Sodium rod-plate heat pipes: fabrication and charging procedures

Abstract Due to its compactness, reliability, long lifetime, and high heat transfer levels, the heat pipe-cooled micro reactor is an interesting alternative for power supply in space systems. In this context, liquid metal heat pipes are the most suitable option for heat removal from the core due to their high operation temperatures (800–1,400 K). A fellowship between the Brazilian Air Force and the Heat Pipe Laboratory (Florianópolis, Brazil) was formed to develop sodium heat pipes for space nuclear applications. A novel flat heat pipe geometry was proposed: rod-plate, a concept where the sharp corners formed between a plate and a rod are utilized as grooves for capillary pumping. The heat pipes were manufactured through diffusion bonding and charged with sodium using an in-house developed setup. Two devices with 500 mm × 60 mm × 12 mm dimensions and different cross-section geometries and filling ratios were tested with different inclination angles and heat load levels. An induction furnace was utilized for evaporator heating, while the condenser remained exposed to the environment. In the experiments, a minimal thermal resistance of 0.023 K/W (45° and 90° tilt angles) and maximum heat flux of 12 W/cm 2 (0° and 5° tilt angles) were obtained.