• Title/Summary/Keyword: 대류계수

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Optimum Performance and Design of a Trapezoidal Fin (사다리꼴 핀의 최적 성능과 설계)

  • Kang, Hyung-Suk
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2006.11a
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    • pp.82-85
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    • 2006
  • A trapezoidal fin with various lateral surface slopes is designed optimally by using one-dimensional analytic method. For four different convection characteristic numbers, the trend of heat loss as a function of fin tip length is shown. The optimum heat loss is somewhat arbitrarily chosen as 92% of the maximum heat loss. The optimum fin length corresponding to this optimum heat loss versus convection characteristic number is presented. The optimum effectiveness and specific effectiveness is presented as a function fin shape factor.

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Analysis of Transient Conduction Heat Loss of Solid Sphere between Constant and Variable Free Convection (상수 또는 변수의 대류 경계조건을 가지는 구의 과도열전도 손실에 대한 해석)

  • Kim, M.J.;Chea, G.H.
    • Journal of Power System Engineering
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    • v.14 no.4
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    • pp.17-22
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    • 2010
  • 본 연구는 구의 과도 열전도에 의한 열손실을 계산하는 데 있어, 외부의 경계조건인 대류의 조건에 해당하는 상황을 상수 및 변수로 가정하였을 경우의 열전달문제를 해석한 것이다. 이 문제를 해결하기 위해 집중열용량법을 사용하고 있으며, 대류열전달계수의 값이 온도의 함수로 변한다고 가정하여 계산하였다. 계산을 수행한 결과 대류경계조건의 값을 상수로 가정한 경우가 열손실이 높이 평가된다는 것을 알았고, 이러한 경향을 상관식으로 정리하였다.

Inverse Estimation of Convective Heat Transfer Coefficient, Emissivity and Flame Heat Flux on the Surface (표면의 대류열전달계수, 방사율 및 화염 열유속 역해석 연구)

  • Yoon, Kyung-Beom;Park, Won-Hee
    • Fire Science and Engineering
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    • v.27 no.6
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    • pp.15-20
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    • 2013
  • The convective heat transfer coefficient, emissivity, and flame heat flux on the surface of Duglas fir are estimated by using repulsive particle swarm optimization. The surface temperature, mass loss rate, and ignition time are measured for various incident heat fluxes from a cone heater of the cone calorimeter. The calculated surface temperatures obtained by using the optimized convective heat transfer coefficient, emissivity and flame heat flux on the surface in this study match well with those obtained from the test. The maximum error between the predicted and measured surface temperatures for the three different external heat fluxes is within 2% showing reasonable agreements. The methodology proposed in this study can be used to obtain various values related to heat transfer on a flaming surface that are difficult to measure in experiments.

Heat transfer in the perturbed boundary layer by cylinder and secondary injection in supersonic flow (초음속유동장 내에 돌출된 실린더와 2차분사 홀 주변에서의 열전달 현상 연구)

  • Yi, Jong-Ju;Yu, Man-Sun;Song, Ji-Woon;Cho, Hyung-Hee
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2007.04a
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    • pp.276-280
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    • 2007
  • In this paper, heat transfer changes due to the shock/boundary layer interaction were investigated on surfaces where protruding bodies such as a cylinder and a secondary jet are mounted. With an infra-red thermography, surface temperature was measured and the measured data was used to obtain the convective heat transfer. Heat transfer phenomena around these two solid and fluid bodies were appeared to be very comparable each other. The inclination of a cylinder and the jet injection ratio were the important factors for the change of heat transfer on the effective surfaces.

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The Effect of Inside and Outside Fluids on the Optimization of a Reversed Trapezoidal Fin (역 사다리꼴 핀의 최적화에 미치는 내 외 유체의 영향)

  • Kang, Hyung-Suk
    • Journal of the Korean Society of Propulsion Engineers
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    • v.11 no.5
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    • pp.14-22
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    • 2007
  • A reversed trapezoidal fin with variable lateral surface slope is optimized using a two-dimensional analytic method. For a fin base boundary condition, convection from the inside fluid to the inside wall and conduction from the inside wall to the fin base are considered. Heat loss from the fin tip surface is not ignored. The maximum heat loss at the practical fin length, the corresponding optimum fin efficiency, fin length and fin base height are presented as a function of the fin inside and outside convection characteristic numbers. One of the results shows that the optimum fin shape becomes 'fatter and shorter' as the ratio of fin tip height to base height increases.

Linear Stability of Variable-Viscosity Fluid Layer under Convection Boundary Condition (대류 조건하의 가변 점성 유체층의 선형 안전성)

  • 송태호
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.16 no.1
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    • pp.132-141
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    • 1992
  • The critical condition for onset of Benard convection with variable viscosity .nu.=.nu.$_{0}$exp(-CT) has been obtained using a linear stability theory. The bottom wall is rigid while the upper surface may be either free or rigid. The two boundaries are subject to convective heat transfer. The critical Rayleigh numbers are presented up to maximum viscosity ratio of 3000. It is greater for smaller upper and/or lower surface Biot numbers. Its dependence on the viscosity ratio is complicated. However, a simple sublayer theory is found to be applicable for extremely large viscosity ratio. In such cases, the critical Rayleigh number and the critical wave number are functions of viscosity ratio and lower surface Biot number.r.

Heat Transfer Measurement in a Supersonic Flowfield by an Infra-red Thermography (적외선 측정 기법을 이용한 초음속 유동내 열전달 측정)

  • Yu, Man-Sun;Yi, Jong-Ju;Song, Ji-Woon;Cho, Hyung-Hee
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2006.11a
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    • pp.359-362
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    • 2006
  • Infra-red thermography was conducted to understand a heat transfer characteristic on a surface protruded to a supersonic flowfield. Surface temperature distribution was obtained under the constant heat flux condition with a infra-red camera and the convective heat transfer coefficient distribution was calculated. Finally, two dimensional distribution of heat transfer coefficient on a surface around a cylinder body was derived.

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Convective Heat Transfer to Water near the Critical Region in Horizontal Rectangular Ducts (수평 직사각 덕트 내 임계점 부근 물의 대류열전달 특성)

  • Lee, Sang-Ho
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.36 no.5
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    • pp.477-485
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    • 2012
  • Fluid flow and heat transfer in horizontal ducts are strongly coupled with large changes in thermodynamic and transport properties near the critical region as well as the gravity force. Numerical analysis has been carried out to investigate convective heat transfer in horizontal rectangular ducts for water near the thermodynamic critical point. Convective heat transfer characteristics, including velocity, temperature, and the properties as well as local heat transfer coefficients along the ducts are compared with the effect of proximity on the critical point. When there is flow acceleration because of a density decrease, convective heat transfer characteristics in the ducts show transition behavior between liquid-like and gas-like phases. There is a large variation in the local heat transfer coefficient distributions at the top, side, and bottom surfaces, and close to the pseudocritical temperature, a peak in the heat transfer coefficient distribution resulting from improved turbulent transport is observed. The Nusselt number distribution depends on pressure and duct aspect ratio, while the Nusselt number peak rapidly increases as the pressure approaches the critical pressure. The predicted Nusselt number is also compared with other heat transfer correlations.

Radative Effect on the Conjugate Mixed Convection-Conduction Heat Transfer along a Vertical Circular Cylindrical Fin (연직 원통윈에서의 혼합대류-전도 복합열전달에 미치는 복사효과)

  • 최상경;여문수;손병진
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.5
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    • pp.1706-1716
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    • 1991
  • 본 연구에서는 혼합대류하는 연직원통휜 열전달에 미치는 복사효과에 Rossel- and 근사해법을 도입한 층류 경계층방정식과 휜 전도방정식을 동시에 해석하여 복사 -전도매개변수(radiation-conduction parameter) M, 대류-전도 매개변수(convectionc- onduction parameter) N$_{c}$, 부력매개변수(buoyancy force parameter) R$_{i}$ 그 리고 횡곡률 매개변수(transverse curvature parameter) .lambda.를 계산 파라미터로 하여 휜 최적설계의 기본이 되는 총열전단률, 무차원 국소등가열전달계수, 무차원 국소열플 럭스 및 휜온도분포를 계산할 수 있는 일반성있는 algorithm을 개발하고 휜 성능에 관 한 결과들을 제공함으로써, 좀 더 완전한 복사 열플럭스를 도입한, 다음 연구를 위한 범용의 기초자료를 얻는데 본 연구의 목적이 있다.

Numerical Study of Mixed Convection Nanofluid in Horizontal Tube (수평원형관내 나노유체의 혼합대류에 관한 수치적 연구)

  • Choi, Hoon-Ki;Lim, Yun-Seung
    • Journal of Convergence for Information Technology
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    • v.9 no.8
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    • pp.155-163
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    • 2019
  • Laminar mixed convection of a nanofluid consists of water and $Al_2O_3$ in a horizontal circular tube has been studied numerically. Two-phase mixture model has been used to investigate hydrodynamic and thermal behaviors of the nanofluid with variables physical properties. Three dimensional Navier-Stokes, energy and volume fraction equations have been discretized using the finite volume method. The Brownian motions of nanoparticles have been considered to determine the thermal conductivity and dynamic viscosity of $Al_2O_3$-Water nanofluid, which depend on temperature. The calculated results show good agreement with the previous numerical data. Results show that in a given Reynolds number (Re), increasing solid nanoparticles volume fraction and Richardson number (Ri) increases the convective heat transfer coefficient and wall shear stress.