Experiments on a Loop Heat Pipe with a 3D Printed Evaporator

The construction and testing of a loop heat pipe with a 3D printed evaporator is described in this paper. The system was developed as part of a larger engineering demonstration unit for thermal management on NASA's Volatiles Investigating Polar Exploration Rover. A state-of-the-art 3D printed evaporator, developed in a previous effort, was used in the current system. This evaporator had a cylindrical geometry with a length of 0.1 m and a diameter of 0.025 m and featured a primary wick with a bubble point pore radius of under 8 µm. The vapor, condenser, and liquid lines were constructed from 0.003 m diameter tubing and routed to conform to the geometry of the rover. A thermal control valve was also incorporated in the loop heat pipe to force the vapor to bypass the condenser at a lower-than-threshold temperature. The loop heat pipe was tested successfully under a range of thermal loads of up to 70 W against a mission-expected load of 50 W. Due to startup difficulties observed at the low condenser temperatures, a series of dedicated startup tests were conducted to identify the underlying causes and to study the effects of major variables, such as the heat location and charge quantity. Based on this analysis, a number of changes were identified to help improve the startup performance of the system.