• 에너지공학
• /
• 제23권2호
• /
• pp.13-20
• /
• 2014

헬리컬 코일이 덕트 내부에 있을 때, 기울기에 따른 자연대류 열전달을 실험적으로 측정하였다. 고부력 조건을 구현하기 위하여 유사성에 기초하여 열전달 실험을 대신하여 물질전달 실험을 수행하였다. RaD 수 $4.55{\times}10^6$에서, 턴(Turn) 수를 1~10, P/D를 1.3~5, 헬리컬 코일의 기울기를 $0^{\circ}{\sim}90^{\circ}$까지 변화시켰다. 헬리컬 코일의 턴 수가 1일 때, 측정된 $Nu_D$ 수는 McAdams의 수평관 자연대류 열전달 상관식과 거의 일치하였다. 기울어진 덕트 내 헬리컬 코일의 자연대류 열전달은 피치, 턴 수, 덕트 높이에 따라 복합적으로 변화하였고 이는 속도 효과, 굴뚝 효과, 예열 효과로 분석되었다. 본 연구의 결과는 Compact heat exchanger에서의 자연대류 열전달에 대한 현상학적 분석에 기여한다.

• 대한기계학회논문집
• /
• 제12권6호
• /
• pp.1415-1427
• /
• 1988

본 연구에서는 막냉각되고 있는 수평평판에서 분사각도와 분사율의 변화가 열 전달계수에 미치는 영향을 주 연구대상으로 하였다. 열전달계수의 측정을 위하여 나 프탈렌 승화법을 이용하였고, 열전달 계수에 가장 큰 영향을 미치는 유동장에 대한 이 해를 위해 슐리렌 광학계를 이용한 유동의 가시화 실험을 수행하였다. 분사각도는 Fig.1에서와 같이 y축 방향으로의 수직분사(case 1), 유동방향(x축방향)dp eogo 35˚ 경사진 분사(case 2), 그리고 유동의 직각방향(Z축)dp eogo 35˚경사진 분사(case 3) 등 3가지의 경우에 대해 실험하였고, 분사율은 0.5, 1.0, 1.8로 변화시켰다.

• 설비공학논문집
• /
• 제17권10호
• /
• pp.898-906
• /
• 2005

The present study has been conducted to investigate convective heat/mass transfer in the cooling passage with bleed holes. The rotating square channel has 40.0 mm hydraulic diameter and the bleed holes on the leading surface of the channel. The hole diameter of bleed hole is 4.5mm and its spacing is ( p/d:4.9) about five times of hole diameter. Exit mass flow rate through bleed holes is $10\%$ of the main mass flow rate and relation number is changed form 0.0 to 0.4. A naphthalene sublimation technique is employed to determine the detailed local heat transfer coefficients using the heat and mass transfer analogy The cooling performance is influenced by exit mass flow rate through bleed holes and Coriolis force of rotating channel for fixed Reynolds number. The heat transfer on the leading surface is decreased due to Coriolis force. However the total heat transfer is enhanced around holes on the leading surface because of trapping flow by bleeding.

• Journal of Mechanical Science and Technology
• /
• 제20권8호
• /
• pp.1275-1283
• /
• 2006

Condensation heat transfer coefficients in a 7.92 mm inside diameter copper smooth tube were obtained experimentally for R22, R134a, and R410A. Working conditions were in the range of $30-40^{\circ}C$ condensation temperature, $95-410 kg/m^2s$ mass flux, and 0.15-0.85 vapor quality. The experimental data were compared with the eight existing correlations for an annular flow regime. Based on the heat-momentum analogy, a condensation heat transfer coefficients correlation for the annular flow regime was developed. The Breber et al. flow regime map was used to discern flow pattern and the Muller-Steinhagen & Heck pressure drop correlation was used for the term of the proposed correlation. The proposed correlation provided the best predicted performance compared to the eight existing correlations and its root mean square deviation was less than 8.7%.

• Nuclear Engineering and Technology
• /
• 제30권1호
• /
• pp.26-39
• /
• 1998

The containment pressure and temperature transient analysis computer code CONTEMPT4/MOD5 is modified to incorporate the passive containment cooling models. The correlations are selected from the existing experimental heat transfer correlations to model the natural and mixed convection in annular space between the containment shell and the shield building. The evaporative heat transfer of the water film on the outer shell of the containment is modeled using the correlations derived from the analogy between the heat and mass transfer. The modified code is applied to the Ap600 containment transient analysis for the model verification and the results are compared to the results of GOTHIC calculation done by Westinghouse. Also, d series of parametric sensitivity studies of heat transfer correlations, water film ratio and delay time of the wet cooling on the containment peak pressure and temperature following LOCA are performed for the containment of 1000MWe passive plant, KP1000.

• 에너지공학
• /
• 제21권1호
• /
• pp.18-25
• /
• 2012

굴뚝내 수직 원형관의 자연대류에서 굴뚝의 입구길이, 출구길이, 그리고 굴뚝의 직경에 따른 열전달 변화를 실험적으로 연구하였다. 상사성을 이용하여 열전달 실험 대신 물질전달 실험을 수행하였다. 직경 0.054 m, 높이 0.03, 0.07, 0.10 m의 원형관에 대하여 굴뚝의 직경을 0.06 m에서 0.14 m까지, 높이를 0.30 m에서 1.10 m까지 변화시켰다. 이는 Pr 수 2,094, $Ra_L$ 수 $4.55{\times}10^9$, $5.79{\times}10^{10}$, 그리고 $1.69{\times}10^{11}$에 해당한다. 굴뚝이 없을 때, 수직 원형관의 열전달은 Le Ferve의 수직평판에 대한 층류 자연대류 상관식과 일치하였다. 출구길이를 증가시키며 실험한 결과, 열전달은 증가하다가 특정 출구길이 이상에서는 일정해 졌다. 반면, 입구길이를 증가시킬 때는 열전달은 감소하다가 특정 입구길이 이상에서는 일정해졌다. 굴뚝효과로 증가된 열전달은 굴뚝의 직경을 증가시킬수록 감소하다가 굴뚝이 없을 때와 같아졌다.

• 한국유체기계학회 논문집
• /
• 제4권3호
• /
• pp.7-13
• /
• 2001

The present study investigates convective heat/mass transfer and flow characteristics inside a cooling passage of rotating gas-turbine blades. The rotating duct has staggered ribs with $70^{\circ}$ attack angle, which are attached on leading and trailing surfaces. Naphthalene sublimation technique is employed to determine detailed local heat transfer coefficients using the heat and mass transfer analogy. Additional numerical calculations are conducted to analyze the flow patterns in the cooling passage. The present experiments employ two-surface heating conditions in the rotating duct because the exposed surfaces to hot gas stream are pressure and suction side surfaces in the middle passages of an actual gas-turbine blade. Secondary flows are generated by Coriolis and centrifugal forces in the spanwise and streamwise directions. The ribs attached on the walls disturb the mainflow resulting in recirculation and secondary flows near the ribbed wall. The local heat transfer and flow patterns in the passage are changed significantly according to rib configurations and duct rotation speeds. Therefore, the geometry and arrangement of the ribs are important for the advantageous cooling performance. The experimental results show that the ribs enhance the heat transfer more than $70\%$ from that of the smooth duct. The duct rotation generates the heat transfer discrepancy between the leading and trailing walls due to the secondary flows induced by the Coriolis force. The overal heat transfer pattern on the leading and trailing walls for the first and second passes are depended on the rotating speed, but the local heat transfer trend is affected mainly by the rib arrangements.

• 대한기계학회논문집B
• /
• 제34권9호
• /
• pp.825-834
• /
• 2010

사각공동내 자연대류 열전달 실험에서, 단열벽에 의해 열전달이 저하가 관찰되는 영역을 실험적으로 그리고 수치해석적으로 평가하였다. $Gr_H$ 수 $1.53\times10^7$부터 $1.01\times10^{10}$까지 변화시키며, 단열벽이 존재할 때와 그렇지 않을 때를 구분하여 열전달률을 측정하였다. FLUENT 실험의 결과를 예측할 수 있는지 확인하고 실험으로 수행하기 어려운 매우 좁은 영역에 대해 FLUENT를 수행하였다. 실험과 FLUENT의 결과를 다른 연구와 비교한 바 일치함을 보였다. 단열벽이 전체 열전달에 미치는 영향은 예상과 같이 단열벽 근처의 매우 좁은 영역에 국한하여 나타남을 확인하였다. 본 연구는 유사성(Analogy) 원리를 이용하여 열전달계를 전기도금계의 물질전달계로 모사하는 방법론을 개발하는 과정에서 실험을 효율화하고자 하는 방안을 강구하기 위하여 추진되었다. 본 연구를 통하여 단열벽간 거리(전극의 폭)를 매우 줄일 수 있는 이론적 근거를 확보하였다.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2001년도 춘계학술대회논문집D
• /
• pp.425-432
• /
• 2001

Single-phase heat transfer coefficients and pressure drops of R-22 were measured in smooth, horizontal copper tubes with inner diameters of 3.36 mm, 5.35 mm, 6.54 mm and 8.12 mm, respectively. The experiments were conducted in the closed loop, which was driven by a magnetic gear pump. Data are presented for the following range of variables: Reynolds from 1000 to 20000. Single-phase heat transfer coefficients increased by $10{\sim}30%$ as the inner diameter of tube was reduced and it was found that a well-known previous correlation, Gnielinski's correlation, was not suitable for the small diameter tubes. But the pressure drop in the small diameter tubes have been shown slightly deviations with Blauius' correlation. Based on an analogy between heat and mass transfer, the new heat transfer correlation is proposed to predict the experimental data successfully.

• Nuclear Engineering and Technology
• /
• 제47권5호
• /
• pp.567-578
• /
• 2015

In a nuclear reactor containment, wall condensation forms with noncondensable gases and their accumulation near the condensate film leads to a significant reduction in heat transfer. In the framework of nuclear reactor safety, the film condensation in the presence of noncondensable gases is of high relevance with regards to safety concerns as it is closely associated with peak pressure predictions for containment integrity and the performance of components installed for containment cooling in accident conditions. In the present study, CUPID code, which has been developed by KAERI for the analysis of transient two-phase flows in nuclear reactor components, is improved for simulating film condensation in the presence of noncondensable gases. In order to evaluate the condensate heat transfer accurately in a large system using the two-fluid model, a mass diffusion model, a liquid film model, and a wall film condensation model were implemented into CUPID. For the condensation simulation, a wall function approach with a heat/mass transfer analogy was applied in order to save computational time without considerable refinement for the boundary layer. This paper presents the implemented wall film condensation model, and then introduces the simulation result using the improved CUPID for a conceptual condensation problem in a large system.