Grain growth-induced thermal property enhancement of NiTi shape memory alloys for elastocaloric refrigeration and thermal energy storage systems. (June 2020)

• Record Type: Journal Article
• Authors: Warzoha, Ronald J.; Vu, Nicholas T.; Donovan, Brian F.; Cimpoiasu, Elena; Sharar, Darin J.; Leff, Asher C.; Wilson, Adam A.; Smith, Andrew N.
• Is Part Of: International journal of heat and mass transfer. Volume 154(2020)
• Publication Date: 2020-06
• Subjects: Thermal conductivity -- Thermoreflectance -- Shape memory alloy -- Latent heat -- Thermal storage; Heat -- Transmission -- Periodicals; Mass transfer -- Periodicals; Chaleur -- Transmission -- Périodiques; Transfert de masse -- Périodiques; Electronic journals; 621.4022
• DOI: 10.1016/j.ijheatmasstransfer.2020.119760
• Languages: English
• ISSNs: 0017-9310

Abstract

Highlights: We use a solution anneal process to induce grain growth in Ni50.75 Ti shape memory alloys (SMAs). Grain size ranges from 40 ± 30 nm to 60 µm. Both thermal conductivity and thermal energy storage capacity are shown to increase with grain size, contrary to typical performance degradation upon the insertion of thermal conductivity enhancers in PCMs. Graphical abstract: Abstract: We interrogate the extent to which grain size plays a role in augmenting the thermal conductivity and thermal energy storage capacity of a NiTi shape memory alloy (SMA) using the optical pump-probe technique frequency-domain thermoreflectance and advanced calorimetry techniques, respectively. To alter grain size, we apply a solution anneal process to a nanograined commercial NiTi sample and show that grain growth (from ~ 40 nm to ~ 60 µm) significantly increases thermal conductivity in both phases and improves the thermal storage capacity of the material by up to a factor of ~ 50. These results are contrary to the performance metrics achieved using conventional mechanisms that improve PCM thermal conductivity, and provide a viable route to develop elastocaloric refrigeration systems with a high coefficient of performance (COP) as well as large figure-of-merit passive thermal regulation methods for cooling high power density electronics.