Padrao, Daniel
(2024)
Thermofluid optimisation of additive manufacturing high heat flux components for fusion.
PhD thesis, University of Nottingham.
Abstract
The divertor is a key component in magnetic confinement fusion as it reduces plasma contamination and protects the inner walls by removing heat and plasma exhaust. Divertors in DEMO (a planned demonstration fusion power plant) are needed to experience peak heat fluxes of up to 70 MW m−2 and neutron doses of 6-7 displacements per atom per full power year for long periods of time with little to no maintenance. Divertor targets experiencing heat fluxes and neutron irradiation doses of this magnitude can melt and suffer from mechanical failures or defects, such as embrittlement. However, novel divertor target structures can overcome this issue by having an optimised geometry which enhances heat transfer, ensuring that the divertor remains within an operational temperature regime where the aforementioned problems are minimised.
Additive manufacturing has been identified as a technology that can have significant potential applications in the nuclear fusion sector, particularly for high heat flux components, due to the freedom in geometric complexity offered. Additively manufactured cellular structures could exhibit improved thermal performances in heat transfer devices as they have high surface-to-volume ratios and enclosed channels, which are conducive for convective heat transfer applications. While interest in studying cellular structures for heat transfer applications has grown in recent years, further research benchmarking their performance against conventional structures, such as pin or fin arrays and circular channels, is necessary. The effect that their design variables, such as volume fraction, have on their thermal and hydraulic performance also needs to be determined.
Here, five cellular structures were examined numerically to determine the impact that different geometrical properties have on their hydraulic and thermal performance. Computational fluid dynamics was used to create useful predictive models for pressure drop and volumetric heat transfer coefficients over a range of flow rates and volume fractions. These can henceforth be used by heat transfer engineers to design appropriate heat sinks. The thermal performance of cellular structures was found to be heavily dependent on internal geometry, with structures capable of distributing thermal energy across the entire fluid volume having greater volumetric heat transfer coefficients than those with only localised areas of high heat transfer and low levels of fluid mixing.
Building on this work, a range of additively manufactured cellular structures were investigated as candidates for novel divertor target structures. Computational fluid dynamic results were verified experimentally using UKAEA’s HIVE, a high heat flux testing facility. It was found that the divertor may be significantly improved by the inclusion of cellular structures, as the examined structures were able to remove 11−28% more energy from the heated surface than a conventional circular channel. The examined structures exhibited greater pressure drops, however.
This investigation has determined that cellular structures show great promise for high heat flux applications in the nuclear fusion sector. Further research is needed to determine whether the enhanced cooling exhibited by the examined cellular structures can offset the additional energy associated with pumping fluids through larger pressure gradients, however. Additionally, the future of additively manufactured fusion components is dependent on the processability of fusion relevant metals. The developed predictive models for the hydraulic and thermal performance of the examined cellular structures can be used in conjunction with other rules, such as the Gibson-Ashby scaling laws for stiffness, to design multifunctional components. The accuracy of the models can be improved by examining additional geometrical properties, such as cell aspect ratio and surface area. Fluid flow dynamics and thermal transport within different cellular structures need to be further investigated and understood such that heat sinks can be designed from first principles.
| Item Type: |
Thesis (University of Nottingham only)
(PhD)
|
| Supervisors: |
Maskery, Ian
Tuck, Christopher
Hancock, David |
| Keywords: |
Additive manufacturing; Nuclear fusion; Computational fluid dynamics
Heat transfer
Surface-based lattice structures |
| Subjects: |
T Technology > TS Manufactures |
| Faculties/Schools: |
UK Campuses > Faculty of Engineering > Department of Mechanical, Materials and Manufacturing Engineering |
| Item ID: |
76949 |
| Depositing User: |
Padrao, Daniel
|
| Date Deposited: |
18 Jul 2024 04:40 |
| Last Modified: |
18 Jul 2024 04:40 |
| URI: |
https://eprints.nottingham.ac.uk/id/eprint/76949 |
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