• Title/Summary/Keyword: Square duct

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Effects of Discrete Ribs on Pressure Drop in a Rotating Two-Pass Duct (단락요철이 회전덕트 내 압력강하에 미치는 영향)

  • Kim Kyung-Min;Lee Dong-Hyun;Cho Hyung-Hee
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.18 no.5
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    • pp.443-450
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    • 2006
  • The present study has been conducted to investigate the effects of rotation on heat/mass transfer and pressure drop characteristics in a two-pass square duct with and without discrete ribs. For stationary cases, the heat/mass transfer on the surfaces with and without discrete ribs is almost the same or reduced. For rotating cases, the gap flow affects differently the heat/mass transfer on leading and trailing surfaces with discrete ribs. On the leading surface of the first pass, the heat/mass transfer is slightly enhanced due to generating strong gap flow. On the trailing surface of the first pass, however, the heat/mass transfer is much decreased because the gap flow disturbs impingement of main flow. The phenomenon, that is, the heat/mass transfer discrepancy between the leading and trailing surfaces is distinctly presented with the increment of rotation number. The friction losses on each surface with discrete ribs are reduced because the blockage ratio decreases for both non-rotating and rotating cases. Therefore, high thermal performance appears in a duct with discrete ribs.

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.

Numerical Study on Heat Transfer Characteristics of Turbulent Flow in Transition Duct (안내덕트 내부 난류유동구조에 따른 열전달 특성변화 수치해석)

  • Yoo, Geun-Jong;Choi, Hoon-Ki;Choi, Kee-Lim
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.35 no.9
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    • pp.923-932
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    • 2011
  • Because of the instability of a flow pattern in the inlet transition square duct (hereinafter referred to as "transition duct") of a heat recovery steam generator (hereinafter referred to as "HRSG") in a combined cycle power plant, the Reynolds number in the first row of a tube bank is differs sharply from that in the sectional area of the transition duct. This causes differences in the heat flux in each tube in the tube bank. The computational fluid dynamics (CFD) predictions provide three-dimensional results for velocity, temperature, and other flow parameters over the entire domain of the duct and HRSG. A renormalization group theory (RNG) based k-${\epsilon}$�� turbulent model is used for obtaining the results cited in this study. A porous media option is used for modeling the tube banks and the number of transfer units method is used for determining the heat transfer characteristics. This study describes a comparison between the numerical simulation results and actual design output.

The Effect of Turbulence Penetration on the Thermal Stratification Phenomenon Caused by Coolant Leaking in a T-Branch of Square Cross-Section

  • Choi, Young-Don;Hong, Seok-Woo;Park, Min-Soo
    • International Journal of Air-Conditioning and Refrigeration
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    • v.11 no.2
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    • pp.51-60
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    • 2003
  • In the nuclear power plant, emergency core coolant system (ECCS) is furnished at reactor coolant system (RCS) in order to cool down high temperature water in case of emergency. However, in this coolant system, thermal stratification phenomenon can occur due to coolant leaking in the check valve. The thermal stratification produces excessive thermal stresses at the pipe wall so as to yield thermal fatigue crack (TFC) accident. In the present study, effects of turbulence penetration on the thermal stratification into T-branches with square cross-section in the modeled ECCS are analysed numerically. Standard k-$\varepsilon$ model is employed to calculate the Reynolds stresses in momentum equations. Results show that the length and strength of thermal stratification are primarily affected by the leak flow rate of coolant and the Reynolds number of duct. Turbulence penetration into the T-branch of ECCS shows two counteracting effects on the thermal stratification. Heat transport by turbulence penetration from main duct to leaking flow region may enhance thermal stratification while the turbulent diffusion may weaken it.

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.

Measurement of Heat Transfer and Friction Coefficients for Flow of Air in Noncircular Ducts At High Surface Temperatures. (공기유동에 대한 고온상태의 비원형 도과내에서의 열전달 및 압력강하의 측정)

  • 이동렬
    • Journal of Advanced Marine Engineering and Technology
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    • v.25 no.3
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    • pp.552-562
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    • 2001
  • Measurement of average of heat transfer and friction coefficients were obtained with air flowing through electrically heated ducts having square, rectangular(aspect ration, 5), and triangular cross section for range of surface temperature from $540^{\circ}$to $1780^{\circ}$ R and Reynolds number from 1000 to 330,000. The results indicates that the effect of heat flux on correlations of the average heat transfer and friction coefficients is similar to that obtained for circular tubes in previous investigation and was nearly eliminated by evaluating the physical properties and density of the air a film temperature halfway between the average surface and fluid bulk temperatures, With the Nusselt and Reynolds numbers on the hydraulic diameter of the ducts, the data for the noncircular ducts could be represented by the same equations obtained in the previous investigation for circular tubes. Correlation of the average difference between the surface corner and midwall temperatures for the square duct was in agreement with predicted values from a previous analysis. However, for the rectangular and triangular ducts, the measured corner temperature was greater by approximately 20 and 35 percent, respectively, than the values predicted by analysis.

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열량계 채널에 대한 3차원 열전달 해석

  • Park, Tae-Seon;Seol, Woo-Seok
    • Aerospace Engineering and Technology
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    • v.2 no.2
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    • pp.142-150
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    • 2003
  • Turbulent flows and related heat transfer in a square heated duct is investigated by a turbulence model and a large eddy simulation. The cooling channel of calorimeter is modeled to the square duct. The nonlinear k-ε-fμ model of Park et al. [3] is slightly modified and their explicit heat flux model is employed. The Reynolds number is varied in the range 4000≤Reb≤20000. The heat transfer is closely linked to the secondary flows which driven by the turbulent motion. Its magnitude is 1~3% of the mean streamwise velocity. The relation of Nu~Re0.8Pr0.34 is validated by comparing with the predicted Nu of k-ε-fμ model. Finally, the coherent structures and thermal fluctuations are scrutinized.

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