Thermal transport in systems with hierarchical bifurcating geometries

Abstract

This work investigates enhanced thermal transport through the use of hierarchical bifurcating geometries. An extensive literature review was performed regarding the use of biologically-inspired geometries to enhance heat transfer. If hierarchical bifurcating, or tree-like, geometries are considered, significant gains in the available surface area for heat transfer can be achieved as the geometric pattern is space-filling. As compared with parallel straight channel heat sinks, hierarchical bifurcating internal flow passages offer the advantages of reduced pressure drop as well as enhanced thermal mixing and increased surface temperature uniformity. In an initial investigation, the effect of scaling on flow networks with hierarchical bifurcating flow passages was examined. It was concluded microscale and mesoscale flow networks offer similar thermal performance while mesoscale flow networks have the additional advantage of reduced pressure drop. When compared to traditional rectangular extended surfaces, fins with tree-like geometries offer an increase in surface area per mass. In a second investigation, the thermal performance of tree-like fins thermally radiating to free space was examined. The tree-like fins were found to be more effective than rectangular fins of equal mass, volume, and base area. Similarly, in a third investigation, the thermal performance of tree-like fins in a naturally convecting environment was examined. The tree-like fins were again found to be more effective at dissipating heat when compared with traditionally employed rectangular fins. In the fourth investigation, hierarchical bifurcating flow passages were utilized in a single-fluid solid-liquid compact heat exchanger. System performance was experimentally investigated and subsequently characterized in a manner similar to traditional compact heat exchangers. The experimental results were non-dimensionalized in order for system performance to be compared with traditional compact heat exchangers as a second fluid stream was absent. In the fifth and final investigation, the effect of bifurcation angle, porosity, and pore size on the fluid behavior through a porous disk with hierarchical bifurcating flow passages was computationally examined. It was concluded that varying bifurcation angles only impacted the flow behavior through, and pressure drop across, porous disks with tree-like flow passages at relatively low porosities and small pore sizes.