• 동력기계공학회지
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• 제5권4호
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• pp.18-23
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• 2001

This paper is to present the results of a comprehensive study on heat transfer in annuli with spirally corrugated inner tubes in the turbulent regime. Tube surface-temperature measurements were used to explain the enhancement phenomena in the annuli with several different corrugated tubes. Nusselt numbers were between 1.1 and 2 times the smooth annulus values. These enhancement values can be used to determine the appropriate range of applicability for spirally corrugated annuli.

• 대한기계학회논문집B
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• 제34권2호
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• pp.203-212
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• 2010

수분류 스프레이 냉각은 많은 산업적인 응용분야에 넓게 사용되고 있다. 본 연구는 수분류 스프레이가 표면거칠기가 주어진 $900^{\circ}C$ 고온강판의 표면에 충돌하는 경우, 열유속 및 열전달계수의 정량적인 측정을 통해 표면거칠기가 수분류 스프레이 냉각에 미치는 영향을 고찰하였다. 이 때의 국소 열유속은 시편, 카트리지히터, 열전대의 조합으로 고안된 고유의 열유속게이지를 제작하여 엄밀하게 측정되었다. 평균 표면거칠기 높이를 기준으로 40, 60, $80{\mu}M$의 3 가지 표면과 매끈한 표면에 대한 수분류 스프레이 냉각 의 열전달 현상이 비교 및 평가되었다. 표면거칠기가 주어진 표면에서의 돌출물은 얇은 열 경계층두께를 통과할 수 있기 때문에 표면거칠기가 주어진 경우에 열전달은 뚜렷하게 증가하였고, 표면거칠기의 의한 열전달 향상 기구는 서로 다른 비등영역에 대해 구분하여 조사되었다.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2005년도 전기학술대회논문집
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• pp.177-182
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• 2005

Many studies have been conducted to increase heat transfer in fluid. One of the various heat transfer enhancement techniques is to suspend fine metallic or nonmetallic solid powder in traditional fluid. Nanofluid is defined at a new kind of heat transfer fluid containing a very small quantity of nanometer particles that are uniformly and stably suspended in a liquid. In this study CuNi or CuAg nano particles are used to investigate heat transfer enhancement. The result shows the thermal conductivity of nanofluid is much higher than that of traditional fluid.

• 대한기계학회논문집B
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• 제32권3호
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• pp.198-206
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• 2008

A numerical study has been carried out to investigate heat transfer enhancement in channel flow using large-scale vortices. A square cylinder, inclined with respect to the main flow direction, is located at the center of the channel flow, generating a separation region and Karman vortices. Two cases are considered; one with a fixed blockage ratio and the other one with a fixed cylinder size. In both cases, the flow characteristics downstream of the cylinder significantly change depending on the inclination angle. As a result, heat transfer from channel wall is significantly enhanced due to increased vertical-velocity fluctuations induced by the large-scale vortices shed from the cylinder. Quantitative results as well as qualitative physical explanation are presented to justify the effectiveness of the inclined square cylinder as a vortex generator to enhance heat transfer from channel wall.

• 수산해양교육연구
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• 제5권2호
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• pp.119-127
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• 1993

This work studies for heat transfer and pressure drop performance of integral inner and outer fin tubes, designed to enhance the heat transfer performance of smooth tubes for in recipro and turbo refrigerator or high performance compact heat exchangers. Eight different inner spiral fin copper tubes with integral fin at outside surfaces were employed to improve boiling heat transfer coeffcient. For comparison, tests were made using a plain tube having the inside diameter and an outside diameter equal to that at the root of the fins for the finned tubes. Pool boiling heat transfer is investigated experimentally and theoretically on single tube arrangement. The refrigerant evaporates at a saturation state of 1 bar on the outside tube surface heated by hot water. The refrigerant R11 ($CFCl_3$) was used at a pressure of $P_s=1bar$ as a convenient test fluid with a boiling temperature of $T_s=23.6^{\circ}C$. The observed heat transfer enhancement of boiling for finned tubes significantly exceeded that to be expected on grounds of increased area. The maximum Vapor - side enhancement(i.e., vapor - side heat transfer coefficient of finned tube/vapor - side coefficient for plain tube) was found to be around 4 at 1299fpm - 30grooves tube.

• 설비공학논문집
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• 제10권6호
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• pp.743-752
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• 1998

Experiments were performed to characterize single-phase heat transfer behavior of submerged liquid jet with multiple nozzle normally impinging on the smooth and extended surfaces. Arrays of 9 and 36 nozzles were used, with diameters of 0.5 to 2.0mm providing nozzle area ratio (AR) from 0.05 to 0.2. The square pin fin arrays were chosen as extended surfaces and the effects of geometrical parameters such as fin height, the ratio of fin width to channel width on heat transfer enhancement were examined. Single nozzle characteristics were also evaluated for comparison. The results clearly showed that heat transfer enhancement could be realized by using multiple nozzles at the constant volume flow rate. The average Nusselt number of multiple nozzle impingement on the smooth surface was correlated by the following equation : Nu/$Pr\frac{1}{3}=0.94 Re^{0.56}N^{-0.12}AR^{0.50}$The average heat transfer coefficients of multiple nozzle impingement on the extended surfaces decreased with increasing fin height and the ratio of fin width to channel width. The effectiveness of ex-tended surfaces ranged from 1.5 to 3.5 depending on the fin height, the ratio of fin width to channel width of pin fin arrays, nozzle number and nozzle area ratio.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.115-118
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• 2002

The present study deals with CFD analysis of a plastic heat exchanger with corrugated wall. This exchanger has sinusoidal corrugations, and the flow through the exchanger is three dimensional. In addition, CFX-5.4, a commercial code utilizing unstructured mesh, was used as a computational method for solving RANS(Reynolds-Averaged Navier-Stokes) equations, and the applied turbulence model is $k-{\varepsilon}$ model. The factors to affect the efficiency of a plastic heat exchanger are heat conductivity, flow characteristics and so on. For those two factors, heat conductivity is fixed by the wall material. Therefore, the How along the corrugation affects the efficiency more, provided the same material. In conclusion, the heat transfer enhancement of a plastic heat exchanger with corrugated wall can be recognized from the flow characteristics such as velocity streamline, local heat transfer coefficient, velocity contour, and pressure contour. To confirm the results, both of the measured and the computational data for pressure loss were compared with each other, and they were identical.

• Composites Research
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• 제26권6호
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• pp.373-379
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• 2013

냉매의 비등이나 응축같은 열전달 향상을 위하여 금속 표면위에 탄소나노튜브(CNT)를 코팅하는 것을 연구하였다. 다중벽 탄소나노튜브/구리 복합소재는 어트리션 볼밀에 의해서 제작되었으며, 정전 도장 장치로 복합 분말을 구리 기판위에 코팅한 후 전기로에서 소결하였다. 본 논문에서는 CNT/Cu 코팅 표면의 분석 및 소결전후의 탄소나노튜브의 변화를 파악하기 위하여 샘플들을 주사전자현미경, EDAX, 라만분광법에 의해 분석하였다. 아울러 열전달 촉진은 비등열전달로 확인하였다.

• Journal of Mechanical Science and Technology
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• 제15권12호
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• pp.1853-1859
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• 2001

An experimental study is presented for a flow field in a two dimensional wavy channels by PIV. This flow has two major applications such as a blood flow simulation and the enhancement of heat transfer in a heat exchanger. While the numerical flow visualization results have been limited to the fully developed cases, existing experimental results of this flow were simple qualitative ones by smoke or dye streak test. Therefore, the main purpose of this study is to produce quantitative flow data for fully developed and developing flow regimes by the Correlation Based Correction PIV (CBC PIV) and to conjecture the analogy between flow characteristics and heat transfer enhancement with low pumping power. Another purpose of this paper is to examine the onset position of the transition and the global mixing, which results in transfer enhancement. PIV results on the Fully developed and developing flow in a wavy channel at Re=500, 1000 and 2000 are obtained. for the case Reynolds Number equals 500, the PIV results are compared with the finite difference numerical solution.

• Advances in nano research
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• 제2권2호
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• pp.99-109
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• 2014

Experiments are performed to investigate the single-phase flow heat transfer augmentation of MWCNT/HT-B Oil in both smooth and micro-fin helical tubes with constant wall temperature. The tests in laminar regime were carried out in helical tubes with three curvature ratios of 2R/d=22.1, 26.3 and 30.4. Flow Reynolds number varied from 170 to 1800 resulting in laminar flow regime. The effect of some parameters such as the nanoparticles concentration, the dimensionless curvature radius (2R/d) and the Reynolds number on heat transfer was investigated for the laminar flow regime. The weight fraction of nanoparticles in base fluid was less than 0.4%. Within the applied range of Reynolds number, results indicated that for smooth helical tube the addition of nanoparticles to the base fluid enhanced heat transfer remarkably. However, compared to the smooth helical tube, the average heat transfer augmentation ratio for finned tube was small and about 17%. Also, by increasing the weight fraction of nanoparticles in micro-fin helical tubes, no substantial changes were observed in the rate of heat transfer enhancement.