Comillas Pontifical University. Madrid (Spain)
July 17th, 2025
Summary:
Current cryogenic systems comprise liquefaction plants using expansive cycles and cryocoolers employing regenerative gas cycles. While liquefaction plants serve large-scale facilities like LHC and ITER, cryocoolers provide compact solutions for applications like MRI equipment. However, cryocoolers face significant limitations below 20 K, where cooling capacity and exergy efficiency decrease substantially due to the relationship between helium's volumetric heat capacities near its critical point and regenerator material properties. This limitation makes cryogenic systems among the highest costs in ultra-low temperature applications. This thesis investigates magnetic refrigeration for cryogenic environments using the magnetocaloric effect as an alternative to conventional methods. Following analysis of previous prototypes and their challenges, ErAl2 emerged as superior to previously used Gd3Ga5O12 in the 4.2-20 K range. A one-dimensional numerical model was developed to estimate cooling power and exergy efficiency characteristics. An experimental test bench based on the single-blow method was designed and constructed to validate the numerical model under cryogenic conditions with magnetic field application. Performance evaluation of both ErAl2 and Gd3Ga5O12 regenerators achieved partial model validation, though external losses and material property uncertainties limited complete confirmation. Results demonstrate substantial potential for magnetic refrigeration to reduce cryogenic cooling costs significantly. A technological roadmap presents critical development steps while mitigating risks, supporting industrial and commercial viability.
Descriptors: Physics, Thermodynamics, Low temperatures
Citation:
C. Hernando, "Modeling and Experimental Research of Cryogenic Magnetic Refrigeration for the 4–20 K Range", PhD. dissertation, Comillas Pontifical University, Madrid, Spain, 2025.
