• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.3
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• pp.315-324
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• 2012

This paper presents a numerical investigation of the deflagration-to-detonation transition (DDT) of flame acceleration by a shock wave filled with an ethylene/air mixture as the combustible gas, considering geometrical changes by using obstacles and bent tubes. The model used consists of the reactive compressible Navier-Stokes equations and the ghost fluid method (GFM) for complex boundary treatment. Simulations with a variety of bent tubes with obstacles show the generation of hot spots through flame and strong shock-wave interactions, and restrained or accelerated flame propagation due to geometrical effects. In addition, the simulation results show that the DDT occurs with a nearly constant chemical heat-release rate of 20 MJ/($g{\bullet}s$) in our numerical setup. Furthermore, the DDT triggering time can be delayed by the absence of unreacted material together with insufficient pressures and temperatures induced by different flame shapes, although hot spots are formed in the same positions.

• 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.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.8
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• pp.75-83
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• 2005

A steady transonic dilute premixed combustion in a diverging channel is investigated by using asymptotic analysis. This model explores the nonlinear interactions between the near-sonic speed of the flow, the small changes in geometry from a straight channel, and the small heat release due to the one-step first-order Arrhenius chemical reaction. The reactive flow is described by a nonhomogeneous transonic small-disturbance (TSD) equation coupled with an ordinary differential equation for the calculation of the reactant mass fraction in the combustible gas. Also the asymptotic analysis reveals the similarity parameters that govern the reacting flow problem. The results show the complicated nonlinear interaction between the convection, reaction, and geometry effects and its effect on the flow behavior.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.2
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• pp.187-194
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• 2001

Spray impingement and fuel film formation models were developed and incorporated into the computational fluid dynamics code. STAR-CD. The spray/wall interaction process was modeled by considering the change of behaviour with surface temperature conditions and the fuel film formation. We divided the behaviour of fuel droplets after impingement into rebound, spread and splash using the Weber number and the parameter K. The Spray impingement model accounts for mass conservation, energy conservation and heat transfer to the impinging droplets. The fuel film formation model was developed by integrating the continuity, Navier-Stokes and energy equations along the direction of fuel film thickness. Validation of the models was conducted using previous diesel spray experimental data and the present experimental results for the gasoline spray impingement. In all the cases, the prediction compared reasonably well with the experimental results. The spray impingement and fuel film formation models have been applied to the spray/wall impingement in high speed direct injection diesel engines.

• Journal of Physiology & Pathology in Korean Medicine
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• v.31 no.2
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• pp.83-93
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• 2017

This study covers pattern differentiation based on Korean medical references, research trend and modern clinical applications about Sleep-Wake disorders of Diagnostic and Statistical Manual of Mental Disorders(DSM-V) published by American Psychiatric Association. Insomnia disorder is mostly caused by yin deficiency of liver-kidney or liver qi depression and main patterns are heart-kidney non-interaction, deficiency-excess complex pattern containing phlegm-heat due to qi stagnation and blood stasis. Hypersomnolence disorder is more due to yang deficiency rather than yin deficiency and it's major pattern is spleen-kidney yang deficiency. Cataplexy is main feature in narcolepsy and corresponds to depressive psychosis or fainting in terms of Korean Medicine and narcolepsy is assumed to be relevant to liver wind. Breathing-related sleep disorders are related with phlegm-fluid retention brought on spleen deficiency with dampness encumbrance. Pattern of circadian rhythm sleep-wake disorders is combined with yin deficiency of liver-kidney or liver qi depression of insomnia disorder and spleen-kidney yang deficiency or dampness-phlegm of hypersomnolence disorder. Yin deficiency with effulgent fire brought on drugs or alcohol is one of main patterns of substance/medication-induced sleep disorder and combined patterns with yin deficiency of liver-kidney and blood stasis or dampness-phlegm-heat are mostly applied clinically. This study drew major and frequently applied patterns of sleep-wake disorders based on Koran medical literature and modern clinical applications. And that can be the groundwork for the task ahead like clinical practice guideline of sleep-wake disorders containing pattern differentiation, diagnosis and prescriptions.

• The Korean Journal of Pain
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• v.11 no.1
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• pp.1-6
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• 1998

Background: The role of nitric oxide(NO) in analgesia from opioids is controversial. On the one hand, IV morphine analgesia is enhanced by IV injection of NO synthase inhibitors. On the other hand, IV morphine results in increased release of NO in the spinal cord. There have been no behavioral studies examining the interaction between IV morphine and intrathecal injection of drugs which affect NO synthesis. Method: Rats were prepared with chronic lumbar intrathecal catheters and were tested withdrawal latency on the hot plate after 3~5 days of surgery. Antinociception was determinined in response to a heat stimulus to the hind paw before and after IV injection of morphine, 2.5 mg/kg. Twenty minutes after morphine injection, rats received intrathecal injection of saline or the NO synthase inhibitors, L-NMMA or TRIM, the NO scavenger, PTIO, or the NO synthase substrate, L-Arginine. Intrathecal injections, separated by 15 min, were made in each rats and measurements were obtained every 5 min. Result: Mophine produced a 60~70% maximal antinociceptive response to a heat stimulus in all animals for 60 min in control experiments. Intrathecal injection of idazoxane decreased antinociception of IV morphine. The NO synthase inhibitors and the NO scavenger produced dose-dependent decreases in antinociceptive effect of morphine, whereas saline as a control group and L-Arginine as the NO substrate had no effect on antinociception of morphine. Conclusion: The present study supports the evidences that systemic morphine increase the nitrite in cerebrospinal fluid and dorsal horn. These data suggest that the synthesis of NO in the spinal cord may be important to the analgesic effect of IV morphine and increased NO in spinal cord has different action from the supraspinal NO.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.5
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• pp.134-142
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• 2011

Although combustion is essential in most energy generation processes, it is one of the major causes of air pollution. Exhaust pipes with circular fin were designed to study the effect of cooling the recirculated exhaust gases (EGR) of Diesel engines on the chemical composition of the exhaust gases and the reduction in the percentages of pollutant emissions. The gases examined in this study were oxides of nitrogen (NOx), carbon dioxide ($CO_2$) and carbon monoxide (CO). In addition, $O_2$ concentration in the exhaust was measured. The designs adopted in this study were about exhaust pipes with solid and hollow fins around them direct surface force measurement in water using a nano size colloidal probe technique. The direct force measurement between colloidal surfaces has been an essential topic in both theories and applications of surface chemistry. As particle size is decreased from micron size down to true Carbon nano Colloid size (<10 nm), surface forces are increasingly important. Nano particles at close proximity or high solids loading are expected to show a different behavior than what can be estimated from continuum and mean field theories. The current tools for directly measuring interaction forces such as a surface force apparatus or atomic force microscopy (AFM) are limited to particles much larger than nano size. This paper use Water and CNC fluid at normal cooling system of EGR. Experimental result showed all good agreement at Re=$2.54{\times}10^4$ by free convection and Re=$3.36{\times}10^4$ by forced air furnace.

• Nuclear Engineering and Technology
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• v.47 no.1
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• pp.11-25
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• 2015

The accident at Japan's Fukushima Daiichi nuclear power plant in March 2011, caused by an earthquake and a subsequent tsunami, resulted in a failure of the power systems that are needed to cool the reactors at the plant. The accident progression in the absence of heat removal systems caused Units 1-3 to undergo fuel melting. Containment pressurization and hydrogen explosions ultimately resulted in the escape of radioactivity from reactor containments into the atmosphere and ocean. Problems in containment venting operation, leakage from primary containment boundary to the reactor building, improper functioning of standby gas treatment system (SGTS), unmitigated hydrogen accumulation in the reactor building were identified as some of the reasons those added-up in the severity of the accident. The Fukushima accident not only initiated worldwide demand for installation of adequate control and mitigation measures to minimize the potential source term to the environment but also advocated assessment of the existing mitigation systems performance behavior under a wide range of postulated accident scenarios. The uncertainty in estimating the released fraction of the radionuclides due to the Fukushima accident also underlined the need for comprehensive understanding of fission product behavior as a function of the thermal hydraulic conditions and the type of gaseous, aqueous, and solid materials available for interaction, e.g., gas components, decontamination paint, aerosols, and water pools. In the light of the Fukushima accident, additional experimental needs identified for hydrogen and fission product issues need to be investigated in an integrated and optimized way. Additionally, as more and more passive safety systems, such as passive autocatalytic recombiners and filtered containment venting systems are being retrofitted in current reactors and also planned for future reactors, identified hydrogen and fission product issues will need to be coupled with the operation of passive safety systems in phenomena oriented and coupled effects experiments. In the present paper, potential hydrogen and fission product issues raised by the Fukushima accident are discussed. The discussion focuses on hydrogen and fission product behavior inside nuclear power plant containments under severe accident conditions. The relevant experimental investigations conducted in the technical scale containment THAI (thermal hydraulics, hydrogen, aerosols, and iodine) test facility (9.2 m high, 3.2 m in diameter, and $60m^3$ volume) are discussed in the light of the Fukushima accident.