• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.1
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• pp.123-130
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• 1999

The objective of the current study is to understand steady 3-dimensional flow phenomena in a bifurcated duct experimentally. A bifurcation model is fabricated with transparent acrylic resin to visualize the whole flow field with the PIV system. The gray level cross-correlation method is applied to the image processing algorithm. The subpixel and the area interpolation methods are used to obtain the final velocity vectors. The finite volume predictions are used to analyze the flow patterns in the bifurcation model. The results of the computer simulation and the PIV experiment for three-dimensional flow show the recirculation zone and the formation of the paired secondary flow distal to the apex of the bifurcation model. The results obtained with the two methods also show that the branch flow strongly strikes the inner wall due to the inertial effect and accompanied helical motion as it flows toward the outer wall.

• Journal of Ocean Engineering and Technology
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• v.13 no.3B
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• pp.29-37
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• 1999

Ventilation of the marine engine room is very important for the health of the workers as well as the normal operation of machines. To find proper ventilation conditions of this engine room, numerical simulation with standard k-${\epsilon}$ model was carried out. In the present study, the marine engine room is separated to two floors with porus horizontal partition and considered as a closed space with a heat source and forced ventilation ducts. The porosity of horizontal partition is found to be important. For the engine room with 2 supply ports & 2 exhaust ports, the increasing of the porosity of horizontal partition is effective to reduce the recirculation flow zone in the second floor. When the engine room is ventilated with three supply air ports & one exhaust port, the increasing of the porosity of horizontal partition is effective to reduce the recirculating flow zone in the exhaust air area, but there is a possibility of local extreme heating at the lower side of engine near bottom.

• Journal of the Korean Society of Visualization
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• v.10 no.1
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• pp.47-54
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• 2012

Single Stage To Orbit (SSTO) missions which require its engines to be operated at varying back pressure conditions, use engines operate at high combustion chamber pressures (more than 100bar) with moderate area ratios (AR 70~80). This ensures that the exhaust jet flows full during most part of the operational regimes by optimal expansion at each altitude. Aero-spike nozzle is a kind of altitude adaptation nozzle where requirement of high combustion chamber pressures can be avoided as the flow is adapted to the outside conditions by the virtue of the nozzle configuration. However, the thrust prediction using the conventional thrust equations remains to be a challenge as the nozzle plume shapes vary with the back pressure conditions. In the present work, the performance evaluation of a new aero-spike nozzle is being carried out. Computational studies are carried out to predict the thrust generated by the aero-spike nozzle in varying back pressure conditions which requires the unsteady pressure boundary conditions in the computational domain. Schlieren pictures are taken to validate the computational results. It is found that the flow in the aero-spike nozzle is mainly affected by the base wall pressure variation. The aerospike nozzle exhibits maximum performance in the properly expanded flow regime due to the open wake formation.

• Journal of Aquaculture
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• v.6 no.4
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• pp.311-321
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• 1993

Ammonia accumulation is regarded as the limiting factor of the first priority in water qualities of aquatic culture systems. Nitrification efficiency and characteristics in seawater were evaluated using Rotating Biological Contactor (RBC) process as a part of the recycling water treatment facilities for marine fish culture system. Ammonia removal efficiency regarded 99.7 to $83.7\%$ at the ammonia surface loading rates of 48 to $393 mg/m^2$ -day. RBC process was able to withstand to the fluctuation of influent ammonia concentrations and loading and produced the stable effluent. The mathematical model on the fixed-film biological reactor developed by Kornegay seemed to be suitable to RBC process kinetic evaluation for the recycling water treatment of the marine fish culture system. Area capacity constant (P) and half-velocity constant (Ks) in the model were 0.188g/m^2$-day and 1.25mg/l, respectively.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.10
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• pp.769-775
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• 2008

In this study, the investigations on the dimpled type Exhaust Gas Recirculation (EGR) cooler have been focused on the high heat exchanger efficiency. To overcome low heat exchanger efficiency of general EGR cooler, the dimpled type EGR cooler was developed. It was ensured the improvement of the performance of the dimpled type EGR cooler related to the heat exchange based on a series of the experiment. These results were caused by the increase of thermal surface area in accordance with the dimple's one. The estimation model of the heat exchanger efficiency using the Effectiveness-NTU method was also developed in order to verify the validity of experimental result. Also, the program for the estimation of the heat exchanger efficiency on the EGR cooler with regard to the dimpled tube shape was developed. Resultantly, it was confirmed that the dimpled type EGR cooler could be served better performance than the conventional one in view of the heat exchanger efficiency.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.235-238
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• 2000

Current diesel engines are usually equipped with turbochargers for improving fuel economy as well as meeting more stringent emission regulations. These turbochargers usually cause noise problems because they spins vey high such as 100,000 to 200,000 rpm, These noises are largely divided into whistle and whine noises. The frequency of whistle noise corresponds to their rotation speed, and the frequency of whine noise does to the multiplication of their rotation speed and the number of compressor blades. Turbocharger manufacturers developed a special type of compressor, effectively compressing air sucked from a duct; Recirculation Compressor Cover (RCC) or Map Width Enhancement (MWE). This special structure improves turbocharger's capability by expanding compressor's working area, but it seriously causes a noise problem, whine noise. There were many trials to surpress the noise occurred inside a compressor such as modification of a compressor, noise baffles or secondary measurements. However, it was currently concluded that the whine noise caused by the special compressor can not be reduced to that done by a standard compressor, and the strength difference of whine noises between the two compressors is not negligible. Thus, the standard compressor is decided to be applied to a newly developing heavy-duty diesel engine in order to resolve the turbocharger noise problem with a stiffened suction duct directly connected to a compressor.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.55-61
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• 2004

Numerical simulations were conducted in a rectangular scramjet combustor with a cavity and/or a step in order to investigate their performances for flame-holding. Flow structures and OH radical profiles in the cavity and the step were calculated. The calculated results showed that the cavity generated a larger recirculation zone than the step that had the same depth. Additionally, the combustor with a cavity could make a large low-velocity area than the combustor with a step. The cavity performance was determined by its depth and length. The cavities with too large or too short length did not work effectively, and a certain aspect ratio showed high performance for flame-holding. There was a minimal depth under which the cavity did not work as flame-holder. The fuel injections upstream the cavity and inside the cavity were also tested to investigate the effects on the cavity performance. The result showed that the fuel injection inside the cavity reduced reaction areas and residence time. Therefore, the upstream injection was preferable to the inside injection.

• Journal of the Korean Society of Visualization
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• v.19 no.3
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• pp.115-122
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• 2021

Oral cancer surgery typically consists of resection of lesion, neck dissection and reconstruction, and it has an impact on the position of hyoid bone. Therefore, morphological change of airway can occur since the geometric parameter of airway is correlated with the hyoid bone. Airflow is affected by geometry of the airway. In this study, flow characteristics were compared between pre- and post-surgery models by both particle image velocimetry (PIV) and numerical simulation. 3D model of upper airway was reconstructed based on CT data. Velocity is accelerated by the reduced channel area, and vortex and recirculation region are observed in pre- and post-surgery models. For the post-surgery model, high pressure distribution is developed by significantly decreased hydraulic diameter, and the longitudinal flow stream is also interrupted.

• Proceedings of the Membrane Society of Korea Conference
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• 1998.06a
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• pp.113-133
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• 1998

In activated sludge process, sludge settling condition is affected by organic loading rate or operation condition, and if settling condition is getting worse, it is common that overall process fails due to wash-out of biomass causing low concentration in the aeration tank. Also activated sludge process has such several problems as requiring large area, consuming a lot of power and producing large volume of sludge. Increased public concern over health and the environment combined with a strong desire to reduce capital, operating and maintenance costs, have created a need for innovative technologies for building new high quality effluents which vail meet 21st century crkeria. MBR(Membrane Bioreactor) process consists of a biological reactor and ultrafiltration(UF) membrane system that replaces the conventional clarifier of an activated sludge process. The main operating advantages of this system are that the quality of the effluent is independent of the settleability of the mixed liquor and that the effluent is free of suspended solids in any operating condition. It is possible to eliminate clarifier and to reduce the volume of aeration tank because it can afford to accumulate high biomass concentration in the bioreactor(20, 000~30, 000mg/L), which would not be possible in a conventional activated sludge process. Therefore, this process reduces overall treatment plant area. In addition to those advantages, Longer SRT condition enables higher sludge digestion in MBR process so the sludge volume produced is 50 to 70% lower than that of conventional activated sludge process There are two kinds of MBR process according to the allocations of membrane. One is cross flow type MBR of which module is located outside of the bioreactor and mixed liquor is driven into the membrane module. The other is submerged type MBR process of which module is submerged in the bioreactor and mixed liquor is generally sucked from the lumen side. addition to that the cake layer is often removed by the uplifting flow of bubbling air. A submerged MBR process is superior to a crossflow MBR in regard to the power consumption because suction pressure of a submerged MBR is generally lower than that of a crossflow MBR which has recirculation pump. A submerged MBR, therefore, has the potential to be applied to small wastewater treatment plants that need low cost treatment systems.

• Journal of fish pathology
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• v.33 no.1
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• pp.7-14
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• 2020

A disease that manifested severe anemia of the gills occurred in the olive flounder (Paralichthys olivaceus), which was cultured for 5-6 months with a recirculation water system in the laboratory. Microscopic observations showed immature parasite in the gills and mature adults in the oral cavity. The matured parasite was 5.60-9.32 (7.42) mm in total length, with 4 pairs of clamps on the pedunculated haptor, which was separated from the body proper by a long isthmus. From the morphological observations of the larvae, it was identified as Neoheterobothirum hirame belonging to the monogenea. The average hematocrite of infected fish was 10.3 ± 2.8%, significantly lower than that of normal flounder 31.4 ± 4.2%. Histopathologically, fish infected with N. hirame exhibited reduced numbers of erythrocytes in blood vessels of the gill filament and lamellae, reduced red pulp area of the spleen, and hepatocyte atrophy. From the above results, the cause of severe anemia in olive flounder was identified as N. hirame infection. This study shows an example where the growth of pathogens can be a problem in the recirculation system due to low water exchange rate.