• Proceedings of the Korean Nuclear Society Conference
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• 1996.05b
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• pp.356-361
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• 1996

물질전달과 열전달의 유사성을 이용하는 나프탈렌 승화법을 핵연료집합체 모델에 적용하여 봉다발에서의 국소 열전달 계수의 분포를 측정하였다. 실험 모델은 가압경수형 원자로에서 나타나는 부수로 즉, 벽면 부수로와 모서리 부수로 및 내부 부수로로 구성되는 3$\times$3 봉다발이다. 봉다발에서의 국소 열전달 계수 값은 부수로의 형상과 인접한 봉 및 벽면의 영향이 크게 작용하는 것으로 측정되었다. 내부 부수로에 둘러져 있는 봉에서의 국소 열전달계수값은 봉과 봉 사이에서는 부수로 중심 방향보다 낮았고, 평균열전달계수는 Dittus-Boelter의 상관식보다 약간 낮은 값을 보였다. 벽면 부수로에 인접한 봉에서의 열전달계수는 벽면의 영향으로 내부 부수로에 있는 봉보다 상대적으로 낮았으며, 모서리 부수로의 봉에서는 벽면의 영향이 증대되어 더욱 낮게 나타났다.

• 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.37 no.1
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• pp.16-21
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• 2013

Nanofluids are suspensions of metallic or nonmetallic nano powders in base liquid and can be employed to increase heat transfer rate in various applications. In this research the heat transfer characteristics has been experimented by alumina(50 nm)/water nano-fluids. Experimental results showed that the increasing the concentration of alumina nanofluids local and average heat transfer coefficient increased. The local heat transfer coefficient of 6 Wt% nanofluid was increased 37~46% than water at X/D=50~120. The average heat transfer coefficient of 6 Wt% nanofluid was rapidly increased than water at Reynolds number 1100~1300.

• Journal of Energy Engineering
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• v.14 no.1
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• pp.30-36
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• 2005

This paper reports the experimental study of the heat transfer characteristics of the wake region behind a cylinder in cross flow. Local heat transfer coefficient was measured from the stagnation point (θ=0°) to 180°, and the variation of Nu in the axial direction along the cylinder was also studied. The results show that the heft transfer rate at the rear (θ=180°) near the duct wall can increase as much as 58% over the 2 dimensional value at the center of the duct. The heat transfer profiles in the wake region also show distinct effects of the aspect ratio and the heat transfer boundary condition.

• Journal of the Korean Society of Propulsion Engineers
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• v.6 no.3
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• pp.37-43
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• 2002

There have been numerous experimental studies for heat transfer measurement technique. This study investigates optical methods for measuring local heat transfer coefficient using thermochromic liquid crystal. Transient and steady methods have been utilized to measure local heat transfer coefficient on a cylinder with a cross flow. The steady method is based on the heat-coating technique and two transient methods adopt by-pass technique and insertion technique, respectively. Both techniques of transient method employ heating technique in which the flow is heated by using the electric heater and cooling technique which cools the preheated cylinder. Experimental results indicate that each methods have nearly similar results. Detailed discussions have been made for its own advantages and disadvantages.

• 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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.1
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• pp.81-88
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• 2014

An experimental study is performed to obtain an average heat transfer coefficient around the perimeter of a near horizontal tube. For the test a stainless steel tube of 50.8 mm diameter submerged in water at atmospheric pressure is used. Both subcooled and saturated pool boiling conditions are considered and the inclination angle of the tube is changed from the horizontal position to $9^{\circ}$ in steps of $3^{\circ}$. In saturated water, the local boiling heat transfer coefficient at the azimuthal angle of $90^{\circ}$ from the tube bottom can be regarded as the average of the coefficients regardless of the tube inclination angles. However, when the water is subcooled the location for the average heat transfer coefficient depends on the inclination angle and the heat flux. It is explained that the major mechanisms changing the heat transfer are closely related with the intensity of the liquid agitation and the generation of big size bubbles through bubble coalescence.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.1
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• pp.112-119
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• 1995

Measurements of the local heat transfer coeffcients on a spherically concave surface with a round impinging jet are presented. The liquid crystal transient method was used for these measurements. This method, which is a variation on the transient method, suddenly exposes a preheated wall to an impinging jet while video recording the response of liquid crystals for the measurement of the surface temperature. The Reynolds numbers used were 1,000, 23,000 and 50,000 and the nozzle-to-jet distance was L/d=2, 4, 6, 8, 10. Presented results are compared to previous measurements for flat plate. In the experiment, the local heat transfer Nusselt numbers on a concave surface are higher than those on a flat plate. Maximum Nusselt number at all region occured at L/d=6 and second maximum in the Nusselt number occured at R/d=2 for both Re=50,000 and Re=23,000 in case of L/d=2 and for only Re=50,000 in case of L/d=4. All other cases exhibit monotonically decreasing value of the Nusselt number along the curved surface.

• Proceedings of the Korean Nuclear Society Conference
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• 1999.10a
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• pp.150.2-150
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• 1999

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.5
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• pp.523-534
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• 1998

The convection heat transfer on horizontal circular tube is studied as a conjugated heat transfer problem. With uniform heat generation in a cylindrical heater placed in a cross flow boundary condition, heat flow that is conducted along the wall of the heater creates a non-isothermal surface temperature and non-uniform heat flux distribution. In the present investigation, the effects of circumferential wall heat conduction on convection heat transfer are investigated for the case of forced convection around horizontal circular tube in cross flow of air and water. Non-dimensional conjugation parameter $ K^*$ which can be deduced from the governing energy differential equation should be used to express the effect of circumferential wall heat conduction. Two-dimensional temperature distribution$ T({\gamma,\theta})$ is presented. The influence of circumferential wall heat conduction is demonstrated on graph of local Nusselt number.