• Title/Summary/Keyword: Enhancement of Heat Transfer

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Effects of Heat Transfer on Geometries of Spirally Corrugated Tubes in Annuli (환형관에서 나선파형관의 형상이 열전달에 미치는 효과)

  • Ahn, Soo-Whan;Oh, Se-Kyung
    • Journal of Power System Engineering
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    • v.5 no.4
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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.

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Heat Transfer Enhancement of Water Spray Cooling by the Surface Roughness Effect (표면거칠기 효과에 따른 스프레이 냉각의 열전달 향상 연구)

  • Lee, Jung-Ho
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.34 no.2
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    • pp.203-212
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    • 2010
  • Water spray cooling has been widely used in a variety of industrial applications. The present study concentrated on quantitative measurements of the heat flux and heat transfer coefficient by water spray as it impinges on the rough surface of a hot steel plate at $900^{\circ}C$. A novel experimental technique was developed for a hightemperature heat flux gauge with a test block, cartridge heaters, and thermocouples that was used to measure the surface heat flux information on the hot steel plate for local heat flux measurements. The roles of the surface roughness on heat transfer are presented in this paper for well-characterized four rough surfaces with average rms roughness heights of $40-80{\mu}M$. The results show that the local heat transfer for rough surfaces is higher than that for a smooth surface. Heat transfer can be significantly increased by the presence of surface roughness elements, which can disrupt the thin thermal boundary layer. In addition, the heat transfer enhancement mechanism on a rough surface can be investigated by a different boiling regime.

The effects of nanofluid containing metal nano-powder on heat transfer (나노금속분말을 혼합한 용액이 열전달에 미치는 영향)

  • Kim, Hye-Min;Choi, Soon-Ho;Jeong, Jae-Hyun;Jeong, Jae-Hyun
    • Proceedings of the Korean Society of Marine Engineers Conference
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    • 2005.06a
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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.

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Effective Heat Transfer Using Large Scale Vortices (대와류를 이용한 채널 내 열전달 증진)

  • Yoon, Dong-Hyeog;Choi, Choon-Bum;Lee, Kyong-Jun;Yang, Kyung-Soo
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.32 no.3
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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.

A Study on Finned Tube Used in Turbo Refrigerator(II) - on boiling heat transfer - (터보 냉동기용 핀 튜브에 관한 연구(II) - 비등 열전달에 관하여 -)

  • Han, Kyu-Il;Kim, Si-Young;Cho, Dong-Hyun
    • Journal of Fisheries and Marine Sciences Education
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    • v.5 no.2
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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.

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A study of single-phase liquid cooling by multiple nozzle impingement on the smooth and extended surfaces (다중노즐에 의해 분사된 평면 및 확장면의 단상액체냉각에 관한 연구)

  • 소영국;박복춘;백병준
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.10 no.6
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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.

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A Study on the Heat Tranfer Enhancement of Heat Exchangers with Corrugated Wall (주름진 판형 열교환기의 성능향상에 관한 연구)

  • Oh Yunyoung;Yoo Seongyeon;Ko Sungho
    • Proceedings of the KSME Conference
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    • 2002.08a
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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.

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A Study on the Sinterning of the Carbon Nanotube/Metal Composites for the Heat Transfer Enhancement (열전달 촉진을 위한 탄소나노튜브(CNT)/금속 복합체 소결 코팅에 관한 연구)

  • Zheng, XiRu;Kim, Min Soo;Park, Chan Woo
    • Composites Research
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    • v.26 no.6
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    • pp.373-379
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    • 2013
  • The coating of metal surface with carbon nanotubes (CNTs) has been studied for the heat transfer enhancement of the boiling and condensation of refrigerant. The MWCNT/copper composite powder was made by the attrition ball milling, which has been coated on the copper wafer by electrostatic powder coating and sintered with electric furnace. In this paper, experiments were performed to assess the characterization and comparison of CNT before and after sinterning and the morphology changes of the CNT/Cu-coated surface. The samples were examined by the scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDAX) and raman spectroscopy. To verify the heat transfer enhancement, boiling heat transfer tests were performed.

An Experimental Study of Developing and Fully Developed Flows in a Wavy Channel by PIV

  • Kim, Sung-Kyun
    • Journal of Mechanical Science and Technology
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    • v.15 no.12
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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.

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Convective heat transfer of MWCNT / HT-B Oil nanofluid inside micro-fin helical tubes under uniform wall temperature condition

  • Kazemia, M.H.;Akhavan-Behabadi, M.A.;Nasr, M.
    • Advances in nano research
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    • v.2 no.2
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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.