Solid state refrigeration processes, such as magnetocaloric and electrocaloric refrigeration, have recently shown to be a promising alternative to conventional compression refrigeration. A new solid state elastocaloric refrigeration process using the latent heats within Shape Memory Alloys (SMA) could also hold potential in this field. This work investigates the elastocaloric effects in Ni-Ti-based superelastic Shape Memory Alloy (SMA) systems for use in an elastocaloric cooling processes. Ni-Ti alloys exhibits large latent heats and a small mechanical hysteresis, which may potentially lead to the development of an efficient environmentally friendly solid-state cooling system, without the need for ozone-depleting refrigerants. A systematic investigation of the SMA is conducted using a novel custom-built scientific testing platform specifically designed to measure cooling process related phenomena. This testing system is capable of performing tensile tests at high rates as well as measuring and controlling the solid-state heat transfer between SMA and heat source/heat sink.
Tests are conducted following a cooling process related training cycle where the material has achieved stabilized behavior. First, a characterization of the elastocaloric material properties is performed followed by an investigation of the material under cooling process conditions.
A comprehensive monitoring of the mechanical and thermal parameters enables the observation of temperature changes during mechanical cycling of the SMA at high strain rates. These observations can be used to study the rate dependent efficiency of the elastocaloric material.
The measurement of the temperature of both the heat source/heat sink and the SMA itself, as well as the required mechanical work during a running cooling process, reveals the influence of the operating conditions on the elastocaloric effect of the material.
Furthermore investigations of the process efficiency at different thermal boundary conditions (temperature of heat source/heat sink), indicates that the process is dependent on the boundary conditions which have to be controlled in order to optimize the efficiency.