• Title/Summary/Keyword: Natural convection heat transfer

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Effect of Natural Convection on the Heat Transfer in a Latent Heat Storage System (잠열축열시스템의 축열과정에서 자연대류의 영향에 관한 연구)

  • Ryu, S.N.;Han, G.Y.
    • Solar Energy
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    • v.19 no.2
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    • pp.29-36
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    • 1999
  • Heat transfer characteristics of a low temperature latent heat storage system during the heat storage stage was examined for the circular finned tubes using fatty acid which shows the big density difference during melting as phase change materials. The heat storage vessel has the dimension of 530 mm height, 74 mm inside diameter and inner heat transfer tube is 480 mm in height and 13.5 mm outside diameter. Hot water was employed as the heat transfer fluid. During the heat storage stage, it was found that both conduction and natural convection were the major heat transfer mechanism. It was also found that the effect of natural convection on the heat transfer was more significant for the unfinned tube system than that for the finned tube system. The experimentally determined overall heat transfer coefficients were in the range of $50{\sim}250W/m^2K$ and the correlation for natural convection heat transfer as a function of Nusselt and Rayleigh number was proposed.

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Conjugate Heat Transfer by Natural Convection from a Horizontal Heat Exchanger Tube with a Long Vertical Longitudinal Plate Fin (단일(單一) 긴 수직평판(垂直平板)핀을 가진 수평전도관(水平傳導管)으로 부터의 자연대류(自然對流))

  • Bai, Dai Sok;Kwon, Sun Sok
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.1 no.1
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    • pp.64-72
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    • 1989
  • Laminar natural convection heat transfer from a horizontal heat exchanger tube with one infinitely long vertical plate fin has been studied by a finite-difference numerical procedure. In predicting convective heat transfer from a circular tube, the thermal boundary condition at solid fluid interface is usually assumed to be isothermal. However, in reality, the thermal boundary condition is not isothermal, and the tube has the thickness and the conductivity. So the temperature at the interface is not known a priori to the calculation. This problem has the conjugate phenomena which occur between the tube conduction and external natural convection, and between the fin conduction and external natural convection. Numerical results are obtained to determine the effects of the conductivity of solid wall and the thickness of tube wall on heat transfer. It is found that the conduction causes significant influence on the natural convection heat transfer at low K and high ${\delta}$.

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Effect of a Centered Conducting Body on Natural Convection Heat Transfer in a Two-Dimensional Cavity (2차원 캐비티내 자연대류 열전달에 대한 열전도 물체의 영향)

  • Myong H. K.;Kim J. E.
    • 한국전산유체공학회:학술대회논문집
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    • 2005.04a
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    • pp.79-84
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    • 2005
  • The numerical solutions are examined on the effect of a centered heat conducting body on natural convection in a 2-D square cavity. The influences of the Rayleigh number, the dimensionless conducting body size, and the ratio of the thermal diffusivity of the body to that of the fluid have been investigated on the natural convection heat transfer in overall concerned region. The analysis reveals that the fluid flow and heat transfer processes are governed by all of them. Results for isotherms, vector plots and wall Nusselt numbers are reported for Pr = 0.71 and relatively wide ranges of the other parameters. Heat transfer across the cavity, in comparison to that in the absence of a body, are enhanced (reduced) in general by a body with a thermal diffusivity ratio less (greater) than unity. The heat transfer are also found to attain a minimum as the body size is increased.

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A Study on the Heat Sink with internal structure using Peltier Module In the Natural and Forced Convection (자연대류와 강제대류에서 펠티에 소자를 이용한 내부터널 구조를 가지는 히트싱크에 관한 연구)

  • Lee, Min;Kim, Tae-Wan
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.15 no.7
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    • pp.4072-4080
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    • 2014
  • The Peltier Module has been used to dissipate the heat from electronic devices and electronic components. In this module, a heat sink is used to release the operating heat into the air outside. This study addressed the heat transfer characteristics for a heat sink with an inner tunnel. Under forced and natural convection conditions, the heat transfer characteristics were different. Therefore, the cooling and heating performances were studied for the heat sink, which has an inner tunnel. The heat transfer conditions were also evaluated by performing an experimental test, which investigated the heat transfer characteristics related to the variance in time and temperature distribution. Experiments on the heat transfer characteristics of the heat sink were conducted based on the forced and natural convection and temperature distribution changes. In the cooling experiment, the A- and B-shaped cooling pin heat sinks decreased the temperature of the forced convection than the temperature of natural convection. In the forced and natural convection, the A- and B-shaped decreased to a minimum of $-15^{\circ}C$. Under the forced and natural convection conditions, A- and B-shaped cooling pin heat sinks decreased the temperature when the voltage was increased. In the heating experiment, the A- and B-shaped cooling pin heat sinks increased the temperature of the forced convection than the temperature of natural convection. In forced convection, when the voltage was $15^{\circ}C$, the temperature of the A-shaped cooling pin heat sink increased to $150^{\circ}C$, and the temperature of the B-shaped cooling pin heat sink increased to $145^{\circ}C$. Under forced and natural convection conditions, the A- and B-shaped cooling pin heat sinks showed an increase in temperature with increasing voltage.

HIGH Ra NUMBER NATURAL CONVECTION IN A TRIANGULAR POOL WITH A HEAT GENERATION (열원이 있는 삼각형 풀의 높은 Ra수 자연대류)

  • Kim, Jong-Tae;Park, Rae-Joon;Kim, Hwan-Yeol;Hong, Seong-Wan;Song, Jin-Ho;Kim, Sang-Baik
    • Journal of computational fluids engineering
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    • v.16 no.3
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    • pp.66-74
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    • 2011
  • A fluid in an enclosure can be heated by electric heating, chemical reaction, or fission heat. In order to remove the volumetric heat of the fluid, the walls surrounding the enclosure must be cooled. In this case, a natural convection occurs in the pool of the fluid, and it has a dominant role in heat transfer to the surrounding walls. It can augment the heat transfer rates tens to hundreds times larger than conductive heat transfer. The heat transfer by a natural convection in a regular shape such as a square cavity or semi-circular pool has been studied experimentally and numerically for many years. A pool of an inverted triangular shape with 10 degree inclined bottom walls has a good cooling performance because of enhanced boiling critical heat flux (CHF) compared to horizontal downward surface. The coolability of the pool is determined by comparing the thermal load from the pool and the maximum heat flux removable by cooling mechanism such as radiative or boiling heat transfer on the pool boundaries. In order to evaluate the pool coolability, it is important to correctly expect the thermal load by a natural convection heat transfer of the pool. In this study, turbulence models with modifications for buoyancy effect were validated for unsteady natural convections by volumetric heating. And natural convection in the triangular pool was evaluated by using the models.

NATURAL CONVECTION IN A TRIANGULAR POOL WITH VOLUMETRIC HEAT GENERATION (삼각형 형상의 풀 내에서 열원에 의한 자연대류 수치해석)

  • Kim, Jong-Tae;Park, Rae-Joon;Kim, Hwan-Yeol;Song, Jin-Ho
    • 한국전산유체공학회:학술대회논문집
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    • 2011.05a
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    • pp.302-310
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    • 2011
  • A fluid in an enclosure can be heated by electric heating, chemical reaction, or fission heat. In order to remove the volumetric heat of the fluid, the walls surrounding the enclosure must be cooled. In this case, a natural convection occurs in the pool of the fluid, and it has a dominant role in heat transfer to the surrounding walls. It can augment the heat transfer rates tens to hundreds times larger than conductive heat transfer. The heat transfer by a natural convection in a regular shape such as a square cavity or semi-circular pool has been studied experimentally and numerically for many years. A pool of an inverted triangular shape with 10 degree inclined bottom walls has a good cooling performance because of enhanced boiling critical heat flux (CHF) compared to horizontal downward surface. The coolability of the pool is determined by comparing the thermal load from the pool and the maximum heat flux removable by cooling mechanism such as radiative or boiling heat transfer on the pool boundaries. In order to evaluate the pool coolability, it is important to correctly expect the thermal load by a natural convection heat transfer of the pool. In this study, turbulence models with modifications for buoyancy effect were validated for unsteady natural convections by volumetric heating. And natural convection in the triangular pool was evaluated by using the models.

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NUMERICAL STUDY ON NATURAL CONVECTION HEAT TRANSFER IN A CAVITY CONTAINING A CENTERED HEAT CONDUCTING BODY (열전도 물체가 존재하는 캐비티내 자연대류 열전달에 대한 수치적 연구)

  • Myong H. K.;Chun T. H.
    • Journal of computational fluids engineering
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    • v.10 no.3 s.30
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    • pp.36-42
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    • 2005
  • The present study numerically investigates the natural convection heat transfer in a 2-D square cavity containing a centered heat conducting body. Special emphasis is given to the influences of the Rayleigh number, the dimensionless conducting body size, and the ratio of the thermal diffusivity of the body to that of the fluid on the natural convection heat transfer in overall concerned region. The analysis reveals that the fluid flow and heat transfer processes are governed by all of them. Results for isotherms, vector plots and wall Nusselt numbers are reported for Pr = 0.71 and relatively wide ranges of the other parameters. Heat transfer across the cavity, in comparison to that in the absence of a body, are enhanced (reduced) in general by a body with a thermal diffusivity ratio less (greater) than unity. It is also found that the heat transfer attains a minimum as the body size is increased with a thermal diffusivity ratio greater than unity.

Numerical Study on Convective Heat Transfer in a Compartment Fire(II) - Mixed Convection - (실내화재에 있어서의 대류열전달에 관한 수치연구(II) -혼합대류-)

  • 박외철;고경찬;이광진
    • Journal of the Korean Society of Safety
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    • v.14 no.3
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    • pp.33-39
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    • 1999
  • In a compartment fire with openings, convective heat transfer consists of natural convection from the hot bodies and forced convection by airflow through the openings. The same finite volume method that was applied to pure natural convection in part I was utilized without modification to the square cavity with two openings. The objective of this study is to investigate effects of the openings on temperature distribution. Flow patterns, temperature distribution and heat transfer were compared for different Rayleigh numbers and with and without the openings.

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Natural Convection Correlation of Circular Finned Tube Heat Exchanger (원형휜-원형관 열교환기에 대한 자연대류 열전달상관식)

  • Kang, Hie-Chan;Jang, Hyun-Soon
    • Journal of Advanced Marine Engineering and Technology
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    • v.32 no.5
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    • pp.747-752
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    • 2008
  • An experimental study has been conducted on the natural convection heat transfer for the 7 kinds of circular finned tube heat exchangers. Empirical correlation was suggested at the range of 3,500

A Method for Detecting Engine Oil Deterioration using Heat Transfer (열전달을 이용한 엔진오일 열화 감지 방법)

  • Kim, Hyung-Pyo
    • Journal of Sensor Science and Technology
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    • v.13 no.2
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    • pp.139-143
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    • 2004
  • This paper presents a method that the engine oil condition is detected using a natural convection heat transfer in a engine oil. A sensor circuit maintains a constant temperature difference between a heat plate and engine oil for detecting a natural convection heat transfer rate on the constant temperature. The natural convection heat transfer rate is measured by a current through the heat plate of the sensor circuit. The sensor is tested by a fresh oil. 6,000 km and 10,000 km driven oil in the oil temperature range from $20^{\circ}C$ to $100^{\circ}C$. In the experimental result, when the current through the heat plate is altered by variation of a engine oil temperature and flows driven oil more than fresh oil, the sensor could inform a engine oil deterioration to a car driver.