• Title/Summary/Keyword: sublimation method

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Effects of Duct Aspect Ratios on Heat/Mass Transfer With Discrete V-Shaped Ribs (쐐기형 단락요철이 설치된 덕트의 종횡비가 열/물질 전달에 미치는 영향)

  • Lee, Dong-Hyun;Rhee, Dong-Ho;Cho, Hyung-Hee
    • Proceedings of the KSME Conference
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    • 2003.04a
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    • pp.1453-1460
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    • 2003
  • The present study investigates the effects of rib arrangements and aspect ratios of a rectangular duct simulating the cooling passage of a gas turbine blade. Two different V-shaped rib configurations are tested with the aspect ratios (W/H) of 3 to 6.82. One is the continuous V-shaped rib configuration with $60^{\circ}$ attack angle, and the other is the discrete V-shaped rib configuration with $45^{\circ}$ attack angle. The square ribs with the pitch to height ratio of 10.0 are installed on the test section in a parallel arrangement for both rib configurations. Reynolds numbers based on the hydraulic diameter are changed from 10,000 to 30,000. A naphthalene sublimation method is used to measure local heat/mass transfer coefficients. For the continuous V-shaped rib configuration, two pairs of counter-rotating vortices are generated in a duct, and high transfer region is formed at the center of the ribbed walls of the duct. However, for the discrete V-shaped rib configuration with $45^{\circ}$ attack angle, complex secondary flow patterns are generated in the duct due to its geometric feature, and more uniform heat/mass transfer distributions are obtained for all tested cases

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Heat/Mass Transfer and Flow Characteristics within a Film Cooling Hole of Square Cross Sections with Asymmetric Inlet Flow Condition (비대칭 입구조건을 갖는 정사각 막냉각홀 내부에서의 열/물질전달 및 유동 특성)

  • Rhee, Dong-Ho;Kang, Seung-Goo;Cho, Hyung-Hee
    • Proceedings of the KSME Conference
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    • 2001.11b
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    • pp.14-21
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    • 2001
  • An experimental study has been conducted to investigate the heat/mass transfer characteristics within a square film cooling hole with asymmetric inlet flow conditions. The asymmetric inlet flow condition is achieved by making distances between side walls of secondary flow duct and film cooling hole different; one side wall is $2D_h$ apart from the center of film cooling hole, while the other side wall is $1.5D_h$ apart from the center of film cooling hole. The heat/mass transfer experiments for this study have been performed using a naphthalene sublimation method and the flow field has been analyzed by numerical calculation using a commercial code. Swirl flow is generated at the inlet region and the heat/mass transfer pattern with the asymmetric inlet flow condition is changed significantly from that with the symmetric condition. At the exit region, the effect of mainstream on the inside hole flow is reduced with asymmetric condition. The average heat/mass transfer coefficient is higher than that with the symmetric condition due to the swirl flow generated by the asymmetric inlet condition.

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Effects of Bleed Flow and Angled Ribs on Heat Transfer Distributions in a Rotating Square Channel (유출유동 및 각도진 요철이 회전하는 사각덕트 내 열전달분포에 미치는 영향)

  • Park, Suk-Hwan;Jeon, Yun-Heung;Kim, Kyung-Min;Lee, Dong-Hyun;Cho, Hyung-Hee
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.31 no.1 s.256
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    • pp.76-82
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    • 2007
  • The present study investigated the effects of channel rotation and bleed flow on heat/mass transfer in a square channel with $45^{\circ}$ rib turbulators. The bleed holes were located between the rib turbulators on the leading surface and those on the trailing surface case by case. The tests were conducted under the conditions of various bleed ratios (0.0, 0.2, 0.4) and rotation numbers (0.0, 0.2, 0.4) at Re=10,000. The results suggested that heat/mass transfer characteristics were influenced by the Coriolis force, decrement of main flow rate, secondary flow by angled ribs and bleed hole location. As the bleed ratio (BR) increased, the heat/mass transfer decreased on both surfaces due to the reduction of main flow rate. With increment of the rotation number, heat/mass transfer also decreased and almost the same because the reattachment of the secondary flow induced by angled ribs was weakened on the leading surface and the secondary flow was disturbed on the trailing surface by the Coriolis force.

Effect of Channel Rotation and Bleed Flow on Heat/Mass Transfer Characteristics in a 90° Ribbed Square Channel (채널회전 및 유출유동이 90도 요철이 설치된 사각채널 내 열/물질전달 특성에 미치는 영향)

  • Park, Suk-Hwan;Jeon, Yun-Heung;Kim, Kyung-Min;Lee, Dong-Hyun;Cho, Hyung-Hee
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.31 no.1 s.256
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    • pp.83-90
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    • 2007
  • The present study investigated the effects of channel rotation and bleed flow on heat/mass transfer in a $90^{\circ}$ ribbed square channel. The bleed holes were located between the rib turbulators on the leading surface and those on the trailing surface case by case. The tests were conducted under the conditions of various bleeding ratios (0.0, 0.2, 0.4) and rotation numbers (0.0, 0.2, 0.4) at Re=10,000. The results suggested that heat/mass transfer characteristics were influenced by the Coriolis force, bleed flow and bleed hole location. The heat/mass transfer on the surface with bleed flow was more increased than that without bleed flow but that on the opposition surface was decreased. Those were due to the effects of the tripping flow and the diminution of main flow rate respectively. The results also showed that the heat/mass transfer characteristics were different according to bleed hole location and channel rotation.

Preparation of particle-size-controlled SiC powder for single-crystal growth

  • Jung, Eunjin;Lee, Myung Hyun;Kwon, Yong Jin;Choi, Doo Jin;Kang, Seung Min;Kim, Younghee
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.27 no.1
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    • pp.57-63
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    • 2017
  • High-purity ${\beta}-SiC$ powders for SiC single-crystal growth were synthesized by direct carbonization. The use of high-purity raw materials to improve the quality of a SiC single crystal is important. To grow SiC single crystals by the PVT method, both the particle size and the packing density of the SiC powder are crucial factors that determine the sublimation rate. In this study, we tried to produce high-purity ${\beta}-SiC$ powder with large particle sizes and containing low silicon by introducing a milling step during the direct carbonization process. Controlled heating improved the purity of the ${\beta}-SiC$ powders to more than 99 % and increased the particle size to as much as ${\sim}100{\mu}m$. The ${\beta}-SiC$ powders were characterized by SEM, XRD, PSA, and chemical analysis to assess their purity. Then, we conducted single-crystal growth experiments, and the grown 4H-SiC crystals showed high structural perfection with a FWHM of about 25-48 arcsec.

Heat/Mass Transfer and Flow Characteristics Within a Film Cooling Hole of Square Cross Sections (II) - Effects of Asymmetric Inlet Flow Condition - (정사각 막냉각홀 내부에서의 열/물질전달 및 유동 특성 (II) - 비대칭 입구조건 효과 -)

  • Rhee, Dong-Ho;Kang, Seung-Goo;Cho, Hyung-Hee
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.7
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    • pp.937-944
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    • 2002
  • An experimental study has been conducted to investigate the heat/mass transfer characteristics within a square film cooling hole with asymmetric inlet now condition. The asymmetric inlet now condition is achieved by making distances between side walls of the secondary now duct and the film cooling hole different; one side wall is $2D_h$ apart from the center of the film cooling hole, while the other side wall is $1.5D_h$ apart from the center of the film cooling hole. The heat/mass transfer experiments for this study have been performed using a naphthalene sublimation method and the now field has been analyzed by numerical calculation using a commercial code. Swirl now is generated at the inlet region and the heat/mass transfer pattem with the asymmetric inlet now condition is changed significantly from that with the symmetric condition. In the exit region, the effect of mainstream on the inside hole now is reduced with the asymmetric condition. The average heat/mass transfer coefficient is higher than that with the symmetric condition due to the swirl now generated by the asymmetric inlet condition.

Effect of Incidence Angle on Turbine Blade Heat Transfer Characteristics (I) - Blade Tip - (입사각 변화에 따른 터빈 블레이드에서의 열전달 특성 변화 (I) - 블레이드 끝단면 -)

  • Rhee, Dong-Ho;Cho, Hyung-Hee
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.31 no.4
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    • pp.349-356
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    • 2007
  • The present study investigated local heat/mass transfer characteristics on the tip of the rotating turbine blade with various incoming flow incidence angles. The experiments are conducted in a low speed annular cascade with a single stage turbine. The blade has a flat tip with a mean tip clearance of 2.5% of the blade chord. The incoming flow Reynolds number is $1.5{\times}10^5$ at design condition. To examine the effect of off-design condition, the experiments with various incidence angles ranging between $-15^{\circ}$ and $+7{\circ}$ were conducted. A naphthalene sublimation method is used to measure detailed mass transfer coefficient on the blade. The results indicated that the incidence angle strongly affects the behavior of tip leakage flow around the blade tip and consequently plays an important role in determining heat transfer characteristics on the tip. For negative incidence angles, the heat/mass transfer in the upstream region on the tip decreases by up to 20%. On the contrary, for positive incidence angles, much higher heat transfer coefficients are observed even with small increase of incidence angle.

Effect of Incidence Angle on Turbine Blade Heat Transfer Characteristics (II) - Blade Surface - (입사각 변화에 따른 터빈 블레이드에서의 열전달 특성 변화 (II) - 블레이드 표면 -)

  • Rhee, Dong-Ho;Cho, Hyung-Hee
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.31 no.4
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    • pp.357-366
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    • 2007
  • The present study investigated local heat/mass transfer characteristics on the surface of the rotating turbine blade with various incidence angles. The experiments are conducted in a low speed annular cascade with a single stage turbine. The blade has a flat tip with the mean tip clearance of 2.5% of the blade chord. A naphthalene sublimation method is used to measure detailed mass transfer coefficient on the blade. At design condition, the inlet Reynolds number is $Re_c=1.5{\times}10^5$ which results in the blade rotation speed of 255.8 rpm. Also, the effect of off-design condition is examined with various incidence angles between $-15^{\circ}$ and $+7{\circ}$. The results indicated that the incidence angle has significant effects on the blade surface heat transfer. In mid-span region, the laminar separation region on the pressure side is reduced and the laminar flow region on the suction side shrinks with increasing incidence angle. Near the tip, the effect of tip leakage flow increases in span wise and axial directions as the incidence angle decreases because the tip leakage flow is formed near the suction side surface. However, the effect of tip leakage flow is reduced with positive incidence angle.

Effects of Bleed Hole on Heat/Mass Transfer in a Rotating Channel with Transverse Ribs (90도 요철이 설치된 회전덕트에서 유출홀이 열/물질전달에 미치는 영향)

  • Park, Suk-Hwan;Jeon, Yun-Heung;Kim, Kyung-Min;Lee, Dong-Hyun;Cho, Hyung-Hee
    • 유체기계공업학회:학술대회논문집
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    • 2005.12a
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    • pp.178-184
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    • 2005
  • The present study investigates the effects of bleed flow on heat/mass transfer and pressure drop in a rotating channel with transverse rib turbulators. The hydraulic diameter ($D_h$) of the square channel is 40.0 mm. The bleed holes are located between the rib turburators on leading surface and the hole diameter (d) is 4.5 mm. The square rib turbulators are installed on both leading and trailing surfaces. The rib-to-rib pitch is 10.0 times of the rib height (e) and the rib height-to-hydraulic diameter ratio ($e/D_h$) is 0.055. The tests were conducted at various rotation numbers (0, 0.2, 0.4), while the Reynolds number and the rate of bleed flow to main flow were fixed at 10,000 and 10%, respectively. The results suggest that the heat/mass transfer characteristics in the internal cooling passage are influenced by rib turbulators, bleed flow and the Cariolis force induced by rotation. For the rotating ribbed passage with bleed flow, the heat/mass transfer on the leading surface is hardly affected by bleed flow, but that on the trailing surface decreases due to the diminution of main flow. The results also show that the friction factor decreases with the bleed flow.

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The Effects of Impingement Hole Arrangements on Heat Transfer of an Impingement/Effusion Cooling System (충돌제트/유출냉각기법에서 분사판의 홀배열이 열전달에 미치는 영향)

  • Choe, Jong-Hyeon;Lee, Dong-Ho;Jo, Hyeong-Hui
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.1
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    • pp.101-109
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    • 2002
  • Two perforated plates are used to investigate local heat/mass transfer characteristics in an impingement/effusion cooling system. A naphthalene sublimation method is conducted to determine the local heat/mass transfer coefficients on the upward facing surface of the effusion plate. Two plates are placed in parallel position with gap distances of 1, 2, 4 and 6 times of effusion hole diameter. The effects of hole arrangements of the plates are studied fur staggered, square, and hexagonal arrays. The experiments are conducted at Reynolds number of 10,000 based on the effusion hole diameter. The results show that the smaller hole size in the staggered array has the higher transfer coefficients on the stagnation region due to the formation of higher momentum flows through the impingement holes. In the square array, heat/mass transfer on the target plate is more uniform as the number of impingement holes increases. High and uniform heat/mass transfer coefficients are obtained for the hexagonal array.