A Shape Memory Alloy Controlled Heat Pipe Based Thermal Switch

This work reports on the design, fabrication and testing of a low temperature shape memory alloy thermal switch for meeting NASA’s thermal management needs on the surface of the moon. The switch is designed to provide on demand heat transfer to cool a liquid oxygen tank while the temperature of the surrounding space environment varies from 40 K to 400 K on the lunar surface. NiTiFe shape memory helical actuators are the sensing and actuating elements in the switch. Heat transfer is accomplished via heat acquisition, transport and rejection in a variable length heat pipe with pentane and R-134a as working fluids. The approach used to design the shape memory elements, quantify the heat transfer at both ends of the heat pipe and the pressures and stresses associated with the actuation are outlined. Testing of the switch is accomplished in a vacuum bell jar with instrumentation feedthroughs, using valves to control the flow of liquid nitrogen and heaters to simulate the temperature changes. Various performance parameters are measured and reported under both transient and steady-state conditions.