• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.2
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• pp.184-195
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• 1995

A theoretical one-dimensional model for the charging process in stratified thermal storage tanks is established presuming that the fluid ensuing from the tank inlet creates a perfectly mixed, layer above the thermocline. Both the generic and asymptotic closed-form solutions are obtained via the Laplace transformation. The asymptotic solution describes the nature of the charging pertaining to the case of no thermal diffusion, whereas the generic solution is of practical importance to understand the role of operating parameters on the stratification. The present model is validated through comparison with available experimental data, where they agree well with each other within a reasonable limit. An interpretation of the exact solution entails two important features associated with the charging process. The first is that an in-crease in the mixing depth $h_m$ causes a relatively slow temperature rise in the perfectly mixed region, but on the other hand it results in a faster decay of the overall temperature gradient across the thermocline. Next is the predominance of the mixing depth in the presence of the prefectly mixed region. In such a case the effect of the Peclet number is marginal and there-fore the thermal characteristics are solely dependent on the mixing depth paticularly for large $h_m$. The Peclet number affects significantly only for the case without mixing. Variation of the storage efficiency in response to the change in the mass flow rate agrees favorably with the published experimental results, which confirms the utility of the present study.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.5
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• pp.819-830
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• 2016

Hydrodynamic characteristics of wave propagation through density stratification have not been identified in details. So this study conducted a numerical simulation using LES-WASS-3D ver. 2.0 for analysis of density current due to water temperature and salinity in order to analyze hydraulic characteristics under wave action in a two-layer density stratified fluid. For the validity and effectiveness of numerical wave tank used, it was compared and analyzed with the experiment to show waveform based on $3^{rd}$-order Stoke wave theory at the internal of a density stratification. Using the results obtained from numerical simulation, the surface and internal wave heights are reduced as the wave propagates in a two-layer density stratified water. And the surface or internal wave attenuation became more serious as the vorticities were increased by the velocity difference of wave propagation due to the upper-lower density difference around the interface of a density stratification. As well, the surface and internal wave attenuations became more serious with higher density difference and depth ratio between upper and lower layers when the wave propagates through a density stratification.

• Nuclear Engineering and Technology
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• v.27 no.1
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• pp.45-52
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• 1995

In influence of the vapor phase turbulent stress (i.e., the too-phase Reynolds stress) to the characteristics of two-phase system in a horizontal pipe has been theoretically investigated. The average two-fluid model has been constituted with closure relations for stratified flow in a horizontal pipe. A vapor phase turbulent stress model for the regular interface geometry has been included. It is found that the second order waves propagate in opposite direction with almost the same speed in the moving frame of reference of the liquid phase velocity. Using the well-posedness limit of the two-phase system, the dispersed-stratified How regime boundary has been modeled. Two-phase Froude number has been found to be a convenient parameter in quantifying the onset of slugging as a function of the global void fraction. The influence of the taper phase turbulent stress was found to stabilize the flow stratification.

• Journal of Korea Water Resources Association
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• v.37 no.3
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• pp.219-231
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• 2004

The use of air diffuser system to ameliorate the reservoir by breaking stratification is now widespread. This study focuses on the hydrodynamic behavior of bubble plumes, which is the major mechanism of destratification and their combined effect of adjacent plumes on destratification efficiency. By introducing 2-phase Computational Fluid Dynamics(CFD) technique, we could suggest the optimal diffuser spacing having optimal destratification efficiency by simply analyzing the complex destratification procedures varying with the seasonal stratification intensity and bubble flow rate. Lab experiments were also carried out to verify CFD model in thermally stratified fresh water which quite differs from former researches using salts. This study showed that the mixing efficiency strongly depends on the spacing of neighboring plumes. When diffuser spacing is lower than 1.5 times the depth, the combined effect is stronger; as Plume Number(PN) is increased, the efficiency is strongly affected by spacing. If the distance is shorter than the depth of water, the efficiency increases linearly in proportion to PN. Otherwise, the efficiency increases non-linearly. These findings suggest that the combined effect should be more quantitatively taken into consideration for design and operation of air-diffuser destratification system, and recommend that the optimal destratification efficiency will be when plume number is 1000 and the spacing between neighboring diffusers is 1.5 times the depth.

• Korean Journal of Radiology
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• v.25 no.2
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• pp.166-178
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• 2024

Objective: This study aimed to determine the predictive performance of non-contrast CT (NCCT) signs for hemorrhagic growth after intracerebral hemorrhage (ICH) when stratified by onset-to-imaging time (OIT). Materials and Methods: 1488 supratentorial ICH within 6 h of onset were consecutively recruited from six centers between January 2018 and August 2022. NCCT signs were classified according to density (hypodensities, swirl sign, black hole sign, blend sign, fluid level, and heterogeneous density) and shape (island sign, satellite sign, and irregular shape) features. Multivariable logistic regression was used to evaluate the association between NCCT signs and three types of hemorrhagic growth: hematoma expansion (HE), intraventricular hemorrhage growth (IVHG), and revised HE (RHE). The performance of the NCCT signs was evaluated using the positive predictive value (PPV) stratified by OIT. Results: Multivariable analysis showed that hypodensities were an independent predictor of HE (adjusted odds ratio [95% confidence interval] of 7.99 [4.87-13.40]), IVHG (3.64 [2.15-6.24]), and RHE (7.90 [4.93-12.90]). Similarly, OIT (for a 1-h increase) was an independent inverse predictor of HE (0.59 [0.52-0.66]), IVHG (0.72 [0.64-0.81]), and RHE (0.61 [0.54-0.67]). Blend and island signs were independently associated with HE and RHE (10.60 [7.36-15.30] and 10.10 [7.10-14.60], respectively, for the blend sign and 2.75 [1.64-4.67] and 2.62 [1.60-4.30], respectively, for the island sign). Hypodensities demonstrated low PPVs of 0.41 (110/269) or lower for IVHG when stratified by OIT. When OIT was ≤ 2 h, the PPVs of hypodensities, blend sign, and island sign for RHE were 0.80 (215/269), 0.90 (142/157), and 0.83 (103/124), respectively. Conclusion: Hypodensities, blend sign, and island sign were the best NCCT predictors of RHE when OIT was ≤ 2 h. NCCT signs may assist in earlier recognition of the risk of hemorrhagic growth and guide early intervention to prevent neurological deterioration resulting from hemorrhagic growth.

• Asian-Australasian Journal of Animal Sciences
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• v.29 no.6
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• pp.807-813
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• 2016

Two experiments were conducted assessing the effects of presence or absence of rumen protozoa and dietary nitrate addition on rumen fermentation characteristics and in vitro methane production in Brahman heifers. The first experiment assessed changes in rumen fermentation pattern and in vitro methane production post-refaunation and the second experiment investigated whether addition of nitrate to the incubation would give rise to methane mitigation additional to that contributed by defaunation. Ten Brahman heifers were progressively adapted to a diet containing 4.5% coconut oil distillate for 18 d and then all heifers were defaunated using sodium 1-(2-sulfonatooxyethoxy) dodecane (Empicol). After 15 d, the heifers were given a second dose of Empicol. Fifteen days after the second dosing, all heifers were allocated to defaunated or refaunated groups by stratified randomisation, and the experiment commenced (d 0). On d 0, an oral dose of rumen fluid collected from unrelated faunated cattle was used to inoculate 5 heifers and form a refaunated group so that the effects of re-establishment of protozoa on fermentation characteristics could be investigated. Samples of rumen fluid collected from each animal using oesophageal intubation before feeding on d 0, 7, 14, and 21 were incubated for in vitro methane production. On d 35, 2% nitrate (as $NaNO_3$) was included in in vitro incubations to test for additivity of nitrate and absence of protozoa effects on fermentation and methane production. It was concluded that increasing protozoal numbers were associated with increased methane production in refaunated heifers 7, 14, and 21 d after refaunation. Methane production rate was significantly higher from refaunated heifers than from defaunated heifers 35 d after refaunation. Concentration and proportions of major volatile fatty acids, however, were not affected by protozoal treatments. There is scope for further reducing methane output through combining defaunation and dietary nitrate as the addition of nitrate in the defaunated heifers resulted in 86% reduction in methane production in vitro.

• Nuclear Engineering and Technology
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• v.53 no.11
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• pp.3635-3642
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• 2021

Natural circulation systems (NCSs) are extensively applied in nuclear power plants because of their simplicity and inherent safety features. For some passive natural circulation systems in floating nuclear power plants (FNPPs), the ocean is commonly used as the heat sink. Condensation induced water hammer (CIWH) events may appear as the steam directly contacts the subcooled seawater, which seriously threatens the safe operation and integrity of the NCSs. Nevertheless, the research on the formation mechanisms of CIWH is insufficient, especially in NCSs. In this paper, the characteristics of flow rate and fluid temperature are emphatically analyzed. Then the formation types of CIWH are identified by visualization method. The experimental results reveal that due to the different size and formation periods of steam slugs, the flow rate presents continuous and irregular oscillation. The fluid in the horizontal hot pipe section near the water tank is always subcooled due to the reverse flow phenomenon. Moreover, the transition from stratified flow to slug flow can cause CIWH and enhance flow instability. Three types of formation mechanisms of CIWH, including the Kelvin-Helmholtz instability, the interaction of solitary wave and interface wave, and the pressure wave induced by CIWH, are obtained by identifying 67 CIWH events.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.110-114
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• 2001

A numerical analysis has been perfonned to estimate the effect of turbulent penetration and thermal stratified flow in the branch lines piping. This phenomenon of thermal stratification are usually observed in the piping lines of the safety related systems and may be identified as the source of fatigue in the piping system due to the thermal stress loading which are associated with plant operating modes. The turbulent penetration length reaches to $1^{st}$ valve in safety injection piping from reactor coolant system (RCS) at normal operation for nuclear power plant when a coolant does not leak out through valve. At the time, therefore, the thermal stratification does not appear in the piping between RCS piping and $1^{st}$ valve of safety injection piping. When a coolant leak out through the $1^{st}$ valve by any damage, however, the thermal stratification can occur in the safety injection piping. At that time, the maximum temperature difference of fluid between top and bottom in the piping is estimated about $50^{\circ}C$.

• Asian Pacific Journal of Cancer Prevention
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• v.16 no.11
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• pp.4665-4669
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• 2015

The aim of this study was to assess the diagnostic value of RASSF1A methylation in renal cell carcinoma. Systematically search were performed using the Pubmed, ProQest and Web of Science for all articles on the association between RASSF1A methylation and renal cell carcinoma before 15 April 2015. After the filtration, 13 studies involving 677 cases and 497 controls met our criteria. Our meta-analysis suggested that hypermethylation of RASSF1A gene was associated with the increased risk of RCC(OR:4.14, 95%CI:1.06-16.1). Stratified analyses showed a similar risk in qualitative detection method(OR:28.4, 95%CI:10.2-79.6), body fluid sample(OR:12.8, 95%CI:5.35-30.8), and American(OR:10.5, 95%CI:1.97-55.9). Our result identified that RASSF1A methylation had a strong potential in prediction the risk of Renal cell carcinoma.

• Journal of ILASS-Korea
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• v.8 no.1
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• pp.23-28
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• 2003

When a cold HPSI (High Pressure Safety Injection) fluid associated with a design basis accident, such as LOCA (Loss of Coolant Accident), enters the cold legs of a stagnated primary coolant loop, thermal stratification phenomena may arise due to incomplete mixing. If the stratified flow enters a reactor pressure vessel downcomer, severe thermal stresses are created in a radiation embrittled vessel wall by local overcooling. Previous thermal-mixing analyses have assumed that the thermal stratification phenomena generated in stagnated loop of a partially stagnated collant loop are neutralized in the vessel downcomer by strong flow from unstagnated loop. On the basis of these reasons, this paper presents the thermal-mixing analysis results in order to identify the fact that the cold plume generated in the vessel downcomer due to the thermal stratification phenomena of the stagnated loop is affected by the strong flow of the unstagnated loop.