Design and development of a shape memory alloy activated heat pipe-based thermal switch

Abstract

This work reports on the design, fabrication and testing of a thermal switch wherein the open and closed states were actuated by shape memory alloy (SMA) elements while heat was transferred by a two-phase heat pipe. The motivation for such a switch comes from NASA’s need for thermal management in advanced spaceport applications associated with future lunar and Mars missions. As the temperature can approximately vary between −233 and 127 ° C during lunar day/night cycles, the switch was designed to reject heat from a cryogen tank into space during the night cycle while providing thermal isolation during the day cycle. A Ni47.1Ti49.6Fe3.3 (at.%) alloy that exhibited a reversible phase transformation between a trigonal R-phase and a cubic austenite phase was used as the sensing and actuating elements. Thermomechanical actuation, accomplished through an antagonistic spring system, resulted in strokes up to 7 mm against bias forces of up to 45 N. The actuation system was tested for more than thirty cycles, equivalent to one year of operation. The thermal performance, accomplished via a variable length, closed two-phase heat pipe, was evaluated, resulting in heat transfer rates of 13 W using pentane and 10 W using R-134a as working fluids. Experimental data were also compared to theoretical predictions where possible. Direct comparisons between different design approaches of SMA helical actuators, highlighting the effects of the helix angle, were carried out to give a layout of more accurate design methodologies.

Thermal diodes, regulators, and switches: Physical mechanisms and potential applications

“…Shape memory alloys: SMAs are promising thermal regulators due to the large mechanical deformation induced when the SMA is heated above the solid-solid phase transition. Benafan et al 108 used SMA springs to create a thermosiphon-based regulator with r ¼ 4, and SMA springs have also been used to regulate fluid flowrate and control the convective heat transfer. 109 SMAs have been combined with bimetallic strips in a thermal diode demonstration.…”

Fluidic and Mechanical Thermal Control Devices

“…Such thermal regulators make use of the thermal expansion of different materials [ 234–236 ] (Section 3.2.1.) or the phase transition in SMAs [ 237–239 ] (Section 3.2.2.). In these thermal regulators, the thermal resistance changes drastically at around the critical temperature of the material used.…”

“…Further, reported characteristic times are of the order of several minutes. [ 239 ] The characteristic time shows hysteresis between the on/off and off/on processes; for example, characteristic times of 45 and 18 min, respectively, were reported for a cryogenic device. [ 234 ]…”

A Comparative Study of Ni49.9Ti50.1 and Ni50.3Ti29.7Hf20 Tube Actuators

“…(b) The Ni 49.9 Ti 50.1 tube was able to produce more axial and angular actuation with less energy input (i.e., using less mechanical force and lower upper cycle temperature) than its Ni 50. 3 Fig. 7d and 8d versus the results of Fig.…”

“…This is mainly attributed to their high energy density which offers more efficient actuation, providing high strokes with desirable features of reduced weight, size, and complexity (Ref [1][2][3][4].…”