Magnetic Refrigeration (at room temperature) Behzad Monfared

Agenda Introduction Computer simulation Prototype Solid-state magnetic refrigeration Future work

Magnetocaloric effect Temperature increase in presence of magnetic field (magnetocaloric effect) Example: Gd (rare-earth metal)

Working principle

Thermodynamic cycle Resembles Brayton cycle Limited span Regeneration

Regeneration

Active regeneration

Porous regenerator Packed bed Parallel plates https://www.wpi.edu/academics/che/HMTL/fbht.html (Tusek et al. 2013) http://dx.doi.org/10.1016/j.ijrefrig.2013.04.001

A built prototype (not ours) Cold heat exchanger Bahl et al., 2012, Thermag V Conf., Grenoble

Technical Aspects of a Magnetic Refrigerator Hydraulics Mechanics Material science Magnetism Thermodynamics Heat transfer - Bed of MC material - Valves and connections - Heat exchangers - Pumping power - Bed of MC material - Heat losses - Heat exchangers - Power transmission losses - Mechanisms - Magnetic and non-magnetic properties - Mechanics of Material - Hysteresis, Volume change, etc. - Magnetocaloric effect - Bed of MC material - Heat exchangers - Energy balance and performance evaluation - Design of the magnet assembly - Field variations (spatial and temporal) - Magnetic forces - Magnetization of the MC materials - Eddy currents

Advantages No leakage of refrigerants Magnetization/demagnetization is reversible unlike compression/expansion Potential for higher efficiency the most promising alternative to vapor-compression technology (compared to Thermoelectric, Stirling, Electrocaloric, etc.) (Qian et al. 2016) http://dx.doi.org/10.1016/j.ijrefrig.2015.10.019

Agenda Introduction Computer simulation Prototype Solid-state magnetic refrigeration Future work

Mathematical model Solid 𝑘 𝑒𝑠 𝜕 2 𝑇 𝑠 𝜕 𝑥 2 + ℎ 𝑠𝑓 𝑎 𝑇 𝑓 − 𝑇 𝑠 − 1−𝜀 𝜌 𝑠 𝑇 𝑠 𝜕𝑠 𝜕𝐵 𝜕𝐵 𝜕𝑡 =(1−𝜀) 𝜌 𝑠 𝑐 𝑝,𝑠 𝜕 𝑇 𝑠 𝜕𝑡 Fluid 𝑘 𝑒𝑓 𝜕 2 𝑇 𝑓 𝜕 𝑥 2 − 𝑉 𝐷 𝑐 𝑝,𝑓 𝜕 𝑇 𝑓 𝜕𝑥 − ℎ 𝑠𝑓 𝑎 𝑇 𝑓 − 𝑇 𝑠 + 𝑑𝑃 𝑑𝑥 𝑉 𝐷 =𝜀 𝜌 𝑓 𝑐 𝑝,𝑓 𝜕 𝑇 𝑓 𝜕𝑡 Monfared and Palm. 2015. "Optimization of layered regenerator of a magnetic refrigeration device." International Journal of Refrigeration 57:103-111. doi: http://dx.doi.org/10.1016/j.ijrefrig.2015.04.019.

Agenda Introduction Computer simulation Prototype Solid-state magnetic refrigeration Future work

Design specifications 200 W cooling capacity over 40 K temperature span Estimated 1.6 COP Magnetic field indicates cost, weight, and size Comparison: (Jacobs et al. 2014) 2000 W over 12 K temperature span with 1.44 T field * defined differently   cooling capacity [W] (zero span) temperature span* [K] (zero load) magnetic field [T] (Zimm et al. 2006) 50 25 1.5 (Okamura et al. 2007) 560 8 1.1 (Vasile and Müller 2006) 360 14 2.4 (Yao et al. 2006) 51 42 (Lozano 2014) 625 1.24

Regenerators

Magnetic circuit

Measured results (1/6 of the capacity)

Materials: the main problem Pulverization (low mechanical strength) Corrosion Non-uniform size of particles Low quality of delivery Resulting in excessive pressure drop, low performance, clogging, etc.

Agenda Introduction Computer simulation Prototype Solid-state magnetic refrigeration Future work

Another work in parallel Low cycle frequency of the conventional magnetic refrigeration systems described Small cooling capacity per kg of magnetocaloric material Large magnets ( 𝑚 𝑚𝑎𝑔 𝑚 𝑀𝐶𝑀 does not increase linearly) Expensive and bulky Solid-state magnetic refrigeration

Solid-state magnetic refrigeration Enhanced conduction in one direction

Agenda Introduction Computer simulation Prototype Solid-state magnetic refrigeration Future work

Future work Solving the remaining problems of the prototype Running systematic experiments to study the effect of different parameters Adjusting the software model using the experimental data Simulating solid-state magnetic refrigeration systems

Thank you