• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.1
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• pp.21-28
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• 2017

Indirect evaporative cooling, which utilizes a cooling effect obtained by the evaporation of water, is energy-effective compared to the conventional vapor compression method. It is also eco-friendly, due to the non-usage of CFC refrigerant. In this study, three indirect evaporative cooler samples of the cross flow type(size: $300mm{\times}300mm{\times}300mm$, channel pitch: $5mm{\times}5mm$, $5mm{\times}7mm$, $7mm{\times}7mm$) were made using plastic/paper composites. Tests were conducted to measure indirect evaporative efficiencies and pressure drops. Results showed that the efficiency was the highest for the $5mm{\times}5mm$ sample, owing to the largest surface area. The saved electrical energy was also the greatest for that sample. The pressure drop of the wet channel was larger than that of the dry channel as expected. A theoretical model was proposed, which underestimated both the indirect evaporation efficiency and the pressure drop.

• Applied Chemistry for Engineering
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• v.24 no.4
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• pp.402-406
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• 2013

In this study, a pitch for melt-electrospinning was prepared from naphtha cracking bottom (NCB) oil by the modification with heat treatment. The softening point and property of the modified pitch was influenced by modification conditions such as nitrogen flow rate, heat treatment temperature, and reaction time. Among these, the heat treatment temperature had a very strong influence on the distribution of molecular weight and softening point of the pitch. The C/H mole ratio and average molecular weight increased with increasing the heat treatment temperature due the decomposition and cyclization reaction of surface-functional groups. In addition, the values of benzene insoluble and quinoline insoluble also tends to decrease, and the width of molecular weight distribution seems to get more narrow. The carbon fiber with a diameter of $4.8{\mu}m$ was prepared from a modified pitch at the softening point of $155^{\circ}C$ by melt-electrospinning. It is believed that the melt-electro spinning method is much more convenient to get the thinner fiber than the conventional melt spinning method.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.9
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• pp.587-595
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• 2017

Recent trends in slim air conditioners require heat exchangers of reduced flow depth. In this study, slim louver fin geometry was obtained using predictive correlations. The deduced geometry yielded 10 mm flow depth, 0.9 mm louver pitch, and $35^{\circ}$ louver angle. Samples were made and tests were conducted. The new slim sample yielded 36% higher j factor and 2.3% higher f factor compared with those of the standard sample. This implies that 26% reduction of heat exchanger volume was possible by reducing the flow depth. In addition, the $j/f^{1/3}$ of the slim sample was 55% larger than that of the standard sample. Furthermore, the results are compared with predictions made using existing correlations.

• Journal of Energy Engineering
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• v.24 no.4
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• pp.105-116
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• 2015

In this study, airside performance of round fin-and-tube heat exchangers are compared with that of the herringbone wave fin-and-tube heat exchangers with an aim to investigate the effect of fin shape on thermal performance. Results show that j factors of the round wave fin are 1.2~22% larger than those of herringbone wave fin. The f factors of the round wave fin are -1.0~29% smaller than those of herringbone wave fin for 1 or 2 row configuration. For 3 row configuration, f factors of the round wave fin are 8.3~23% larger. The reason may be attributed to the reduced recirculation zone in the valley of the fin for round wave fin as compared with that of the herringbone wave fin. For round wave fin, the effect of fin pitch on j and f factor is not significant. In addition, j factors decrease as the number of tube row increases. On the other hand, f factors are independent of the number of tube row. A new correlation was developed based on the present data.

• Korean Chemical Engineering Research
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• v.54 no.2
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• pp.268-273
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• 2016

To improve mechanical strength of carbon foams, the carbon black (CB) added carbon foams were fabricated by impregnating different contents of carbon black (CB) and mesophase pitch using polyvinyl alcohol (PVA) solution into polyurethane foam and being followed by heat treatment. The cell wall-thicknesses of carbon foams were controlled by adding amounts of CB, and it was confirmed that the compressive strength of carbon foams was increased as increasing cell wall-thickness. The compressive strength had the highest value of $0.22{\pm}0.05MPa$ with the highest bulk density of $0.44g/cm^3$ when adding 5 wt% CB in carbon foam. However, the thermal conductivity was decreased by adding CB in carbon foam. The results indicated that the thermal conductivities of carbon foams were reduced by increased interlayer spacing ($d_{002}$) with the addition of CB in carbon foams.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.9
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• pp.5778-5788
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• 2015

In this study, wet surface heat transfer and friction characteristics of compound enhanced fin-and-tube heat exchangers were experimentally investigated. Louver-finned heat exchangers were also tested for comparison purpose. The effect of fin pitch on j and f factor was negligible. Both j and f factor decreased as number of tube row increased. Compound enhanced fin samples yielded higher j and f factors than louver fin samples. For one row, j and f factors of compound enhanced fin samples were 11% and 43% higher than those of louver fin samples. For two row, those were 8% and 50%, and for three row, those were 17% and 53%. Heat transfer capacities at the same pressure drop of the compound enhanced fin samples were 2.0% for one row, 3.1% for two row and 8.4% for three row larger than those of louver fin samples, Data were compared with predictions of existing louver fin correlations.