Elastocaloric Cooling on the Miniature Scale: A Review on Materials and Device Engineering

Abstract

This Review covers the fundamentals of operation and scaling of elastocaloric cooling devices as well as current developments of elastocaloric shape‐memory alloy (SMA) films and the engineering of SMA film‐based cooling devices. Sputter‐deposited TiNiCuCo alloys showing ultra‐low fatigue enable unique functional properties such as tailored transformation temperature gradients. Two substantially different concepts for the development of elastocaloric cooling demonstrators are discussed. One concept relies on heat transfer by mechanical contact between the elastocaloric SMA film and solid heat sink and source elements. The second concept makes use of the heat transfer between the elastocaloric SMA film and a heat transfer fluid, including the advanced technology of active regeneration. Demonstrators based on a single SMA film reach device temperature spans of 14 K and a high specific cooling power of up to 18 W g−1. The performance characteristics are compared with other solid‐state caloric cooling technologies.

Future prospects for elastocaloric devices

“…Major challenges to commercialization are currently being addressed by researchers across a range of disciplines. The temperature span of systems is increasing through development of new system configurations [21] and new materials [14]. The fatigue life of the refrigerant is being addressed through ultralow fatigue materials [16] and through operating in compression [34].…”

“…Systems can be built from single ribbons or a cascade of ribbons to increase the overall system temperature span. These 'one shot' demonstrators have been reported in several configurations and with several NiTi based alloys [19,20] and are discussed in more detail in [21]. These systems use a solid eCM refrigerant that directly cools a small thermal reservoir, usually in the form of a metal block.…”

“…These areas are the most important if the technology is to realize the energy savings predicted by the DOE [9] and to make a serious reduction in energy consumption. EC has been suggested for miniature scale applications [21] and cryogenic applications may also pose opportunities for energy savings [30], but those are not discussed here. In order to enter the space cooling market an idealized temperature span for the elastocaloric cooler is from 10°C to 35°C [4] and for refrigeration the span can be considered from −10°C to 30°C [31], although the actual numbers can vary significantly based on application and geography.…”

“…If we consider a 20 000 h lifetime operating at 1 Hz, the required lifetime will be 72 000 000 cycles. In operation as an EC, eCE lifetimes on the order of hundreds of cycles [21] to between 5000 and 6000 cycles [25] have been reported for materials in tension. Perhaps the most promising path to achieving a useful fatigue life is by operating the material in compression rather than tension, and it has been shown that a range of eCMs show high eCE in compression along with potentially much higher fatigue life [34].…”

Energy Applications of Magnetocaloric Materials

“…Several researchers have concluded that caloric (ferroic) refrigeration and heat‐pumping technologies, which are still in the research and development phase, are the most important option for the future . These solid‐state technologies variously utilize magnetocaloric, electrocaloric, and mechanocaloric effects. A material that exhibits more than one of these effects is described as a multicaloric (multiferroic) material with multicaloric effects .…”