• The KSFM Journal of Fluid Machinery
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• v.13 no.5
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• pp.43-53
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• 2010

This study investigates a design optimization of a rotating two-pass rectangular cooling channel with staggered arrays of pin-fins. The radial basis neural network method is used as an optimization technique with Reynolds-averaged Navier-Stokes analysis of fluid flow and heat transfer with shear stress transport turbulent model. The ratio of the diameter to height of the pin-fins and the ratio of the streamwise spacing between the pin-fins to height of the pin-fin are selected as design variables. The optimization problem has been defined as a minimization of the objective function, which is defined as a linear combination of heat transfer related term and friction loss related term with a weighting factor. Results are presented for streamlines, velocity vector fields, and contours of Nusselt numbers, friction coefficients, and turbulent kinetic energy. These results show how fluid flow in a two-pass square cooling channel evolves a converted secondary flows due to Coriolis force, staggered arrays of pin-fins, and a $180^{\circ}$ turn region. These results describe how the fluid flow affects surface heat transfer. The Coriolis force induces heat transfer discrepancy between leading and trailing surfaces, having higher Nusselt number on the leading surface in the second pass while having lower Nusselt number on the trailing surface. Dean vortices generated in $180^{\circ}$ turn region augment heat transfer in the turning region and in the upstream region of the second pass. As the result of optimization, in comparison with the reference geometry, thermal performance of the optimum geometry shows the improvement by 30.5%. Through the optimization, the diameter of pin-fin increased by 14.9% and the streamwise distance between pin-fins increased by 32.1%. And, the value of objective function decreased by 18.1%.

• Korean Journal of Ichthyology
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• v.2 no.1
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• pp.28-35
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• 1990

The genus Periophthalmus collected from the west and south coasts of Korea, from 1983 to 1987 is reviewed and discussed taxonmically. Among them, Periophthalmus sp. is distinguished morphologically from P. cantonensis and other species of the genus Periophthalmus. The external features of Periophthalmus sp. are similar to those of P. cantonensis. However, it is clearly observed that Periophthalmussp. is differ from P. cantonensis in marginal band and height of 1st dorsal fin, membrane of pelvic fin, number of longitudinal scale~and number of 2nd dorsal soft rays.

• Korean Journal of Ichthyology
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• v.10 no.2
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• pp.250-259
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• 1998

This study was carried out to reveal the taxonomic status of the two mullets, Chelon affinis and Chelon haematocheilus from Korea by comparison of their morphological characteristics. Chelan affinis, occurred in the southern coastal area, is a distinct species characterized by having a keel on the middorsal line in front of the spinous dorsal fin. However, Chelon haematocheilus, found in the all coastal areas of Korea excluding Cheju island is easily distinguished from the former in having the deep flat head. By comparison of five groups of Chelan haematocheilus, Kunsan group is slightly differed from others in the height of anal fin and caudal peduncle length. Although Chelon affinis is similar with Chelan haematocheilus in the view of meristic characters, they are distinguished from each other in the number of pyloric caeca and lateral line scales.

• International Journal of Air-Conditioning and Refrigeration
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• v.13 no.2
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• pp.71-82
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• 2005

The shape of $7\times7$ pin-fins heat sink is optimized numerically to obtain the minimum pressure drop and thermal resistance. In this study, the fin height (h), fin width (w), and fan-to-heat sink distance (c) are chosen as the design variables and the pressure drop $({\Delta}P)$ and thermal resistance $(\theta_j)$ are adopted as the objective functions. To obtain the optimum design values, we used the finite volume method for calculating the objective functions, the BFGS method for solving the unconstrained non-linear optimization problem, and the weighting method for predicting the multi-objective problem. The results show that the optimum design variables for the weighting coefficient of 0.5 are as follows: W=4.653 mm, h=59.215mm, and c=2.667mm. The objective functions corresponding to the optimal design are calculated as ${\Delta}P=6.82$ Pa and $(\theta_j)=0.56K/W$. The Pareto solutions are also presented for various weighting coefficients and they will offer very useful data to design the pin-fins heat sink.

• Journal of Advanced Marine Engineering and Technology
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• v.24 no.4
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• pp.414-420
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• 2000

In this paper, evaporation heat transfer characteristics at a inner grooved tube were studied using a new natural refrigerants R-290, R-600a and HCFC refrigerant R-22. Experiments were performed in the inner tube with outside diameter of 12.70mm, having 75 fins with a fin height of 0.25mm. The following results were obtained from this research. On the evaporating heat transfer characteristics, the maximum increment of heat transfer coefficient was found in R-290. Average heat transfer coefficient was obtained the maximum value in R-290 and the minimum value in R-22. It reveals that the natural refrigerant can be used as a substitute for R-22. In the grooved inner tube, 70% of the increment of the heat transfer coefficient was obtained compared to the smooth tube. Comparing the heat transfer coefficient between experimental results and simulation data of other's, the Kandlikar's correlated equation was closely approximated to the author's experimental results in the smooth tube or grooved inner one.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.10
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• pp.938-946
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• 2005

Shape optimization of internally finned circular tube has been peformed for periodically fully developed turbulent flow and heat transfer. The physical domain considered in this study is very complicated due to periodic boundary conditions both streamwise and circumferential directions. Therefore, Pareto frontier sets of a heat exchanger can be acquired by coupling the CFD and the multi-objective genetic algorithm, which is a global optimization technique. The optimal values of fin widths $(d_1,\;d_2)$ and fin height (H) are numerically obtained by minimizing the pressure loss and maximizing the heat transfer rate within ranges of $d_1=0.2\sim1.5\;mm,\;d_2=0.2\sun1.5\;mm,\;and\;H=0.2\sim1.5\;mm$. The optimal values of the design variables are acquired after the fifth generation and also compared to those of a local optimization algorithm for the same geometry and conditions.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.4 s.235
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• pp.460-468
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• 2005

Analyses of flow and heat transfer characteristics and shape optimization of internally finned circular tubes have been performed for three-dimensional periodically fully developed turbulent flow and heat transfer. CFD and mathematical optimization are coupled in order to optimize the shape of heat exchanger. The design variables such as fin widths $(d_{1},\;d_{2})$ and fin height (h) are numerically optimized by minimizing the pressure loss and maximizing the heat transfer rate for limiting conditions of $d_{1}=0.2\~1.5\;mm,\;d_{2}=0.2\~1.5\;mm,$ and $h=0.2\~1.5mm$. Due to the periodic boundary conditions along main flow direction, the three layers of meshes are considered. The flow and thermal fields are predicted using the finite volume method and the optimization is carried out by means of the sequential quadratic programming (SQP) method which is widely used in the constrained nonlinear optimization problem.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.53 no.6
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• pp.960-964
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• 2020

For the first time, a single specimen (68.47 mm in total length) of Lumpenopsis pavlenkoi Soldatov, 1916 belonging to the family Stichaeidae was collected from the northernmost area of the eastern coast of Korea (Gosung, Gangwon Province) in April, 2020, using square net (1.0 m width, 0.3 m height, 2.0 mm mesh size). This species is characterized by elongated and compressed body, absence of lateral line and cirri on head, presence of scales on cheek, dorsal fin with only 50 spines, anal fin with 2 spines and 30 soft rays, and separated operculum and isthmus. The body is yellowish with 7 saddles. The new Korean name "Kko-ma-be-do-ra-chi-sog" is proposed for the genus Lumpenopsis, and "Deung-jeom-kko-ma-be-do-ra-chi" is proposed for the species L. pavlenkoi.

• Journal of Energy Engineering
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• v.14 no.4 s.44
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• pp.241-247
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• 2005

Heat transfer enhancement and pressure loss penalty caused by three-row winglets built in three-row tube-bundles in an in-line arrangement, are compared between 'common flow up' and 'common flow down' winglet configurations. The 'common flow down' winglet-pairs recommended by the previous researchers bring about $10\%$ to $25\%$ increase in heat transfer enhancement and $20\%$ to $35\%$ increase in pressure loss penalty, in comparison with fin-tube bundles without winglets. For the 'common flow up' winglet-pairs, the spanwise distance between the trailing edges (${\Delta}y$) of winglet pairs was changed and investigated. Two types ot winglet are applied for triangular and rectangular shapes. In the triangular winglets with ${\Delta}y$=5 mm in in-line tube bundles, the heat transfer increased up to $10\%$, and simultaneously the pressure loss decreased by $8\%$ to $15\%$ for the Reynolds number (based on two times channel height) ranging from 300 to 2700, when the 'common flow up' winglets were built in. The performance of fin-tube bundles with triangular winglets is much superior to the rectangular one, because of the smaller pressure-loss penalty.

• Journal of the Korea Institute of Military Science and Technology
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• v.16 no.6
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• pp.847-856
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• 2013

In this study, thermal performance of recuperators with plain and offset strip fins is investigated to enhance the thermal efficiency of a micro gas turbine. Thermal cycle analysis is conducted to determine major design parameters of a single-pass counterflow recuperator. In order to evaluate the performance of the recuperator, the effectiveness and the pressure drop in the recuperators are chosen as the objective function and the design constraint, respectively. The optimized geometries for internal structure of the recuperators with plain and offset strip fins are obtained with varying the fin spacing and height. From the result, the recuperator with offset strip fins has better thermal performance when the fin spacing, s, is smaller than 1.45mm and the thermal performance of the recuperator with plain rectangular fins is higher than that with offset strip fins in the region of $s{\geq}1.45mm$. In addition, it is found that the entrance region effect and the longitudinal wall heat conduction effect should be taken into account for accurately predicting the thermal performance of the recuperators with both plain and offset strip fins.