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Title: Porous metals with novel structures for optimum heat exchange performance
Author: Baloyo, J.
ISNI:       0000 0004 6059 0540
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2016
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With advancing technology, the demand for effective cooling techniques for thermal management applications has increased significantly over the last years. Open-celled porous metals are ideal and effective cooling solutions due to their superior thermal properties allied with their permeability for fluid flow. In particular, porous copper produced by the Lost Carbonate Sintering (LCS) process is an excellent candidate for thermal management applications due to its ability to transport a high amount of heat over a small volume, when allied with fluid flow. This study aims to develop LCS porous copper with tailored, non-homogeneous structures to maximise the heat transfer performance for use in thermal management. The structural, fluid flow and heat transfer properties were studied on a number of LCS porous copper samples with different pore size, porosity and structure. Structural analysis showed that the pore morphology within the LCS porous copper specimens closely resembled that of the potassium carbonate (space-holder) powder used in LCS. Necking between the copper particles in the matrix ensured good mechanical strength and resulted in inter-particle pores connecting the larger pores formed by the space-holder. In addition to homogeneous porous structure, non-homogeneous porous structures, such as horizontal bilayer (HB), segmented vertical bilayer (SVB), integrated vertical bilayer (IVB), multi-boundary segmented structures (SS) and structures with directional porosity (DP), were successfully produced using the LCS process. The fluid flow properties of the LCS porous structures were measured using a purpose-built apparatus. The pressure drop fitted well with the Forchheimer's equation and the resulting air and water permeabilities were found to be independent of the sample's length. For homogeneous structures, the permeability increased with increasing porosity and decreasing pore size. For horizontal bilayer structures, the majority of the flow preferred the higher porosity layer. For both segmented vertical bilayer and integrated vertical bilayer structures, the lower porosity layer limited the overall permeability. For segmented vertical bilayer and multi-boundary segmented structures, the presence of hard boundaries had negligible effect on the overall permeability. For directional porosity structures, a greater permeability was observed due to the addition of the open tubular channels. The heat transfer performance of the LCS porous copper structures was characterised by the heat transfer coefficient. For homogeneous structures, an optimum porosity of 60% was found to offer the highest heat transfer coefficient. For horizontal bilayer structures, a higher heat transfer performance was observed when the higher porosity layer was placed next to the heat source. For vertical bilayer structures, the layer porosity combination greatly affected the heat transfer performance. For integrated vertical bilayer structures, optimum porosity combinations had an overall porosity in the range of 55% - 65%, and having the higher porosity layer by the water inlet gave a higher heat transfer coefficient. For segmented vertical bilayer structures, the presence of the 80% layer allied with the presence of a hard boundary resulted in the best heat transfer performance. Unlike in the integrated vertical bilayer structures, having the lower porosity layer by the water inlet offered better heat transfer performance for segmented vertical bilayer structures. For multi-boundary segmented structures, increasing the number of hard boundaries increased the overall heat transfer performance. Samples with directional porosity showed a three- to eight-fold increase in heat transfer coefficient compared to their homogeneous counterparts. Apart from the horizontal bilayer structures, the heat transfer performance of the non-homogeneous structures was greater than their homogeneous counterparts.
Supervisor: Zhao, Y. Y. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral