• 한국수산과학회지
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• 제19권3호
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• pp.274-280
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• 1986

대, 소조기에 마산만에서 연속관측한 자료를 사용하여 만구 단면의 유속 변동특성을 구명하기 위하여 net velocity와 RMS속도의 등양선 및 순 유출입량을 계산하여 검토하였다. 최강유속은 수도 중앙과 서부의 4m 이하의 표층에서 나타나고, 최대 유입속도 24cm/sec 최대 유출속도는 15 cm/sec이다. 최강유속 시간임에도 불구하고 4m 이심에서는 유속이 약하여 $0{\sim}2cm/sec$에 불과하다. 만구 단면의 가장자리의 상층에 역류가 존재한다. net velocity는 비가 오지 않은 대조기의 경우 유출유속은 만구단면 서부에서 나타나며, 유입유속은 단면 동부에서 나타난다. 비온 직후의 소조기에는 이와 정반대로 흐른다. RMS속도의 최대 세기는 대조기에 $11.3{\sim}15.0cm/sec$, 소조기에 $7{\sim}10.3cm/sec$로서 단면 서부의 표층에 있으며, 매 조석주기마다 거의 동일위치에서 계속 존재한다. 순 통과유량은 건기에 $-39.7m^3/sec$, 우기 $-170m^3/sec$로서 유출이 탁월하다. 항유성분은 건기에는 조석잔차류가 우세하지만, 소조기의 강우시에는 밀도류가 우세한 것으로 추리된다.

• 한국산업보건학회지
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• 제29권3호
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• pp.343-350
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• 2019

Objectives: This study aims to identify whether ventilation conditions and their effectiveness can be significantly improved in an experimental chamber by increasing the mixing factor (K-Factor). Methods: In a chamber with a volume of $1m^3$, air velocity was measured at six different points with four roof fans in the upper part of the chamber being operated in order. The impact of the ventilation conditions was analyzed when the flow rates were increasing and the first inlet of the chamber was either open or closed. Smoke patterns were also observed at four corner points where ventilation was limited. Kruskal Wallis and Mann-Whitney tests were performed to compare air velocities measured in the chamber. Results: The air velocities measured at only the third point increased significantly from $0.03{\pm}0.03m/s$ (door open) and $0.05{\pm}0.06m/s$ (door closed) with two fans, $0.08{\pm}0.08m/s$ with three fans, and $0.09{\pm}0.09m/s$ with four fans operating (p<0.05). However, air velocities at the four corner points did not significantly increase. Smoke patters also showed that the open inlet of the chamber had no effect on improvement of ventilation conditions and effectiveness. Conclusions: In this study, the air velocities at six points in the chamber did not significantly increase despite the increase in the mixing factor and flow rates of ventilation in the controlled environment. Therefore, the inflow of outdoor air throughout an open inlet and installation of a forced ventilation system can potentially increase the indoor air velocity and improve ventilation condition without an increase in the mixing factor.

• 동의생리병리학회지
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• 제16권3호
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• pp.464-471
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• 2002

Author applied several engineering methodologies to classical ultrasonic nebulizer to cope with it's demerits. After several trials and errors, we got the several meaningful results. To evaluate the modified ultrasonic nebulizer for inhalation toxicology of cadmium, author used light-scattering photometer. This paper is the one part of inhalation exposure systems for inhalation toxicology study of cadmium. According to the testing conditions, source temperature 50℃ and inlet-duct band temperature 150℃, aerosol generation results for sodium chloride and cadmium chloride were as followings: Coefficients of variation(CV) of sodium chloride and cadmium chloride for repeated trials were 3.38 and 4.77 for 10g, 2.47 and 5.02 for 5g, and 4.70 and 2.98 for 2.5g. All the CVs were within 10% of acceptance variability. Count Per Minute(CPM) changes of NaCl and CdCl₂ for 5 repeated trials were similar. CPM ratios of CdCl₂/NaCl were 1.13 for 10g, 0.76 for 5g, and 1.06 for 2.5g. Relative aerosol generation of cadmium chloride to sodium chloride was the highest in 10g. Efficiency increases of 24.50% for 5g NaCl, 14.91 % for 2.5g NaCl, and 16.48% for 2.5g CdCl₂ with respect to theoretical efficiency were observed but 0.04% efficiency decrease was observed in 5g CdC₂. According to the modifications of source temperature(20, 50, 70℃) and inlet-duct band temperature(20, 50, 100, 150, 200℃), aerosol generation results for NaCl and CdCl₂ were as followings: CPM trends for each quantity excepting 10g NaCl in inlet-duct band temperature 200℃ were similar, and the highest CPM was observed in source temperature 70℃ to each inlet-duct band temperature. The highest CPMs to 10, 5, and 2.5g NaCl were observed in source temperature 70℃ and inlet-duct band temperature 20℃. Aerosol generation of cadmium chloride was increased with the higher source temperature, excepting inlet-duct band temperature 200℃. The highest CPMs for 10, 5, and 2.5g CdCl₂ were observed in source temperature 70℃ and inlet-duct band temperature 20℃, and this trend was similar to NaCl aerosol generation The highest CPMs for 10, 5, and 2.5g CdCl₂ were observed in source temperature 70℃ and inlet-duct band temperature 20℃, and this result was similar to NaCl aerosol generation. Observed efficiencies of 5 and 2.5g NaCl were similar to ifs theoretical efficiency but -3.08% efficiency decrease of 5g CdCl₂, 17.47% efficiency increase of 2.5g CdCl₂ were observed. CPM ratio of CdCl₂/NaCl of 10g was different to 5 and 2.5g, and 2.5g ratio was higher than 5g ratio. In conclusion, to get maximum aerosol generation for NaCl and CdCl₂ will be the conditions that set the appropriate inlet-duct band temperature for each materials and increase the source temperature. Sodium chloride can be used to evaluate the performance and predict the concentration for cadmium aerosol in aerosol generator and inhalation exposure system.

• 한국전산유체공학회지
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• 제19권3호
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• pp.20-23
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• 2014

The flow pattern inside the inlet chamber of the tube side is one of the key parameters influencing on the performances of the shell-and-tube type of heat exchangers(STHE). In order to improve the flow distribution, the baffle shaped as the porous plate is installed in the inlet chambers. In the present study, numerical simulation has been performed to investigate the flow features of the tube side of the STHE in sense of the hydraulic performances. The flow fields have been analysed by the three-dimensional Navier-Stokes solvers with the proper turbulent models. Computational domain is ranged in the whole of the tube side of the STHE. The numerical results showed that the presence of the baffles improves the redistribution of the flow injecting to the tube bundels. The good agreements of the numerical results with the experimental results of PIV measurements have been shown for the validation of the numerical methods adopted in the present papers.

• 한국연소학회지
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• 제18권1호
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• pp.21-26
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• 2013

In the Shell coal gasification process, the syngas produced in a gasifier passes through a syngas cooler for steam production and temperature control for gas cleaning. Fly slag present in the syngas may cause major operational problems such as erosion, slagging, and corrosion, especially in the upper part of the syngas cooler (gas reversal chamber, GRC). This study investigates the flow, heat transfer and particle behaviors in the GRC for a 300 MWe IGCC process using computational fluid dynamics. Three operational loads of 100%, 75% and 50% were considered. The gas and particle flows directly impinged on the wall opposite to the syngas inlet, which may lead to erosion of the membrane wall. The heat transfer to the wall was mainly by convection which was larger on the side wall at the inlet level due to the expansion of the cross-section. In the evaporator below the GRC, the particles were concentrated more on the outer channels, which needs to be considered for alleviation of fouling and blockage.

• International Journal of Fluid Machinery and Systems
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• 제3권2호
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• pp.129-136
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• 2010

The attachment of inducer upstream of main impeller is an effective method to improve the suction performance of turbopump. However, various types of cavitation instabilities are known to occur even at the designed flow rate as well as in the partial flow rate region. The cavitation surge occurring at partial flow rates is known to be strongly associated with the inlet back flow. In the present study, in order to understand the detailed structure of internal flow of inducer, we firstly carried out the experimental and numerical studies of non-cavitating flow, focusing on the flow field near the inlet throat section and inside the blade passage of a two bladed inducer at a partial flow rate. The steady flow simulation with cavitation model was also made to investigate the difference of flow field between in the cavitating and no-cavitating conditions.

• 대한기계학회논문집B
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• 제28권8호
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• pp.902-909
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• 2004

A steady-state Reynolds averaged Navier-Stokes simulation was conducted to investigate the distribution of the Reynolds stress tensor inside tip leakage vortex of a linear compressor cascade. Two different inlet flow angles ${\beta}=29.3^{\circ}$(design condition) and $36.5^{\circ}$(off-design condition) at a constant tip clearance size of $1\%$ blade span were considered. Classical methods of solid mechanics, applied to view the Reynolds stress tensor in the principal direction system, clearly showed that the high anisotropic feature of turbulent flow field was dominant at the outer part of tip leakage vortex near the suction side of the blade and endwall flow separation region, whereas a nearly isotropic turbulence was found at the center of tip leakage vortex. There was no significant difference in the anisotropy of the Reynolds normal stresses inside tip leakage vortex between the design and off-design condition.

• 대한조선학회논문집
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• 제47권4호
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• pp.553-564
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• 2010

This paper studies on the rudder shapes for the suppression of the cavitation around a horn-type rudder. To improve the problems due to cavitation, there have been several studies. However, these some studies are recognized as incomplete ways to suppress the rudder cavitation. In this study, the section shapes to suppress the cavitation phenomena are determined by moving the location of maximum thickness for reducing the curvature variation and changing the radius of leading edge. Also, in the pintle part, the curvature radius of the inlet outlet edge of rudder plate is changed. During the design of rudder shape, two-dimensional numerical simulations are firstly performed because those offer some advantages with that cavitation phenomena becomes predictable for a short time, and then the three-dimensional numerical simulations are performed to confirm the determination. The time mean distribution of the propeller slipstream is imposed on the inlet boundary condition. As some results, this paper shows the effects reducing the range of the occurrence of cavitation, and suggests the references on the design of a horn-type rudder for the suppression of cavitation phenomena.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.780-785
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• 2009

The photovoltaic/thermal collectors (PV/T collectors) combine the solar thermal collector and photovoltaic modules. They can produce thermal energy in the form of hot air or hot water, and converts solar radiation into electricity. The collecctors can improve the electrical performance of PV modules as the heat from the PV module carried away by the thermal part of the system keeping temperatures lower. The basic water cooled PVT collector has metallic water pipes attached to the back of a PV collector. There are main parameters affecting the performance (electrical and thermal) of PVT collectors. This paper analyzed the experimental performance of glazed water PVT module, considering the parameters of solar radiation, inlet water temperature and ambient temperature. It found that solar radiation is the dominant factor for the electrical performance of the collector, and for the thermal performance the inlet water temperature and ambient temperature appeared to be more related.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.432-435
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• 2008

Launch vehicle for injecting the satellite into its orbit is composed with propulsion system, guidance and navigation system, telemetry and so on. Among the others, the propulsion system is the most important part, because that is the key factor of failure of launch vehicle. Especially, the most of failures were occurred in time of engine startup. Therefore, the study of the conditions for stable engine startup is needed at the first step of development. The many researches were accomplished for mathematical modeling, stable startup engine and control of liquid propellant rocket engine. But the cavitation problem that can be occurred at an inlet of pump associated with propellant feeding system wasn't considered in these works. In this paper, propulsion system model was integrated with clustered engines and propellant feeding system for the simulations of engine startup. As the results of simulations, the requirements were deduced for the stable engine startup without the cavitation at an inlet of pump.