Thermal hysteresis and its impact on the efficiency of first-order caloric materials

Cooling with caloric materials could be an option to replace compressor-based cooling systems in the future. In addition to the advantage of avoiding dangerous liquid coolants, one often cites a possible higher efficiency of the calorific cooling systems compared to compressor-based systems. But is that true? The aim of this work is to assess the efficiency potential of caloric cooling systems on a very basic material level. We placed our focus on materials with a first-order phase change since they generally show a large caloric response. We derive a relation between thermal hysteresis and the dissipative losses due to hysteresis. To predict the efficiency, this relation is integrated in a Carnot-like cycle. This approach was chosen to get access to the efficiency reduction due to hysteresis without any further losses due to other nonidealities of the thermodynamic cycle. As a main finding, we present a direct relation between thermal hysteresis and the expected maximum exergy or second-law efficiency of a caloric cooling device. These results indicate that, for many caloric materials, the thermal hysteresis needs to be further reduced to be able to compete with the efficiency of compressor-based systems.