Material-based figure of merit for caloric materials

Abstract

The efficient use of reversible thermal effects in magnetocaloric, electrocaloric, and elastocaloric materials is a promising avenue that can lead to a substantially increased efficiency of refrigeration and heat pumping devices, most importantly, those used in household and commercial cooling applications near ambient temperature. A proliferation in caloric material research has resulted in a wide array of materials where only the isothermal change in entropy in response to a handful of different field strengths over a limited range of temperatures has been evaluated and reported. Given the abundance of such data, there is a clear need for a simple and reliable figure of merit enabling fast screening and down-selection to justify further detailed characterization of those material systems that hold the greatest promise. Based on the analysis of several well-known materials that exhibit vastly different magnetocaloric effects, the Temperature averaged Entropy Change is introduced as a suitable early indicator of the material's utility for magnetocaloric cooling applications, and its adoption by the caloric community is recommended.

Non-hysteretic first-order phase transition with large latent heat and giant low-field magnetocaloric effect

“…In magnetic fields exceeding 2 T (Supplementary Note 8) the maximum Δ S begins to saturate, reaching −37 J kg −1  K −1 in 7 T. The steady but slow increase of Δ S with field above 2 T is due to the conventional spin contribution, but the discontinuity of Δ S observed for all Δ B  ≥ 2 T remaining constant around ~−26 J kg −1  K −1 which, as expected 26 , is very close to the entropy change associated with FOMT determined from both the Clausius–Clapeyron equation and from heat capacity. For a field change of 1 T, the coefficient of refrigerant performance (CRP) is about 0.70 and the temperature averaged entropy change (TEC3) is about −17.1 J kg −1  K −1 27,28 . These figures of merit are comparable to or higher than the most promising magnetocaloric materials in the cryogenic regime 27,28 .…”

“…For a field change of 1 T, the coefficient of refrigerant performance (CRP) is about 0.70 and the temperature averaged entropy change (TEC3) is about −17.1 J kg −1  K −1 27,28 . These figures of merit are comparable to or higher than the most promising magnetocaloric materials in the cryogenic regime 27,28 . With the exceptionally small hysteresis, particularly large Δ S and Δ T ad in moderate magnetic fields, Eu 2 In outperforms all known magnetocaloric materials in this temperature range 3–6 .…”

Magnetic and magnetocaloric properties of DyCo2Cx alloys

“…The relative cooling power (RCP) was calculated by the following equation: has been suggested as a more suitable indicator of materials utility for magnetocaloric cooling [36]:…”

“…ΔTlift is the desired temperature span of the device. Tmid is the temperature at the center of the average chosen by sweeping over the available ΔS(T)ΔH,T data and selecting the value that maximizes TEC(ΔTlift) for the given ΔTlift [36]. The calculated TEC(10) for the DyCo2Cx alloys (x=0, 0.05, 0.1, and 0.15) are listed in Table 1 ("10" corresponds to the value of the temperature lift, i.e.…”

Energy Applications of Magnetocaloric Materials

“…In this regard, there is an ongoing debate among researchers about which parameters to take into consideration. For example, in the recent publications of Niknia et al and Griffith et al, who investigated different figures of merit for their potential use as indicators of the refrigeration capability of a magnetocaloric material. In vapor‐compression refrigeration, the refrigerant's capacity is defined by the enthalpy change that occurs during the evaporation (or cooling process).…”