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Radiator stagnation is being explored to design single loop thermal control systems using Galden HT170 for heat rejection systems requiring large turn-down ratios. A previous Small Business Innovation Research (SBIR) Phase 1 studied sequential stagnation in a system of different length tubing. As part of a follow-on Phase 2, tests were performed to study the effects of adding a facesheet in a manner consistent with typical spacecraft radiator effectiveness. Onset of stagnation for different tubes was demonstrated for a given inlet temperature by lowering mass flow rate. Temperature and/or mass flow rate were increased to investigate stagnation recovery. A Thermal Desktop® model was built to simulate the test. Test results and modeling comparisons are presented.

Paragon Space Development Corporation is developing a single-loop, non-toxic, active pumped thermal control design for robust, reliable operation near stagnation regimes as experienced in low power/cold environments. This research uses a safe fluid named Galden® HT170, manufactured by Solvay Solexis that has lower temperature stalling characteristics over typical space-based radiator fluids such as propylene glycol/water (PGW). A test bed and stagnation test article were designed, built and then modeled using Thermal Desktop® software to explore tube stagnation using Galden. Tube stagnation was sequentially controlled in each tube in a predictable manner, while collecting data to validate models. The data compared well to the modeling results. Fluid-compatibility results also showed no degradation to the fluid or to the aluminum tubing and weld materials and structures