ABSTRACT

A thermomagnetic generator is a promising technology to harvest low-grade waste heat and convert it into electricity. To make this technology competitive with other technologies for energy harvesting near room temperature, the optimum thermomagnetic material is required. Here we compare the performance of a state of the art thermomagnetic generator using gadolinium and La-Fe-Co-Si as thermomagnetic material, which exhibit strong differences in thermal conductivity and type of magnetic transition. gadolinium is the established benchmark material for magnetocaloric cooling, which follows the reverse energy conversion process as compared to thermomagnetic energy harvesting. Surprisingly, La-Fe-Co-Si outperforms gadolinium in terms of voltage and power output. Our analysis reveals the differences in thermal conductivity are less important than the particular shape of the magnetization curve. In gadolinium an unsymmetrical magnetization curve is responsible for an uncompensated magnetic flux, which results in magnetic stray fields. These stray fields represent an energy barrier in the thermodynamic cycle and reduce the output of the generator. Our detailed experiments and simulations of both, thermomagnetic materials and generator, clearly reveal the importance to minimize magnetic stray fields. This is only possible when using materials with a symmetrical magnetization curve, such as La-Fe-Co-Si.

摘要

热磁发电机是一项很有前途的技术，可以收集低品位废热并将其转化为电能。为了使这项技术与其他接近室温的能量收集技术竞争，需要最佳的热磁材料。在这里，我们比较了使用钆和 La-Fe-Co-Si 作为热磁材料的最先进的热磁发电机的性能，它们在热导率和磁转变类型方面表现出很大的差异。钆是磁热冷却的既定基准材料，与热磁能量收集相比，它遵循反向能量转换过程。令人惊讶的是，La-Fe-Co-Si 在电压和功率输出方面的性能优于钆。我们的分析表明，热导率的差异不如磁化曲线的特定形状重要。在钆中，不对称的磁化曲线导致未补偿的磁通量，从而导致杂散磁场。这些杂散场代表热力学循环中的能量屏障并降低发电机的输出。我们对热磁材料和发电机的详细实验和模拟清楚地揭示了最小化杂散磁场的重要性。这仅在使用具有对称磁化曲线的材料时才有可能，例如 La-Fe-Co-Si。这些杂散场代表热力学循环中的能量屏障并降低发电机的输出。我们对热磁材料和发电机的详细实验和模拟清楚地揭示了最小化杂散磁场的重要性。这仅在使用具有对称磁化曲线的材料时才有可能，例如 La-Fe-Co-Si。这些杂散场代表热力学循环中的能量屏障并降低发电机的输出。我们对热磁材料和发电机的详细实验和模拟清楚地揭示了最小化杂散磁场的重要性。这仅在使用具有对称磁化曲线的材料时才有可能，例如 La-Fe-Co-Si。