• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1835-1840
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• 2004

The HANARO, a multi-purpose research reactor of 30 MWth, open-tank-in-pool type, has been under normal operation since its initial criticality in February, 1995. The HANARO is composed of inlet plenum, grid plate, core channel with flow tubes and chimney. The reactor core channel is located at about twelve meters (12 m) depth of the reactor pool and cooled by the upward flow that the coolant enters the lower inlet of the plenum,. rises up through the grid plate and the core channel and comes out from the outlet of chimney. A guide tube is extended from the reactor core to the top of the reactor chimney for easily un/loading a target under the reactor normal operation. But active coolant through the core can be quickly raised up to the top of the chimney through the guide tube by a jet flow. This paper describes an analytical analysis that is the study of the flow behavior through the guide tube under reactor normal operation and unloading the target. As results, it was conformed through the analysis results that the guide jet is suppressed under the top of the chimney after modifying the orifice diameter of 37.5 mm to 31 mm.

• International Journal of Air-Conditioning and Refrigeration
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• 제16권4호
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• pp.117-123
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• 2008

The present study is directed at flow and heat transfer of $CO_2$ and oil mixtures in a circular tube. PAG and POE oils are considered in this study. Flow characteristics of $CO_2$ and oil mixtures have been investigated by flow visualization. Pressure drop has been measured in the range of operating mass flow rate from 0.1 to 0.4 kg/min in a circular tube. Heat transfer characteristics of $CO_2$/oil mixtures have been investigated using a counterflow heat exchanger. In case of pure liquid $CO_2$ as well as $CO_2$ and POE mixtures, flow are seen to be uniform so that $CO_2$ and POE oil are still miscible even at flowing state. However, it is found that $CO_2$ and PAG are not miscible. Pressure drop of $CO_2$/PAG mixtures are much higher than that of $CO_2$/POE mixtures as well as pure $CO_2$ at a fixed mass flow rate. As the concentration of POE oil is increased from 0 to 5 wt%, pressure drop is increased. However, heat transfer rate and heat transfer coefficient of $CO_2$/POE mixtures are much higher than that of $CO_2$/PAG mixtures. The f-factor correlation and Nusselt number correlation for $CO_2$/POE oil mixtures are suggested in this paper.

• 한국가시화정보학회지
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• 제7권1호
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• pp.29-34
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• 2009

During the past three or four decades, the characteristics of turbulent flow have been studied extensively because of their scientific and academic importance. This research deals with the periodic flow oscillation without swirling flow in a 180 degree circular tube using hot wire anemometry, microphone and accelerometer. The frequency regions are observed through the structured oscillation from spectrum. This work carried out to measure the sound level for each Reynolds number, $6{\times}10^4$, $8{\times}10^4$ and $1{\times}10^5$ respectively at the test tube without swirl flow.

• 대한기계학회논문집B
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• 제21권11호
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• pp.1552-1561
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• 1997

In this numerical study, it is investigated for the ice-formation phenomena for water flow in a concentric tube. The freezing layers of ice in both the inner and outer wall of a concentric tube are simultaneously considered. In the solution strategy, the complete set of governing equations in both the solid and liquid regions are resolved. Numerical results are obtained by varying the inner/outer wall temperatures and Reynolds number. The results show that the inner/outer wall temperatures have the great effect on the thickness of the solidification layer thereof. The shapes of ice layer in both the inner and outer wall can be expressed as a function of inverse Graetz number. As the wall temperature in inner or outer tube decreases, the heat transfer coefficients in both inner and outer ice layer surfaces increase absolutely.

• 설비공학논문집
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• 제9권4호
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• pp.454-461
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• 1997

Heat transfer and pressure drop for single phase flow of water in circular smooth and micro-fin tubes are measured. Copper tubes of 9.52 and 7mm outer diameter were used. The internal roughness in micro-fin tubes was formed by spiral grooves having $25^{\circ}$ helx angle, 0. 12mm fin height and 0.454mm pitch in 9.52mm tubes; $18^{\circ}$ helix angle, 0.15mm fin height and 0.322mm pitch in 7mm tubes. The measured friction factor and heat transfer coefficient are compared with relevant previous works, and the correlations for micro-fin tube are developed.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2007년도 동계학술발표대회 논문집
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• pp.185-190
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• 2007

For the successful design of heat exchangers, it is very important to understand local heat transfer characteristics on the circular cylinder of the cross flow heat exchangers. In this study, the heat exchanger using screen is developed to enhance heat transfer. The naphthalene sublimation technique is employed to measure the local heat transfer coefficients in the heat exchanger. The experiments are performed for single circular tube, in-line array tube bank with and without heat transfer promoter. Local Nusselt numbers of single circular tube and tube bank with heat transfer promoter are investigated and compared to those of without heat transfer promoter.

• 한국가시화정보학회지
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• 제9권2호
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• pp.21-26
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• 2011

Hydrodynamic focusing technique to generate focused flow has been used for flow cytometry in microfluidic devices. However, devices with circular capillary tubes made of glass are not suitable for flow visualization or optical signal detection because the rays of light are distorted at the curved interface. We devised a new acrylic chamber assembled with a pulled micropipette and a rectangular microchannel made of glass. This new channel geometry enabled us to visualize the three-dimensional (3D) flow characteristics with confocal imaging technique. We analyzed the 3D hydrodynamic focusing in a circular capillary tube and a rectangular microchannel over a practical range of flow rates, viscosities and pressure drops.

• International Journal of Air-Conditioning and Refrigeration
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• 제14권1호
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• pp.14-18
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• 2006

This study was performed to investigate the heat transfer characteristics of the circular fin-tube heat exchanger. This paper contains the experimental data for the seven kinds of fin geometries. The correlation of Stasiulevicius agreed with the experimental data at high Reynolds number, however not well at low Reynolds number. The Nusselt number was well correlated with Graetz number, and showed a transition near Gz=10. An empirical correlation proposed in the present study agreed well with the experimental data.

• Journal of Mechanical Science and Technology
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• 제17권10호
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• pp.1520-1532
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• 2003

An experiment was performed to obtain the local heat transfer coefficient and Nusselt number in a circular duct with a 180$^{\circ}$ bend for Re=6 x 10$^4$, 8 x 10$^4$ and 1 x 10$\^$5/ under swirling flow and non-swirling flow conditions. The test tube with a circular section was made from stainless steel having a curvature ration of 9.4. Current heat flux of 5.11 kW/㎡ was applied to the test tube by electrical power and the swirling motion of air was produced by a tangential inlet to the pipe axis at 180$^{\circ}$. Measurements of local wall temperatures and the bulk mean temperatures of air were made at four circumferential positions at 16 stations. The wall temperatures showed a reduced distribution curve at the bend for the non-swirling flow, but this effect did not appear for the swirling flow. The Nusselt number distributions for the swirling flow, which was calculated from the measured wall and the bulk temperatures, were higher than that of the non-swirling flow. The average Nusselt number of the swirling flow increased by about 90-100%, compared to that of the non-swirling flow. The Nu/Nu$\_$DB/ values at the 90$^{\circ}$ station for non-swirling flow and swirling flow were approximately 2.5 and 4.8 at Re=6x10$^4$ respectively. The values agree well with Said's results for non-swirling flow.

• 대한기계학회논문집B
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• 제35권2호
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• pp.105-112
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• 2011

본 연구의 목적은 나선형 원형핀-튜브 증발기의 열전달 성능에 관하여 해석적으로 연구하는 것이다. 이를 위하여 두 가지 냉매인 R134a 와 R600a 에 대하여 냉매의 질량유량, 공기온도, 공기풍량 및 튜브직경 변화에 대하여 나선형 원형핀-튜브 증발기의 열전달 성능변화를 고찰하였다. 본 연구에서 개발된 증발기 성능해석 프로그램은 실험결과와 평균 8.3% 오차 범위 안에서 잘 예측되었다. 결과적으로, 동일한 냉매유량 범위에서 R600a 를 사용하는 경우가 R134a 를 사용하는 경우보다 더 우수한 열전달율을 나타내었다. 열전달량은 풍량 및 공기온도가 증가할수록 증가하였으나 열전달량은 튜브두께가 증가할수록 감소하였다.