• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.4 no.3
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• pp.155-162
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• 1992

Theoritical Study is performed on heat transfer and fluid flow induced by square-ribbed roughness elements in a concentric annulus. The fluid properties were assumed to be constant, and the radius($r_m$) of the maximum speed point was found by using the principle of equation of Leung and Labib. The Nusselt number and friction factor as a function of the Reynolds number($R_e=10^4$, $5{\times}10^4$, $7{\times}10^4$, $10^5$) in artifical roughness $S/{\epsilon}=5,10,20,30$, $P/{\epsilon}=2,5,8$ and prandtl number = 0.72 have been discussed. In this study, it has been found that the Nusselt number and friction factor of rough wall are larger than those of smooth ones.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.4
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• pp.270-274
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• 2016

The effect of the rib angle-of-attack on heat transfer in the convergent channel with ${\vee}/{\wedge}$-shaped ribs was examined experimentally. Four differently angled ribs (a = $30^{\circ}$, $45^{\circ}$, $60^{\circ}$, and $90^{\circ}$) were placed to only the one sided wall. The ribbed wall was manufactured with a fixed rib height (e) of 10 mm and rib spacing (p)-to-height (e) ratio of 10. The convergent channel had a length of 1,000 mm and a cross-sectional areas of $100mm{\times}100mm$ at inlet and $50mm{\times}100mm$ at exit. The measurement was conducted for the Reynolds numbers ranging from 22,000 to 75,000. The results show that the Nusselt number is generally higher at higher Reynolds number and that an angle-of-attack of $45^{\circ}$ at the ${\wedge}$-shaped rib produces the greatest Nusselt number.

• Journal of Korean Society of Steel Construction
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• v.14 no.4
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• pp.499-508
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• 2002

A simple design method for rib-reinforced seismic steel moment connections has been recently proposed based on the equivalent strut model. An experimental program was implemented to verify the proposed design method, as well as develop the schemes that will prevent cracking at the rib tip where stress concentration was evident. All specimens designed using the proposed method were able to develop a satisfactory connection plastic rotation of 0.04 radian. In addition to rib reinforcement, slight beam flange trimming pushed the plastic hinging and local buckling of the beam away from the rip tip and effectively reduced cracking potential at the rib tip. Using strain gage readings, the strut action of the rib and resulting reverse shear in the beam web were also experimentally identified.

• Proceedings of the KIPE Conference
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• 2012.07a
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• pp.501-502
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• 2012

본 논문에서는 입력 단 센서를 제거한 태양광 AC 모듈 인터리브드 플라이백 인버터의 최대 전력점 추종 및 전류 평형 제어 기법을 제안한다. 기존 제어 방식들의 수행을 위해서는 입력 전압 $V_{pv}$, 입력 전류 $I_{pv}$ 센서와 각 상 스위치 단의 전류 센서들이 필요하나 4개의 센서와 주변 회로는 AC 모듈의 사이즈, 부피 및 가격을 증가시킨다. 이러한 문제점들을 해결하기 위해 제안하는 방식은 각 상의 전류 센서만을 사용하여 최대 전력점 추종 및 전류 평형 제어를 동시에 수행한다. 제안한 시스템의 타당성을 이론적 분석과 시뮬레이션을 통해 검증한다.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.4
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• pp.195-200
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• 2015

The thermal performance in the channels with two-wall rectangular convergent/divergent cross-sectional areas along the axial distance was investigated experimentally. The ribbed rectangular convergent/divergent channels were manufactured with a fixed rib height (e) = 10 mm and the ratio of rib spacing (p) to height (e) = 10. Three different parallel angled ribs (a = $30^{\circ}$, $45^{\circ}$, and $60^{\circ}$) were each placed on the channel's one sided wall only. The convergent channel of $D_{ho}/D_{hi}=0.67$ and the divergent channel of $D_{ho}/D_{hi}=1.49$ were considered. The ribbed divergent channel produced better thermal performance than the ribbed convergent channel in three different restrictions; identical flow rate, identical pumping power, and identical pressure loss.

• Journal of Korean Society of Steel Construction
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• v.19 no.6
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• pp.621-632
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• 2007

The purpose of this study was the estimation and formulation of orthotropic flexural rigidities considering the deformed shape for a plate stiffened with rectangular ribs. Analytical results of methods modifying the flexural rigidity of the x-direction, the y-direction or both directions were compared at the center, the x-directional quarter point and the y-directional quarter point of stiffened plates loaded at the center. The composite method modifying the flexural rigidity of both directions improves the accuracy compared with the other methods. Moreover, the ratio of modified coefficients for each directional rigidity can be expressed as a function corresponding to each dimension of stiffened plates. The application of modified coefficient functions to various types of stiffened plates with different boundary conditions, aspect ratios and rib arrangement shows that the increment of the error ratio is small compared with examples of this study and the application of proposed functions shows more accurate results than previous methods modifying the flexural rigidity. Therefore, by using the modified coefficient functions proposed in this study, the orthotropic plate analysis of plates stiffened with rectangular ribs can easily achieve more accurate displacement results.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.26 no.4
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• pp.175-180
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• 2014

Experimental investigations of the heat transfer and friction factors in the ribbed divergent rectangular channel with the channel exit hydraulic diameter to inlet hydraulic diameter ratio of 1.16 were performed. The surface heaters were mounted onto the two opposite walls. The main experimental parameter is the ratio of rib pitch (p) to height (e), at which the ratios (p/e) of 6, 10, and 14 are considered in the channel with ribs on one wall only. The straight ribbed square channel is also considered as a comparison. The major findings are that the ratio of p/e = 6 shows the highest values in the heat transfer and the ratio of p/e = 10 indicates the greatest friction factor in the ribbed divergent channel. Editor's note:No major changes or corrections needed. Well written.

• Journal of Advanced Marine Engineering and Technology
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• v.34 no.5
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• pp.638-644
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• 2010

Numerical predictions of a fully developed turbulent flow through a square duct ($30mm{\times}30mm$) with twisted tape inserts and with twisted tape plus interrupted ribs are respectively conducted to investigate regionally averaged heat transfer and flow patterns. A rib height-to-channel hydraulic diameter(e/$D_h$) of 0.067 and a lengthto-hydraulic diameter(L/$D_h$) of 30 are considered at Reynolds number ranging 8,900 to 29,000. The interrupted ribs are axially arranged on the bottom wall. The twisted tape is 0.1 mm thick carbon steel sheet with diameter of 28 mm, length of 900 mm, and 2.5 turns. Each wall of the square channel is composed of isolated aluminum sections. Two heating conditions are investigated for test channels with twisted tape inserts and rib turbulators: (1) electric heat uniformly applied to four side walls of the square duct, and (2) electric heat uniformly applied to two opposite walls of the square channel. The results show that uneven surface heating enhances the heat transfer coefficient over uniform heating conditions, and significant improvements can be achieved with twisted tape inserts plus interrupted ribs.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.10
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• pp.773-778
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• 2015

The local heat transfer and pressure drop of developed turbulent flows in convergent/divergent channels with square axial cross-sectional areas were experimentally investigated to improve the channel design, such as a gas turbine cooling system. Square convergent/divergent channels with one ribbed wall were manufactured with a fixed rib height e of 10 mm and a ratio of rib spacing p to height e of 10. The measurement was conducted for Reynolds numbers from 15,000 to 89,000. Convergent, divergent, and straight channels with ratios $D_{ho}/D_{hi}$ of 0.75, 1.33, and 1.0, respectively, are considered. Of the three channel types, the ribbed divergent channel was found to produce the best thermal performance under identical flow rate, pumping power, and pressure loss conditions.

• Journal of Korean Society of Steel Construction
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• v.16 no.4 s.71
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• pp.479-492
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• 2004

When U-ribs of steel deck plates are connected at the field, overhead welding should be done with backing strips. Misalignments may occur and lead to eccentric moments as well as high stress concentrations at welded joints. In this study, stress analyses and fatigue tests were carried out. Stress analyses for U-ribs' welded joints with backing strips were performed with different misalignments, root shapes, root gaps, and backing strip sizes. From the stress analyses, the stress concentration factors increased with increasing misalignments and root gaps. With the fixed misalignments and root gaps, the stress concentration factors obtained in the case of the semi-circle root shape were lower than those in the case of the right-angle root shape. It was verified that backing strip sizes have little influence on stress concentration factors. The fatigue tests for U-ribs' welded joints with backing strips indicated that increased misalignments shorten fatigue life drastically and cracks usually initiate at the root of the base metal and are propagated to the weld bead surface. Based on the results of the stress analyses, root-shape control methods were developed to mitigate stress concentration by changing welding condition control, radius curvature, and flank angle.