• Nuclear Engineering and Technology
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• 제37권6호
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• pp.525-536
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• 2005

The interfacial area transport equation dynamically models the changes in interfacial structures along the flow field by mechanistically modeling the creation and destruction of dispersed phase. Hence, when employed in the numerical thermal-hydraulic system analysis codes, it eliminates artificial bifurcations stemming from the use of the static flow regime transition criteria. Accounting for the substantial differences in the transport mechanism for various sizes of bubbles, the transport equation is formulated for two characteristic groups of bubbles. The group 1 equation describes the transport of small-dispersed bubbles, whereas the group 2 equation describes the transport of large cap, slug or chum-turbulent bubbles. To evaluate the feasibility and reliability of interfacial area transport equation available at present, it is benchmarked by an extensive database established in various two-phase flow configurations spanning from bubbly to chum-turbulent flow regimes. The geometrical effect in interfacial area transport is examined by the data acquired in vertical fir-water two-phase flow through round pipes of various sizes and a confined flow duct, and by those acquired In vertical co-current downward air-water two-phase flow through round pipes of two different sizes.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.1123-1128
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• 2009

The refrigerant R-134a flow distributions are experimentally studied for a round header/ten flat tube test section simulating a brazed aluminum heat exchanger. Three different inlet orientations (parallel, normal, vertical) were investigated. Tests were conducted with downward flow for the mass flux from 70 to $130\;kg/m^2s$ and quality from 0.2 to 0.6. In the test section, tubes were flush-mounted with no protrusion into the header. It is shown that normal and vertical inlet yielded approximately similar flow distribution. At high mass fluxes or high qualities, however, slightly better results were obtained for normal inlet configuration. The flow distribution was worst for the parallel inlet configuration. Possible explanation is provided based on flow visualization results.

• 한국지반환경공학회 논문집
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• 제16권6호
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• pp.39-43
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• 2015

This study extends the Distributed Temperature Sensing (DTS) application to delineate the saturated zones in shallow sediment and evaluate the groundwater flow in both downward and upward directions. Dry, partially and fully saturated zones and water level in the subsurface can be recognized from this study. High resolution seepage velocity in vertical direction was estimated from the temperature data in the fully saturated zone. By a single profile, water level can be detected and seepage velocity in saturated zone can be estimated. Furthermore, thermal gradient analysis serves as a new technique to verify unsaturated and saturated zones in the subsurface. The vertical seepage velocity distribution in the recognized saturated zone is then analyzed with improvement of Bredehoeft and Papaopulos' model. This new approach provides promising potential in real-time monitoring of groundwater movement.

• 한국산업보건학회지
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• 제10권1호
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• pp.18-31
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• 2000

A stack must be designed to 1) reduce or eliminate rainfall or snowfall into a industrial exhaust system, 2) minimize a resistance to flow, 3) maximize the vertical dispersion of the contaminated air and 4) minimize maintenance. The weather cone stacks and the elbow-type stacks are very popular in Korea. But they add some resistance to the exhaust system resulting in reduction of air flow rate, but also deflect the noxious contaminants downward in undiluted form. To solve these problems, ACGIH (American Conference of Governmental Industrial Hygienists) suggested the vertical discharge stack with concentric space between the upper stack with larger diameter and the lower stack with smaller diameter. The preliminary test showed that the vertical discharge stacks did not have the good rainfall protection. The reversed cone were newly devised to satisfy the requirements for the good stack. Subsequently, the amount of rain being penetrated through the stacks was measured while the stacks were simultaneously and naturally exposed to rain in the same area outside. Test results indicate that none of the stacks tested completely exclude rain. The efficiency of rainfall protection and the pressure loss coefficient were compared. The temporary conclusion was reached to the point that the reversed cone stack is the best one. Further research is underway.

• Nuclear Engineering and Technology
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• 제36권2호
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• pp.142-152
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• 2004

The liquid entrainment and vapor pull-through offtake model of RELAP5/MOD3 had been developed for SBLOCA (Small Break Loss of Coolant Accident). The RELAP5/MOD3 model for horizontal volumes accounts for the phase separation phenomena and computes the flux of mass and energy through a branch when stratified conditions occur in the horizontal pipe. In the case of CANDU reactor, this model should be used in the coolant flow of 95 feeders connected to the reactor header component under the horizontal stratification in header. The current RELAP5 model can treat the only 3 directions junctions; vertical upward, downward, and side oriented junctions, and thus improvements for the liquid entrainment and vapor pull-through model were needed for considering the exact angles. The RELAP5 off-take model was modified and generalized by considering the geometric effect of branching angles. Based on the previous experimental results, the critical height correlation was reconstructed by use of the branch line connection angle and validation analyses were also performed using SET. The new model can be applied to vertical upward, downward and angled branch, and the accuracy of the new correlations is more improved than that of RELAP5.

• Nuclear Engineering and Technology
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• 제55권3호
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• pp.1118-1124
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• 2023

Experimental study on the fluidelastic instability (FEI) of a curved tube bundle in single phase downward cross flow is investigated for the design qualification and analysis input preparation of helical coiled steam generator tubing. A 6×9 normal square curved tube array with equal and different vertical/horizontal pitch-to-diameter ratio was under-tested up to 6 m/s in term of gap flow velocity to measure the critical velocity for FEI. The critical velocity for FEI was measured at the turning point from the vibration amplitude plot along the gap flow velocity. Our test results were compared with straight tube results and published data in the design guideline. The applicability of the current design guidelines to a curved tube bundle is also assessed. We found that introducing frequency difference in a curved tube array increases the critical velocity for fluidelastic instability.

• 대한기계학회논문집B
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• 제35권7호
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• pp.701-708
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• 2011

기울어진 평판에서 발생하는 자연대류 열전달현상을 $R_{a_L}$ $1.69{\times}10^{11}$과 $7.23{\times}10^{12}$에 대하여 실험적으로 연구하였다. 유사성을 이용하여 열전달실험을 물질전달 실험으로 대체하였고 물질전달계로 전기도금계를 사용하였다. 평판의 기울기는 상향수평에서 하향수평까지 $10^{\circ}$씩 변화시켰다. 하향평판에서는 수직 벽면에 대한 자연대류 열전달 상관식에서 g 대신 g $cos{\theta}$로 대체함으로써 열전달계수를 구할 수 있다는 기존의 이론과 일치하는 결과를 얻었다. 상향평판의 경우 경계층이 벽면을 따라 발달되는 경우와 벽면으로부터 박리되는 2가지 영역으로 구분되는데 박리에 따른 열전달 증가를 확인하였다. 아울러 도금패턴을 이용하여 박리지점을 시각화하였고 박리지점에 대한 분석이 수행되었다.

• 설비공학논문집
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• 제12권2호
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• pp.150-160
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• 2000

Turbulent natural convective flow and heat transfer in a square enclosure with horizontal partition are investigated numerically. The enclosure is composed of a lower hot and a upper cold horizontal walls and adiabatic vertical walls. Partitions carried with the upward, downward, and both control plates are attached perpendicularly to the one of the vertical insulated walls, respectively. The low Reynolds number $k-\varepsilon$ model is adopted to calculate the turbulent thermal convection. The governing equations are solved by using the finite element method with Galerkin method. The computations have been carried out by varying the length of partition, the position of control plates, and the Rayleigh number based on the temperature difference between two horizontal walls and the enclosure height for water(Pr=4.95). When the control plates are attached at the edge of partition, the stability of oscillating flow grows wrose with the increase of Rayleigh number and the partition length. The heat transfer rate has been reducer than that of no control plate due to the restraint of control plates with the increase of Rayleigh number.

• 대한기계학회논문집
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• 제18권5호
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• pp.1330-1337
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• 1994

This study is to predict the lateral dispersion of the particles with time in a vertical pipe. Particle is released downward and located in the center of a pipe through which stationary, homogeneous turbulent air is flowing. We assume that gas turbulence velocities have a Gaussian probability density distribution and the presence of particle is not to alter turbulent structures. Particle trajectory is computed by numerically integrating the particle Lagrangian equation of motion, with a random sampling to determine the fluctuating air velocity experienced by each particle, which considered inertia effect and crossing-trajectories effect. The result shows characterestics of particle dispersion according to flow field condition and droplet size by using the parameters and scales, which expressed characterestics of flow field and particle. Predictions agree reasonably with experimental data.

• 태양에너지
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• 제15권2호
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• pp.77-90
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• 1995

본 연구는 용융점 온도가 $0^{\circ}C$인 순수 물이 수직원통형 빙축열조 내에 각각 형상비(H/R)가 4와 2인 형태로 채워져 있을 경우 수직원관 내로 유입되는 작동유체의 온도를 $-10^{\circ}C$, 유량을 10 liter/min로 고정시킨 후 유동방향을 상향과 하향으로 변화시켰을 경우 시간경과에 따라 나타나는 물의 응고형상, 수직원통의 온도분포, 수직원관의 온도분포, 축열량에 대한 열전달현상을 실험적으로 규명한 것이다. 축열조내 물의 온도분포는 초기온도가 $7^{\circ}C$인 경우 냉각과정중 축열조내 상부가 하부보다 높고 시간경과 후 물의 최대밀도점인 $4^{\circ}C$ 이하에서는 축열조 하부가 상부보다 높으며, 초기온도가 $4^{\circ}C$와 $1^{\circ}C$인 경우는 물의 밀도값이 최대점인 $4^{\circ}C$ 이하이므로 실험시작 초기부터 하부가 상부보다 온도분포가 높게 나타났다. 응고과정 시에는 동일한 초기온도 하에서 작동유체의 유동방향이 상향일 경우가 하향일 경우보다 축열조내 자연대류 유동이 활발하여 액상의 평균온도는 빠르게 강하되고 수직원관 외벽면의 상 하부 온도차이도 적으며, 응고형상은 축열조내 물의 초기온도가 $7^{\circ}C$와 $4^{\circ}C$ 일 때 상 하부에서 고르게 진전된다. 축열조내 물의 초기온도가 $1^{\circ}C$인 경우는 전도열전달의 영향이 지배적이므로 응고층의 생성은 작동유체 유동방향으로 형성되어진다. 축열량은 형상비에 관계없이 초기온도가 높을수록 크게 나타났으며, 동일한 초기온도 하에서도 작동유체의 유동방향이 상향으로 유입될 경우가 하향에 유입되는 경우보다 시간경과 후 크게 나타났다.