High-capacity high-power thermal energy storage using solid-solid martensitic transformations

Abstract

A new concept of fabricating thermal energy storage modules using high-conductivity, solid-solid, shape memory alloys is demonstrated here to eliminate the capacity-power tradeoff common in solid-liquid designs. First, three compositions of Nickel titanium were solution heat treated and characterized using differential scanning calorimetry and Xenon Flash to down-select to a promising material (Ni50.28Ti49.36) with a transformation temperature of 78 ˚C, volumetric latent heat of 183 MJm−3, and thermal conductivity in the Austenite and Martensite phases of 12.92 and 12.64 Wm−1K−1, respectively. Next, four parallel-plate thermal energy storage demonstrators were designed, fabricated, and tested in a thermofluidic test setup. These include a baseline sensible heating module (aluminum), a conventional solid-liquid PCM module (aluminum/1-octadecanol), an all-solid-solid PCM module (Ni50.28Ti49.36), and a composite solid-solid/solid-liquid PCM module (Ni50.28Ti49.36/1-octadecanol). We are able to demonstrate a 1.73–3.38 times improvement in volumetric thermal capacity and a 2.03–3.21 times improvement in power density by using NiTi. These experimental results are bolstered by analytical models to explain the observed heat transfer physics, extrapolate to additional use cases, and reveal a 5.86 times improvement in thermal time constant. This work demonstrates the ability to build high-capacity and high-power thermal energy storage modules using multifunctional shape memory alloys and opens the door for leap ahead improvement in transient thermal management.