Modeling and Analysis of a Shape Memory Alloy-Based Adaptive Regulator for Thermal Management

The goal of this work is to develop and model an adaptive thermal management system formed by shape memory alloy (SMA) helical springs and stretchable selective emitters. Emitters are prepared by depositing a metallic layer on an elastomeric film (3M VHB 4910). Strain changes in the film induce alterations of the surface corrugation of the metallic layer, which enables adjustments of its emissivity spectrum. SMAs are materials that undergo moderate recoverable deformations driven by temperature changes. SMA springs are used here as adaptive deformation enablers (both as actuator and thermal sensor). The thermal management system is created by connecting stretchable emitters and SMA springs in series. When the temperature of the system is increased by sunlight irradiation, the SMA springs undergo contractions which elongate the stretchable emitters, flattening their corrugated metallic layer, thereby leading to an increase in their solar reflectivity and allowing radiative cooling. When the system temperature is decreased, the SMA springs relax and allow the emitters to recover their original surface corrugation, leading to an increase in their solar absorptivity and allowing radiative heating. This repeatable process allows the system to exhibit open-loop adaptive regulation of its temperature under varying solar irradiation. A reduced-order model of the system is derived to perform feasibility studies of the concept and results demonstrating the functionality of the system are presented.