• Title/Summary/Keyword: Number of Heating Walls

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Effect of Number of Heating Walls on Heat Transfer in Ribbed Rectangular Channel (거친 사각채널에서 가열 벽면의 수가 열전달에 미치는 효과)

  • Bae Sung Taek;Ahn Soo Whan;Kim Myoung Ho;Lee Dae Hee;Kang Ho Keun
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.17 no.6
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    • pp.514-520
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    • 2005
  • Surface heat transfer of a fully developed turbulent air flow in a $45^{\circ}$ inclined ribbed square duct with two and four heating walls was experimentally investigated, at which the experimental works were peformed for Reynolds numbers ranging from 7,600 to 26,000. The pitch-to-rib height ratio, p/e, was kept at 8 and rib-height-to-channel hydraulic diameter ratio, $e/D_h$ was kept at 0.0667. The channel length-to-hydraulic diameter ratio, $L/D_h$ was 60. The heat transfer coefficient values were decreased with the increase in the number of heat-ing walls. Results of this investigation could be used in various applications of internal channel turbulent flow involving roughened walls.

Characteristics of Heat Transfer in the Ribbed Rectangular Channel with Variable Heating Condition

  • Kim Won-Cheol;Putra Ary Bachtiar Krishna;Kang Ho-Keun;Ahn Soo-Whan
    • International Journal of Air-Conditioning and Refrigeration
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    • v.15 no.1
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    • pp.10-16
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    • 2007
  • Surface heat transfer of a fully developed turbulent air flow in a $45^{\circ}$ inclined ribbed square duct with two and four heating walls was experimentally investigated, at which the experimental works were performed for Reynolds numbers ranging from 7,600 to 24,900. The pitch-to-rib height ratio, p/e was kept at 8 and rib-height-to-channel hydraulic diameter ratio, $e/D_h$ was kept at 0.0667. The channel length-to-hydraulic diameter ratio, $L/D_h$ was 60. The heat transfer coefficient values were decreased with the increase in the number of heating walls. Results of this investigation could be used in various applications of internal channel turbulent flow involving roughened walls.

Effects of Number of Heating Walls on Heat Transfer in the Rough Square Channel with Twisted Tape (테이프가 있는 거친 사각채널에서 가열벽면의 수가 열전달에 미치는 효과)

  • Ahn, S.W.;Kim, M.H.;Bae, S.T.;Kang, H.K.
    • Journal of Power System Engineering
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    • v.10 no.3
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    • pp.17-22
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    • 2006
  • Surface modifications like rib-roughening and displaced insert devices like the twisted tape are commonly used in applications such as compact heat exchangers and cooling systems. In this paper, regionally averaged heat transfer distributions in square channels with twisted tape inserts and with twisted tape inserts plus interrupted ribs are respectively investigated. The square ribs are arranged to follow the trace of the twisted tape and along the flow direction defined as axial interrupted ribs. Each wall of the square channel is composed of isolated aluminum sections. Regionally averaged Nusselt number and channel averaged Nusselt number in turbulent air flows are presented for Reynold numbers from 8,900 to 29,000. We have obtained the following conclusions from the experimental study: 1) The local Nusselt number in the two-sided heated case is higher than that in the four-sided heated condition. 2) In the 4 heating wall channel with twisted tape inserts, Nusselt number based on bottom wall temperature is enhanced by 1.2 - 1.6 times if adding the axial interrupted ribs on the bottom wall only. 3) The twisted tape with interrupted ribs under the two-sided heating condition produces the highest heat transfer coefficient.

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Effect of Number of Heating Walls on Heat Transfer in the Reciprocating Square Channel (왕복운동을 하는 사각채널에서 가열벽면의 수가 열전달에 미치는 효과)

  • Kim Myung Ho;Bae Sung Taek;Ahn Soo Whan
    • Journal of Advanced Marine Engineering and Technology
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    • v.29 no.2
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    • pp.161-167
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    • 2005
  • The improvements of the propulsive engine efficiencies could reduce the fuel consumption. Therefore. for a marine main diesel engine the substantial increase of stroke bore ratio. so that the engine speed can be significantly reduced in order to increase the Propulsive efficiency. As a typical example. a Sulzer RTA 60C engine has acylinder diameter of 600 mm and each cylinder is capable of delivering 2.369 kW in the speed range 91-114 rpm. In order to Provide basic data for thermal system of marine engine. this work performs an experimental study of heat transfer in a square channel with one rib-roughened wall under sin91e mode of reciprocating oscillation. A selection of heat transfer measurements illustrates the manner by which the reciprocating channel with two opposite heating walls has the higher heat transfer Performance than with four heating wall.

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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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 Convective Heat Transfer and Flow Characteristics in Inclined Rectangular Enclosures with Localized Heating from Below (밑면에서 부분가열을 받는 경사4각형 밀폐공간내의 자연대류 열전달 및 유동특성)

  • Kim, Sang-Ho;Chung, In-Kee;Kim, Jung-Yeup
    • The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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    • v.13 no.3
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    • pp.148-156
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    • 1984
  • The effect of inclination on the steady, two-dimensional, laminar natural convection in rectangular enclosures with localized heating from below has been investigated numerically. The enclosure was uniformly heated with a partial heat source at the center of the bottom wall and cooled from the upper wall while the other walls were insulated. The governing equations were solved numerically by using the ADI finite difference method with the SOR method. The computations were carrid out with air, Pr =0.733, in the Grashof number range, $1\times10^4\~3\times10^4$, for the inclination of the enclosures was varied from $0^{\circ}\;to\;90^{\circ}$. The effects of Grashof number and aspect ratio on the inclination for the transition of the flow pattern in enclosures were determined. From the results, it was found that the transition angles of the flow in the enclosures were greater in localized heating than in uniform heating from below, and that the inclination was to strongly effect on the heat transfer and the flow pattern within the enclosure.

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Natural Convection in a Rectangular Enclosure with Localized Heating from Below (사각공간내에서의 부분바닥가열에 의한 자연대류에 관한 연구)

  • Han, H.T.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.7 no.2
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    • pp.287-297
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    • 1995
  • In this study, the geometry consists of a two-dimensional rectangular enclosure with localized heating from below. The size and the location of the heater on the floor has been varied, and one of the vertical walls remains at a low temperature simulating a cold window. The governing equations for momentum, energy and continuity, which are coupled with turbulent equations have been solved using a finite volume method. A low Reynolds number $k-{\varepsilon}$ model has been incorporated to solve the turbulent kinetic energy and the dissipation rate. The heat transfer characteristics and the thermal environmental characteristics of the room have been obtained for various system parameters in a room with a partially heated floor.

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Numerical Analysis of Heat Transfer in the Ribbed Channel Inserted with Tape (테이퍼가 설치된 리브(rib)이 있는 채널의 열전달에 대한 수치해석)

  • Kang, Ho-Keun;Ahn, Soo-Whan
    • Journal of Advanced Marine Engineering and Technology
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    • v.34 no.5
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    • pp.638-644
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    • 2010
  • Numerical predictions of a fully developed turbulent flow through a square duct ($30mm{\times}30mm$) with twisted tape inserts and with twisted tape plus interrupted ribs are respectively conducted to investigate regionally averaged heat transfer and flow patterns. A rib height-to-channel hydraulic diameter(e/$D_h$) of 0.067 and a lengthto-hydraulic diameter(L/$D_h$) of 30 are considered at Reynolds number ranging 8,900 to 29,000. The interrupted ribs are axially arranged on the bottom wall. The twisted tape is 0.1 mm thick carbon steel sheet with diameter of 28 mm, length of 900 mm, and 2.5 turns. Each wall of the square channel is composed of isolated aluminum sections. Two heating conditions are investigated for test channels with twisted tape inserts and rib turbulators: (1) electric heat uniformly applied to four side walls of the square duct, and (2) electric heat uniformly applied to two opposite walls of the square channel. The results show that uneven surface heating enhances the heat transfer coefficient over uniform heating conditions, and significant improvements can be achieved with twisted tape inserts plus interrupted ribs.

Effects of Swirl Flow Generated by Twisted Tape on Beat Transfer and Friction Factor in a Square Channel (사각 채널에서 테이프에 의한 스월유동이 열전달과 마찰계수에 미치는 효과)

  • Ahn, Soo-Whan;Kang, Ho-Keun;Putra, Ary Bachtiar Krishna
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.31 no.11
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    • pp.912-917
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    • 2007
  • Regionally averaged heat transfer distributions and friction factors in square channels with twisted tape inserts and with twisted tape inserts plus interrupted ribs are experimentally investigated. The effects of surface heating condition on heat transfer enhancement are also investigated. Each wall of the square channel is composed of isolated aluminum plates. The interrupted square ribs are arranged along the axial flow direction on the bottom wall only. Experimental tests are performed for Reynolds numbers ranging from 8,900 to 29,000. The results are compared with those of previous investigations for circular tube with axial interrupted ribs and twisted tape inserts.