Dissertation Defense – David Catalini
DEVELOPMENT OF COOLING SYSTEMS WITH ACTIVE ELASTOCALORIC REGENERATORS
Date/Time: Tuesday, December 15th of 2020, 3:30 PM EST
List of committee members
- Professor Reinhard Radermacher, Chair
- Professor Ichiro Takeuchi
- Professor Yunho Hwang
- Professor Olivier Bauchau
- Professor Marino di Marzo
- Professor Bao Yang
- Chun-cheng Piao, Ph.D.
Zoom or Webex Link: https://umd.zoom.us/s/98205535196
Abstract: The vapor compression cycle (VCC) has been developed and optimized over a century to provide cooling in buildings (residential and commercial) and vehicles. However, its usage has resulted in unpredicted environmental damage such as depleting the ozone layer and promoting global warming when the refrigerant fluid leaks into the atmosphere. Because of this, it is important to develop a superior technological alternative without the environmental costs. One way to tackle this problem is to develop heat pumping cycles using solid-state refrigerants: a solid is incapable of leaking into the atmosphere. Yet, a solid-refrigerant cannot flow to deliver cooling the same way a refrigerant-fluid does. This required a system conceptual redesign, which started with near-room temperature cooling with magnetocaloric materials in 1976 and elastocaloric materials in 2012.
The ability of the cooling system to pump heat across a large temperature span is called the “temperature lift”. The amount of heat the system can absorb while maintaining that temperature lift is called the “cooling capacity”. An effective way to develop these technical capabilities is first to achieve a large temperature lift and second to increase cooling capacity to match the requirements.
In his work four different system configurations were studied with the following objectives: maximizing the temperature lift of the system and measuring the cooling capacity. During the process, new challenges were identified and addressed. The first configuration was based on the thermal-wave heat recovery strategy, while the other three were a 1-stage, 2-stage and reciprocating variants of the active regeneration cycle.
From the studied configurations the thermal-wave-based cycle achieved a low temperature lift of 8K, at large average strain of 4.5%, and the largest cooling capacity of 120W. Active regeneration-based cycles achieved the largest temperature lift of 21.3K, at a low average strain of 3.5%, but a low cooling capacity of between 16 and 25W. This dissertation shows there is a fundamental limitation in active regeneration cycles applied to single composition elastocaloric materials that limits the maximum applicable average strain, which in turn affects the cooling capacity. Different alternatives to address this issue, as well as suggestions to improve the overall thermal and structural performance of the system are reviewed.