• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.3
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• pp.348-357
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• 1998

The flow characteristics inside U-bend tube of the laminated plate heat exchanger were numerically investigated. The behavior of fluid flow, and the variations of the faulty area and friction factor are examined according to the distance between the span and the wall and the diameter of the round attacked to the end of span. The results show that the diameter(d) of the round attached to the span is mainly associated with the smooth circulation of fluid flow rather than the size of faulty area and the friction factor. As the distance($\ell$) between the span and the wall decreases, the faulty area decreases, however the friction factor dramatically increases. It is also found that one can obtain a good result in the view of the flow characteristics and pressure drop at d=7.5mm and $\ell$=30.5mm.

• Investigative Magnetic Resonance Imaging
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• v.2 no.1
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• pp.83-88
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• 1998

Purpose : Authors correlated the three-dimensional time-of-flight MRA signal intensity characteristics and flow profile simulated by computer in an experimental flow phantom model. Materials and Methods : The three-dimensional time-of-flight MRA was performed in a fusiform flow phantom and analyzed the flow signal. computer assisted flow simulation was performed in same flow geometry. The MRA signal intensity and flow velocity distribution and direction was compared. Results : The flow was depicted as homogeneous signal internsity in inlet and outlet area and inhomogeneous signal intensity in fusiform area. Typically, the flow was depicted as target appearance in transition area to outlet. Whereas mean signal internsity decreased slowly in fusiform area, it rapidly dropped and resumed in transition area to outlet. In computer assisted flow simulation, Whereas there were flow velocity decrease and flow direction change to peripheral in entrance to fusiform area, ther were rapid flow velocity resuming and flow direction change to central in transition area to outlet. Conclusion : The signal loss and target appearance in transition area to outlet is characteristic of fusiform flow. These signal changes correlate with abrupt flow velocity and direction change well.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.534-537
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• 2008

Growing attention has been given to sterilizing and antibacterial effects of nano-silver, recently. Nano-silver solution can be applied to the heat exchanger in an air conditioner to prevent bad smell or bacteria. The present study is directed at the nozzle spray characteristics over a heat exchanger. This problem is of particular interest in the design of a nano-silver HVAC system. The effects of nozzle position and flow rate on the spray area over a horizontal surface have been investigated for various nozzles. The results obtained indicate that spray area is increased as the height of spray position is increased or mass flow rate is increased. The wetted area over a practical heat exchanger is also studied at a given nozzle height. It is found that the wetted area is gradually increased with an increase in the flow rate. However, the effect of flow rate on the wetted area is a little affected by flow rate in the range of too much flow rate. It is also found that the wetted area is decreased as the inclination angle of a heat exchanger is increased.

• Journal of the Korean Society of Safety
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• v.37 no.1
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• pp.1-11
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• 2022

This numerical study investigates the effects of the size of the natural smoke vent area (10% and 1% of the floor area) and the location of the fire source (i.e., at the side and center of the stage) on the temperature distribution in the compartment and velocity distribution and mass flow rate of flow through a natural smoke vent for a reduced-scale model of a theater stage. Then, the mass flow rate of outflow through the natural smoke vent in the event of a fire for a real-scale theater stage was examined. The case with the larger natural smoke vent area and central fire source location showed lower temperature distributions and higher mass flow rates of outflow and inflow than the case with the smaller natural smoke vent area and side fire source location. The trends of the temperature distributions were closely related to those of the mass flow rates for the outflow and inflow. Additionally, the case with the larger natural smoke vent area and central fire source location exhibited the most non-uniform flow velocity distribution in all cases tested. A bidirectional flow, in which the outflow and inflow occur simultaneously, was observed through the natural smoke vent. In the event of a fire situation in a real-scale theater stage, it was predicted that the case with the larger natural smoke vent area and central fire source location would have a mass flow rate of outflow that is 43.53 times higher than that of the case with the smaller natural smoke vent area and side fire source location. The present results indicate that the natural smoke vent location should be determined by considering the location in a theater stage where a fire can occur.

• Journal of Korean Society on Water Environment
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• v.31 no.2
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• pp.196-208
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• 2015

This study analyzed the characteristics of sewer flow and its water quality, and investigated changes in the characteristics in three areas where the sewer rehabilitation projects have been carried out. In S1 area, the patterns of the flow became regular and the range of the fluctuation decreased after the sewer rehabilitation. The flow and its BOD concentration increased. The infiltration/inflow and exfiltration showed clear distinction before and after the sewer rehabilitation in this area. In S2 area, the patterns and the range of the fluctuation of the flow made no differences before and after the sewer rehabilitation. The flow decreased slightly and its BOD concentration increased considerably after the sewer rehabilitation. Big decrement in stormwater inflow but small in exfiltration appeared in this area. In S3 area, the patterns and the range of the fluctuation of the flow made no differences before and after the sewer rehabilitation. The flow decreased slightly and its BOD concentration increased in a small rate in this area.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3086-3091
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• 2007

When a molten corium is relocated in a lower head of a reactor vessel, the ERVC (External Reactor Vessel Cooling) system is actuated as coolant is supplied into a reactor cavity to remove a decay heat from the molten corium during a severe accident. To achieve this severe accident mitigation strategy, the two-phase natural circulation flow in the annular gap between the external reactor vessel and the insulation should be formed sufficiently by designing the coolant inlet/outlet area and gap size adequately on the insulation device. For this reason, one-dimensional natural circulation flow tests were conducted to estimate the natural circulation flow under the ERVC condition of APR1400. The experimental facility is one-dimensional and scaled-down as the half height and 1/238 rectangular channel area of the APR1400 reactor vessel. As the water inlet area increased, the natural circulation mass flow rate asymptotically increased, that is, it converged at a specific value. And the circulation mass flow rate also increased as the outlet area, injected air flow rate, and outlet height increased. But the circulation mass flow rate was not changed along with the external water level variation if the water level was higher than the outlet height.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.5 s.236
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• pp.554-560
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• 2005

A new method to improve the efficiency of a hydrogen fuel cell system was introduced by using variable sonic/supersonic ejectors. To obtain the variable area ratio of the nozzle throat to ejector throat which controls the mass flow rate of the suction flow, the ejectors used a movable cylinder inserted into a conventional ejector-diffuser system. Experiments were carried out to understand the flow characteristics inside the variable ejector system. The secondary mass flow rates of subsonic and supersonic ejectors were examined by varying the operating pressure ratio and area ratio. The results showed that the variable sonic/supersonic ejectors could control the recirculation ratio by changing the throat area ratio, and also showed that the recirculation ratio increased fur the variable sonic ejector and decreased for the variable supersonic ejector, as the throat area ratio increases.

• Particle and aerosol research
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• v.9 no.3
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• pp.139-147
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• 2013

The performances of indoor air cleaners including particle cleaning capacity and collection efficiency are usually tested at the condition of the maximum air flow rate of the air cleaners. However, the power consumption of the air cleaners is highly dependent on the air flow rate of the individual air cleaners. Therefore, there seems to be an optimized air flow rate for the air cleaning capacity considering power consumption. In this study, clean air delivery rate(or standard useful area as suggested room size) and power consumption have been investigated for different maximum air flow rates of 15 air cleaners and then compared those for different air flow rate modes of the individual 5 air cleaners selected from the 15 cleaners. For the maximum air flow rate conditions of 15 air cleansers, the power consumption per unit area was less related to the maximum air flow rate. However, for the different air flow rate modes of the selected 5 air cleaners, the lower power consumption per unit area was corresponding to the lower air flow rate mode of the individual air cleaners. When considering the operation time to the desired particle concentrations, there was an optimized one in the medium air flow rate modes for the individual air cleaners. Therefore, not only the maximum air flow rate but also lower air flow rates of individual air cleaners should be considered for estimating air cleaning capacity based on energy consumption per unit area.

• Journal of the Korean Society of Safety
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• v.33 no.1
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• pp.128-134
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• 2018

With the increase in frequency of typhoons and heavy rains following the climate change, the scale of damage from the calamities in the mountainous areas has been growing larger and larger, which is different from the past. For the case of Korea where 64% of land is consisted of the mountainous areas, establishment of the check dams has been drastically increased after 2000 in order to reduce the damages from the debris flow. However, due to the lack of data on scale, location and kind of check dams established for reducing the damages in debris flow, the measures to prevent damages based on experience and subjective basis have to be relied on. Under this study, the high-precision DEM data was structured by using the terrestrial LiDAR in the Jecheon area where the debris flow damage occurred in July 2009. And, from the numerical models of the debris flow, Kanako-2D that is available to reflect the erosion and deposition action was applied to install the erosion control facilities (water channel, check dam) and analyzed the effect of reducing the debris flow shown in the downstream.After installing the erosion control facilities, most of debris flow moves along the water channel to reduce the area to expand the debris flow, and after installing the check dam, the flow depth and flux of the debris flow were reduced along with the erosion. However, as a result of analyzing the diffusion area, flow depth, erosion and deposition volume of the debris flow generated from the deposition part after modifying the location of the check dams with the damages occurring on private residences and agricultural land located on the upstream area, the highest reduction effect was shown when the check dam is installed in the maximal discharge points.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.7 no.3
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• pp.8-14
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• 2011

The clogging of the flow area at the tube support plates(TSPs), especially at the upper TSPs results in the water level oscillation of a steam generator during normal operation. A reduction of the TSP flow area causes to increase in pressure drop within the two-phase flow zone, which destabilizes the boiling flow through the tube bundle. This phenomenon was occasionally observed at a few domestic and foreign nuclear power plants. One of the methods for defining the flow area clogging is visual inspection, which is the most effective inspection method. The results of the visual inspection for TSPs' flow area are clogging images on TSPs' quartrefoil lobes. These images are complexly distorted due to lens aberration and external factors like the distance to a subject and angle etc. In this work, we developed the analysis algorithm for clogging image of the TSP flow area of steam generators. For this purpose, we designed an image verification device applicable to the camera employed in the field for visual inspection and then, we demonstrated the validity of image analysis algorithm by using this device and commercial autoCAD program.