Better Bubblers: Jet Impingement Within a Dead-End Channel

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In the high pressure aluminium die casting (HPADC) and injection moulding (IM) industries, a unique flow field is used to cool slender mould protrusions: a jet impingement confined within a dead-end channel, known in industry as a 'bubbler'. These devices are used ubiquitously, however their implementation within a mould has been constrained by the limitations of 2D machining; recent advances in Additive Manufacturing (AM) now offer timely and novel opportunities to improve their design. Our challenge is that the heat- and flow-regime associated with a bubbler has received limited attention in the literature, so an improved understanding is required to access the optimum cooling performance that the AM of these devices can enable. The goal of this project is therefore to establish the heat and flow phenomenology associated with bubblers, and to develop novel methods that will enable their design to be optimised for AM, to be achieved though the following objectives:1) Development of a highly-resolved computational fluid dynamics (CFD) dataset that reveals the bubbler heat- and flow-configuration in detail. Isothermal and conjugate heat transfer (CHT) wall-resolved large eddy simulations (LES) of the basic co-annular flow-field will be performed, and validated against the experimental dataset.2) Elucidation of the flow physics via the collection and analysis of experimental results. Particle image velocimetry (PIV) data will be obtained using a novel cold-flow optical experimental rig, and used to parameterise the basic flow-field and to validate the isothermal simulations. Heat transfer data will be obtained using Coventry's existing aluminium casting experiment, for validation of the CHT simulations.3) Development of novel shape optimisation methods for HPADC inserts. The adjoint method finds the gradient of the governing Navier-Stokes equations, enabling tailored shape deformation in pursuit of a particular objective function, which will need to be developed to enable the maximisation of heat removal and heat-flux uniformity across the protrusion. An optimised geometry will then be laser sintered by our partners at CastAlum Ltd., to be tested experimentally and demonstrated in an industrial setting.This will lead to:- A thorough description of the coupling of fluid dynamics and heat-transfer behaviour arising from inherent and induced boundary and free shear-layer turbulence in annularly confined jet-impingement, achieved through the application of LES and PIV, with a novel focus upon heat transfer through both the impingement surface and the annular confining wall, leading to;- Significantly improved bubbler operating parameters providing efficient heat removal rates, and correlations for their prediction for a full suite of configurations;- An optimisation strategy for HPADC that maximises heat removal and heat flux uniformity, that will accelerate the adoption of AM methods within the industry.In parallel, the project will advance modelling techniques, and set new benchmarks in the numerical simulation of jet-impingement that will have use far-beyond the nominal application. The work will be of direct benefit to UK HPADC and IM industries, laying rigorous theoretical foundations that, allied with the flexibility in design provided by AM, will better control the heat removal from the most problematic areas of their moulds, resulting in reduced cycle times thereby increasing product volume, extending the life of the expensive tools, and maintaining product quality over extended (150k+) cycles. It will therefore provide industry with a pronounced commercial advantage and reduction in the overall production plant life cycle costs. A bubbler's flow field arises in other engineered systems, from high pressure jet cutting, to electronics cooling, and even to artificial lung ventilation.