Development of Thermoelastic Cooling Systems

Abstract

Thermoelastic cooling, or elastocaloric cooling, is a cutting-edge solid-state based alternative cooling technology to the state-of-the-art vapor compression cooling systems that dominate the world today. Being environment friendly without any global warming potential, these thermoelastic cooling systems could reduce energy expenses and carbon emission since they are potentially more efficient than the vapor compression cycle (VCC). Nevertheless, as a result of its immature nature, its realistic application potential requires comprehensive research in material fundamentals, cycle design, system simulation, the proof-of-concept prototype development and testing. Therefore, understanding the performance potential and limitations of this emerging new cooling technology, building the theoretical framework and guiding future research are the objectives of this dissertation. Thermodynamic fundamentals of elastocaloric materials are introduced first. Cycle designs and theoretical performance evaluation are presented together with a detailed physics-based dynamic model for a water-chiller application. The baseline system coefficient of performance (COP) is 1.7 under 10 K system temperature lift. To enhance the system performance, a novel thermo-wave heat recovery process is proposed based on the analogy from the highly efficient “counter-flow” heat exchanger. Both the theoretical limit of the “counter-flow” thermo-wave heat recovery and the practical limitations by experimentation have been investigated. The results indicated that 100% efficiency is possible in theory, 60% ~ 80% heat recovery efficiency can be achieved in practice. The world first of-its-kind proof-of-concept prototype was designed based on the dynamic model, fabricated and tested using the proposed heat recovery method. Maximum cooling capacity of 65 W and maximum water-water temperature lift of 4.2 K were measured separately from the prototype. Using the validated model, performance improvement potentials without manufacturing constraints in the prototype are investigated and discussed. The COP is 3.4 with the plastic insulation tube and tube-in-tube design, which can be further improved to 4.1 by optimizing the system operating parameters. A quantitative comparison is made for thermoelastic cooling and other not-in-kind cooling technologies in order to provide insights on its limitations, potential applications, and directions for future research. Though under current research status, the system efficiency is only 0.14 of Carnot efficiency, which is less than 0.21 for conventional VCC systems, the framework carried out in this dissertation shows a technically viable alternative cooling technology that may change the future of our lives.