| This dissertation tests the constructal method by optimally designing several high performance multi-scale heat exchangers (e.g., channels, fins, enclosures, etc.). The first step taken towards optimized structures is the definition of the objectives and constraints. The outcome of this process is the optimal architecture of the structure. Four main classes of configurations were investigated: (I) Optimal spacings of symmetric and asymmetric heated channels in natural and forced convection (Ch. 2 and 9); (II) Discrete heated surfaces in natural and forced convection (Ch. 3, 4 and 8); (III) Maximum heating or cooling with the use of extended surfaces (Ch. 5 and 7); (IV) Development and test of a dendritic counterflow heat exchanger (Ch. 6). The first class of systems deals with the generation of optimal internal flow structure in a package with heat sources cooled either by forced or natural convection. In the natural convection problem (Ch. 2) it is shown numerically that the entire flow geometry of a vertical diverging or converging channel with laminar natural convection can be optimized for maximal heat transfer rate density (total heat transfer rate per unit of flow system volume).; The second class of configurations (Ch. 3, 4 and 8) deals with the discovery of the optimal distribution of discrete heat sources cooled by laminar natural and forced convection.; The third class of configurations is a new design concept for generating multi-scale structures for maximum heating (Ch. 5) or cooling (Ch. 7) per unit of volume. In Chapter 5, a control volume of cold fluid is filled with vertical equidistant heated blades of decreasing lengths. Chapter 7 shows how to shape rectangular high-conductivity inserts (fins) that are mounted on the rim of and protrude into a disc-shaped body that generates heat.; The last class of problems consists of the evaluation of the theoretical and experimental (Ch. 6) performance of balanced two-stream counterflow heat exchangers, in which each stream flows as a tree network through its allotted space.; Finally, in the last chapter (Ch. 10) we reflect on the course of the thesis by stressing the importance of the competition between global objectives versus constraints. Furthermore, we show several common features that emerge from the many and diverse applications of the constructal method. (Abstract shortened by UMI.)... |
