Chikhareva Maria, Vaidyanathan Raj
Department of Materials Science and Engineering, University of Central Florida, Orlando, FL 32816, USA.
Nanomaterials (Basel). 2023 Jul 25;13(15):2159. doi: 10.3390/nano13152159.
Shape memory alloy (SMA) heat engines possess an inherent property of sensing a change in temperature, performing work, and rejecting heat through the shape memory effect resulting from a temperature-induced phase transformation. This work presents a framework for the design and implementation of an SMA-based Stirling heat engine for maximum torque or speed incorporating and combining mechanical, thermal, and material aspects. There is a growing need for such engines for reliable thermal management and energy recovery in both ground and space applications. Mechanical aspects were addressed from force balances in the SMA element and focused on the resulting stress distribution. Thermal aspects considered heat transfer between the SMA element and both the heat source and the heat sink. Materials aspects considered the chemical, elastic, and frictional contributions to the enthalpy of the transformation. The roles of nano- and microstructure through composition, precipitates, variant interfaces, training, cycling, texture, defects, nucleation sites (bulk vs. surface), and multi-step transformations (e.g., a trigonal R-phase transformation) in NiTi based-alloys are also emphasized. The aforementioned aspects were combined to present a figure of merit to aid in the design and implementation of a Nitinol Stirling heat engine operating to maximize torque or maximize speed.
形状记忆合金（SMA）热机具有一种内在特性，即能够感知温度变化、做功并通过温度诱导相变产生的形状记忆效应排出热量。这项工作提出了一个框架，用于设计和实现基于SMA的斯特林热机，以实现最大扭矩或速度，并结合了机械、热和材料方面的因素。在地面和太空应用中，对这种用于可靠热管理和能量回收的发动机的需求日益增长。从SMA元件中的力平衡入手探讨机械方面，并着重研究由此产生的应力分布。热方面考虑了SMA元件与热源和散热器之间的热传递。材料方面考虑了化学、弹性和摩擦对转变焓的贡献。还强调了通过成分、析出物、变体界面、训练、循环、织构、缺陷、形核位置（体相与表面）以及多步转变（例如三角R相转变）在镍钛基合金中的纳米和微观结构的作用。将上述各方面结合起来，给出了一个品质因数，以辅助设计和实现运行时扭矩或速度最大化的镍钛诺斯特林热机。
