Critical Review on Mechanical Heat Switches for Space Applications

Abstract

Thermal switches are typically used to regulate the heat flow between two surfaces. They are broadly categorized as mechanical, gas-gap, superconducting, and magneto-resistive heat switches. Out of these, the mechanical heat switch (MHS) can be used in a wide temperature range of 0.1 K – 400 K. Moreover, the other features of MHS, such as cost-effectiveness, different actuation methods, flexibility in design, and broad applicability, made it a suitable choice over a wide range of cryogenic to room temperature applications. Based on different actuation methods, the MHS can be further subclassified in piezoelectric actuated (PZA), paraffin wax (PFW), differential thermal expansion (DTE), and shape memory alloy (SMA) type of heat switches. This work presents a broad overview of different kinds of mechanical heat switches (MHS) and compares their performances and physical parameters. The switching ratio, mode of actuation, overall size to weight ratio, the initial gap between the two plates, contact forces, and time of actuation are all key elements in the selection and design of thermal switches. Moreover, the present review also discusses the working principle of different MHS, their advantages/disadvantages, and significant design parameters as per their applicability in various engineering and space applications. The study suggests that the DTE type MHS can enforce approximately 30 times extra contact force compared to the rest of the MHS. The high- er contact leads to lower thermal contact resistance and a higher switching ratio of DTE compared to other MHS. Moreover, the higher working range (0.1 K –100 K) made it suitable for space applications.