DIODIFY ENG
DIODIFY: Advanced thermal management with thermal diodes in systems with cyclical temperature changes
DIODIFY is a scientific research cooperation between the Republic of Slovenia and the French Republic within the framework of the PROTEUS Program in the years 2025 – 2027.
The Slovenian part is co-financed by ARIS.
We collaborate with Prof. Karl Joulain and Prof. Younes Ezzahri, Université de Poitiers.
A thermal diode is a thermal control component that allows the heat flow crossing the element to be different depending on the direction of heat propagation. It exhibits a so-called thermal rectification. Depending on the thermal bias applied, heat flux is greater in the forward direction across the thermal diode than in the reverse direction. Unlike thermal switches, which necessitate external energy input for operation, thermal diodes offer the advantage of autonomous functionality since their properties only depend on the temperature applied at their ends.
These diodes are particularly valuable for managing heat flux in systems subject to cyclical temperature changes. One common application is their integration into thermal systems to manage their temperatures. For instance, let us consider a thermal system related to an external environment at a certain cycling temperature T with such a thermal diode. If the diode blocks the heat flux when the external temperature is greater than a critical value and lets it flow in the opposite case, the system will be passively managed at a temperature around this critical value. Additionally, thermal diodes hold significant potential for caloric energy conversion, which serves as the primary focus of this project. The operation of magnetocaloric refrigerators or heat pumps in a thermodynamic cycle needs a magnetocaloric material to be magnetized or demagnetized while being isolated or thermally related to a heat source or a heat sink at different steps of the cycle. When integrated into such a system, thermal diodes enable the operation of magnetocaloric refrigerators or heat pumps without the need for moving parts or additional external energy input. With a suitable design of thermal diodes, one can imagine a magnetocaloric device working passively while being only submitted to magnetization and demagnetization processes. The same method can also be used in electrocaloric devices, where electrocaloric material undergoes polarization and depolarization effects.
In this project, we aim to establish the requirements for thermal diodes to operate efficiently in a magnetocaloric device across temperature ranges below and above room temperature. We will focus on thermal diodes made of materials that have their thermal properties that change strongly with their temperature. Phase change materials, such as Vanadium dioxide (VO2), which exhibit an insulation to metal transition phase, are good candidates. Leveraging state-of-the-art materials, we will conduct numerical simulations and generate maps depicting the requisite characteristics of thermal diodes for a magnetocaloric application. We will have to design two types of diodes. One diode should be conducting below a critical temperature and blocking above whereas a second diode should be blocking below a critical temperature and conducting above. Our focus will extend beyond single-layer conduction thermal diodes to encompass multilayered or composite conduction thermal diodes and thermal radiation thermal diodes.
To conduct these numerical simulations, we will utilize the TCCbuilder software, an open-source tool developed by the University of Ljubljana group, specifically designed for designing thermal control circuits using thermal control elements. This software has proved to be very efficient in the modelling and the functioning of thermal circuits in the permanent or time-dependent regime. Once the characteristics of thermal diodes are determined, we will propose a design for a magnetocaloric device composed of a agnetocaloric material and the diodes we will have conceived. At the end of the project, we will consider building a proof of the concept device and testing its performances.
