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이정헌(Junghun Lee),김정완(Jungwan Kim),홍희기(Hiki Hong),남영석(Youngsuk Nam) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11
In this work, we investigated the performance of single and double-glazed flat plate solar collector using a numerical approach. 1D and 3D models were developed by the thermal network model and the finite element model, respectively. We incorporated two different types of glasses with and without anti-reflection (AR) coating whose average transparency was measured to be 0.915 and 0.966 respectively. The loss coefficient of single and double glazed collectors were extracted to be ~3.234 and ~2.789, respectively, due to the decrease of convective loss for the double glazed design. With the AR coating, the single and double glazed collector showed ~88.8% and ~87.9% of the absorption capability, which makes the double-glazed design perform better than the single one. In addition, we investigated the spectral response of Cu-based nanostructured absorber plates and compared their performance with the conventional TiNOX absorber plates.
서동현(Donghyeon Seo),이정헌(Junghun Lee),이충엽(Choongyeop Lee),남영석(Youngsuk Nam) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
With a water shortage emerging as a world-wide issue, moisture in air has been receiving great attention as a clean and cheap water resource. In this study, we investigate how the wetting state of Cu based nano-engineered tube surfaces influences the water-harvesting performance via steam or dewing by testing bare, hydrophobic, superhydrophilic, superhydrophobic, and oil-infused superhydrophobic tube type condensers. On the basis of the force balance between the gravitational force and the pinning force, the sliding and dripping mass of condensates are quantified and the predictions were consistent with the experimental observations. It was found that the low viscosity oil-infused surface having low contact angle hysteresis exhibits the highest droplet mobility and the best water-harvesting performance in the steam condition. This is in contrast to a dewing harvesting result where the most efficient surfaces consist of bare and superhydrophilic surfaces. Despite of the similar super-saturation level, in the dewing environment, the droplet growth only depends on thermal diffusion between humid air and the substrate. Therefore the nucleation rate becomes as important as the droplet mobility in dewing harvesting. However, the saturated tiny droplets can easily stick and grow on the surface regardless of the nucleation barrier and eventually high droplet mobility becomes the most dominant factor for steam harvesting.