Abstract
An analytical approach for computing the coefficient of refrigeration performance (CRP) was described for materials that exhibited a giant inverse magnetocaloric effect (MCE), and their governing thermodynamics were reviewed. The approach defines the magnetic work input using thermodynamic relationships rather than isothermal magnetization data discretized from the literature. The CRP was computed for only cyclically reversible temperature and entropy changes in materials that exhibited thermal hysteresis by placing a limit on their operating temperature in a thermodynamic cycle. The analytical CRP serves to link meaningful material properties in first-order MCE refrigerants to their potential work and efficiency and can be employed as a metric to compare the behaviors of dissimilar alloy compositions or for materials design. We found that an optimum in the CRP may exist that depends on the applied field level and Clausius–Clapeyron (CC) slope. Moreover, through a large literature review of NiMn-based materials, we note that NiMn(In/Sn) alloys offer the most promising materials properties for applications within the bounds of the developed framework.
Highlights
Academic Editors: Tarek BachaghaGiant inverse magnetocaloric materials have gained recent attention in the scientific community due to their high magnetic-to-thermal energy conversion efficiencies and potential for eliminating environmentally harmful chemicals typically used in conventional vapor-compression refrigeration units
We aim to develop an analytical form for the coefficient of refrigeration performance (CRP) that accounts for the cyclic irreversibility in first-order materials
From Equations (19) and (20), assuming the only applied force is μ0 H under isothermal conditions and that the magnetocaloric material was originally in the M-phase μ H =0 at the M f 0 temperature, the refrigeration capacity (RC) can be defined as RC = ∆S M→ A |∆Tad |
Summary
Giant inverse magnetocaloric materials have gained recent attention in the scientific community due to their high magnetic-to-thermal energy conversion efficiencies and potential for eliminating environmentally harmful chemicals typically used in conventional vapor-compression refrigeration units. 20 years following their work, Pecharsky and Gsneidner conceived a similar metric, namely the relative cooling power, RCP, which was applied to the first-order magnetostructural transition observed in GdSiGe [10,11] They employed the RCP to compare materials that exhibited a second-order magnetic transition, such as pure Gd [10]. We aim to analytically compute the metric so that commonly measured and reported materials properties can be used to quickly compare the performance of novel magnetocaloric materials In this way, solid refrigerants that exhibit a first-order magnetostructural transition with transformation hysteresis can be quickly assessed. The development of the analytical CRP is followed with a discussion and examples used for comparing the caloric effects in first-order magnetostructural materials
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