• Title/Summary/Keyword: Primary surface heat exchanger

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EFFECTS OF CHANNEL ASPECT RATIO ON FLOW AND HEAT TRANSFER CHARACTERISTICS OF PRIMARY SURFACE HEAT EXCHANGER FOR ORC (유기랭킨사이클(ORC)을 위한 주전열면 열교환기의 채널 종횡비에 따른 유동 및 열전달 특성)

  • Sung, M.J.;Ahn, J.
    • Journal of computational fluids engineering
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    • v.18 no.4
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    • pp.35-40
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    • 2013
  • A series of numerical simulation has been carried out to study thermo-hydraulic characteristics of a primary surface type heat exchanger, which is designed for the evaporator and condenser of a geothermal ORC. Working fluid is geothermal water at hot side and R-245fa, which is a refrigerant designed for ORC, at cold side. Aspect ratio of the channel and Reynolds number are considered as design parameters. Nusselt number is presented for the Reynolds number ranging from 50 to 150 and compared to existing correlations. The result shows that higher aspect ratio channel gives better heat transfer performance within the range of investigation.

Effects of Duct Aspect Ratio on Heat Transfer in Wavy Duct of Heat Exchanger of Gas Turbine (가스터빈용 열교환기의 주름진 덕트에서 종횡비 변화가 열전달 특성에 미치는 영향)

  • Kim, Han Ho;Hwang, Sang Dong;Cho, Hyung Hee;Cho, Jae Ho;Jeon, Seung Bae
    • 유체기계공업학회:학술대회논문집
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    • 2001.11a
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    • pp.339-344
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    • 2001
  • The present study investigates convective heat/mass transfer and flow characteristics in wavy ducts of primary surface heat exchanger. Experiments using a naphthalene technique are carried out to determine the local transfer characteristics for flow in the corrugated wall duct. The aspect ratios of the rectangular duct cross-section are 7.3, 4.7 and 1.8 with a corrugation angle of $145^{\circ}$. The Reynolds numbers, based on the duct hydraulic diameter, are ranged from 1000 to 5000. The local heat/mass transfer measurement is conducted in the spanwise directions. The results show that Tayler-Gortler vortices exist on the pressure surface. Flow separation on the suction surface appears at a high Reynolds number resulting in a sharp decrease in the local transfer rates, but relatively high transfer rates are obtained in the reattachment region.

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Effects of Reynolds Number on Flow and Heat/Mass Characteristics Inside the Wavy Duct (Reynolds 수에 따른 꺾어진 덕트에서 열/물질전달 특성 고찰)

  • 장인혁;황상동;조형희
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.15 no.10
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    • pp.809-820
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    • 2003
  • The present study investigates effects of flow velocity on the convective heat/mass transfer characteristics in wavy ducts of a primary surface heat exchanger application. Local heat/mass transfer coefficients on the wavy duct sidewall are determined by using a naphthalene sublimation technique. The flow visualization technique is used to understand the overall flow structures inside the duct. The aspect ratio and corrugation angle of the wavy duct is fixed at 7.3 and 145$^{\circ}$ respectively, and the Reynolds numbers, based on the duct hydraulic diameter, vary from 100 to 5,000. The results show that there exist complex secondary flows and transfer processes resulting in non-uniform distributions of the heat/mass transfer coefficients on the duct side walls. At low Re (Re<1000), relatively high heat/mass transfer regions like cell shape appear on both pressure and suction side wall due to the secondary vortex flows called Taylor-Gortler vortices perpendicular to the main flow direction. However, at high Re (Re>1000), these secondary flow cells disappear and boundary layer type flow characteristics are observed on pressure side wall and high heat/mass transfer region by the flow reattachment appears on the suction side wall. The average heat/mass transfer coefficients are higher than those of the smooth circular duct due to the secondary flows inside wavy duct. And also friction factors are about two times greater than those of the smooth circular duct.

Experimental Investigation on the Performance of a Scroll Expander for an Organic Rankine Cycle (유기랭킨사이클(ORC)을 위한 주전열면 열교환기의 채널주름비에 따른 유동 및 열전달특성)

  • Sung, Min-Je;Ahn, Joon
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.26 no.4
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    • pp.158-162
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    • 2014
  • A series of numerical simulation has been carried out to study thermo-hydraulic characteristics of a primary surface type heat exchanger, which is designed for the evaporator and condenser of a geothermal ORC. Working fluid is geothermal water at hot side and R-245fa, which is a refrigerant designed for ORC, at cold side. Amplitude ratio of the channel and Reynolds number are considered as design parameters. Nusselt number is presented for the Reynolds number ranging from 50 to 150 and compared to analytic solutions. The result shows that higher amplitude ratio channel gives better heat transfer performance within the range of investigation.

Effects of Corrugation Angle on Local Heat/Mass Transfer in Wavy Duct of Heat Exchanger (열교환기 내부 유로의 꺾임각 변화에 따른 국소 열/물질전달 특성 고찰)

  • Jang, In-Hyuk;Hwang, San-Dong;Cho, Hyung-Hee
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.28 no.7
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    • pp.789-799
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    • 2004
  • An experimental study is conducted to investigate the effects of duct corrugation angle on heat/mass transfer characteristics in wavy ducts of a primary surface heat exchanger application. Local heat/mass transfer coefficients on the wavy duct sidewalls are determined by using a naphthalene sublimation technique. The corrugation angles(${\alpha}$) of the wavy ducts are 145$^{\circ}$, 130$^{\circ}$, 115$^{\circ}$ and 100$^{\circ}$. And the Reynolds numbers based on the duct hydraulic diameter vary from 300 to 3,000. The results show that at the low Re(Re $\leq$1000), the secondary vortices called Taylor-Gortler vortices perpendicular to the main flow direction are generated due to effect of duct curvature. By these secondary vortices, high heat/mass transfer regions are formed on both pressure-side and suction-side walls. At the high Re(Re $\geq$ 1000), these secondary flows are vanished with helping flow transition to turbulent flow and the regions which show high heat/mass coefficients by flow reattachment are formed on suction side. As corrugation angle decreases, the local peak Sh induced by Taylor-Gortler vortices increase at Re $\leq$1000. At high Re(Re $\geq$ 1000), by the existence of different kind of secondary flows called Dean vortices, non-uniform Sh distribution appears along spanwise direction at the narrow corrugation angle (${\alpha}$=100$^{\circ}$). Average Sh also increase by the enhanced effect of secondary vortices and flow reattachment. More pumping power (pressure loss) is required with the smaller corrugation angle due to the enhancement of flow instability.

Effects of Aspect Ratio on Local Heat/Mass Transfer in Wavy Duct (열교환기 내부 유로 종횡비 변화에 따른 국소 열/물질전달 특성 고찰)

  • Jang In Hyuk;Hwang Sang Dong;Cho Hyung Hee
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.17 no.6
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    • pp.569-580
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    • 2005
  • The present study investigates the convective heat/mass transfer characteristics in wavy ducts of a primary surface heat exchanger. The effects of duct aspect ratio and flow velocity on the heat/mass transfer are investigated. Local heat/mass transfer coefficients on the corrugated duct sidewall are determined using a naphthalene sublimation technique. The aspect ratios of the wavy duct are 7.3, 4.7 and 1.8 with the corrugation angle of $145\Omega$. The Reynolds numbers, based on the duct hydraulic diameter, vary from 300 to 3,000. The results show that at the low Re(Re $\leq$ 1000) the secondary vortices called Taylor-Gortler vortices perpendicular to the main flow direction are generated due to effect of duct curvature. By these secondary vortices, non-uniform heat/mass transfer coefficients distributions appear. As the aspect ratio decreases, the number of cells formed by secondary vortices are reduced and secondary vortices and comer vortices mix due to decreased aspect ratio at Re$\leq$1000. At Re >1000, the effects of corner vortices become stronger. The average Sh for the aspect ratio of 7.3 and 4.7 are almost same. But at the small aspect ratio of 1.8, the average Sh decreases due to decreased aspect ratio. More pumping power (pressure loss) is required for the larger aspect ratio due to the higher flow instability.

Effects of Corrugation Angle on Local Heat/mass Transfer in Wavy Duct. (열교환기 내부 유로 꺾임각 변화에 따른 국소 열/물질전달 특성 고찰)

  • Jang, In-Hyuk;Hwang, Sang-Dong;Cho, Hyun-Hee
    • Proceedings of the KSME Conference
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    • 2003.11a
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    • pp.97-102
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    • 2003
  • An experimental study is conducted to investigate the effects of duct corrugation angle on heat/mass transfer characteristics in wavy ducts by using a naphthalene sublimation technique. The corrugation angles of the wavy ducts are $145^{\circ}$ , $130^{\circ}$ and $115^{\circ}$ . and the Reynolds numbers based on the duct hydraulic diameter vary from 300 to 3,000. At the low $Re(Re{\leq}1000)$, high heat/mass transfer regions are formed by the secondary vortex flows called Taylor-Gortler vortices on both pressure-side and suction-side walls. At the high $Re(Re{\geq}1000)$, the effects of these secondary flows are vanished. As corrugation angle decreases, the local peak Sh induced by Taylor-Gertler vortices are increased and average Sh also enhanced. More pumping power (pressure loss) is required with the smaller corrugation angle due to the stronger secondary vortex flows.

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Effects of Channel Amplitude Ratio on Flow and Heat Transfer Characteristics of Primary Surface Heat Exchanger for ORC (유기 랭킨 사이클용 스크롤 팽창기 성능 시험에 관한 연구)

  • Moon, Je-Hyeon;Park, Keun-Tae;Kim, Hyun-Jin
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.26 no.4
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    • pp.151-157
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    • 2014
  • An algebraic scroll expander has been fabricated and tested in a R134a Rankine cycle with heat source of 20 kW. For the operating conditions of 20~26 bar and $90{\sim}93^{\circ}C$ at the expander inlet and 8~9 bar at the outlet, the expander produced the shaft output power of about 0.6~0.7 kW in the operating speed range of 1500~2000 rpm. These correspond to the expander efficiency of 40~45%. The volumetric efficiency increased with increasing of the expander speed, reaching to 80% at 2000 rpm. Comparing to numerical simulation results, mechanical efficiency from the test data was found to be considerably low by as much as 30%, indicating that reduction in the frictional loss should be made to improve the scroll expander efficiency.

High Temperature Corrosion of Alloy 617 in Impure Helium and Air for Very High-Temperature Gas Reactor (초고온가스로용 Alloy 617의 불순물 함유 헬륨/공기 중에서 고온부식 특성)

  • Jung, Sujin;Lee, Gyeong-Geun;Kim, Dong-Jin;Kim, Dae-Jong
    • Corrosion Science and Technology
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    • v.12 no.2
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    • pp.102-112
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    • 2013
  • A very high-temperature gas reactor (VHTR) is one of the next generation nuclear reactors owing to its safety, high energy efficiency, and proliferation-resistance. Heat is transferred from the primary helium loop to the secondary helium loop through an intermediate heat exchanger (IHX). Under VHTR environment Alloy 617 is being considered a candidate Ni-based superalloy for the IHX of a VHTR, owing to its good creep resistance, phase stability and corrosion resistance at high temperature. In this study, high-temperature corrosion tests were carried out at 850 - $950^{\circ}C$ in air and impure helium environments. Alloy 617 specimens showed a parabolic oxidation behavior for all temperatures and environments. The activation energy for oxidation was 154 kJ/mol in helium environment, and 261 kJ/mol in an air environment. The scanning electron microscope (SEM) and energy-dispersive x-ray spectroscopy (EDS) results revealed that there were a Cr-rich surface oxide layer, Al-rich internal oxides and depletion of grain boundary carbide after corrosion test. The thickness and depths of degraded layers also showed a parabolic relationship with the time. A corrosion rate of $950^{\circ}C$ in impure helium was higher than that in an air environment, caused by difference in the outer oxide morphology.