed and numerically evaluated. The results were later used as the basis for the design of the magnet assembly.

Featured research (11)

Open access paper! Magnetocaloric energy conversion represents an alternative to existing refrigeration, heat pump and energy harvesting technologies. A crucial part of a magnetocaloric device concerns the magnetic field source. It uses mainly rare-earth materials and consists of moving parts and a drive system while displaying a limited energy efficiency and unavailability of fast and variable control of the magnetic field. Recent advances in efficient heat transfer for high-frequency magnetic cooling call for new developments of magnetic field sources that can operate with high efficiency at high frequencies. We report the concept of an electro-permanent magnetic (EPM) field source that efficiently recovers magnetic energy. In contrast to existing magnets, it allows very well-controlled operation without any moving parts. The main objective of this paper is to present a numerical and experimental study in which such an EPM was designed, built and tested. An extensive numerical investigation of the proposed design was carried out in terms of various geometrical and operating parameters. One of the design variations was built and experimentally evaluated for its energy efficiency and temperature increase at various operating frequencies. We demonstrate an energy efficiency of these magnets of over 80% and operation with frequencies up to 50 Hz, which is crucial for future high-power-density and high-frequency magnetocaloric devices. Considering high energy efficiency at high operating frequencies, such EPMs would allow for miniaturization, making them a viable option for future compact magnetocaloric devices.
Thermal switches are advanced heat-management devices that represent a new opportunity to improve the energy efficiency and power density of caloric devices. In this study we have developed a numerical model to analyze the operation and the performance of static thermal switches in caloric refrigeration. The investigation comprises a parametric analysis of a realistic ferrofluidic thermal switch in terms of the maximum temperature span, cooling power and COP. The highest achieved temperature span between the heat source and the heat sink was 1.12 K for a single embodiment, which could be further developed into a regenerative system to increase the temperature span. A sensitivity analysis is conducted to correlate the relationship between the input parameters and the results. We show that thermal switches can be used in caloric devices even when switching ratios are small, which greatly extends the possibilities to implement different types of thermal switches.
Condensation of humid air is a very important process in thermal and process engineering, as well as in several industrial applications. It is also a subject of many currently research-intensive scientific domains, such as atmospheric water harvesting and seawater desalination. The nature of (water) vapor condensation in the presence of non-condensable gas (NCG) such as air differs significantly from the case with the pure, quiescent vapor condensation. In the literature, simple models that describe the condensation of the forced flow of water vapor in the presence of air on a series of vertical flat plates forming vertical channels are hard to find. Some existing models are complex, as computationally extensive numerical calculations are required. Here we present a simple and computationally efficient semi-empirical correlation that describes the condensation of the forced flow of humid air on a condenser geometry consisting of a series of vertical flat plates forming vertical channels. The correlation accounts air as a non-condensing gas, different heights of vertical plates and different thermal-hydraulic parameters. The applicable range of this theoretical and experimental study with respect to the plate height, temperatures of humid air and plate’s wall, air mass fraction in humid air, Reynolds and Schmidt numbers of humid air is: 0.03 – 0.074 m, 29.5 – 77.3 °C, 10.5 – 58.9 °C, 0.683 – 0.974, 1362 – 5180 and 0.622 – 0.630, respectively. The correlation has been experimentally validated and shows excellent agreement, as 90% of theoretically predicted values are within ±12% of experimental data.
In recent years, intensive studies on thermal control devices have been conducted for the thermal management of electronics and computers as well as for applications in energy conversion, chemistry, sensors, buildings, and outer space. Conventional cooling or heating techniques realized using traditional thermal resistors and capacitors cannot meet the thermal requirements of advanced systems. Therefore, new thermal control devices are being investigated to satisfy these requirements. These devices include thermal diodes, thermal switches, thermal regulators, and thermal transistors, all of which manage heat in a manner analogous to how electronic devices and circuits control electricity. To design or apply these novel devices as well as thermal control principles, this paper presents a systematic and comprehensive review of the state‐of‐the‐art of fluidic and mechanical thermal control devices that have already been implemented in various applications for different size scales and temperature ranges. Operation principles, working parameters, and limitations are discussed and the most important features for a particular device are identified.

Lab head

Andrej Kitanovski
Department
  • Faculty of Mechanical Engineering
About Andrej Kitanovski
  • see si.linkedin.com/pub/andrej-kitanovski/49/159/424/

Members (16)

Jaka Tušek
  • University of Ljubljana
Urban Tomc
  • University of Ljubljana
Primož Poredoš
  • Shanghai Jiao Tong University
Uros Plaznik
  • Kolektor Etra d.o.o
Stefano Dall'Olio
  • University of Ljubljana
Boris Vidrih
  • University of Ljubljana
Parham Kabirifar
  • University of Ljubljana
Katja Klinar
  • University of Ljubljana
Boris Vidrih
Boris Vidrih
  • Not confirmed yet
Vidrih Boris
Vidrih Boris
  • Not confirmed yet