KIT demonstrates heat-driven solid-state cooling prototype
South Korea – Researchers at Karlsruhe Institute of Technology (KIT) and the University of Tsukuba have demonstrated a miniature solid-state cooling system in which heat provides the mechanical force needed to drive elastocaloric cooling.
Using an external heat source at 130°C, the prototype produced a device-level temperature span of 2.2 K and specific cooling power of 3.3 W/g. The work points to a possible future route for using waste heat or solar thermal energy to reduce the electrical input required for some cooling applications.
Heat drives elastocaloric cooling
Elastocaloric cooling exploits temperature changes in shape-memory alloys as they are mechanically loaded and unloaded. The KIT-led system couples two ultra-thin metallic films: a titanium-nickel actuator film converts heat into mechanical movement, which then loads and unloads a titanium-nickel-iron film to produce the cooling effect.
The crucial innovation is that we combine two complementary functions of shape memory alloys, with one film converting heat into mechanical work and the other film converting this work into cold
Dr Jingyuan Xu, Karlsruhe Institute of Technology
When the actuator was electrically heated to 86°C, the device achieved a temperature span of 4.0 K and specific cooling power of 4.4 W/g.
In a separate configuration using an external solid heat source at 130°C, it achieved a 2.2 K temperature span and 3.32 W/g specific cooling power. The externally heated prototype delivered around 2.09 mW of absolute cooling power at zero temperature lift, illustrating the miniature scale of the current system.
Potential to reduce electrical demand
The significance of the external-heat experiment is that thermal energy replaced the main electrically driven actuation step. This raises the prospect of future systems using waste heat or solar thermal energy to provide part of the energy needed for cooling.
The laboratory apparatus still used electrically powered components to move the heat-source and heat-sink elements, meaning the prototype was not completely electricity-independent. The researchers describe the approach as a route towards “electricity-minimised” cooling.
Scaling remains the challenge
KIT says the researchers are investigating the use of multiple films in parallel to increase cooling capacity. Potential applications identified by the team include processor cooling using locally available waste heat and thermal management of vehicle electronics.
Heat distribution, thermal resistance, actuator synchronisation and uniform loading are among the issues that will need to be addressed as the technology is scaled.
For the HVAC sector, the research is an early indication of how thermal energy could be used to drive solid-state cooling. Whether the concept can ultimately deliver practical cooling capacities, useful temperature lifts and competitive system efficiency remains to be demonstrated.
