The Development of Additively Manufactured Heat Pipes

Reducing energy demand throughout the entire economy is a key aspect in cutting our dependency on fossil fuels and combating the effects of climate change. As a passive thermal transfer device, heat pipes have an opportunity to reduce system complexity, parasitic losses as well as overall system volume and mass. Several performance restrictions including viscous, sonic, entrainment, capillary and boiling limits are present. A clear opportunity is present for AM to reduce manufacturing lead times and improve heat pipe performance. Enhancing internal wick structure characteristics tailored to the local fluid properties while also eliminating the entrainment limit will be key benefits of AM designs. AM improves the manufacturability of novel biomimetic-based wick designs that may otherwise be impossible to manufacture through conventional techniques. An AM wick structure may be manufactured through altering the machine parameters to replicate the sintering process or utilising defined lattices.

This interdisciplinary research includes the design, manufacture and characterisation of additively manufactured octahedral micro-lattice structures. Structures have been evaluated based on their geometric accuracy, surface roughness and porosity in addition to their permeability and capillary performance. A novel Lattice Analysis Tool (LAT) has been developed to efficiently analyse the pore characteristics of the structures and micro-XCT has also been employed to analyse their internal features. Capillary performance has been determined through a capillary rate-of-rise experiment with thermography equipment to detect the rise front. The forced fluid flow experiment has been conducted to measure the pressure drop through the lattice structures which feed into determining their permeability. Further trials will be undertaken to see the effects of chemical polishing to reduce internal pressure losses through the higher surface roughness that is often inherent with AM components.

The research conducted is prerequisites for the development of heat pipes. On completion, the results may be used to develop design tools for additively manufactured heat pipes in addition to developing methodologies to reduce internal pressure drops of lattice-based heat sinks and heat exchangers. Furthermore, LAT has been released as an opensource software under the GNU General Public License for all to use and further develop.