Session: 04-09: SMA Enabled Smart Structures

Paper Number: 110889

110889 - Systematic Thermo-Mechanical Validation of Numerous Tensile-Loaded NiTi Wire Bundles Used for Elastocaloric Heating and Cooling 

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 [6]. 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. 

To guide the development of an optimized device with specific performance and efficiency requirements, a simulation framework describing the fully coupled thermo-mechanical behavior of the EC cooling unit has been developed [7]. This framework, implemented in MATLAB, accounts for all the device’s interacting sub-units: mechanical kinematic model, SMA bundle model, as well as the heat exchange and transfer in the fluid [8], [9].

The first experiments show a strong dependency between the fluid flow rate and the resulting temperature [10], which correlates to the simulations [8].

Recently, the existing demonstrator has been equipped with a temperature measurement system consisting of 62 micro PT-100 sensors with a low time constant to monitor the temperature development in the heat transfer unit. In addition, the mechanical part is extended with a torque sensor to measure the dynamic torque and enables the analysis of the loading and unloading force of the bundles. In combination with the existing air flow measurement system, the calculation of the system COP is possible. 

This work presents the needed mechanical power input and themal power output with the temperature evolution for different air flow rates and rotation frequencies: Resulting in different thermal power output up to 80 W and mechanical power input down to 15 W by using conventional available superelastic NiTi wires.

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]       F. Welsch et al., “Continuous Operating Elastocaloric Heating and Cooling Device: Model-Based Parameter Study With Airflow Losses,” 2019, DOI:10.1115/SMASIS2019-5636.

[9]       F. Welsch et al., “System Simulation of an Elastocaloric Heating and Cooling Device Based on SMA,” 2020, DOI:10.1115/SMASIS20-2262.

[10]     S.-M. Kirsch et al., “Continuous operating elastocaloric heating and cooling device: Air flow investigation and experimental parameter study,” 2019, DOI:10.1115/SMASIS2019-5633.

Presenting Author: Susanne-Marie Kirsch Center for Mechatronics and Automation Technology

Presenting Author Biography: Susanne-Marie Kirsch studied Mechatronics at Saarland University and received her Master of Science in 2015 with a thesis on conception, design and construction of a testing unit for determination of the dynamic long-term behavior of plastics. Since her degree, she has been working as a Ph.D. student at Saarland University, in the lab for measurement technology and the intelligent material systems lab. Within the DFG priority program Ferroic Cooling, she continues her experience of engineering in developing an elastocaloric cooling device and measurement systems. 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.