A study of micro-scale, fractal-like branching flow networks for reduced pumping power and improved temperature uniformity

Graduation date: 2002A first generation, one-dimensional predictive model is proposed for\ud designing heat sinks with fractal flow networks. A three-dimensional\ud computational fluid dynamics (CFD) model is analyzed as a means for validating\ud the model and identifying areas for improvement.\ud Two separate CFD models were developed. One was analyzed with\ud conjugate heat transfer whereas the other was not. For the conjugate heat transfer\ud model, heat flux was provided at a single surface, simulating a heat source. Energy\ud addition to the latter model, referred to as the non-conjugate model, was uniform to\ud all surfaces and was developed to assess the assumptions employed in the one-dimensional\ud model.\ud Both CFD models were run with and without variable properties and are\ud compared to results with a series of parallel channels with identical convective\ud surface areas. In all cases, with and without conjugate heat transfer and with and\ud without variable fluid properties, the fractal flow network showed lower maximum\ud surface temperatures than the straight channel network for identical pumping\ud powers. The pumping power, however, was determined assuming constant fluid\ud properties.\ud The variation in fluid viscosity with temperature was determined to have a\ud significant impact on the pressure distribution, which indicates that variable fluid\ud viscosity needs to be included in the one-dimensional model.\ud Also varied in the analyses were heat sink material, heat flux and flow rate.\ud Qualitative results show that temperature variations within the copper substrate are\ud less significant than in the stainless steel substrate. All analyses, including the one-dimensional\ud model, were restricted to laminar flow conditions