Vascular design for compactness : transient volumetric cooling

Abstract

Paper presented at the 7th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Turkey, 19-21 July, 2010.

The drive toward greater cooling densities in generating an entirely new literature on vascular designs: tree-shaped flow architectures that offer dramatically superior volumetric functionalities for smart materials, such as volumetric cooling, self-healing and functionally graded material properties. In this paper we review our group's progress with the constructal design of dendritic flow architectures for cooling. We describe the development of cooling architectUres consisting of trees. Such vasculatUres provide volumetric bathing for a slab with flow entering from one side and exiting through the other side. The volumetric generation rate is uniform. The volume fraction occupied by all the channels is fixed, as a consequence of the fact that the leading constraints on high-density design are fixed weight (solid volume) and fixed volume (solid and channel volume). Minimized are the global thermal resistance (or hot-spot temperature ), the global fluid flow resistance, and the volume fraction of material with temperatures close to the hot-spot temperature. For steady state operation, we show that there is an architecture with a certain number of bifurcation levels that meets the multiple objectives. Unsteady state performance is also provided by the dendritic designs. A time delay separates the sensing of overheating from the start of the flow of coolant The longest time delay that allows the vasculature to keep all the temperatures below the permissible level is reported as a function of the complexity of the tree architecture.