Magnetocaloric cooling is an emerging technology for room temperature refrigeration. It has the potential to surpass the established gas-vapor compression refrigeration system in terms of efficiency. It also eliminates direct greenhouse gas emissions. It is based on the magnetocaloric effect, i.e., the temperature change exhibited by certain ferromagnetic materials upon magnetization and demagnetization. Key components of application-aimed systems are the Active Magnetic Regenerator (AMR) and the permanent magnet assembly. The system operates with a periodically changing fluid flow. The cyclic magnetization and demagnetization of the AMR is achieved by the movement of the permanent magnet assembly. This results in a heightened temperature span along the AMR and an output of cooling power.
Numerical optimization of the system is key to achieving high performance and energy efficiency. Recently, Wiesheu et al. (https://doi.org/10.1016/j.ijrefrig.2023.04.014) demonstrated that topology and shape optimization based on field profiles can significantly improve the design. However, simulation and optimization of AMR and assembly are still performed sequentially. The AMR is studied using a given magnetization profile. The magnet assembly is arranged to maximize the generated air gap field.
In a joint project with the startup Magnotherm, TU Darmstadt is working on the coupling of magnet and AMR simulation. They compute the generated magnetic field. This field is then given as input to a transient convection-diffusion problem, which describes the heat transfer in the AMR. When the cyclic steady state is found, key performance metrics can be calculated. These metrics include cooling power and coefficient of performance. These can then be used in the objective function of an optimization. In this way, the permanent magnet assembly can be optimized for system performance rather than a surrogate metric.
The team at TU Darmstadt consists of Prof. Sebastian Schöps, Prof. Oliver Weeger, Boian Balouchev, Yusuf Elbadry, Melina Merkel, Michael Wiesheu. Magnotherm is represented by Dr. Maximilian Fries, Dimitri Benke and Tim Sittig.
The research is funded by the LOEWE Project 1450/23-04 via the Hessian Ministry of Science and Art and the Hessen-Agentur.