UPCOMING DISSERTATION DEFENSE – NEHEMIAH EMAIKWU


Author: Nehemiah Emaikwu


Committee Members: Professor Reinhard Radermacher, Chair
Professor Ichiro Takeuchi, Co-Chair
Professor Yunho Hwang
Professor Amr Baz
Professor Bao Yang
Professor Peter B. Sunderland

Date: Friday, April 15th, 2022

Time: 1:30 PM

Location: EGR-2164 (DeWALT Conference Room)


Abstract: Elastocaloric solid-state refrigerants rival conventional refrigerants in lower environmental impact, but require significant advancements to gain widespread implementation. Two barriers which prevent adoption are low temperature lift and poor fatigue life. This dissertation addresses those challenges through a single, scalable architecture with the objectives of 1) designing high-performing elastocaloric devices, and 2) maximizing temperature lift. The developed prototype consists of 23 shortened and thermally insulated Ni-Ti tubes in a staggered pattern that exchange energy with the surrounding fluid medium through their external surface areas. They are contained inside of a 3D-printed plastic that provides alignment and restricts heat transfer to other components. A top loader and fixed bottom plate transfer compressive loads to the tubes, and a 3D-printed housing encapsulates all four parts.
Single, two, and three-stage configurations were experimentally investigated. A sensitivity analysis was conducted on the single-stage device and identified fluid-solid ratio, loading/unloading time, and strain as three parameters that could increase temperature span by over 1.5 K each. The combination of these findings resulted in a maximum steady-state temperature span of 16.6 K (9.7 K in heating and 6.8 K in cooling) at 4% strain and under zero load conditions. The temperature lift was increased in the two and three-stage configurations which achieved 20.2 K and 23.2 K, respectively, under similar operating conditions.
Validated 1D numerical models developed for this work confirm that the multi-staging approach positively impacts thermal response, though with decaying significance as the number of banks increase. By minimizing the water volume in the fluid loop, the three-stage device was able to develop a larger lift of 27.4 K. The tubes used in the single and two-stage tests also withstood over 30,000 cycles without failure, showing promising fatigue life behavior and emphasizing the viability of this alternative cooling technology.

Join Zoom Meeting: https://umd.zoom.us/j/4660347520

Meeting ID: 466 034 7520