Introduction of novel method of cyclic self-heating for the experimental quantification of the efficiency of caloric materials shown for LaFe_11,4Mn_0,35Si_1,26H_x

Abstract

Hysteresis and the associated production of dissipative heat during first order phase transitions are often major contributors to thermodynamic losses in caloric heat pumps. The figure of merit (FOM), defined as the ratio of adiabatic temperature change and the thermal hysteresis of the caloric material, quantifies these losses, and can also be used to calculate the maximum potential efficiency of a caloric material in a thermodynamic cycle. This paper presents a novel and simple method to determine the heat loss and thus the FOM can be determined from self-heating of the caloric material during repeated field cycling. As this method mainly requires temperature readings and the ability to cycle the caloric material in a field, most test setups that directly measure the adiabatic temperature change should already be able to perform dissipative heat measurements with this technique. With the presented method, we were able to determine the efficiency of a commercial LaFeSiMnH-sample with a high degree of accuracy. A maximum FOM of 37 ± 1 was determined for the selected LaFeSiMnH-sample. In an ideal cascaded magneto caloric system, this corresponds to a system efficiency of 90%, with an ideal heat regeneration this could theoretically even be increased to 97%.