Enhancement of extended surface heat transfer using fractal-like geometries

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University of Alabama Libraries

This work investigates a technique to improve extended surface heat transfer through the use of fractal-like geometric patterns. When fractal-like geometries are considered, significant gains in the available surface area for fins can be achieved without large increases in fin volume or mass. For certain fractal patterns, the surface area of a fin can even be increased while reducing the mass of the fin. This would provide direct benefit for situations where the extended surface volume is restricted or minimized weight is desired. Fractal-like geometries are presented to increase the effectiveness and effectiveness per unit mass of fins for natural convection heat transfer as well as increase effectiveness per mass for radiation heat transfer. Common extended surface heat transfer methods and developments were reviewed to obtain an understanding of the focus and limitations of previous work. Based on this literature review, it has been observed that the use of fractal-like geometries has been utilized for engineering applications. However, the use of fractal-like geometries for extended surface heat transfer has not been studied and therefore justified an investigation into their behavior. In an initial investigation, fractal-like fins were manufactured in the patterns of the baseline and first three iterations of the Sierpinski carpet (base width of 0.1016 m, 0.0508 m, 0.0254 m) and modified Koch snowflake (base width of 0.1016 m) in order to quantify practicality and thermal performance. It was observed that fractal-like fins could result in increased fin effectiveness per unit mass by as much as 59%. Motivated by the initial experimental results, subsequent studies utilized computational modeling with a commercially available, industry standard computational modeling program. A computational investigation of iii natural convection heat transfer from fractal-like fins was able to further support conclusions of the experimental results as well as model an additional iteration. Fin effectiveness per unit mass was increased by a minimum of 37% for the conditions tested. Finally, a computational investigation of radiation heat transfer from fractal-like fins showed that fin effectiveness per unit mass increased by a minimum of 25% for the conditions tested.

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Mechanical engineering