The availability of efficient heat switches, which facilitate the dissipation of heat to the environment at high temperatures (>15 c) and prevent heat exchange at low temperatures (6 w/k and an off…

This is a $600,000 grant awarded by the National Aeronautics and Space Administration (NASA) to The Washington University in St. Louis to design, fabricate, and characterize a passive, temperature-actuated liquid metal heat switch. The heat switch is intended to facilitate the dissipation of heat at high temperatures and prevent heat exchange at low temperatures, with a targeted on/off conductance ratio of over 500:1. The proposed innovation builds on the university's expertise in thermal management, phase change materials, and droplet dynamics. It has the potential to enable flexible thermal control systems for manned and unmanned lunar and deep space exploration missions. This grant does not have a small business or socioeconomic set-aside designation, as The Washington University is a large private research institution.

The availability of efficient heat switches, which facilitate the dissipation of heat to the environment at high temperatures (>15 c) and prevent heat exchange at low temperatures (6 w/k and an off conductance ~ 1 MW/k. Furthermore, the switch is compact, light-weight, and is passively temperature-actuated. Supported by preliminary results, which yielded a conductance ratio of 72:1, we propose to design, fabricate, and characterize a robust heat switch based on room-temperature liquid metal. The proposed heat switch will be based on the manipulation of a liquid metal within a 9 CM long, 4 CM wide, and 1 MM tall channel. The presence or the absence of the liquid metal near a heat source affects heat flow from the source to the sink by a factor of 500 or more. Gallium-based alloys have the highest thermal conductivities of all liquids (17-40 w/m-k VS. 0.02 (air) to 0.6 (water) w/m-k), and allow for easy manipulation, are thermally and chemically stable, and adapt easily to different topologies. The switch will be passively controlled based on thermal expansion mismatch. At high temperatures, i.e., in the on state, the metal will be in its liquid state and connect the heat source to the heat sink. At low temperatures, i.e., in the off state, the metal will disconnect the inner components of the vehicle with the shell and solidify in the off position. The switch will enable control of heat flows over multiple time scales and different levels of heat load. Our passive liquid metal heat switch not only uniquely meets all of the criteria described in the NASA research announcement, but IT also potentially allows the integration into flexible thermal management systems. To successfully achieve the targeted performance goals (500+ : 1 switching ratio,>3 w/k on conductance), we build upon the PI s expertise in the thermal management of high-power electronics, phase change heat transfer, and droplet wetting dynamics. To evaluate the progress of the proposed effort, we define the following milestones: year 1 will focus on the thermo-chemical characterization of the liquid mental and thermal prototype design, fabrication, analysis, and optimization. Year 2 will focus on the development and characterization of the actuation mechanism for on/off switching and durability testing. Finally, year 3 will explore the integration of the heat switch with flexible materials. We envision that this project will unlock fundamental design guidelines for the fabrication of thermal switches, capacitors and rectifiers (diodes). As the only heat switch to satisfy all of the required and desired features of passive tunable thermal management systems, this proposed switch will be uniquely applicable to manned and UN-manned lunar and deepspace explorations, and could therefore serve as a disruptive advance in the tunable thermal management of spacecraft systems.