Honors College Thesis
 

Preliminary Numerical Study of a Condenser Using Fractal-Like Patterned Hydrophobic and Hydrophilic Strips

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  • Condensers are vital components of power plants and are often one of the most major cost concerns when planning construction. Generally speaking, the surface area required to dissipate the heat generated in the boiler is so great that enormous and expensive structures are necessary. The usage of a hybrid surface may be able to reduce the amount of area required to dissipate the same amount of heat. Dropwise condensation that occurs on hydrophobic surfaces is more efficient than filmwise condensation that occurs on hydrophilic surfaces, but droplets that coalesce can form a film that lowers the heat transfer coefficient. Using hydrophilic strips to wick away condensation from areas with hydrophobic condensation may provide a way to keep dropwise condensation efficient. This study measured the effects of dropwise contact angle, fractal level, hydrophilic strip width, and the ratio between lengths of strips with at different fractal levels on a fractal-like patterned hybrid exchanger. By solving a series of equations simultaneously on multiple control volumes over the entire heat exchanger, the impact each varied parameter had on the overall heat transfer was measured. Hydrophobicity was found to have a positive yet small relationship with the area-weighted convective heat transfer coefficient, h ̅. The maximum fractal level saw decreases in h ̅ with increases in the maximum fractal level, implying that using fractal patterned exchangers may not have merit in decreasing the overall condenser area in a worst-case scenario. The hydrophobicity of the dropwise sections saw a small but positive increase in h ̅ when the hydrophobic contact angle was increased. Numerical data for hydrophilic strip width implied that increasing the width only results in lower h ̅. Lastly, the fractal length ratio saw decreases in h ̅ when the fractal length ratio was increased. The changes in heat flux were much smaller than the changes in the heat transfer coefficient, as the thermal resistance through the coolant was much greater than that through the condensation, so the effect of changing certain parameters of the exchanger was lessened.
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