• 한국연소학회:학술대회논문집
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• 2015.12a
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• pp.107-108
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• 2015

The acoustic optimization of a swirl coaxial jet injector mounted upstream a combustion chamber is investigated to tackle combustion instabilities. The least damped modes are extracted with the help of the dynamic mode decomposition (DMD). The sensitivity of the heat release perturbation to the velocity perturbation for the second longitudinal mode is investigated by combining the Crocco's equation and the inhomogeneous wave equation and computing the flame transfer function (FTF). DMD and FTF results agree in terms of the optimized injector length.

• Journal of the Korean Society for Marine Environment & Energy
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• v.6 no.1
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• pp.3-10
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• 2003

Oil drop formation during the underwater oil discharge is investigated experimentally. The focus is placed on the size of the drops formed with the variation of discharge speed and nozzle diameter. As the Reynolds number based on the nozzle diameter increases, the droplet size decreases first and then increases until an explosive atomization occurs. The length of the jet attached to the nozzle Increases with the Reynolds number and then decreases. The transition occurs when the flow becomes asymmetry.

• Journal of ILASS-Korea
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• v.29 no.2
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• pp.91-97
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• 2024

When investigating the droplet, spray, and impact of liquid on a solid plate, backlight imaging has been widely used to understand these phenomena. However, some previous studies have suffered from poor image quality. In this study, various combinations of image processing algorithms, such as white image correction, histogram equalization, CLAHE, Otsu's binarization, and multi-Otsu's binarization, have been applied to flash boiling spray images to enhance image quality for qualitative observation and semi-quantitative spray angle evaluation. To acquire images with high contrast for qualitative observation, applying CLAHE was effective, making small droplets and detailed shapes of the jet noticeable. However, when images were averaged to determine spray angle or penetration length based on intensity, this method induced artifact unphysical patterns, thus requiring careful consideration. Based on the algorithm proposed in this study, the spray angle variation according to injection pressure and temperature has been calculated, showing a reasonable trend.

• Journal of Embryo Transfer
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• v.31 no.3
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• pp.261-265
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• 2016

The aim of the present study was to evaluate and estimate timing of artificial insemination (AI) in Hanwoo heifer (Korean native cattle) that is the most popular breed of beef cattle in Korea. To determine changes in body weight of heifers around AI, body weight were measured at different stages either before or after AI. We found that daily body weight gain was higher in the pregnant cows after AI. We also investigate correlation between body mass measured by shoulder height and body length, and conception rates, used (body length+ height)2 instead of height2 for body mass index (BMI), and found that relatively more BMI heifers (>55) showed higher conception rates. Finally, we estimated body weight by measuring should height (SH), heart girth (HG), and body length (BL); $BW=3.93372^*HG-2.90985^*SH-0.021^*BL$. In addition, we observed that HG is most closely correlated with BW; $y(BW)=1.77355^*x(HG)$, $R^2=0.98881$. In summary, we can determine the best timing of AI using body measurement and its application including BMI.

• Journal of the Korean Society of Propulsion Engineers
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• v.2 no.2
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• pp.83-87
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• 1998

To reduce the supersonic jet noise from the liquid rocket engine, water injetion silencers were designed and tested. Test variables were the mass flow rate of water jet, the length of primary pipe and the diameter of expansion pipe. Followings are the results of this study. 1. From the same mass flow rate of water, longer primary pipe was more effective to reduce the noise. 2. Noise level was significantly reduced with increasingly water flow rate. 3. The optimum water flow rate was 10～12 times of the propellant flow rate. 4. By installing expansion pipe, noise level was reduced approximately 30㏈ compared to without expansion pipe

• Nuclear Engineering and Technology
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• v.49 no.7
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• pp.1442-1450
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• 2017

In liquid metal fast breeder reactors, postulated failures of the plant protection system may lead to serious unprotected accidental consequences. Unprotected transients are generically categorized as transient overpower accidents and transient under cooling accidents. In both cases, core meltdown may occur and this can lead to a molten fuel coolant interaction (MFCI). The understanding of MFCI phenomena is essential for study of debris coolability and characteristics during post-accident heat removal. Sodium is used as coolant in liquid metal fast breeder reactors. Viewing inside sodium at elevated temperature is impossible because of its opaqueness. In the present study, a methodology to depict MFCI phenomena using a flat panel detector based imaging system (i.e., real time radiography) is brought out using a woods metal-water experimental facility which simulates the $UO_2-Na$ interaction. The developed imaging system can capture attributes of the MFCI process like jet breakup length, jet front velocity, fragmented particle size, and a profile of the debris bed using digital image processing methods like image filtering, segmentation, and edge detection. This paper describes the MFCI process and developed imaging methodology to capture MFCI attributes which are directly related to the safe aspects of a sodium fast reactor.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.4
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• pp.604-613
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• 2002

Generation characteristics of electrospray droplets for highly viscous liquid have been investigated by measuring size distributions of droplets emitted from the Taylor cone using glycerol solutions with various conductivities. Because of very small volatility of glycerol, droplet sizes can be measured by an aerodynamic size spectrometer (TSI Aerosizer DSP) with negligible evaporation of droplets. For highly conducting and viscous liquid, the sizes of the droplets electrosprayed from the Taylor cone are found to be relatively insensitive to applied voltages and the electrosprays assisted by the corona discharge call produce monodisperse droplets as long as the corona intensity is not too high. Near the minimum flow rate where a liquid cone is stable, the spray tends to consist of a one -peak monodisperse distribution of drop lets. However, at high flow rates, the spray bifurcates into bimodal distributions, which are consistent with the result of the previous study for less viscous liquids than our liquids. For liquid flow rates (Q) below 1 nl/s, the measured droplet diameters by the aerosizer are in the range of 0.30 to 1.2 ${\mu}{\textrm}{m}$ for the glycerol solutions. The diameters of monodisperse droplets scale approximately with $r^*=Q_$\tau$(Q$\tau$){^1/3}$ where $r^*$ is a characteristic length and $\tau$is the electrical relaxation time of the fluid. However, when compared with several represe ntative scaling laws, the droplet diameters are two to six factors greater than those predicted by the scaling laws. This may be closely related to the combined effect of the much higher viscosity and the electrical charge on the jet breakup of glycerol so solution.

• Journal of the Korean Society of Safety
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• v.33 no.1
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• pp.22-27
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• 2018

Many electronic devices are powered by various rechargeable batteries such as lithium-ion recently, and occasionally the batteries undergo thermal runaway and cause fire, explosion, and other hazards. If a battery fire should occur in an electronic device of vehicle and aircraft cabin, it is important to quickly extinguish the fire and cool the batteries to minimize safety risks. Attempts to minimize these risks have been carried out by many researchers but the results have been still unsatisfied. Because most rechargeable batteries are operated on the ion state during charge and discharge of electricity and the combustion of ion state has big difference with normal combustion. Here we focused on the effect of ions including an electron during combustion process. The effects of an ionized fuel on the flame stability and the combustion products were experimentally investigated in the propane jet diffusion flames. The burner used in this experiment consisted of 7.5 mm diameter tube for fuel and the propane was ionized with th ionizer (SUNJE, SPN-11). The results show that toe overall flame stability and shape such as flame length has no significant difference even in the higher ion concentration. However the fuel ionization affects to the pollutant emissions such as NOx and soot. NOx and CO emissions measured in post flame region decreased by fuel ionization, especially high fuel velocity, i.e. high ion density. TGA analysis and morphology of soot by TEM indicates that the fuel ionization makes soot to be matured.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.9
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• pp.623-629
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• 2017

Flow structure and mixing characteristics in a micro combustor with a multi-hole baffle were numerically studied using the Reynolds stress model. The multi-hole baffle has geometrical features to produce multiple three-dimensional vortices inside combustion chamber. When the thickness of the baffle's geometrical factors changes, variations of vortical structures occur variously. Among these vortices, the vortex generated from the fuel stream exerts a critical influence on the mixing enhancement. The three-dimensional vortical structure, in its development state, was strongly dependent on the baffle thickness. In particular, as the baffle thickness decreases to values less than the diameter of the fuel hole, the jet stream in baffle holes changes from the parabolic to saddleback profile type. The sizes of recirculation zones inside combustion chamber and the mixing state were closely affected by the structure of the jet streams.

• Journal of Forest and Environmental Science
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• v.33 no.4
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• pp.342-347
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• 2017

Since the first report of the oak wilt disease at 2004 in Korea, the disease distributed over Korean peninsula and are still giving severe damages. The management of oak wilt disease in Korea has mainly focused on the control of insect vector, Platypus koryoensis. Neverthless the effective method for evaluating the pathogenicity of the pathogen, Raffaelea quercus-mongolicae (Rqm), and for screening chemical or biological agents with strong inhibitory activity against the pathogen, is absolutely necessary, an reliable method is not available so far. This study was conducted to develop the effective method for evaluating the pathogenicity of Rqm in oak trees. The culture suspensions of Rqm were artificially injected to the saplings of Quercus acutissima by using ChemJet tree injector. Three months after treatments, the treated saplings were cut and dipped into 1% fuchsin acid solution. There were significant differences in non-conductive area (%), discoloration area (%) and vertical discoloration length between the pathogen-injected and distilled water-injected control treatments. These results indicated that the pathogen is the causal agent for the dysfunction of water conductive tissue, which will finally result in wilt symptom. Re-isolation of the pathogen and PCR detection using specific primers for the pathogen also confirmed the presence of Rqm in the sapwood chips of the pathogen-injected saplings. These observations would be greatly applied to other related researches for evaluating the pathogenicity of tree wilt pathogens and biocontrol efficacy of the selected antagonistic microorganisms, in case that the wilt symptom is not easily shown by artificial inoculation of the causal agent.