Session: 04-09: SMA Enabled Smart Structures

Paper Number: 111395

111395 - Investigation of the Thermal Heat Exchange Between NiTi-Wire Bundles and Airflow for Different Wire Arrangements 

Nickel-Titanium (NiTi)-based shape memory alloys (SMAs) enable new sustainable and environmentally friendly solid-state heating and cooling technologies. Elastocaloric (EC) heat pump systems exploit superelastic SMAs as a non-volatile, inflammable, and non-global-warming refrigerant, in contrast to the well-established vapor compression technology [1], [2]. The high specific latent heat released or absorbed during mechanical loading or unloading of the SMA material leads to a high temperature change in the material. As a result of the small required work input to induce the phase transformation, a high coefficient of performance (COP) can be achieved by this technology [3]. The potential of these alloys can be exploited through an adequate thermodynamic cycle, efficient mechanical system design, and choice of suited EC materials [4].

In the last few years, a continuously operating EC fluid heat pump system based on SMAs has been developed [5]. This device consists of a fluid heat exchange system and an integrated loading unit to elongate the numerous SMA wire bundles. The versatile design enables independent modification of the process parameters such as type of SMA material, load profile, rotation frequency, fluid duct geometry, flow direction, inlet temperature, and flow rate, which can be optimized by a system simulation tool [7]. 

Recently, the air-cooling behavior of single wires has been analyzed, and intensive parameter studies on different wire diameters and airflow rates have been performed [8]. Also, the bundle arrangement influences the air temperature changes ΔTair as well as the achievable cooling power. These results show that the influence of the wire bundle on ΔTair differs from the single wire, indicated by a worse heat transfer from the wire bundle to air similar to a wire with a larger diameter, which is presumably caused by the mutual interaction of the wires [6]. 

For optimizing the heat transfer using bundles, the influence of different angles of attack between the wire arrangement and the airflow is investigated in this work.

For this purpose, the temperature development in the bundle and the possible effects on the thermal performance are presented.

Literature

[1]       S. Fähler et al., “Caloric Effects in Ferroic Materials: New Concepts for Cooling,” 2012, DOI:10.1002/adem.201100178.

[2]       W. Goetzler et al., “Energy Savings Potential and RD&D Opportunities for Non-Vapor-Compression HVAC Technologies,” 2014, DOI:10.2172/1220817.

[3]       Y. Wu et al., “Elastocaloric cooling capacity of shape memory alloys – Role of deformation temperatures, mechanical cycling, stress hysteresis and inhomogeneity of transformation,” 2017, DOI:10.1016/j.actamat.2017.06.012.

[4]       M. Schmidt et al., “Elastocaloric cooling: From fundamental thermodynamics to solid state air conditioning,” 2016, DOI:10.1080/23744731.2016.1186423.

[5]       S.-M. Kirsch et al., “NiTi-Based Elastocaloric Cooling on the Macroscale: From Basic Concepts to Realization,” 2018, DOI:10.1002/ente.201800152.

[6]       N. Michaelis et al., “Investigation of Elastocaloric Air Cooling potential based on Superelastic SMA wire bundles,” 2020, DOI:10.1115/SMASIS2020-2404.

[7]       F. Welsch et al., “Elastocaloric cooling: System design, simulation, and realization,” 2018, DOI:10.1115/SMASIS2018-7982.

[8]       N. Michaelis et al., “Experimental parameter identification for elastocaloric air cooling,” 2019, DOI:10.1016/j.ijrefrig.2019.01.006.

Presenting Author: Felix Welsch Center for Mechatronics and Automation Technology

Presenting Author Biography: Felix Welsch studied Mechatronics at Saarland University and finished his Master of Science in 2015 with a thesis on the development of a test method for determining biaxial material properties of plastics. Currently he is working as a research assistant at Saarland University in the intelligent material systems lab. Within the DFG priority program Ferroic Cooling, he continues his experience of engineering in modelling and developing an elastocaloric cooling device. Furthermore, the development of scientific test stands especially for smart actuators, as well as solutions based development on SMAs is part of his research work.