• 설비공학논문집
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• 제17권6호
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• pp.529-535
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• 2005

This study experimentally examines the air-side performance of spiral finned tube heat exchangers. The effects of fin spacing, fin height, and tube alignment were investigated. Reduction of fin spacing decreased the Colburn j factor. However, the effect of fin height on the Colburn j factor was negligible. An increase of tube row decreased the Nusselt number for both staggered and in-line tube alignments. However, the decrease of the Nusselt number for the in-line tube alignment was much more significant than that of the staggered tube alignment. The average Nusselt number of the staggered tube alignment was larger than that of the in-line tube alignment by $10\%$ when the Reynolds number ranged from 300 to 1700. An empirical correlation of the Nusselt number was developed by using geometric parameters of heat exchanger and correction factors. The correction factor considered the effects of tube alignment and number of tube rows on the heat transfer. The proposed correlation yielded a mean deviation of $4\%$ from the present data.

• Journal of Mechanical Science and Technology
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• 제16권5호
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• pp.676-682
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• 2002

The laminar convective heat transfer in ventilated space with various horizontal partitions was studied numerically and experimentally For the numerical study, the governing equations were solved by using a finite volume method for various numbers Re, Gr, Pr and partition numbers. The experimental study was conducted by using a holographic interferometer. The isotherms and velocity vectors have been presented for various parameters. As the number and length of partition increased, convective heat transfer decreased. Based on the numerical data, correlation equations were obtained for the mean Nusselt number in term of Gr/Re$^2$. In the region of Gr/Re$^2$$\leq$ 1, the mean Nusselt number was small, but in the region of Gr/Re$^2$> 1, the mean Nusselt number was constant.

• 한국결정성장학회지
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• 제31권3호
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• pp.127-136
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• 2021

This paper is dedicated to numerical simulation for diffusion-advective convection in a square cavity during physical vapor transport of Hg₂Br₂. Flow characteristics of the temperature difference between the source and crystal regions, 50℃ (300℃ → 250℃), partial pressures of component argon of 20 Torr and 100 Torr are investigated and presented as velocity vectors and streamlines, isotherms and iso-mass concentrations contours. Moreover, alterations of average Nusselt and average Sherwood numbers with (a) the source and crystal regions, (b) the pressures of component argon of 20 Torr and 100 Torr are analyzed and addressed in details. Both average Nusselt and average Sherwood numbers are seen to decrease with the increasing values of the partial pressures of component argon. Also, it is found that for the two different partial pressures of component argon, average Nusselt numbers at the source region are greater than at the crystal region, and inversely, average Sherwood numbers at the crystal region are greater than the source region by a factor of 3.

• 대한기계학회논문집B
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• 제38권11호
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• pp.935-942
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• 2014

본 연구에서는 내부에 고온의 원형 실린더가 위치한 저온의 기울어진 사각 밀폐계에서 Prandtl 수 변화에 따른 밀폐계 내부 자연대류 현상에 대한 수치해석을 수행하였다. Rayleigh 수가 $10^3$, $10^4$, $10^5$ 그리고 밀폐계의 각도가 $0^{\circ}$, $15^{\circ}$, $30^{\circ}$, $45^{\circ}$ 인 경우에 대해서 Prandtl 수를 0.1, 0.7, 7 로 변화시키며 Prandtl 수의 영향을 분석하였다. Prandtl 수의 변화에 따른 밀폐계 내부의 자연대류 현상은 실린더 표면과 밀폐계 벽면의 평균 Nusselt 수, 밀폐계 내부의 등온선 및 유선을 바탕으로 분석되었다. Prandtl 수가 0.7, 7 인 경우에는 각도 및 Rayleigh 수에 관계없이 열유동은 정상상태의 특성을 보였지만 Prandtl 수가 0.1 인 경우에는 Rayleigh 수가 $10^5$ 이고 밀폐계의 각도가 $0^{\circ}$ 와 $45^{\circ}$ 일 때 시간에 따라 열유동장이 변하였다. 실린더 표면과 밀폐계 벽면의 평균 Nusselt 수는 Rayleigh 수가 $10^5$ 인 경우, 각도에 관계없이 Prandtl 수가 클수록 증가하였다. 특히 Rayleigh 수가 $10^5$ 이고 Prandtl 수가 0.1 일 때 밀폐계의 각도가 $45^{\circ}$ 인 경우 실린더 표면과 밀폐계 벽면의 평균 Nusselt 수가 크게 증가하였다.

• 대한기계학회논문집B
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• 제30권7호
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• pp.656-662
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• 2006

The effects of concave hemispherical surface with inclined angle on the local heat transfer from a turbulent round jet impinging were experimentally investigated using transient liquid crystal method. This method suddenly exposes a preheated wall to an impinging jet and then the video system records the response of liquid crystals for the measurement of the surface temperature. The Reynolds numbers were used 11000, 23000 and 50000, nozzle-to-surface distance ratio from 2 to 10 and the surface angles $\alpha=0^{\circ},\;15^{\circ},\;30^{\circ}\;and\;40^{\circ}$. Correlations of the stagnation point Nusselt number according to Reynolds number, jet-to-surface distance ratio and dimensionless surface angle are investigated. In the stagnation point, in term of $Re^n$, n ranges from 0.43 in case of $2{\leq}L/d\leq6$ to 0.45 in case of $6. The maximum Nusselt number occurs in the direction of upstream. The displacement of the maximum Nusselt number from the stagnation point increases with increasing surface angle or decreasing nozzle-to-surface distance. The maximum displacement is about 0.7 times of the jet nozzle diameter.

• 에너지공학
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• 제5권2호
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• pp.203-208
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• 1996

본 연구에서는 감손우라늄칩을 처리하기 전의 시험단계로서 감손우라늄칩의 산화처리시 발생되는 산화열에 의한 산화장치 내부의 온도상승 및 외부로의 열전달을 해석하기 위해 산화장치 내부에 히터를 설치하여 실험을 수행하였다. 히터의 발생열량을 달리하면서 시간에 따른 열전달 특성을 알아내기 위하여 열유속, Nusselt 수, Grashof수와 Rayleigh 수를 구하고, Nusselt 수와 Rayleigh 수의 관계를 구하였다.

• Journal of Advanced Marine Engineering and Technology
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• 제37권7호
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• pp.677-684
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• 2013

A lot study of convection heat transfer on internal flow has been extensively conducted in the past decades using of high specific surface area, increasing heat transfer coefficient, swirling flow and improving the transport properties. This study concerned with the application of a tangential slot swirl generator for improving heat transfer in a horizontal circular copper tube. The Al particles(about $100{\sim}130{\mu}m$) was employed for this experimental work. 3D PIV(particle image velocimetry) technique has employed to measure velocity profiles of Al particles with and without swirl flow. The copper tube is heated uniformly by winding of a heating coil for heat transfer work, having a resistance of 9 ohm per meter. Experiments are performed in the Reynolds number range of 6,800~12,100 with swirl and without swirl using Al particles. Experimental data for comparison of Nusselt number is presented that of with swirl and without swirl along the test tube for the Reynolds numbers. The Nusselt number is improved with increasing of Reynolds numbers or swirl intensities along the test tube. The Nusselt number with swirl flow is about 60.0% to 119.0% higher than that obtained by the Dittus-Boelter equation.

• 태양에너지
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• 제11권2호
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• pp.63-69
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• 1991

장방형 발열체 주위에서의 열전달 현상을 고찰하기 위하여, 주위유체가 공기인 정상 층류상태에서 수직단열판에 한변의 길이가 L인 2개의 등온 사각비임이 부착된 경우 사각비임으로부터의 전열특성을 상 하 비임사이의 간격($0.5{\le}D/L{\le}3.0$)과 Grashof 수를 변수로하여 수치해석 하였다. D/L가 증가함에 따라 하부비임의 하향면과 상부비임의 측면을 제외한 나머지 비임표면의 국소 Nusselt 수는 증가하였으며 최대전체평균 Nusselt 수를 갖는 최적비임간격은 D/L=2.6에서 나타났다. 본 연구는 전자장비나 Computer 등에서 발생되는 열의 방열문제, 그리고 기판상의 Micro-chip 및 부품 등의 효율적인 배열에 관한 기초자료를 제시하는데 목적이 있다.

• Journal of Advanced Marine Engineering and Technology
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• 제22권5호
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• pp.588-594
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• 1998

Heat transfer characteristics of distance between impinging surface and a plane jet were experi-mentally investigated. The local heat transfer coefficients were measured by a thermochromic liq-uid crystal(TLC) The jet Reynolds number studied was varied over the range from 10,000310 to 30,000310 the nozzle-to-plate distance (H/B) from 4 to 10. It was observed that the Nusselt number increases with Reynolds number the occurrence of the secondary peak in the Nusselt number is within the potential core region the potential core of the jet flow can reach the impinging surface so that the wall jet can a transition from laminar to turbulent flow resulting in a sudden increase in the heat transfer rate.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2798-2803
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• 2008

The confined slot air jet impinging normally on a moving flat surface has been investigated numerically by using commercial CFD code Ansys CFX-V11. Turbulent flows are modeled using k-w turbulence model. Two-dimensional turbulent flow is considered. Calculations were conducted for a nozzle-to-plate spacing of eight slot nozzle width, at three Reynolds number(Re=4500, 6700 and 10,000) and four surface-to-velocity ratios i.e. 0, 0.25, 0.5 and 1. Results are compared against corresponding cases for heat transfer from a stationary plate. Local Nusselt number is calculated under constant wall temperature condition. The analysis reveals that the average Nusselt number increases considerably with the jet exit Reynolds number, but decrease with the plate velocity.