A Multi-Environment Thermal Control System With Freeze-Tolerant Radiator

Abstract

Future space exploration missions require advanced thermal control systems (TCS) to dissipate heat from spacecraft, rovers, or habitats operating in environments that can vary from extremely hot to extremely cold. A lightweight, reliable TCS is being developed to effectively control cabin and equipment temperatures under widely varying heat loads and ambient temperatures. The system uses freeze-tolerant radiators, which eliminate the need for a secondary circulation loop or heat pipe systems. Each radiator has a self-regulating variable thermal conductance to its ambient environment. The TCS uses a nontoxic, waterbased working fluid that is compatible with existing lightweight aluminum heat exchangers. The TCS is lightweight, compact, and requires very little pumping power. The critical characteristics of the core enabling technologies were demonstrated. Functional testing with condenser tubes demonstrated the key operating characteristics required for a reliable, freeze-tolerant TCS, namely (1) self-regulating thermal conductance with short transient responses to varying thermal loads, (2) repeatable performance through freeze-thaw cycles, and (3) fast start-up from a fully frozen state. Preliminary coolant tests demonstrated that the corrosion inhibitor in the water-based coolant can reduce the corrosion rate on aluminum by an order of magnitude. Performance comparison with state-of-the-art designs shows significant mass and power saving benefits of this technology.

Physical mechanisms for delaying condensation freezing on grooved and sintered wicking surfaces

“…The sintered wick's surface could not propagate solely by ice bridging due to its topography, but also employed stochastic freezing and cascade freezing, which prompted more varied freezing times and an average of 10.9 minutes with average droplet diameters of 97.4 ± 32.9 µm at freezing. The topography of the wicked surfaces influenced the location of droplet nucleation and, therefore, the ability for droplet-to-droplet interaction during the freezing process.Heat pipes are a critical component in heat management systems, from laptops [1] to spacecraft [2]; the usefulness of heat pipes comes from their ability to passively transfer heat without additional equipment [1,[3][4][5][6]. For space applications, heat pipes can be exposed to the freezing temperatures of spaceresulting in the solidification of the working fluid [6, 7], thereby reducing or preventing function [6, 8], decreasing performance [9], or damaging the wick [7,9].…”

“…Heat pipes are a critical component in heat management systems, from laptops [1] to spacecraft [2]; the usefulness of heat pipes comes from their ability to passively transfer heat without additional equipment [1,[3][4][5][6]. For space applications, heat pipes can be exposed to the freezing temperatures of spaceresulting in the solidification of the working fluid [6, 7], thereby reducing or preventing function [6, 8], decreasing performance [9], or damaging the wick [7,9].…”