As an eco-friendly alternative, elastocaloric cooling promises to become an alternative to the prevalent vapor compression-based process. The main advantage of the elastocaloric cooling process consists in avoiding ozone exhausting cooling media. Moreover, large latent heats and a small required work input during the application of elastocaloric materials (mostly Ni-Ti based shape memory alloys - SMAs) result in an efficient cooling process so that it is rated as the most efficient and therefore promising future air conditioning method by the US Department of Energy \[1\]. The latent heats of the material become accessible under tensile loading and unloading of the sample. Adiabatic loading at a high strain rate leads to a phase transformation and a temperature increase of the material whereas fast unloading leads to a temperature decrease. This material behaviour is caused by the crystallographic phase transformation from austenite to martensite and vice versa. Based on these material properties, elastocaloric cooling processes can be implemented in SMA based cooling devices.

For the wire-based air cooling demonstrator developed by Kirsch et al. \[2\] bundles consisting of 30 wires each are used to achieve a relevant cooling power. So far, the air cooling behaviour of single wires has been analyzed and intensive parameter studies on different wire diameters and airflow rates has been performed \[3\]. Based on these experiments this work aims at analysing how the bundle arrangement influences the coherent air temperature ΔT as well as the achievable cooling power.

Therefore, a scientific test setup is developed, which offers the ability to determine the air cooling potential of elastocaloric wire bundles under varying conditions like wire arrangement, material composition, and process parameters. The test bench consists of an air duct to apply a flat airflow with a definable flow rate during loading and unloading, an infrared camera to determine the temperature distribution of the bundle and three temperature sensors spread over the width of the air duct which provide the air temperatures.

This contribution presents experimental results of the influence of different airflow rates and wire arrangements on the cooling behaviour of the wire bundle. In addition, the air conditioning performance of the wire bundle is compared to the performance achieved by the single SMA wires to estimate to what extent the bundle arrangement helps to improve the thermal power.

 

\[1\]         W. Goetzler, R. Zogg, J. Young, and C. Johnson, “Energy Savings Potential and RD & D Opportunities for Non- Vapor-Compression HVAC Technologies,” *US Dep. Energy*, no. March, p. 3673, 2014.

\[2\]         S.-M. Kirsch, F. Welsch, N. Michaelis, M. Schmidt, A. Schütze, and S. Seelecke, “Continuously Operating Elastocaloric Cooling Device based on Shape Memory Alloys: Development and Realization,” in *Thermag VIII*, 2018, no. 0039, pp. 238–243.

\[3\]         N. Michaelis, F. Welsch, S.-M. Kirsch, M. Schmidt, S. Seelecke, and A. Schütze, “Experimental parameter identification for elastocaloric air cooling,” *Int. J. Refrig.*, vol. 100, pp. 167–174, 2019.

 


Investigation of Elastocaloric Air Cooling Potential Based on Superelastic SMA Wire Bundles

Division / Sponsors: 
Aerospace Division

Paper Proceedings: https://asmedigitalcollection.asme.org/SMASIS/SMASIS2020/volume/84027

SMASIS2020 - Virtual Conference

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.