• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2003년도 유체기계 연구개발 발표회 논문집
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• pp.489-495
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• 2003

A high performance and low noise refrigerator fan has been developed in order to satisfy the customer's high quality needs, that is, luxury, big size and low noise. In this study, the characteristics of a new developed fan and a current fan was calculated and compared by using numerical simulation. Rotation of a fan makes cold air circulation inside a refrigerator. A numerical simulation of air flow shows distribution and local flow regime of a cold air flow circulation, and revealed a cause of low noise as well. Optimization of a duct shape also decreased noise level.

• International Journal of Fluid Machinery and Systems
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• 제9권4호
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• pp.325-331
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• 2016

A bathtub vortex above the outlet of a rotating barrel is simulated. By analyzing the Ekman layer theory, it can be found that the main flow circulation is inversely proportional to the thickness of Ekman layer. The thicker the Ekman boundary layer, the weaker the rotational strength and the shorter of the length of gas core is. According to this law, models of barriers with rods of different heights are established. The reduction of air-core length in this air entrainment vortex and weakening the strength of rotation field were achieved.

• 한국안전학회지
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• 제19권1호
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• pp.1-5
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• 2004

In the present study, the gas injection system based on air-water model was designed to investigate the flow characteristics of liquid phase. A PIV system was applied to analyze the flow pattern in a ladle which gas stated to rise upward from the bottom. Gas flow is one of most important factors which could feature a flow pattern in a gas injection system. As the gas injected into the liquid, the kinetic energy of bubble transfer to liquid phase and a strong circulation flow develops in the liquid phase. Such a flow in the liquid develops vortex and improve the mixing process. Due to the centrifugal force, circulation flow was well developed near both wall sides and upper region respectively. Increasing gas flow was helpful to remove dead zone but, weak flow zone still exists in spite of the increasement of gas flow rate.

• 한국가시화정보학회지
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• 제20권2호
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• pp.55-62
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• 2022

We experimentally investigate a rising toroidal bubble impacting a free surface. The toroidal bubble is created by releasing pulsed air. By adjusting the volume and circulation of the toroidal bubble, the characteristics of interactions between the toroidal bubble and the free surface are identified. Because of the impact by the toroidal bubble, the free surface is convexly deformed upwards above the center point of the toroidal bubble, while the edge of the deformed free surface is pulled down. When the circulation of the bubble becomes stronger, the surface which was pulled down breaks eventually, and air above the free surface is entrained into water, forming an unstable toroidal bubble. The deformations at the center and edge of the free surface are in a linear relationship with the Froude number and the Weber number, respectively.

• 한국환경과학회지
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• 제27권8호
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• pp.621-629
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• 2018

Many chemically active species such as ${\cdot}H$, ${\cdot}OH$, $O_3$, $H_2O_2$, hydrated $e^-$, as well as ultraviolet rays, are produced by Dielectric Barrier Discharge (DBD) plasma in water and are widely use to remove non-biodegradable materials and deactivate microorganisms. As the plasma gas containing chemically active species that is generated from the plasma reaction has a short lifetime and low solubility in water, increasing the dissolution rate of this gas is an important challenge. To this end, the plasma gas and water within reactor were mixed using the air-automizing nozzle, and then, water-gas mixture was injected into water. The dissolving effect of plasma gas was indirectly confirmed by measuring the RNO (N-Dimethyl-4-nitrosoaniline, indicator of the formation of OH radical) solution. The plasma system consisted of an oxygen generator, a high-voltage power supply, a plasma generator and a liquid-gas mixing reactor. Experiments were conducted to examine the effects of location of air-automizing nozzle, flow rate of plasma gas, water circulation rate, and high-voltage on RNO degradation. The experimental results showed that the RNO removal efficiency of the air-automizing nozzle is 29.8% higher than the conventional diffuser. The nozzle position from water surface was not considered to be a major factor in the design and operation of the plasma reactor. The plasma gas flow rate and water circulation rate with the highest RNO removal rate were 3.5 L/min and 1.5 L/min, respectively. The ratio of the plasma gas flow rate to the water circulation rate for obtaining an RNO removal rate of over 95% was 1.67 ~ 4.00.

• 한국환경과학회지
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• 제18권11호
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• pp.1271-1281
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• 2009

The heavy snowfall event over the eastern part of Seoul, Korea on Mar. 04, 2008 has been abruptly occurred after the frontal system with the heavy snowfall event had been past over the Korean peninsula on Mar. 03, 2008. Therefore, this heavy snowfall event couldn't be predicted well by any means of theoretical knowledges and models. After the cold front passed by, the cold air mass was flown over the peninsula immediately and became clear expectedly except the eastern part and southwestern part of peninsula with some large amount of snowfall. Even though the wide and intense massive cold anticyclone was expanded and enhanced by the lowest tropospheric baroclinicity over the Yellow Sea, but the intrusion and eastward movement of cold air to Seoul was too slow than normally predicted. Using the data of numerical model, satellite and radar images, three dimensional analysis Products(KLAPS : Korea Local Analysis and Prediction System) of the environmental conditions of this event such as temperature, equivalent potential temperature, wind, vertical circulation, divergence, moisture flux divergence and relative vorticity could be analyzed precisely. Through the analysis of this event, the formation and westward advection of lower cyclonic circulation with continuously horizontal movement of air into the eastern part of Seoul by the analyses of KLAPS fields have been affected by occurring the heavy snowfall event. As the predictability of abrupt snowfall event was very hard and dependent on not only the synoptic atmospheric circulation but also for mesoscale atmospheric circulation, the forecaster can be predicted well this event which may be occurred and developed within the very short time period using sequential satellite images and KLAPS products.

• 한국해양학회지:바다
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• 제18권4호
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• pp.266-276
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• 2013

바다-육지-대기로 이루어진 기후 시스템에서 가장 큰 탄소의 저장고는 바다이다. 바다가 대기로부터 탄소를 흡수하는 주요 수단은 생물 활동에 의한 것으로서, 광합성에 의해 유기 물질로 동화된 탄소가 해저로 침강하고 분해되는 과정에서 깊은 바다물은 탄소를 축적하게 된다. 이러한 탄소 수송 작용을 생물 펌프라 부르며, 해수면 탄소 농도를 낮춤으로써 대기 중 이산화탄소 분압을 낮은 상태로 유지해주는 중요한 기작이다. 생물 펌프에 의해 해저에 축적된 탄소는 해양 순환에 의해 해수면에 돌아오고, 해양-대기 기체 교환에 의해 대기로 배출된다. 바다가 대기와 소통하는 이산화탄소의 양은 과거 빙하기-간빙기 기후 변동과 관련하여 과거 수십만년동안 대기 중 이산화탄소 분압변화에 주도적인 역할을 하여 온 것으로 알려져 있다. 본 논문에서는 바다에서 일어나는 탄소 순환을 간단하게 소개하고, 해양 순환의 변화가 어떻게 탄소 순환을 변형시키고, 대기 중 이산화탄소에 영향을 미치는지를 기후 변동의 관점에서 살펴보고자 한다.

• 한국수소및신에너지학회논문집
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• 제33권4호
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• pp.419-429
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• 2022

Effects of operating variables on temperature profile and performance of 3 MWth chemical looping combustion system were estimated by mass and energy balance analysis based on configuration and dimension of the system determined by design tool. Air reactor gas velocity, fuel reactor gas velocity, solid circulation rate, and solid input percentage to fluidized bed heat exchanger were considered as representative operating variables. Overall heat output and oxygen concentration in the exhaust gas from the air reactor increased but temperature difference decreased as air reactor gas velocity increased. Overall heat output, required solid circulation rate, and temperature difference increased as fuel reactor gas velocity increased. However, overall heat output and temperature difference decreased as solid circulation rate increased. Temperature difference decreased as solid circulation rate through the fluidized bed heat exchanger increased. Effect of each variables on temperature profile and performance can be determined and these results will be helpful to determine operating range of each variable.

• 한국수소및신에너지학회논문집
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• 제29권4호
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• pp.393-400
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• 2018

To confirm the operating range of two oxygen carriers for chemical looping combustion system, the effects of operating variables on solid circulation rate were measured and discussed using a two-interconnected circulating fluidized bed system at ambient temperature and pressure. Moreover, suitable operating ranges to avoid choking of the fast fluidized bed (air reactor) were confirmed for two oxygen carriers. A continuous long-term operation of steady-state solid circulation more than 24 hours was also demonstrated within the operating windows. Finally we could confirm that those two oxygen carriers are suitable for chemical looping combustion system with high solid circulation rate and smooth solid circulation.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1897-1902
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• 2003

An 1/21.6 scaled experimental facility was prepared utilizing the results of a scaling analysis to simulate the APRI400 reactor and insulation system. The behaviors of the boiling-induced two-phase natural circulation flow in the insulation gap were observed, and the liquid mass flow rates driven by natural circulation loop were measured by varying the wall heat flux, upper exit slot area and configuration. And non-heating experiments have also been performed and discussed to certify the hydraulic similarity of the heating experiments by injecting air equivalent to the steam generated in the heating experimental condition.