Variable View Factor Two-Phase Radiator

The proposed program will develop a novel Vapor-Pressure-Driven Variable-View-Factor Radiator that is deployable, operates with variable geometry (i.e., form factor) and offers high turndown ratio. The device utilizes two-phase heat transfer and novel geometric features that adaptively (and reversibly) adjust the view factor in response to internal pressure in the radiator. The radiator folds into a closed shape to minimize the view factor when cold, and opens up to maximize the view factor when heated. Prototypes demonstrated in Phase I prove the feasibility and highlight the advantages of a two-phase radiator over shape memory alloy technologies.nbsp; Structural and thermal simulation studies confirmed the viability of the concept.At low temperatures, the view factor of emissive surfaces of the radiator to the heat sink is near zero, so the only heat lost is that which is emitted from the insulated outer surfaces of the radiator. The flexible section of the radiator is an elastic envelope enclosing a saturated working fluid. When the temperature of the radiator increases, the corresponding increase in vapor pressure generates a net force on the interior walls of the envelope which causes the elastic walls to bend so that the structure opens and the view factor increases. The increase in view factor reduces thermal resistance of heat rejection which enables inherently passive thermal control. Additionally, the entire structure of the radiator consists of cavities filled with saturated fluid acting like heat pipes, so the radiating surface will be nearly isothermal, achieving a radiator panel efficiency near one. In Phase I, modeling and prototyping indicates that the baseline geometry proposed can achieve a thermal turndown ratio of 37:1.