The development of a liquid cooling test system for the analysis of porous surfaces

<p>Closed-loop liquid cooling systems are used in a wide variety of high temperature environments, as liquids tend a higher thermal conductivity than air. Microchannels and porous microstructures have proved to be useful in improving the cooling capabilities of cooling systems, due to their increased surface area in contact with the cooling fluid. This thesis describes the design, development, and evaluation of a closed-loop liquid cooling test system. This system was utilised in analysing the thermal properties of porous microstructures for use in improving cooling capabilities. Flow rate and pressure sensors were fitted onto a standard closed loop liquid cooling system design, and thermocouples were attached to the system to measure the temperature at various points, as well as measure heat flux. Using these measurements, the thermal and hydraulic resistances of the system could be calculated. Various substrates were fabricated using both freeze casting and other techniques, and the thermal and hydraulic resistances of these substrates were characterized using the test system. The test system performed very well, with results matching the trends as expected from theory. However, no improvement in heat transfer was observed from microstructured silver surfaces compared to a solid copper reference surface. This may be due to the formation of oxides and/or sulphides on these silver surfaces, resulting in a reduction in the convective heat transfer from these layers.</p>

The development of a liquid cooling test system for the analysis of porous surfaces

<p>Closed-loop liquid cooling systems are used in a wide variety of high temperature environments, as liquids tend a higher thermal conductivity than air. Microchannels and porous microstructures have proved to be useful in improving the cooling capabilities of cooling systems, due to their increased surface area in contact with the cooling fluid. This thesis describes the design, development, and evaluation of a closed-loop liquid cooling test system. This system was utilised in analysing the thermal properties of porous microstructures for use in improving cooling capabilities. Flow rate and pressure sensors were fitted onto a standard closed loop liquid cooling system design, and thermocouples were attached to the system to measure the temperature at various points, as well as measure heat flux. Using these measurements, the thermal and hydraulic resistances of the system could be calculated. Various substrates were fabricated using both freeze casting and other techniques, and the thermal and hydraulic resistances of these substrates were characterized using the test system. The test system performed very well, with results matching the trends as expected from theory. However, no improvement in heat transfer was observed from microstructured silver surfaces compared to a solid copper reference surface. This may be due to the formation of oxides and/or sulphides on these silver surfaces, resulting in a reduction in the convective heat transfer from these layers.</p>

Band Structure and Energy Level Alignment of Chiral Graphene Nanoribbons on Silver Surfaces

Chiral graphene nanoribbons are extremely interesting structures due to their narrow band gaps and potential development of spin-polarized edge states. Here, we study their band structure on low work function silver surfaces. The use of a curved Ag single crystal provides, within the same sample, regions of disparate step structure and step density. Whereas the former leads to distinct azimuthal growth orientations of the graphene nanoribbons atop, the latter modulates the substrate’s work function and thereby the interface energy level alignment. In turn, we disclose the associated charge transfer from the substrate to the ribbon and assess its effect on the nanoribbon’s properties and the edge state magnetization.