Variable property fluids for dynamic environments

Often in developing a thermal control system for environment control and life support systems a heat transfer fluid is selected on the basis of compromises between its heat transfer characteristics, operating range, and safety, among other parameters. The resulting choice is often a mediocre fluid with less than ideal performance or a complicated multi-fluid system. This study seeks to establish the merit of a fluid system having dynamic fluid properties, and whether better performance can be had from a dynamic fluid. Specifically, this study considers a representative water-based solution as the working fluid in a system where fluid properties are adjusted in response to the thermal environment and identifies whether turn-down ratio for heat rejection can be improved. Spacecraft designed to meet current safety standards use a two-loop thermal control architecture. This project explores the merit of dynamic fluids as a technology to enable single loop architecture. A dynamic fluid is a solution or suspension where the composition is adjusted to tailor fluid properties throughout a mission to a spacecraft's environment. Often in developing a thermal control system for environment control and life support systems a heat transfer fluid is selected on the basis of compromises between its heat transfer characteristics, operating range, and safety, among other parameters. The resulting choice is often a mediocre fluid with less than ideal performance or a complicated multi-fluid system. This study seeks to establish the merit of a fluid system having dynamic fluid properties, and whether better performance can be had from a dynamic fluid. Specifically, this study considers a representative water-based solution as the working fluid in a system where fluid properties are adjusted in response to the thermal environment and identifies whether turn-down ratio for heat rejection can be improved. This study modeled a conventional single loop vehicle thermal control system with a dynamic fluid in one case and a static fluid in another. The dynamic fluid was modeled over a range of compositions where the static fluid contained a representative constant composition. The results of this model show up to a 17% improvement in turn-down with the selected fluid. This enhancement becomes single-loop enabling when employed in conjunction with variable heat rejection technology. Thermal desktop modeling of a simple vehicle thermal control system with freezable (also known as stagnating) radiator technology indicates that system turn-down can be improved significantly, approaching a 6:1 system turndown through to the lower freezing point of the dynamic fluid. More »