Constructal vascular composites for cooling and heating.

摘要

Constructal theory regards the generation of flow configuration as a physics phenomenon, and places the occurrence of this phenomenon on the basis of a principle of physics (the constructal law). In this thesis the constructal law is used as a scientific principle to design smart materials. The challenge is to vascularize a solid body with the ultimate objective of building into the body structure multiple functions such as self-healing and self-cooling. Self-healing smart materials vascularized with tree-shaped flow architectures matched canopy to canopy are optimized in two and three dimensional domains to provide greatest point to volume, volume to point flow by a single stream bathing every subvolume of the material. The flow architectures have optimal ratios of channel sizes before and after branching. The vascular designs in two dimensions show that it is more beneficial to bathe the entire volume with a single (optimized) one-stream architecture than to bathe it with several streams that serve small clusters of volume elements. When the design has freedom to morph from two dimensions to three dimensions, it is shown that the flow architecture that provides greatest global flow conductance is the three-dimensional compounding of trees matched canopy to canopy. The dendritic design must become more complex (with more levels of bifurcations) as the volume inhabited by the flow design increases.;Smart materials that are required to self-cool as well as to self-heal are also studied. Arrays of parallel channels and dendritic tree-shaped flow architectures are employed into a solid body experiencing intense heating from one side and being protected with a single-phase coolant from the other side. The objective is to find the channel configuration that maintains the least nonuniform temperature distribution in the solid (i.e., the coolest hot spots). The optimal spacing between channels and the minimum hot-spot excess temperature are deduced analytically for the parallel channel structures. Theses analytical results are verified based on numerical simulations of the conjugate heat transfer in channels and surrounding solid material. Similar numerical simulations are conducted for dendritic tree-shaped flow architectures having one to four levels of bifurcation, and compared with the parallel channel architectures. It is shown that the trees design is very effective, and that there is an optimal number of bifurcation levels for a specified porosity and pressure drop number. Tree designs are more effective than designs with parallel channels when the pressure drop number and the porosity are sufficiently large.