Active magnetocaloric heat pipes provide enhanced specific power of caloric refrigeration

Today almost all refrigeration systems are based on compressors, which often require harmful refrigerants and typically reach 50% of the Carnot efficiency. Caloric cooling systems do not need any detrimental fluids and are expected to reach 60–70% of the Carnot limit. Current caloric systems utilise the active magnetocaloric regeneration principle and are quite cost-intensive, as it is challenging to achieve large cycle frequencies and thus high specific cooling powers with this principle. In this work, we present an alternative solution where the heat transfer from the heat exchangers to the caloric material is predicated on condensation and evaporation of a heat transfer fluid. Using thermal diodes, a directed heat flow is generated. Thereby we were able to build a cooling unit achieving a specific cooling power of 12.5 W g−1 at a cycle frequency of 20 Hz, which is one order of magnitude larger than the state-of-the-art. There is an ever-increasing requirement for coolant systems and current apparatus typically exhibits low efficiency as well as relying on environmentally detrimental refrigerants. Here, the authors report a design involving a caloric material and the condensation and evaporation of a heat transfer fluid, which achieves a marked increase in performance in comparison to other types of system.