Performance evaluation of lattice-based wicking structures and surface roughness reduction in additively manufactured heat pipes

Hughes, Llywelyn ORCID: https://orcid.org/0000-0003-4007-340X 2024. Performance evaluation of lattice-based wicking structures and surface roughness reduction in additively manufactured heat pipes. PhD Thesis, Cardiff University. Item availability restricted.

Preview	PDF (Thesis) - Accepted Post-Print Version Download (23MB) | Preview
	PDF (Cardiff University Electronic Publication Form) Restricted to Repository staff only Download (341kB)

Abstract

This thesis investigates the integration of Additive Manufacturing (AM) and heat pipe technologies. Reducing energy demand throughout the entire economy is key to cutting our dependency on fossil fuels and combating the effects of climate change. As passive thermal transfer devices, heat pipes present an opportunity to reduce system complexity and parasitic losses as well as overall system volume and mass. With the development and identified applications of AM increasing globally, an opportunity arises to integrate AM into heat pipe technologies, contributing to the benefits of Industry 4.0. This integration has several advantages including improved system integration, reduced heat transfer interface resistances and enhanced manufacturability of novel and innovative wicking structures which may otherwise be impossible to create. However, whilst AM’s potential is undeniable, challenges such as the inherently high surface roughness, dimensional accuracy at micro-scale level and achievable pore dimensions may influence overall performance as characterised throughout this thesis. A range of Body-Centred Cubic AlSi10Mg lattice structures ranging in cell sizes and strut thicknesses down to 0.70mm and 0.15mm, respectively, were manufactured in both horizontal and vertical orientations to push the boundaries of Laser Powder Bed Fusion with commercially available feedstock. The samples underwent rigorous testing to characterise their geometric accuracy with the use of 3D profilometry, standard microscopy, SEM, μXCT and a newly developed Lattice Analysis Tool (LAT). Further experiments were conducted and benchmarked against other literature-based AM and conventional wicking structures to determine their capillary performance and permeability; two key heat pipe performance indicators. The vertical samples were overall found to be superior to the horizontally printed equivalents with sample V12 showing most promising results indicating an optimal capillary performance of 0.782μm and a Darcyan permeability of 2.16x10-9 m2. Chemical polishing of the AlSi10Mg lattice samples was undertaken for the first time to investigate the effects of reducing surface roughness on the fluidic performance of the wicking structures. Results found the complete removal of agglomerated particles and a 60% reduction in surface roughness, 36.8% increase in capillary performance and a 130% increase in permeability. The identified delay in the onset of the Forchheimer regime, together with ii the improvements in capillary performance, shows the potential of chemical polishing in allowing for extended operating flows, thermal loads and heat pipe lengths increasing their scope of applications. The advantages and limitations of the AM wicking structures identified in this research make them particularly suited for applications working with gravity (as opposed to against gravity with condenser below evaporator) or in zero gravity environments such as spacecraft technology in addition to other high value sectors. This study highlights the potential of AM wicking structures for heat pipe applications and their performance enhancement through post-processing offering significant prospects for future developments.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Engineering
Uncontrolled Keywords:	1). Additive Manufacturing 2). Heat Pipes 3). Chemical Polishing 4). Surface Roughness 5). Capillary pressure 6). Permeability
Date of First Compliant Deposit:	7 March 2025
Last Modified:	07 Mar 2025 15:33
URI:	https://orca.cardiff.ac.uk/id/eprint/176705

Actions (repository staff only)

Edit Item