O. Benafan, R. Vaidyanathan, University of Central Florida, Orlando, FL; W. Notardonato, NASA, Kennedy Space Center, FL; B. J. Meneghelli, ASRC Aerospace Corporation, Titusville, FL
Advanced thermal management technologies for both ground and space-based aerospace applications place size, weight and power restrictions on design. This works reports on the design, fabrication and testing of a variable length heat pipe thermal switch that utilizes shape memory NiTiFe helical springs as the actuating elements. The switch is designed with the objective of providing on demand heat transfer to cool a liquid oxygen tank maintained at 92 K while the temperature of the surrounding space environment on the moon varies between 40 K to 400 K. During thermal contact, heat is rejected via a closed cycle boiling, evaporation and condensation process in a variable length, two-phase heat pipe with pentane and R-134a as working fluids. Such a switch eliminates complexity when compared to state-of-the-art competing systems while being amenable to implementation in spaceport technologies that have cryogenic liquefaction, densification and zero boil-off needs. A Ni47.1Ti49.6Fe3.3 alloy was used that exhibits phase transformations between a cubic and a trigonal R-phase in order to benefit from dimensional stability, low hysteresis and improved fatigue life typical associated with such R-phase transformations. In order to compensate for the low (approx. 1 %) transformation strain, the alloy was fabricated into helical springs. Key aspects associated with the design of NiTiFe springs are presented along with detailed comparisons involving theoretical, finite element and experimental approaches. An instrumented vacuum bell jar with controlled liquid nitrogen flow and heaters was used to test the switch while measuring test variables such as load, temperature and displacement. Actuation and thermal performance parameters are measured, quantified and reported along with analytical and theoretical predictions. Financial support from NASA KSC (NAS10-03006) is gratefully acknowledged.
Summary: Advanced thermal management technologies for both ground and space-based aerospace applications place size, weight and power restrictions on design. This works reports on the design, fabrication and testing of a variable length heat pipe thermal switch that utilizes shape memory NiTiFe helical springs as the actuating elements. The switch is designed with the objective of providing on demand heat transfer to cool a liquid oxygen tank maintained at 92 K while the temperature of the surrounding space environment on the moon varies between 40 K to 400 K. During thermal contact, heat is rejected via a closed cycle boiling, evaporation and condensation process in a variable length, two-phase heat pipe with pentane and R-134a as working fluids. Such a switch eliminates complexity when compared to state-of-the-art competing systems while being amenable to implementation in spaceport technologies that have cryogenic liquefaction, densification and zero boil-off needs. A Ni47.1Ti49.6Fe3.3 alloy was used that exhibits phase transformations between a cubic and a trigonal R-phase in order to benefit from dimensional stability, low hysteresis and improved fatigue life typical associated with such R-phase transformations. In order to compensate for the low (approx. 1 %) transformation strain, the alloy was fabricated into helical springs. Key aspects associated with the design of NiTiFe springs are presented along with detailed comparisons involving theoretical, finite element and experimental approaches. An instrumented vacuum bell jar with controlled liquid nitrogen flow and heaters was used to test the switch while measuring test variables such as load, temperature and displacement. Actuation and thermal performance parameters are measured, quantified and reported along with analytical and theoretical predictions. Financial support from NASA KSC (NAS10-03006) is gratefully acknowledged.
