• Title/Summary/Keyword: Heat flux

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A Study on the Analysis of Surface Heat Flux Using the Transient Heat Flux Method (비정상열유속 기법을 이용한 표면 열유속 해석에 관한 연구)

  • Yi, Jong-Ju
    • Journal of the Korea Institute of Military Science and Technology
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    • v.13 no.3
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    • pp.503-510
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    • 2010
  • The quick variation of the canister wall temperature causes the modification of the shape of canister wall. This paper is the possibility of adoption and the error analysis about the transient heat flux method. The commercial code(Fluent Ver6.2.16) was employed for the calculation of surface temperature in the case of steady and unsteady heat flux condition. Based the surface temperature variation and surface material property, transient heat flux method can calculate the surface heat flux. In the case of steady heat flux condition, the error is about 2%, and in the case of unsteady heat flux condition, the error is about 3.6%. With the unsteady heat flux condition, the time which reach the maximum surface heat flux is almost same between the numerical analysis and transient heat flux method.

Performance Comparison of an Urban Canopy Model under Different Meteorological Conditions (기상 조건에 따른 도시 캐노피 모형의 성능 비교)

  • Ryu, Young-Hee;Baik, Jong-Jin;Lee, Sang-Hyun
    • Atmosphere
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    • v.22 no.4
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    • pp.429-436
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    • 2012
  • The performances of the Seoul National University Urban Canopy Model (SNUUCM) under different meteorological conditions (clear, cloudy, and rainy conditions) in summertime are compared using observation dataset obtained at an urban site. The daily-averaged net radiation, sensible heat flux, and storage heat flux are largest in clear days and smallest in rainy days, but the daily-averaged latent heat flux is similar among clear, cloudy, and rainy days. That is, the ratio of latent heat flux to net radiation increases in order of clear, cloudy, and rainy conditions. In general, the performance of the SNUUCM is better in clear days than in cloudy or rainy days. However, the performance in simulating sensible heat flux in clear days is as poor as that in rainy days. For all the meteorological conditions, the performance in simulating latent heat flux is worst among the performances in simulating net radiation, sensible heat flux, and latent heat flux. The normalized mean error for latent heat flux is largest in rainy days in which the relative importance of latent heat flux in the surface energy balance becomes greatest among the three conditions. This study suggests that improvements to the parameterization of processes that are related to latent heat flux are particularly needed.

ACCURATE ESTIMATION OF GLOBAL LATENT HEAT FLUX USING MULTI-SATELLITE DATA

  • Tomita Hiroyuki;Kubota Masahisa
    • Proceedings of the KSRS Conference
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    • 2005.10a
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    • pp.14-17
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    • 2005
  • Global latent heat flux data sets are crucial for many studies such as those related to air-sea interaction and climate variation. Currently, various global latent heat flux data sets are constructed using satellite data. Japanese Ocean Flux data sets with Use of Remote sensing Observations (J-OFURO) includes one of the satellite-derived global latent heat flux data (Kubota et aI., 2000). In this study, we review future development of J-OFURO global latent heat flux data set. In particular, we investigate usage of multi-satellite data for estimating accurate global latent heat flux. Accurate estimation of surface wind speeds over the global ocean is one of key factors for the improved estimation of global latent heat flux. First, we demonstrate improvement of daily wind speed estimation using multi-satellites data from microwave radiometers and scatterometers such as DMSP/SSMI, ERS/AMI, QuikSCAT/SeaWinds, AqualAMSR-E, ADEOS2/AMSR etc. Next, we demonstrate improvement of global latent heat flux estimation using the wind speed data derived from multi-satellite data.

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Development of High-Temperature Heat Flux Gauge for Steel Quenching (강재 급속냉각용 고온 열유속게이지 개발)

  • Lee, Jungho
    • Journal of the Korean Society for Heat Treatment
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    • v.23 no.6
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    • pp.323-330
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    • 2010
  • The present study was motivated by increasing demands on quantitative measurements of the heat flux through the water cooling and quenching process of hot steel. The local heat flux measurements are employed by a novel experimental technique that has a function of high-temperature heat flux gauge in which test block assemblies are directly used to measure the heat flux variation during water cooling and quenching of hot steel. The heat flux can be directly achieved by Fourier's law and is also compared with numerical estimation which is solved by inverse heat conduction problem (IHCP). The high-temperature heat flux gauge developed in this study can be applicable to measure cooling rate and history during the actual cooling applications of steelmaking process. In addition, the measurement uncertainty of heat flux is calculated by a quantitative uncertainty analysis which is based on the ANSI/ASME PTC 19.1-2005 standard.

An Experimental Study of Critical Heat Flux in Non-uniformly Heated Vertical Annulus under Low Flow Conditions

  • Chun, Se-Young;Moon, Sang-Ki;Baek, Won-Pil;Chung, Moon-Ki;Masanori Aritomi
    • Journal of Mechanical Science and Technology
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    • v.17 no.8
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    • pp.1171-1184
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    • 2003
  • An experimental study on critical heat flux (CHF) has been performed in an internally heated vertical annulus with non-uniform heating. The CHF data for the chopped cosine heat flux have been compared with those for uniform heat flux obtained from the previous study of the authors, in order to investigate the effect of axial heat flux distribution on CHF. The local CHF with the parameters such as mass flux and critical quality shows an irregular behavior. However, the total critical power with mass flux and the average CHF with critical quality are represented by a unique curve without the irregularity. The effect of the heat flux distribution on CHF is large at low pressure conditions but becomes rapidly smaller as the pressure increases. The relationship between the critical quality and the boiling length is represented by a single curve, independent of the axial heat flux distribution. For non-uniform axial heat flux distribution, the prediction results from Doerffer et al.'s and Bowling's CHF correlations have considerably large errors, compared to the prediction for uniform heat flux distribution.

Measurement of Heat Flux in Rocket Combustors Using Plug-Type Heat Flux Gauges

  • Kim, Min Seok;Yu, I Sang;Kim, Wan Chan;Shin, Dong Hae;Ko, Young Sung
    • International Journal of Aeronautical and Space Sciences
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    • v.18 no.4
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    • pp.788-796
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    • 2017
  • This paper proposes a new measurement method to improve the shortcomings of an existing integral method for measuring heat flux in plug-type heat flux gauges in the high-temperature and high-pressure environments of liquid-rocket combustors. Using the existing integral measurement method, the calculation of the surface area for the heat flux in the gauge exhibits error in relation to the actual surface area. To solve this problem, transient profiles obtained from ANSYS Fluent were used to calculate unsteady heat flux as it adjusted to the measured temperature. First, a heat flux gauge was designed and manufactured specifically for use in the high-temperature and high-pressure conditions that are similar to those of liquid rocket combustors. A calibration test was performed to prove the reliability of the manufactured gauge. Then, a combustion experiment was conducted, in which the gauge was used to measure unsteady heat flux in a liquid rocket combustor that used kerosene and liquid oxygen as propellants. Reasonable heat flux values were obtained using the gauge. Therefore, the proposed measurement method is considered to offer significant improvement over the existing integral method.

A Study of a Heat Flux Mapping Procedure to Overcome the Limitation of Heat Flux Gauges in Fire Tests (화재실험시 열유속 센서 사용의 단점을 보완한 Heat Flux Mapping Procedure에 관한 연구)

  • Choi, Keum-Ran
    • Journal of the Korean Society of Safety
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    • v.20 no.4 s.72
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    • pp.171-179
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    • 2005
  • It is essential to understand the role of wall lining materials when they are exposed to a fire from an ignition source. Full-scale test methods permit an assessment of the performance of a wall lining material. Fire growth models have been developed due to the costly expense associated with full-scale testing. The models require heat flux maps from the ignition burner flame as input data. Work to date was impeded by a lack of detailed spatial characterization of the heat flux maps due to the use of limited instrumentation. To increase the power of fire modeling, accurate and detailed heat flux maps from the ignition burner are essential. High level spatial resolution for surface temperature can be provided from an infrared camera. The objective of this study was to develop a heat flux mapping procedure for a room test burner flame to a wall configuration with surface temperature information taken from an infrared camera. A prototype experiment was performed using the ISO 9705 test burner to demonstrate the developed heat flux mapping procedure. The results of the experiment allow the heat flux and spatial resolutions of the method to be determined and compared to the methods currently available.

A Low-Reynolds Number Second Moment Closure for Turbulent Heat Fluxes (저레이놀즈수 2차 모멘트 난류 열유속모형 개발에 관한 연구)

  • 신종근;최영돈;이건휘
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.12
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    • pp.3196-3207
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    • 1993
  • A second moment turbulent closure for the turbulent heat flux near a wall is developed by modification of model constants in pressure interaction term as the variables of the turbulent Reynolds number using the universal properties of turbulent heat flux near the wall. The present model shows that model constant for the wall reflection term in pressure interaction is most important in modelling of the near wall heat flux. Fully developed pipe flows with constant wall heat flux are tested to validate the proposed model. In most of calculation region, the predicted turbulent properties agree better with the experimetal data than the results from standard algebraic heat flux model which use the uniform model constants.

A study on the measurement of Radiative Heat flux form the flame(I) -Design and Calibration of a Heat flux meter- (화염으로부터의 복사 열유속의 계측 I)

  • 정종수;인종수;김승수
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.14 no.2
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    • pp.484-491
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    • 1990
  • A heat-flux meter has been designed and manufactured to measure the heat flux from the flame. A calibration method of the heat-flux meter by a calibration furnace has also been proposed. The k-type (Chromel-Alumel) thermocouple material has been used as the material for the beat-flux meter. The electormotive force (e.m.f.) from the K-type thermocouple is shown to be linearly proportional to the heat flux absorbed. The characteristics of the heat-flux meter become better as the radius of heat absorbing disk becomes larger and its thickness thinner.

Subcooled Burnout Heat Flux on a Heated Surface with Impinging Water Jet (충돌수분류(衝突水噴流)에 의한 서브쿨 Burnout열류속(熱流束)에 관한 연구)

  • Ohm, K.C.;Lee, J.S.;Park, S.Y.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.8 no.4
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    • pp.527-536
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    • 1996
  • Convective nucleate boiling and burnout heat flux have been studied on a flat, downward facing, constant heat flux surface cooled by an impinging water jet. The tests are progressed from low, nonboiling power to high, burnout heat flux power. The jet velocity and the subcooling do not affect the nucleate boiling curve of $q{\sim}{\Delta}T_{sat}$ diagram, but the supplementary water height affects the curve. For the case of dimensionless height of supplementary water S/D=1, the boiling curve shift to the heigher heat flux than that of S/D=0 or S/D=2. Burnout heat flux is enhanced with increasing jet velocity and subcooling. Also. by using the supplementary water(S/D=1 or S/D=2), burnout heat flux is larger than that of the simple water jet(S/D=0). A generalized correlation for the burnout heat flux data in the present boiling system with an impinging water jet is successfully evolved.

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