回热型静止式热磁发电机中的换热和回热分析

Heat Transfer and Regeneration Analysis on a Regenerative Static Thermomagnetic Generator

静止式热磁发电机因结构简单、可靠性高等优势而在低品位热源利用领域具有重要的发展前景,但热磁材料热容导致的无效吸热量严重制约了热磁发电机效率的提升。为了克服这一难题,提出一种采用交变流动换热的静止式热磁发电机,其特有的回热结构,有望显著降低换热器的换热量,进而提升整机热效率。首先介绍回热型静止式热磁发电机的整机结构,然后对其回热的实现机理进行了深入分析,并通过理论分析和数值模拟考察了其换热、回热性能与流道结构尺寸、运行参数的关系。结果表明,其换热性能与无量纲缓冲区长度和无量纲流体振幅均呈正比,而回热性能与无量纲流体振幅呈反比。进一步的数值模拟表明,其换热和回热性能随频率的降低而显著提升。在频率为0.2Hz时,该结构可使热磁发电的热效率提升1.5倍,但其回热性能仍有很大的提升空间。

Static thermomagnetic generators have a promising prospect in harvesting low-grade thermal energy for their structural simplicity,high reliability,and other advantages.However,the heat capacity of thermomagnetic materials,which will result in useless heat absorption,hinders it from achieving effective power generation.To address this issue,a static thermomagnetic generator adopting oscillating flow heat transfer was proposed in this paper.The unique regeneration design may well decrease the load of the heat exchangers dramatically,therefrom improve the overall thermal efficiency.The structure of the regenerative static thermomagnetic generator was introduced firstly,then the mechanism of regenerative heat transfer was unveiled in detail,and the dependence of heat transfer and regenerative performance on the flow channel dimensions and operating parameters was investigated theoretically and numerically.According to the calculations,the heat transfer performance increased with the dimensionless buffer-tube length and dimensionless fluid-flow amplitude while the regenerative performance deteriorated with increasing dimensionless fluid-flow amplitude.Further numerical study indicates that low frequency improves the heat transfer and regenerative performance significantly.At a frequency of 0.2 Hz,the novel design shows an increase in thermal efficiency by a factor of 1.5 compared with the conventional configuration.However,the regenerative performance is far from its theoretical limit,much work remains to be done to improve it further.