• Title/Summary/Keyword: Free-Stream Temperature

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Simultaneous determination of reference free-stream temperature and convective heat transfer coefficients (자유흐름온도와 대류열전달계수를 동시에 측정할 수 있는 실험 방법에 대한 연구)

  • Jeong, Gi-Ho;Song, Ki-Bum;Kim, Kui-Soon
    • Proceedings of the KSME Conference
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    • 2001.06d
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    • pp.419-424
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    • 2001
  • This paper deals with the development of a new method that can obtain heat transfer coefficient and reference tree stream temperature simultaneously. The method is based on transient heat transfer experiments using two narrow-band TLCs. The method is validated through error analysis in terms of the random uncertainties in the measured temperatures. It is shown how the uncertainties in heat transfer coefficient and tree stream temperature can be reduced. The general method described in this paper is applicable to many heat transfer models with unknown free stream temperature.

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An Experimental Study on a Simultaneous Determination of Reference Free-Stream Temperature and Convective Heat Transfer Coefficients (자유흐름온도와 대류열전달계수를 동시에 측정할 수 있는 방법에 대한 실험적 연구)

  • 송기범;정기호;성영식;김귀순
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.10
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    • pp.1465-1471
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    • 2002
  • This paper deals with the development of a new method that can obtain the heat transfer coefficient and the reference free stream temperature simultaneously. The method is experimentally verified through comparison with results in convective heat transfer experiments of a circular impinging jet using two narrow-band TLCs. The general method described in this paper is highly recommended to many heat transfer models with the unknown or ambiguous free stream temperature.

Simultaneous Determination of Reference Free-Stream Temperature and Convective Heat Transfer Coefficients (자유흐름 온도와 대류열전달 계수를 동시에 측정할 수 있는 실험 방법에 대한 연구)

  • Jeong, Gi-Ho;Song, Ki-Bum;Kim, Kui-Soon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.12
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    • pp.1707-1714
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    • 2002
  • This paper deals with the development of a new method that can obtain heat transfer coefficient and reference free stream temperature simultaneously, The method is based on transient heat transfer experiments using two narrow-band TLCs. The method is validated through error analysis in terms of the random uncertainties in the measured temperatures. It is found that the errors could be reduced more than 2 times less. The general method described in this paper is applicable to many heat transfer models with unknown free stream temperature.

The effect of free stream turbulence on the near wake behind a circualr cylinder (원주의 근접후류에 대한 자유흐름 난류강도의 영향)

  • 김경천;정양범
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.6
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    • pp.2062-2072
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    • 1991
  • The effect of free stream turbulence on the flow characteristics behind a circular cylinder is investigated in the present experimental study. The various free stream turbulent intensities are generated by different combinations of cylinder locations and grid shapes. Split film sensor with constant temperature anemometer is used to measure the local instantaneous velocity components. Experimental results demonstrate the large scale coherent structures are rapidly distorted and the Strouhal number is decreased with increasing free stream turbulent intensity.

COMPUTATIONS OF NATURAL CONVECTION FLOW WITHIN A SQUARE CAVITY BY HERMITE STREAM FUNCTION METHOD (Hermite 유동함수법에 의한 정사각형 공동 내부의 자연대류 유동계산)

  • Kim, J.W.
    • Journal of computational fluids engineering
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    • v.14 no.4
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    • pp.67-77
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    • 2009
  • This paper is a continuation of a recent development on the Hermite-based divergence-free element method and deals with a non-isothermal fluid flow driven by the buoyancy force in a square cavity with temperature difference across the two sides. Two Hermite functions are considered for numerical computations in this paper. One is a cubic function and the other is a quartic function. The degrees-of-freedom of the cubic Hermite function are stream function and its first and second derivatives for the velocity field, and temperature and its first derivatives for the temperature field. The degrees-of-freedom of the quartic Hermite function include two second derivatives and one cross derivative of the stream function in addition to the degrees-of-freedom of the cubic stream function. This paper presents a brief review on the Hermite based divergence-free basis functions and its finite element formulations for the buoyancy driven flow. The present algorithm does not employ any upwinding or a stabilization term. However, numerical values and contour graphs for major flow variables showed good agreements with those by De Vahl Davis[6].

Unsteady Conjugate Heat Transfer Analysis of a Cooled Turbine Nozzle with High Free Stream Turbulence

  • Seo, Doyoung;Hwang, Sunwoo;Son, Changmin;Kim, Kuisoon
    • International Journal of Aeronautical and Space Sciences
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    • v.18 no.2
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    • pp.279-289
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    • 2017
  • In this study, a series of conjugate heat transfer (CHT) analyses are conducted for a stage of a fully cooled high-pressure turbine (HPT) at elevated levels of free stream turbulence (Tu = 5% and 25.7%). The goal of the analyses is to investigate the influence of high turbulence intensity on the fluid-thermal characteristics of a nozzle guide vane (NGV). The turbine inlet temperature is defined by considering a typical radial temperature distribution factor (RTDF). The Unsteady Reynolds Average Navier-Stokes (URANS) CHT simulations are carried out using CFX 15.0, a commercial CFD package. The presented CFD modeling approach for high turbulence intensity is verified with the experimental data from two types of NASA C3X NGVs with films. The computation grid is generated for both the fluid and solid domains. The fluid domain grid is created using a tetrahedral grid system with prism layers because of its complex geometry, and the solid domain grid is composed of only tetrahedral elements. The analytical results are compared to understand the effect of turbulence on flow characteristics and metal temperature distributions. The results obtained in this study provide useful insights on the effects of high free stream turbulence and unsteadiness. The results also lead to the proposal of meaningful turbine design guidelines.

Main-stream Partial Nitritation - Anammox (PN/A) Processes for Energy-efficient Short-cut Nitrogen Removal (주공정에서 아질산화-혐기성 암모늄 산화법에 의한 단축질소제거공정 연구동향)

  • Park, Hongkeun;Rhu, Daehwan
    • Journal of Korean Society on Water Environment
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    • v.34 no.1
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    • pp.96-108
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    • 2018
  • Large efforts have recently been made on research and development of sustainable and energy-efficient short-cut nitrogen removal processes owing to strong attention to the energy neutral/positive wastewater treatment system. Anaerobic ammonium oxidizing bacteria (anammox bacteria) have been highlighted since 1990's due to their unique advantages including 60% less energy consumption, nearly 100% reduction for carbon source requirement, and 80% less sludge production. Side-stream short-cut nitrogen removal using anammox bacteria and partial nitritation anammox (PN/A) has been well established, whereas substantial challenges remain to be addressed mainly due to undesired main-stream conditions for anammox bacteria. These include low temperature, low concentrations of ammonia, nitrite, free ammonia, free nitrous acid or a combination of those. In addition, an anammox side-stream nitrogen management is insufficient to reduce overall energy consumption for energy-neutral or energy positive water resource recovery facility (WRRF) and at the same time to comply with nitrogen discharge regulation. This implies the development of the successful main-stream anammox based technology will accelerate a conversion of current wastewater treatment plants to sustainable water and energy recovery facility. This study discusses the status of the research, key mechanisms & interactions of the protagonists in the main-stream PN/A, and control parameters and major challenges in process development.

An Experimental Study of Film Cooling Characteristics at Supersonic Free Stream Conditions (초음속 주유동 환경에서의 막냉각 특성 시험 연구)

  • Kim, Manshik;Lee, Dong Min
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.45 no.4
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    • pp.342-348
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    • 2017
  • In this paper, film cooling characteristics at supersonic free stream conditions were examined experimentally by applying an IR-thermography. Film cooling experiments were carried out in a free-jet facility at Mach number of 3.0 and with unit Reynolds number of $42.53{\times}10^6$ and $69.35{\times}10^6$ using wedge shaped film cooling model which has a converging film cooling nozzle. Film cooling efficiency was calculated by measuring the surface temperature of PEEK(Polyether Ether Ketone) and the effects of angle of attack and blowing ratios on the film cooling efficiency were examined. The measured wall temperature was significantly reduced by the film cooling flow compared with the results without the film cooling flow. The usefulness of film cooling was also confirmed by the surface heat flux calculated using the surface temperature history of PEEK. As the blowing ratio increases the protected area of PEEK was also expanded along the direction of free stream and film cooling flow.

Heat Transfer and Flow Measurements on the Turbine Blade Surface (터빈 블레이드 표면과 선형익렬에서의 열전달 및 유동측정 연구)

  • Lee, Dae Hee;Sim, Jae Kyung;Park, Sung Bong;Lee, Jae Ho;Yoon, Soon Hyun
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.23 no.5
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    • pp.567-576
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    • 1999
  • An experimental study has been conducted to investigate the effects of the free stream turbulence intensity and Reynolds number on the heat transfer and flow characteristics In the linear turbine cascade. Profiles of the time-averaged velocity, turbulence intensity, and Reynolds stress were measured in the turbine cascade passage. The static pressure and heat transfer distributions on the blade suction and pressure surfaces were also measured. The experiments were made for the Reynolds number based on the chord length, Rec = $2.2{\times}10^4$ to $1.1{\times}10^5$ and the free stream turbulence intensity, $FSTI_1$ = 0.6% to 9.1 %. The uniform heat flux boundary condition on the blade surface was created using the gold film Intrex and the surface temperature was measured by liquid crystal, while hot wire probes were used for the flow measurements. The results show that the free stream turbulence promotes the boundary layer development and delays the flow separation point on the suction surface. It was found that the boundary layer flows on the suction surface for all Reynolds numbers tested with $FSTI_1$ = 0.6% are laminar. It was also found that the heat transfer coefficient on the blade surface increases as the free stream turbulence intensity increases and the flow separation point moves downstream with an increasing Reynolds number. The results of skin friction coefficients are in good agreement with the heat transfer results in that for $FSTI_1{\geq}2.6%$, the turbulent boundary layer separation occurs.

A Numerical Study on the Toxic Gaseous and Solid Pollutant Dispersion in an Open Atmosphere (고-기상 유해물질 대기확산에 관한 수치해석)

  • 이선경;송은영;장동순
    • Journal of the Korean Society of Safety
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    • v.9 no.1
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    • pp.146-154
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    • 1994
  • A series of numerical calculations are performed in order to investigate the dispersion mechanism of toxic gaseous and solid pollutants in extremely short-term and short range. The calculations are carried out in an open space characterized by turbulent boundary layer. The simulation is made by the use of numerical model, in which a control-volume based finite difference method is used together with the SIMPLEC algorithm for the resolution of the pressure-velocity coupling problem. The Reynolds stresses are solved by two-equation, k-$\varepsilon$ model modified for buoyancy. The major parameters consider-ed in this study are temperature, velocity and Injection height of toxic gases, environmental conditions such as temperature and velocity of free stream air, and topographic factor. The results are presented and discussed in detail. The flow field is commonly characterized by the formation of a strong recirculation zone due to the upward motion of the hot toxic gas and ground shear stress. The driving force of the upward motion is explained by the effect of thermal buoyancy of hot gas and the difference of inlet velocity between toxic gas and free stream.

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