• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.1 no.4
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• pp.265-275
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• 1989

An experimental study of decaying swirl air flow has been obtained by tangential inlet in a straight tube with Reynolds number range 20,000~40,000. The friction factor, swirl angle, velocity profiles and turbulent intensity are measured by using micro-manometer and hot-wire anemometer. It is found that the swirl flow behaviors depend on the swirl intensity along the test tube.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.1
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• pp.122-130
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• 1998

The present work analyzes the pressure drop and heat transfer characteristics of the plate heat exchanger with staggered dimples. The flow is assumed to be constant property, three dimensional and laminar. A thermal boundary condition is uniform wall temperature and it is assumed that the flow is periodically fully developed. Elliptic grid generation is used for proper modelling of the internal tube geometry with dimples. Computations have been carried out for a variety of geometric parameters, Reynolds number, and Prandtl number. The friction factor ratio and the ratio of a module average Nusselt number are presented for the cases considered in this study. It is found that the distance between dimples has a substantial effect on the pressure drop and heat transfer.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.4
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• pp.423-430
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• 1998

Single phase heat transfer coefficients were measured for turbulent water flow in a micro-fin tube by using Wilson plot technique. An experiment for counterflow heat exchange between the micro-fin tube and its outer annulus passage was performed. The annulus side heat transfer resistance was varied and the overall heat transfer coefficients were measured. The single-phase heat transfer coefficients in a micro-fin tube were obtained by Wilson plot technique. Nusselt numbers based on the real heat transfer area and the nominal area were about 35% and 50% larger than those for smooth tube respectively Also, single-phase heat transfer correlations based on real heat transfer area and nominal area have been proposed for a micro-fin tube.

• Particle and aerosol research
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• v.9 no.4
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• pp.271-277
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• 2013

This article reports the drag reduction phenomenon of aqueous suspensions containing carbon nanotubes (CNTs) flowing through horizontal tubes. Stable nanofluids were prepared by using a surfactant. It is found that the drag forces of CNT nanofluids were reduced at specific flow conditions compared to the base fluid. It is found that the friction factor of CNT nanofluids was reduced up to approximately 30 % by using CNT nanofluids. Increased kinematic viscosities of CNT nanofluids are suggested to the key factors that cause the drag reduction phenomenon. In addition, transition from laminar to turbulent flow is observed to be delayed when CNT nanofluids flow in a horizontal tube, meaning that drag reduction occurs at higher flow rates, that is, at higher Reynolds numbers.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 2003.11a
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• pp.153-158
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• 2003

This study concerns the characteristics of helical flow in a concentric annulus with a diameter ratio of 0.52 and 0.9, whose outer cylinders are stationary and inner ones are rotating. Pressure losses and skin friction coefficients have been measured for fully developed flows of water and 0.2％ aqueous of sodium carboxymethyl cellulose(CMC), respectively, when the inner cylinder rotates at the speed of 0∼500rpm. The effect of rotation on the skin friction is significantly dependent on the flow regime. In all flow regimes, the skin friction coefficient is increased by the inner cylinder rotation. The change of skin friction coefficient corresponding to the variation of rotating speed is large for the laminar flow regime, whereas it becomes smaller as Re increases for the transitional flow regime and, then, it gradually approach to zero for the turbulent flow regime.

• 한국가스학회:학술대회논문집
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• 1997.09a
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• pp.284-291
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• 1997

배관망의 해석은 유체역학을 필요로 하며 관내의 유체의 거동과 운전 상태에 따른 유동해석을 위해 여러 식들이 사용되어왔다. 본 연구에서는 정상상태의 유량방정식을 사용해 경인지역가스 배관망에 대한 수학적 모델을 만들고 모사 및 분석을 수행하였다. 개발된 수학적 모델에서 얻어진 데이터에 통계학적인 방법을 도입해 통계학적 모델을 만듦으로써 통계학적 모델을 이용한 배관망 해석의 가능성에 대해 검토하였다.

• Proceedings of the KAIS Fall Conference
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• 2009.12a
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• pp.271-274
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• 2009

연구에서는 두 가지 종류의 미세관을 사용하여 증류수 및 0.1vol.%, 0.3vol.%의 농도를 가지는 은 나노유체의 층류 유동 조건인 Re 수 500~2500의 범위에서 대류 열전달 실험을 수행하였다. 열전달 계수 실험 결과 0.1vol.%의 경우 증류수에 비해 약 3~69%의 향상이 있었고 0.3vol.%의 경우 약 35~125%의 열전달 계수의 향상이 있었다.

• Journal of computational fluids engineering
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• v.12 no.3
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• pp.41-46
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• 2007

Dynamic behavior of immiscible gas bubble attached to the wall in channel flow plays very important role in many engineering applications. Special attention has been paid to micro direct methanol fuel cell(${\mu}$DMFC) where surface tension becomes dominant factor with minor gravitational effect due to its reduced size. Therefore, displacement of $CO_2$ bubble generating on a cathode side in ${\mu}$DMFC can be very difficult and efficient removal of $CO_2$ bubbles will affect the overall machine performance considerably. We have focused our efforts on studying the dynamic behavior of immiscible bubble attached to the one side of the wall on 2D rectangular channel subject to external shear flow. We used Level Contour Reconstruction Method(LCRM) which is the simplified version of front tracking method to track the bubble interface motion. Effects of Reynolds number, Weber number, advancing/receding contact angle and property ratio on bubble detachment characteristic has been numerically identified.

• Journal of the Korean Society of Industry Convergence
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• v.5 no.3
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• pp.193-200
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• 2002

An experimental study was performed to study heat transfer characteristics for turbulent flow in an axisymmetric annuli. The air flow temperature and the local Nusselt number in turbulent flow were measured or calculated for Re=30,000, 40,000, 50,000, 60,000, 70,000 and 80,000. The local Nusselts number were compared to that obtained from Dittus-Boelter equation with turbulent flow. The results show that the flow enhances the heat transfer in the initial and exit portion of the test tube.

• Journal of the korean Society of Automotive Engineers
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• v.10 no.2
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• pp.15-22
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• 1988

실제의 흡기관에서는 단면이 일정한 직관이 아니며, 피스톤기관의 흡기관은 단면변화가 불가피하여 액적은 소성으로 인한 관벽과의 충돌로 부착하게 되고 액적부유율은 더욱 작게 된다는 D.A. Trayser, W.E. Ranz등의 보고가 있다. 또 보제행남들은 액막류의 발생이 유해배기 가스를 증가시키고 액막류의 감소는 기통사이의 연료분배의 불균일도를 저하시키므로 NOx, HC, CO가 크게 감소된다고 보고하였다. 이와같이 액막유의 존재는 각 실린더에 유입하는 연료의 질적차이를 가져오기 때문에 액막유를 분리제거하는 방법의 연구도 많이 이루어지고 있으나 아직 실용상에 문제가 많은 것으로 남아있다. 따라서 본 고에서는 이와같이 문제되고 있는 흡기관내 액막유동의 거동을 고찰하기 위하여 액막두께 변동을 측정하는 방법에 대하여 저자들이 사용하였던 방법과 그외 초음파를 이용한 액막두께 측정법을 소개하고자 한다.