Geometric Design Methods for Conducting Solids Cooled by Conjugate Heat Transfer Including Surface Radiation
The objective of this dissertation is to develop and investigate design methods for conducting solids cooled by multimode heat transfer, including surface radiation. The goal is to determine solid shapes with reduced or minimal overall thermal resistances. The influence of radiation on the predicted optimal shapes and thermal performance is investigated.First, a heuristic, evolutionary design method (EDM) is developed that iteratively adjusts a discrete solid shape based on local surface heat fluxes and temperatures. The EDM is initially applied to a conjugate conduction-free convection problem and compared to a solid replicated from a benchmark topology optimization (TO) study. While the EDM does not achieve the thermal performance of the benchmark solid, it does reduce the overall thermal resistance from an initial, arbitrary geometry. The effects of radiation are then incorporated into the physical model and EDM, which is applied to a range of solid emissivities and domain sizes. It is found that radiation has a significant influence on the thermal behavior (fluid flow and temperature distribution) and therefore on the predicted optimal solid shapes. In general, increasing the strength of radiation results in increased symmetry about the vertical centerline for both the thermal behavior and predicted solid geometries. Next, to isolate the effects of radiation, a coupled conduction-radiation problem is considered, and a heuristic solid growth method (SGM) is introduced that is similar in concept to the EDM. The SGM is distinct in that it incrementally adds solid material to the domain, so the solid mass is not constant throughout the design process. It is demonstrated that the relative strength of radiation has a significant effect on the solid growth and thermal performance. The SGM is also compared to a formal TO method that neglects the effects of radiation in obtaining optimal solid shapes. It is found that when a low amount of solid material or a relatively low solid thermal conductivity is considered, the SGM produces favorable solid configurations with lower overall thermal resistances. The effects of radiation are then incorporated into a formal TO method, by introducing a dual solid method (DSM) that utilizes both a discrete and continuous description of the solid material distribution. The discrete description is used to model radiation heat transfer, while the continuous solid description is used in conjunction with a TO method to adjust the solid shape. It is once again shown that the effects of radiation have a strong influence on the predicted optimal solid shapes and thermal performances. Lastly, a comparison of heuristic (SGM) and formal (DSM) design methods is made. When a high thermal conductivity solid is considered, the DSM achieves a lower overall thermal resistance. However, somewhat surprisingly, the SGM produces shapes having better thermal performance when a low solid thermal conductivity is considered.
Mechanical engineering, Conjugate Heat Transfer, Free convection, Heat Sink Design, Thermal Radiation, Topology Optimization
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