• Transactions of the Korean Society of Mechanical Engineers
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• v.8 no.4
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• pp.351-359
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• 1984

본 연구에서는 열전달계수의 이와같은 변수의 영향에 대하여 연구하였다. 그리고 이론적 연구가 수행되지 않는 기하학적 형태에 대한 열전달 계수의 Rayleigh수 와 간격비 및 Prandtl수에 관한 간단한 상관관계식을 제시하였다.

• 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.

• Journal of Energy Engineering
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• v.13 no.4
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• pp.275-280
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• 2004

Augmentation of heat transfer by ultrasonic vibration in pipes are investigated. Measurements of convective heat transfer coefficients on circular pipe walls are made with and without ultrasonic vibration applied to water. These data are compared with each other to quantify the effects of ultrasonic vibration on heat transfer enhancement. Numerical analysis has been also performed in order to extend the ranges of examined temperature and flow rate. FLUENT Ver.6.1 is used to simulate velocity and temperature fields and evaluate heat transfer coefficient with and without ultrasonic vibration. The results show that the ultra- sonic vibration enhances the Nusselt number of forced convection flow and the increase rate strongly depends on flow rate.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.1
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• pp.9-15
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• 2013

The effective use and management of energy resources has been issued to solve the global warming problem and petrolium price increase. To improve the energy efficiency of a heat exchanger, a new countermeasure is required and the heat transfer research of nano-fluids as a new working fluid is needed. This study was carried out with increasing the Reynolds number and the vol% of nano-fluids in the inlet temperature of $25^{\circ}C$ and $50^{\circ}C$. As the result, the higher the entrance temperature is, the higher the convective heat transfer coefficient is.

• Plant Journal
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• v.15 no.1
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• pp.25-30
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• 2019

In this study, by varying flow patterns, which is one of the hydraulic factors of FAC, a strategy to reduce pipe wall thinning by mass transfer has been investigated. A similarity between heat transfer and mass transfer was verified via theoretical analysis, and local convective heat transfer coefficients were analyzed using a commercial numerical analysis program. When ribs were installed inside and outside of the internal surface in the straight section of the pipe, the maximum local heat transfer coefficient was shown to decrease substantially by up to 24.9% compared to the basic flow depending on the position and shape of ribs. If a guide vein was inserted in the pipe elbow, the maximum local heat transfer coefficient decreased by up to 26.7% compared to the basic flow depending on the internal surface area of the pipe by the guide vein.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.8
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• pp.1003-1009
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• 2012

Heat exchanger has been widely used in the industry which needs energy transport, and the application of the plate type heat exchanger having high efficiency has been greatly increased. In this study main design parameters are analyzed and new equations are induced. The induced formulation was compared with a commercial program in order to design an optimal heat exchanger. The equations of heat transfer coefficient and pressure drop for Chevron angles are introduced as functions of Reynolds number. The program implemented the equations is tested with Chevron angle variation. The results show that the convective heat transfer coefficients take errors within 8% and the pressure drops have errors within 5% in the analysis conditions.

• 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.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.7
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• pp.702-708
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• 2015

Two-phase flow boiling experiments were conducted using FC-72 as the working fluid. The micro-channels consisted of 15 channels with a depth of 0.2 mm, width of 0.45 mm, and length of 60 mm. Tests were performed over a mass flux range of $200-400kg/m^2s$, heat flux range of $5.6-49.0kW/m^2$, and vapor quality range of 0.02-0.93. Based on the results of the experiment, the heat transfer mechanism by nucleate boiling was dominant at a lower vapor quality (x<0.2), whereas that in the region of a vapor quality greater than 0.2 was complexly influenced by nucleate boiling and forced convection boiling. The nucleate boiling and forced convection boiling could be expressed as functions of the boiling number and convection number, respectively. In addition, the heat transfer coefficient obtained by the experiment was compared with the heat transfer coefficient by the existing correlation.

• 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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.9
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• pp.891-896
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• 2011

In this study, experiments were carried out to investigate the convective heat transfer characteristics of rectangular microchannels. The sample used in the experiments contained 20 rectangular microchannels in parallel. The channels had a hydraulic diameter of 700 ${\mu}m$. Distilled water was used as the working fluid. In the experiments, the Reynolds number ranged from 400 to 800, heat flux ranged from 35 to 85 kW/$m^2$, and the inlet fluid temperature was $20^{\circ}C$. As a result, the convective heat transfer coefficient increased upon increasing the Reynolds number and ranged from 4.6 to 6.4 kW/$m^2/^{\circ}C$ in the thermally fully developed region. Moreover, the higher the Reynolds number, the longer the thermal entry length in the rectangular microchannels. However, it was observed that a variable heat flux did not affect the thermal entry length. In conclusion, a correlation was proposed to indicate the heat transfer characteristics in a thermally fully developed region.