D.F. Pineda Quijano | TU Delft Repository

Advanced Magnetocaloric Regenerators for Heat Pump Applications

Doctoral thesis (2025) - D.F. Pineda Quijano, E.H. Brück, C.A. Infante Ferreira

Heat pumps are expected to play a central role in the decarbonization of the built environment, yet the environmental and safety limitations of conventional vapor-compression systems demonstrate the need for alternative technologies. Magnetocaloric heat pumps (MCHPs) offer a promising pathway by avoiding high-GWP, toxic, or flammable refrigerants while enabling competitive performance. This thesis investigates key engineering and system-level aspects of MCHPs for residential applications, with particular emphasis on the design of active magnetocaloric regenerators (AMRs) using numerical analysis and the experimental characterization of their flow and heat transfer behavior. To begin, layered AMRs composed of MnFePSi materials were evaluated using a one-dimensional model to assess several Curie temperature distribution strategies—including linear and sigmoidal gradients, as well as a linear gradient combined with thicker end layers. The results show that this last configuration reduces sensitivity to temperature variations, an advantage for systems exposed to fluctuating ambient conditions. Building on these regenerator-level insights, the seasonal performance of an MCHP system was assessed using the performance map of a 12-layer MnFePSi AMR, which was embedded into a system model representing a residential MCHP consisting of 69 such regenerators. Through continuous modulation of flow rate and cycle frequency combined with modular capacity control, the system reached an estimated seasonal coefficient of performance (SCOP) of 4.5 under realistic heating-season conditions. To further support the development of these systems, an experimental setup was designed to characterize pressure drop and heat transfer in AMRs manufactured by an extrusion-based additive process. A geometric model was developed to estimate parameters such as equivalent particle diameter and void fraction, the latter showing good agreement with X-ray tomography. Using measured pressure-drop and flow-rate data, a friction factor correlation was established, with behavior lying between that of packed beds and parallel plates. Although heat transfer measurements showed limited reproducibility, the methodology forms a basis for future refinement. Taken together, these findings advance the design, modeling, and characterization of AMRs and support the continued development of magnetocaloric heat pumps for residential use. ...

Heat pumps are expected to play a central role in the decarbonization of the built environment, yet the environmental and safety limitations of conventional vapor-compression systems demonstrate the need for alternative technologies. Magnetocaloric heat pumps (MCHPs) offer a promising pathway by avoiding high-GWP, toxic, or flammable refrigerants while enabling competitive performance. This thesis investigates key engineering and system-level aspects of MCHPs for residential applications, with particular emphasis on the design of active magnetocaloric regenerators (AMRs) using numerical analysis and the experimental characterization of their flow and heat transfer behavior. To begin, layered AMRs composed of MnFePSi materials were evaluated using a one-dimensional model to assess several Curie temperature distribution strategies—including linear and sigmoidal gradients, as well as a linear gradient combined with thicker end layers. The results show that this last configuration reduces sensitivity to temperature variations, an advantage for systems exposed to fluctuating ambient conditions. Building on these regenerator-level insights, the seasonal performance of an MCHP system was assessed using the performance map of a 12-layer MnFePSi AMR, which was embedded into a system model representing a residential MCHP consisting of 69 such regenerators. Through continuous modulation of flow rate and cycle frequency combined with modular capacity control, the system reached an estimated seasonal coefficient of performance (SCOP) of 4.5 under realistic heating-season conditions. To further support the development of these systems, an experimental setup was designed to characterize pressure drop and heat transfer in AMRs manufactured by an extrusion-based additive process. A geometric model was developed to estimate parameters such as equivalent particle diameter and void fraction, the latter showing good agreement with X-ray tomography. Using measured pressure-drop and flow-rate data, a friction factor correlation was established, with behavior lying between that of packed beds and parallel plates. Although heat transfer measurements showed limited reproducibility, the methodology forms a basis for future refinement. Taken together, these findings advance the design, modeling, and characterization of AMRs and support the continued development of magnetocaloric heat pumps for residential use.

Seasonal COP of a residential magnetocaloric heat pump based on MnFePSi

Journal article (2024) - Diego Pineda Quijano, Beatriz Fonseca Lima, Carlos Infante Ferreira, Ekkes Brück

The performance of a magnetocaloric heat pump (MCHP) consisting of active magnetocaloric regenerators (AMR) of 12 layers of MnFePSi magnetocaloric materials (MCM) with a linear distribution of Curie temperatures was investigated using a 1D numerical model. The model predicted the heating power and coefficient of performance (COP) of the AMR for a fixed temperature span of 27 K, between 281 K and 308 K, and variable flow rate and AMR cycle frequency. A maximum applied magnetic field strength of 1.4 T was used. A well-insulated house with a maximum heating power demand of 3 kW (under quasi steady state conditions) was considered. Ambient temperature in The Netherlands was taken as a reference for the estimation of the seasonal heating power demand. Without optimizing the design of the AMR, the model predicts a maximum single-AMR heating power equal to 43.5 W when the AMR operates at 3 Hz and 3 L min^-1, and a maximum COP equal to 5.8 when it operates at 1.5 Hz and 1 L min^-1 Considering the maximum heating power of a single AMR, approximately 69 AMRs are needed to provide the design heating power demand of the house. It was found that it is possible to achieve an AMR seasonal COP of 5.6 by continuously adjusting the flow rate and frequency of operation of the MCHP along with the ON/OFF switching of some groups of AMRs in order to adjust the heating power of the MCHP to the heating power demand of the house. ...

Layering strategies for active magnetocaloric regenerators using MnFePSi for heat pump applications

Journal article (2023) - Diego Pineda Quijano, Carlos Infante Ferreira, Ekkes Brück

The development of affordable magnetocaloric materials (MCM) with a giant magnetocaloric effect (MCE) has brought magnetocaloric heat pumps a step closer to commercialization. The narrow temperature range in which these materials exhibit a large MCE demands the use of several materials with Curie temperatures covering the temperature span of the heat pump in a so-called layered active magnetocaloric regenerator (AMR). How to place these materials in the AMR in terms of distribution of Curie temperatures and thickness of each layer is still a topic of study. In this research we used a one dimensional numerical model to unveil potential benefits of either using a distribution of Curie temperatures that follows a sigmoidal shape or using thicker layers at the cold and hot ends of the AMR along with a linear distribution of Curie temperatures. We found that these AMRs are less sensitive to changes in the hot and cold reservoir temperatures compared to an AMR that uses just a linear distribution of Curie temperatures with uniform layer length, but only the one with thicker ends produces similar heating capacities and second law efficiencies. The heating capacity of the simulated AMR with a sigmoidal distribution of Curie temperatures varies only 5.6 % in a high utilization scenario, flow rate 37.5 g/s and a frequency of 0.75 Hz, when the hot side temperature changes from 308 K to 312 K and the temperature span is 18 K while the corresponding change is 8.7 % for the AMR with thicker end layers, and 37.9 % for the one with a linear distribution of Curie temperatures. For the considered geometry and operating conditions, the maximum heating capacities with temperature span 27 K in the high utilization scenario are 28.6 W, 23.0 W, and 28.5 W, whereas the corresponding second law efficiencies are 33.2%, 27.3 %, and 32.7% for the AMRs with linear distribution of Curie temperatures, sigmoid distribution, and linear distribution with thicker ends respectively. ...

The development of affordable magnetocaloric materials (MCM) with a giant magnetocaloric effect (MCE) has brought magnetocaloric heat pumps a step closer to commercialization. The narrow temperature range in which these materials exhibit a large MCE demands the use of several materials with Curie temperatures covering the temperature span of the heat pump in a so-called layered active magnetocaloric regenerator (AMR). How to place these materials in the AMR in terms of distribution of Curie temperatures and thickness of each layer is still a topic of study. In this research we used a one dimensional numerical model to unveil potential benefits of either using a distribution of Curie temperatures that follows a sigmoidal shape or using thicker layers at the cold and hot ends of the AMR along with a linear distribution of Curie temperatures. We found that these AMRs are less sensitive to changes in the hot and cold reservoir temperatures compared to an AMR that uses just a linear distribution of Curie temperatures with uniform layer length, but only the one with thicker ends produces similar heating capacities and second law efficiencies. The heating capacity of the simulated AMR with a sigmoidal distribution of Curie temperatures varies only 5.6 % in a high utilization scenario, flow rate 37.5 g/s and a frequency of 0.75 Hz, when the hot side temperature changes from 308 K to 312 K and the temperature span is 18 K while the corresponding change is 8.7 % for the AMR with thicker end layers, and 37.9 % for the one with a linear distribution of Curie temperatures. For the considered geometry and operating conditions, the maximum heating capacities with temperature span 27 K in the high utilization scenario are 28.6 W, 23.0 W, and 28.5 W, whereas the corresponding second law efficiencies are 33.2%, 27.3 %, and 32.7% for the AMRs with linear distribution of Curie temperatures, sigmoid distribution, and linear distribution with thicker ends respectively.