• Proceedings of the KSME Conference
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• 2000.11b
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• pp.105-111
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• 2000

A numerical study has been performed to obtain the heat transfer and pressure drop characteristics for shell-and-tube heat exchanger with various shapes of tubes. The Tubes have variation of Aspect Ratio, Pitch and Rotation. Results are presented as plots of Colburn j factor and friction factor f against Aspect Ratio, Pitch and Rotation. As Aspect Ratio increases, j factor and f factor decreases. As Pitch increases, j factor decreases. j/f have optimized Pitch for each Aspect Ratio. Accordingly, there is fitness of Aspect Ratio and Pitch fur most effective cases. The Rotation of tubes are of no meaning for both heat transfer and pressure drop.

• The KSFM Journal of Fluid Machinery
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• v.16 no.6
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• pp.40-47
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• 2013

In this paper, a numerical study was performed to investigate the performance characteristics of a pre-heater. The effects of fin pitch and fin array type(in-line, staggered, leaned array) were reported in terms of Colburn j-factor and Fanning friction factor f, as a function of Re. Three-dimensional numerical simulation has been performed by using flow analysis program, FLUENT 13.0. The results show that Colburn j-factor decreases with the decrease of fin pitch attached in the annular tube. But the fin pitch has little effect on f-factor. The staggered array and leaned array show improved heat transfer performance compared with in-line array, so that Colburn j-factor was increased. It also shows that the f-factor of leaned array is the highest in the studied range of Reynolds number.

• Journal of Advanced Marine Engineering and Technology
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• v.26 no.1
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• pp.59-67
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• 2002

The comparison of $J_{Rice}$-resistance considering a few strength ratio in Rice J-integral formula and $J_{\delta}$-resistance curves converted from experimental CTOD using appropriate strength chosen according to strain hardening level, n=10.6 (A533B steel) and n=8.1 (BS4360 steel) is carried out. The optimal dimensionless strength ratio like the factor of revision, (see full text)reflecting strain hardening level in Rice\`s experimental formula is found out and the reliability of appropriate reference strength chosen according to strain hardening level in different materials is investigated through doing that CTOD is transformed from $J_{\delta}$-integral using relationship between J-integral and CTOD. The results are as follows; 1) The optimal factor of revision is when m equals to 3 in (see full text) for Rice's and the above optimal factor of revision multiplies by coefficient, η in Rice's experimental formula instead of n=2, 2) and the pertinent reference strength for high strain hardening material like BS4360 steel is ultimate strength, $\sigma_{u}$ and for material like A533B steel is ultimate-flow strength, $\sigma_{u-f}$. The incompatible of the behavior of both experimental J-resistance curves using Rice's formula and CTOD-resistance curves for A533B and BS4360 steel by Gordon, et al., could be corrected using the optimal factor of revision in Rice\`s and the pertinent reference strength in J=$m_{j}$${\times}$$\sigma_{i}$${\times}$CTOD.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.2
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• pp.423-431
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• 2013

The k-factor method has been widely used in design of steel-concrete composite bridges to determine indeterminate stresses. The accuracy of k-factor method is examined by a comparative analysis with the equivalent load method in a continuous 2-span composite bridge. To improve the accuracy, the direction of creep stress has to be modified and the variety of section must be considered. This paper suggests j-factor method which can improve the accuracy of k-factor method with simple modification.

• Journal of Convergence Society for SMB
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• v.6 no.3
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• pp.65-69
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• 2016

We investigated refractive errors and corneal power with 3 factors such as M, $J_0$, and $J_{45}$ as power vector to find out the changes of refractive errors of the before and after cataract surgery in 119 adults aged 45~85 years with cataract. After the surgery, the 3 factors were changed as $-0.29{\pm}2.38D$ to $-0.18{\pm}0.69D$ in spherical equivalent power which is the M factor, $-0.34{\pm}0.68D$ to $-0.05{\pm}0.42D$ in the $J_0$ factor, and $0.11{\pm}0.45$ to $0.02{\pm}0.17$ in the $J_{45}$ factor. Before and after the surgery, corneal mean refractive power, $J_0$, and $J_{45}$ were changed from $44.11{\pm}1.61D$ to $44.20{\pm}1.58D$, $0.01{\pm}0.50D$ to $0.08{\pm}0.49D$, and $0.02{\pm}0.29$ to $0.08{\pm}0.49$, respectively. The results showed that $J_0$ was the highest relativeness in correlation of the pre- and post-surgery for refractive errors, mean corneal power was the highest correlation for corneal power factor, and corneal power factor was the higher correlation much more than refractive error factor.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.29 no.4
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• pp.149-158
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• 2017

In general, the air-side j and f factors of evaporators or condensers are obtained through single-design tests performed under air-dry and wet-bulb temperatures. Considering that the indoor or outdoor air temperatures vary significantly during the operation of an air conditioner, it is necessary to confirm that the experimentally-obtained j and f factors are widely applicable under variable air conditions. In this study, a series of tests were conducted on a two-row slit-finned heat exchanger to confirm the applicability. The results showed that, for the dry-surface condition, the changes of the tube-side water temperature, water-flow rate, and air temperature had virtually no effect on the air-side j and f factors. For the wet condition, however, the f factor was significantly affected by these changes; contrarily, the j factor is relatively independent regarding this change. The formulation of the possible reasoning is in consideration of the condensation behavior underneath the tube. The wet-surface j and f factors are larger than those of the dry surface, with a larger amount for the f factor.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.05a
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• pp.645-646
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• 2012

• International conference on construction engineering and project management
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• 2013.01a
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• pp.315-320
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• 2013

The aim of this study is to compare efficiency and Total Factor Productivity(TFP) between Korean and Japanese construction firms in Korea and Japan over the period of 2005-2011. The results of this study are as follows. Efficiency scores of Korean construction firms are 0.797, and Japanese construction firms are 0.921. Second, annual total factor productivity growth of Korean construction firms is 0.5% and technical progress do much for TFP decrease. However Japanese construction firms marked annual increasing of 2.5% of TFP. Third, technical progress contributed in TFP increase of construction firms in Korea. Korean construction firms, however, relatively lagged behind Japanese construction firms in technical progress. Therefore, Korean construction firms need strategies to achieve technical advances including adopting new technology or process innovation to maintain competitiveness, survive, and develop in the future competition with Japan.

• Applied Chemistry for Engineering
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• v.17 no.5
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• pp.476-482
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• 2006

An experimental study has been performed to investigate the characteristics of air-side heat transfer and friction of a fined tube heat exchanger under heating conditions. Air enthalpy calorimeter was used to obtain the performance evaluation and analysis of the fined tube heat exchanger. Eight finned tube heat exchangers with slit fin, louver fin, and plain fin were used. The air-side heat transfer coefficient was calculated by the log-mean-temperature-difference. Air-side heat transfer and friction were presented in terms of j factor and friction factor on Reynolds number. From the experimental result, it was found that the variations of air-side heat transfer and friction of fined tube heat exchanger with the change of the fin configuration, row number, fin pitch, and tube circuit were obtained. j factor and friction factor decreased with Reynolds number increased. The tube circuit affected the air-side heat transfer and friction. In the case of slit and louver fin, j factor of 1st row was higher than that of 2nd row. But, with increasing Re, j factor was reversed. The characteristics of j factor and friction factor of 2nd row heat exchanger were different according to the kind of fins.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.10a
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• pp.357-358
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• 2009