Regenerator design for elastocaloric cooling system for military vehicles

Elastocaloric refrigeration based on shape memory alloys is a promising alternative to vapor-compression systems due to its potential high efficiency and environmentally benign character. It is an ideal candidate for air conditioning (A/C) of military vehicles that are exposed to threats where flammability of refrigerants is unacceptable to ensure the safety and survivability of warfighters. One major barrier to elastocaloric cooling is that the most widely available material, Nitinol, requires very high forces and large actuators to produce useful temperature changes needed for A/C applications. Our team developed an active regenerator concept based on thin Nitinol strips incorporated into a composite structure that is actuated by bending. This combination of bending structure and active material greatly reduces the forces and size of actuators needed for elastocaloric devices.

We present modeling and experimental results of an elastocaloric regenerator designed for a compact, high-power-density air conditioning system capable of replacing compressors and meeting safety requirements for military vehicles. The regenerator design is based on the previously developed low-force concept. The combined structure activates the Nitinol strips by stretching them due to bending. Two active Nitinol sections are loaded in opposing directions, with one increasing tension while the other reduces tension for a balanced structure. Evaluation of different passive structures, loading methods, Nitinol configurations, and material properties demonstrate how this approach can provide a feasible path to compact, efficient, and safe cooling systems.

This work was supported by the Department of Defense (MIPRHQ0642384973) through the U.S. Department of Energy under Contract No. DE-AC02-07CH11358.