• 한국자동차공학회논문집
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• 제5권1호
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• pp.49-58
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• 1997

In this paper, a transfer function was obtained for a PWM high speed solenoid valve controlled metal belt CVT system. The transfer function was defined as the ratio of speed ratio to PWM duty ratio and derived in time domain by linear regression analysis from the experimental results. The transfer function obtained showed different dynamic characteristics for the up and down shift. Also, LQG/LTR controller was designed for the CVT system using the transfer function. It is seen from the experimental results that LQG/LTR control showed good performance for the speed ratio tracking and disturbance rejection. The phase difference and relatively slow response are considered due to the inaccuracy os the transfer functions, which resulted from the inherent nonlinearities of the transmission characteristics of the metal belt CVT.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2297-2302
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• 2007

Numerical simulations are conducted to analyze conjugate heat transfer characteristics in a ribbed channel. In this simulation, the effects of Reynolds number and heat capacity of the solid channel wall on convective heat transfer are observed in the turbulent flow regime. In the case of the conducting wall against isothermal wall, the relative ratio of the thermal resistance between the solid wall and the flow field varies with Reynolds number. Thus the characteristics of the conjugate heat transfer are changed with the Reynolds number. Heat capacity ratio affects the temperature fluctuation inside solid wall. The temperature fluctuation inside the solid wall decreases with increasing the heat capacity of the solid wall so that the convective heat transfer increases. When the thermal conductivity ratio is smaller than 10, the effects of flow characteristics on heat transfer are changed.

• 설비공학논문집
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• 제24권1호
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• pp.45-50
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• 2012

The plate fin and tube type of heat exchanger is widely used in air conditioner, and the heat exchanger is assembled by the mechanical expansion of copper tubes and fastening the aluminum fin. The objective of the present study is to investigate how the mechanical expansion of copper tube affects on the heat transfer performance of a plate fin and tube type heat exchanger. This study has been performed by experimental and numerical methods. The numerical and experimental results show that the tube expansion ratio has a influence on the heat transfer performance. Within the tested expansion ratio, the contact pressure shows the peak value and it decreases as the expansion ratio increases. Air-side heat transfer coefficient increases until the expansion ratio reaches 1.23, and then decreases with the similar pattern to the contact pressure. Also, contact heat transfer coefficient shows the maximum when the contact pressure is highest as well as the air-side heat transfer coefficient.

• Journal of Welding and Joining
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• 제19권5호
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• pp.486-491
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• 2001

The effect of S content in welding wires on spattering characteristics and droplet transfer phenomena was studied. In MAG welding using 80%Ar-$20%CO_2$ shielding gas, spattering characteristics and droplet transfer phenomena were varied with S content of wire. Sulfur addition in wire reduced surface tension of droplet and weld pool, and made arc more stable in MAG welding. With increasing S content, the spattering ratio and the ratio of large size spatter ($d{\geq}1.0mm$) were reduced in short circuit transfer mode. In spray transfer mode, spattering ratio, however was increased when sulfur was added more than 0.020wt.% because surface tension of droplets and weld pool was reduced too much even though arc stability was improved.

• 대한기계학회논문집B
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• 제40권4호
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• pp.237-243
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• 2016

호기성 수처리 과정의 폭기에 소요되는 에너지의 이용효율을 높이기 위해서는 물질전달 특성뿐만 아니라 소요동력에 대한 연구가 필요하다. 본 논문은 수직 2 상 유동 및 물질전달 특성에 미치는 오리피스 노즐형상과 소요동력의 영향에 대한 실험적 연구를 목적으로 한다. 측정 변수들을 이용하여 유량비, 소요동력, 물질전달 계수 그리고 물질전달 효율을 산출하였다. 소요동력이 커지면 물질전달 계수는 증가하는 반면에 유량비와 물질전달 효율은 감소하였다. 무차원 면적비가 작은 오리피스 노즐의 유량비, 물질전달 계수 및 효율이 높게 나타났다. 물질전달 특성에 미치는 유량비, 소요동력 그리고 프라우드 수의 영향을 평가하기 위한 실험식을 제시하였다.

• 한국분무공학회지
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• 제27권3호
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• pp.126-133
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• 2022

The objective of this is to experimentally investigate the effect of mixed jet on the oxygen transfer characteristics with the primary nozzle area ratio of an annular nozzle ejector for the application of a microbial fuel cell. A direct visualization method with a high speed camera system was used to capture the horizontal mixed jet images, and a binarization technique was used to analyze the images. The clean water unsteady state technique was used for the oxygen transfer measurement. The air-water mixed jet discharging into a water tank behaved similar to a buoyancy or horizontal jet with the primary nozzle area ratio. It was found that an optimum primary nozzle area ratio was observed where the oxygen transfer performance reached its maximum value due to the decrease of air volume fraction and the increase of jet length and air bubble dispersion.

• 대한교통학회지
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• 제26권4호
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• pp.217-227
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• 2008

이용자가 수용 가능한 환승시간 및 환승거리의 결정은 환승시스템을 계획하는 단계에서 가장 우선적으로 고려되어야 한다. 환승 자체가 불가능한 경우, 환승시스템 구성요소의 개선은 환승을 선택하는데 있어서 전혀 영향을 주지 못한다. 한계환승도보거리는 이용자의 처음교통수단에서 다음 교통수단까지의 합리적인 도보거리와 대기시간으로 결정되어져야한다. 대중교통 네트워크나 환승시스템 계획단계에서 환승서비스 권역을 좀 더 현실적으로 결정하기 위해서는 이용자 속성이 고려되어야 한다. 따라서 본 연구에서는 환승에 초점을 맞추어 이루어 졌으며, 대중교통 이용자 인적속성에 따라 수용하는 환승거리와 시간이 다를 것이라는 가정을 한 후 대중교통 이용자 인적속성에 따라 환승시간별 환승률 산정 모형을 개발을 하는것을 목적으로 하였다. 이 중 한계환승시간과 상관관계가 높고, 환승시간에 따른 명확한 차이가 있는 성별, 월평균 수입별, 대중교통 환승횟수로 한정하여 환승시간별 환승률, 환승거리별 환승률의 결정모형을 개발하였다.

• 대한기계학회논문집B
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• 제28권8호
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• pp.921-928
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• 2004

Measurements of local heat/mass transfer coefficients in rotating two-pass ducts are presented. Ducts of three different aspect ratios (W/H), 0.5, 1.0 and 2.0, are employed with a fixed hydraulic diameter ($D_h$) of 26.7 nm. $90^{\circ}$-rib turbulators are attached on the leading and trailing walls symmetrically. The rib height-to-hydraulic diameter ratio ($e/D_h$) is 0.056, and the rib pitch-to-rib height ratio (p/e) is 10. The experimental conditions are the same as those of the previous part of the study. As the rib height-to-duct height ratio (e/H) increases, the core flow is more disturbed and accelerated in the midsections of ribs. Therefore, the obtained data show higher heat/mass transfer in the higher aspect ratio duct. Dean vortices also augment heat/mass transfer in the turn and in the upstream region of the second pass. However, the effect becomes less significant for the higher aspect ratio because the surface area increases in the present geometric condition. The effect of rotation produces heat/mass transfer discrepancy.

• 대한기계학회논문집B
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• 제25권12호
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• pp.1676-1683
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• 2001

An experimental study on condensation heat transfer characteristics of helically coiled spiral tubes was performed. The refrigerant is R-113. A refrigerant loop was established to measure the condensation heat transfer coefficients. Experiments were carried out uniform heat flux of 15 kw/m$^2$, refrigerant quality of 0.1∼0.9, curvature ratio of 0.016, 0.025 and 0.045. The curvature of a coil was defined as the ratio of the inside diameter of the tube to the diameter of the bending circle. To compare the condensation heat transfer coefficients of coiled spiral tubes, the previous results on coiled plain tubes and straight plain tubes were used. The results shows that the condensation heat transfer coefficients of coiled spiral tubes largely increase, as increasing Re and quality, compared to those of coiled plain tubes and straight plain tubes. As increasing degree of subcooling, however, the condensation heat transfer coefficients on coiled spiral tubes decrease. It is found that the heat transfer enhancement is more better than coiled plain tubes and straight plain tubes, as increasing curvature ratio.

• 대한기계학회논문집B
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• 제39권10호
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• pp.817-824
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• 2015

본 논문은 수직 오리피스 노즐의 유동 및 물질전달 특성에 대한 실험적 연구를 목적으로 한다. 구동유체 및 부유체의 유량, 용존산소 농도 그리고 소비 전력을 측정하였으며, 고속 카메라를 이용한 직접 촬영 기법으로 수직 혼합유동의 가시화 이미지를 획득하였다. 측정자료를 이용하여 질량비, 총괄 산소전달 계수 그리고 물질전달 성능계수를 도출하였다. 구동압력이 증가하면 질량비는 약간 감소하는 반면에, 산소전달 계수와 소비전력은 증가하였다. 구동압력이 증가하고 질량비가 작아지면, 기포의 미세화가 촉진되고 확산도가 증대되기 때문에 산소 전달율이 증가하였다.