• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.11
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• pp.1485-1495
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• 1997

The present study investigates heat/mass transfer around film cooling jets and circular cylinders to compare the characteristics of each other. Experiments are conducted to obtain the detailed heat/mass transfer coefficients of flat plate with injections through an array of holes and for flows around an array of protruding circular cylinders using the naphthalene sublimation technique. The inclination angles of cylinders are set to the same ones of jets; a, the angle between the jet and the surface is fixed at 30 deg. through the whole experiments and .betha., the angle between the projection of the jet on the surface and the direction of main stream is adjusted to 0 deg., 45 deg. and 90 deg. to investigate the effect of variation of injection angles. The influence of blowing rates of jets and those of cylinder length to diameter ratios are also investigated. The results indicate that the increase of angle .betha. influences the spanwise uniformity of heat/mass transfer remarkably for both jets and cylinders, but that variation of cylinder length to diameter ratios has weaker effects on heat/mass transfer coefficients than that of blowing rates.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.12 no.1
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• pp.25-30
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• 1976

In the area of the Far East Asia, cyclones are observed 157ea in winter season during the years(1966-1974). Some of them are most difficult to be forecasted due to the extreme irregulalities, have carried out synoptic analysis. The rapid development of cyclones can be attributed to the descending of cold air mass surrounding the axis of the Jet Stream due to the cyclonic rotation, and the lowering of the Jet axis. The Relationships between upper trough line and max. (or min) axis of upper air temperature on the 700mb contributes to the development of the cyclones.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.49 no.2
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• pp.234-240
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• 2016

We examined the diffusion of contaminants released from the southern coast around Fukushima, Japan, during the passage of typhoons using a three-dimensional numerical model (POM) to track diffusing radioactivity (RA) released from the nuclear power plant at Fukushima following the accident caused by the giant tsunami event in March 2011. Radioactive contaminants released during the passage of typhoons may have significantly affected not only Japanese but also Korean coastal waters. The model domain covered most of the northwestern Pacific including marginal seas such as the East/Japan Sea and the Yellow Sea. Several numerical experiments were conducted case studies focusing on the westward diffusion from the southern coast of Japan of contaminants derived from the source site (Fukushima) according to various attributes of the typhoons, such as intensity, track, etc. The model produced the following results 1) significant amounts of contaminants were transported in a westward direction by easterly winds favorable for generating a coastal air stream along the southern Japanese coast, 2) the contaminants reached as far as Osaka Bay with the passage of typhoons, forced by a 5-day positive sinusoidal form with a (right-) northward track east of Fukushima, and 3) the range of contamination was significant, extending to the interior of the East/Japan Sea around the Tsugaru Strait. The model suggests that contaminants and/or radioactivity released from Fukushima with the passage of typhoons can affect Korean waters including the northeastern East/Japan Sea around the Tsugaru Strait, especially when the typhoon tracks are favorable for generating a westward coastal air stream along the southern Japanese coast.

• Tunnel and Underground Space
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• v.16 no.6 s.65
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• pp.526-535
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• 2006

An experimental study was carried out on a reduced scale tunnel model to grasp the behavioral feature of fire-induced smoke in the long tunnels. Based on Froude modeling, the 1/50 scaled tunnel model (20 m long) was constructed by acrylic tubes and paraffin gas was released inside the tunnel to simulate the 20 MW fire-induced smoke. me test results show, that after approximately 2 minutes of fire generation, was descended from the tunnel ceiling through the decrease of buoyancy, then it was symmetrically propagated about 90 meters for 4 minutes before jet fans were operated. The smoke was effectively controlled when the jet fans were operated and an air stream velocity was getting closed to reach a critical velocity (the minimum air velocity that requires to suppress the smoke spreading against the longitudinal ventilation flow during the tunnel fire situations). It was also found out that a range of smoke was spreaded about 3 meters from the origin of fire but the range was not propagated to the escape direction anymore. The early stage of the In operation, however, showed that the smoke was hardly controlled. It means that the operation of emergency ventilation system has many dangerous factors such as an intercepting breathing zone.

• 한국연소학회:학술대회논문집
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• 2003.05a
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• pp.93-101
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• 2003

The extinction of unsteady diffusion flame was experimentally studied in an opposing jet counterflow burner using diluted methane. The stabilized flame was perturbed by linearly varying velocity change that was generated by pistons installed on both sides of the air and fuel stream. As the results, the extinction of unsteady flame is dependent not only on the history of unsteadiness, but also on the initial condition. We found that there are several unsteady effects on the flame extinction. First, the extinction strain rates of unsteady cases are extended well beyond steady state extinction limits. Second, as the slope of the strain rate change increases, the unsteady extinction strain rate becomes larger. Third, the extension of unsteady extinction strain rate becomes smaller as the initial strain rate increases. We also found that the extension of the extinction limit mainly results from the unsteady response of the reaction zone because there is no retardation effect of a mixing layer for our experimental condition.

• Archives of Plastic Surgery
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• v.46 no.6
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• pp.603-607
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• 2019

During a full-thickness skin graft procedure, the thickness of the harvested donor skin is adjusted based on the location of the recipient site and the judgment of the surgeon. Conventionally, the thickness of the harvested skin is roughly adjusted using surgical instruments such as scalpels and scissors. However, this method is not only time-consuming, but also requires effort to obtain both the desired thickness of the harvested skin and a smooth surface of that skin. Moreover, there is a possibility of skin perforation. Hence, the authors devised a method of adjusting harvested skin thickness using the Versajet Hydrosurgery System. The Versajet device is a handheld hydrosurgical tool that delivers a high-speed jet stream of saline solution, which enables the precise debridement of tissue. This method makes it easier and faster for the surgeon to obtain the desired thickness of harvested skin. In addition, by obtaining a smooth surface and an even thickness of harvested donor skin, this technique may lead to improved graft viability.

• Atmosphere
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• v.25 no.1
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• pp.129-140
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• 2015

The statistical analysis of aviation turbulence occurred over South Korea and East Asia regions is performed, using pilot reports (PIREPs) during December 2002~November 2012 that were provided by the Korea Aviation Meteorological Agency (KAMA) and the National Center for Atmospheric Research (NCAR). In South Korea, the light (LGT)- and moderate or greater (MOG)-level turbulence events occurred most frequently in spring and winter due to strong vertical wind shear below or above jet stream in these seasons. Spatially, the LGT- and MOG-level events occurred mainly along domestic flight routes. The higher occurrences of the LGT- and MOG-level convectively induced turbulence (CIT) events show in spring and summer when convective systems frequently affect the Korean peninsula. The results are generally similar to a previous study on the aviation turbulence over South Korea during 2003~2008, except that MOG-level CIT events occurred more in February, June, and October. Over East Asia region, the LGT- and MOG-level events appeared mostly in summer and spring, respectively, and the highest occurrence is over the southeast region of Japan and Kamchatka peninsula near Russia.

• Journal of Environmental Health Sciences
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• v.23 no.1
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• pp.28-33
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• 1997

This study was carried out to investigate factors affecting anaerobic digestion enhancement of waste activated sludge(WAS). In order to this investigation, the degradability and rupture of microorganisms cell present in WAS, and mesophilic anaerobic digestion(MAD) of these compounds, were also evaluated. The micro-organisms cell in WAS were ruptured by a mechanical jet stream and smashed under pressure of 30 bar. The rupture level of micro-organisms cell in WAS were determined using phosphate, soluble protein and soluble chemical oxygen demand (SCOD)concentrations. It was found that the rupture level of micro- organisms cell within WAS increased with increasing pretreatment times, and the pretreated WAS once under pressure of 30 bar resulted in an increase in VS removal and methane production of 5%, 9% over the intact WAS of 35%, 71%, respectively, in batchwise MAD of 6-day and 14-day retention time. With the pretreatment and MAD of 6-day retention time used, mesophlic bioconvertibility as the biogasification of WAS were found to be significantly higher biogas of 1, 850 ml than 300 ml under intact WAS. In conclusion it can be stated mechanical pretreatment enhances WAS bioconvertibility, while under identical treatment conditions, resulted in a considerable decrease in the bioconvertibility of intact WAS.

• Atmosphere
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• v.19 no.3
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• pp.255-268
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• 2009

Based on the pilot reports (PIREPs) collected in South Korea from 2003 to 2008 and corresponding Regional Data Assimilation and Prediction System (RDAPS) analysis data of 30 km resolution, we validate the Korean Integrated Turbulence Forecasting Algorithm (KITFA) system that predicts clear-air turbulence (CAT) above the Korean peninsula. The CATs considered in this study are the upper level (higher than 20000 ft) turbulence excluding convectively induced turbulences. In the KITFA system, there are two main processes for predicting CATs: to select CAT indices and to determine their weighting scores. With the PIREPs observed for much longer period than those used in the current operational version of the KITFA system (March 4-April 8 of 2002), three improvable processes of the current KITFA system, re-calculation of weighting scores, change of method to calculate weighting scores, and re-selection of CAT indices, are tested. The largest increase of predictability is presented when CAT indices are selected by using longer PIREP data, with the minor change using different methods in calculation of weighting scores. The predictability is the largest in wintertime, and it is likely due to that most CAT indices are related to the jet stream that is strongest in wintertime. This result suggests that selecting proper CAT indices and calculating their weighting scores based on the longer PIREPs used in this study are required to improve the current KITFA.

• Journal of the Korean Society of Combustion
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• v.14 no.1
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• pp.31-38
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• 2009

The effects of acoustic excitation of coaxial air on mixing enhancement and reduction of nitrogen oxides (NOx) emission were investigated. A compression driver was attached to the coaxial air supply tube to impose excitation. Measurements of NOx emission with frequency sweeping were performed to observe the trend of NOx emission according to the fuel and air flow conditions and to inquire about the effective excitation frequency for reducing NOx. Then, Schlieren photographs were taken to visualize the flow field and to study the effect of excitation. In addition, phase-locked particle image velocimetry (PIV) was performed to acquire velocity field for each case and to investigate the effect of vortices more clearly. Direct photographs and OH chemiluminescence photographs were taken to study the variation of flame length and reaction zone. It was found that acoustic forcing frequencies close to the resonance frequencies of coaxial air supply tube could reduce NOx emission. This NOx reduction was influenced by mixing enhancement due to large-scale vortices formed by fluctuation of coaxial air jet velocity.