• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.6 no.2
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• pp.155-165
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• 1994

In this study, the following factors are investigated from experiments for a vertical parallel plate heat exchanger under the frosting condition ; the growth of frost layer, the characteristics of heat and mass transfer, the change of mass flow rate of the air passing through the heat exchanger, and the pressure drop of the air in the heat exchanger. The amount of heat and mass flux of water vapor transferred from the air stream to the heat exchanger surface is large at the early stage of frosting and then decreases dramatically, and the extent of decreasing rate becomes moderate with time. The frost layer formed near the inlet of the heat exchanger is thicker and denser than that formed near the outlet. It is found that the gradient of the amount of frost along the flow direction increases with time. In the early period of frost formation, the thermal resistance between the air and the cooling plate increases dramatically and then the extent of change decreases with time. Initially the convective thermal resistance is dominant. Then, while the convective thermal resistance decreases with time, the conductive thermal resistance continues to increase with time and finally the conductive thermal resistance becomes dominant.

• Journal of the Korean Institute of Educational Facilities
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• v.25 no.6
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• pp.21-28
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• 2018

To compare the physical quantity of students circulation along the moving path during recess of a variation type operation middle school, five points were actually observed. The flow coefficient for these points was calculated, and the change in flow coefficient was verified and tracked over time. During the operation of the classroom, the characteristics of crowdedness and congestion time depending on the physical conditions of the frequently moved paths were shown. Even in the same corridor, the difference between the flow coefficient and the congestion time of the corridor facing the open space and the blocked space was noticeably different. As a result, detailed factors such as free walking speed, the degree of freedom of passing and the possibility of collision were also identified. This means that detailed countermeasures for the student's path should be considered first when planning the moving space of a variation type school, and identifying the characteristics of these factors could be used as useful basic materials for developing various models of classroom space.

• The Journal of Engineering Geology
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• v.30 no.4
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• pp.423-433
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• 2020

Direct current (DC) electric fields have been used for electro-osmotic dewatering. Under DC conditions, however, the electrical contact resistance between the electrode and the dewatering material increases considerably during the process of dewatering. Such a circumstance hinders the continuation of effective electro-osmotic dewatering. To reduce this hindrance, an applied pulse electric field with periodic reversals of the electrode polarity should improve electro-osmotic dewatering. In this study, electro-osmotic dewatering under pulse conditions was experimentally investigated for electrode polarity reversals. During the dewatering process, the pulse electric field was able to reduce the hindrance caused by the DC, resulting in an increased final dewatered amount relative to that under a DC electric field. For a constant applied voltage, the reversed polarity condition, under which the electric current passing through the material was almost unchanged with time, yielded the maximum final dewatered amount. This technique can be used to enhance drainage from a water storage facility during a period of extreme drought and the seawater desalination plants using reverse osmosis in drought stricken coastal regions.

• Journal of Korean Society of Forest Science
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• v.97 no.4
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• pp.363-367
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• 2008

The purpose of this study was to evaluate the change of the amount of soil erosion by comparisons between burned and unburned area after forest fire. The amount of soil erosion in burned area was more high 11.2 times in year of fire, 8.4 times in 1 later year, 2 times in 5 later year and 1.3 times in 10 later year than in unburned area. The ratio of soil erosion in burned area was reduced to 98% of 10 later year as compared to the year of fire. Therefore, the soil erosion in the burned area almost tended to stabilization like unburned area passing ten year after forest fire. The most affecting factors on the amount of soil erosion in burned and unburned area were unit rainfall, number of unit rainfall and number of rainfall accumulated.

• Journal of the Korean Society for Railway
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• v.15 no.2
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• pp.141-146
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• 2012

The rail surface defects which are generated on repeated rolling contact fatigue are getting increased according to high speed, high density, and minimum weight. In addition, Increasing noise and vibration are affected by these also impact load generated as well. Because of this phenomenon, more serious and critical damages were occurred. In fact, in order to control them, the rail grinding amount in Korea. This study evaluated how depth of hardening on rail surface is formed and suggested optimal rail grinding amount by RCF(rolling contact fatigue) test with generated contact pressure between KTX wheel and UIC60 rail by applying FEM analysis. Therefore, the amount was generated approximately 0.2mm/20MGT to maintain integrity of rail surface by getting rid of depth of hardening on rail according to rail accumulated passing tonnage.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.8 no.4
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• pp.13-18
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• 1999

Recently among after-treatment devices which have high possibility of utility diesel oxidation catalyst(DOC) is concerned over the world. DOC oxidizes pollutants by means of activate-reaction during by-passing in the catalyst in doing so conversion efficiency of PM, CO and HC is high and this device does not have an effect on engine performance because back pressure is not nearly increased, But as a small amount of sulfur content in fuel is oxidized it makes sulfate which is absorbed on the surface of catalyst. So in this study the experiment is carried out by means of using ordinary fuel(0.1wt%) and low sulfur fuel(0.05wt%) with DOC and the emission gas of diesel engine is measured.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.205-210
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• 2002

As the deposits of natural sands have slowly been depleted, it has resulted in an increase in manufactured fine aggregate (MFA). Standard specifications for fine aggregate for concrete contained in KS F 2558 permit a maximum of 7 percent finer than the No. 200 sieve (75${\mu}{\textrm}{m}$). Since the production process for MFA normally generates 10 to 20 percent of micro fines-which is defined as aggregates passing the No. 200 sieve (75${\mu}{\textrm}{m}$)-more than permitted by specifications, Excess fines must be removed by screening and/or washing operations. The amount of by-products will continue to grow as production increases with environmental discharge restrictions. This fundamental study focuses on experimental research for the adequacy of use of micro fines included in crushed aggregate using methylene blue test. Total of 63 types of sands from seven different rocks were tested. Based on the test results, the methylene blue test was turned out to be a good indicator of the quality of micro fines for concrete and a supplementary article and an amendment of the KS standard were recommended.

• Journal of Power System Engineering
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• v.9 no.2
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• pp.45-49
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• 2005

Liquefied natural gas takes up six hundredths of the volume of natural gas, which makes storage and transportation much easier. To send out natural gas via a pipeline network across the nation, high-pressure LNG pumps supply highly compressed LNG to high-pressure vaporization facilities. The Number of high-pressure LNG pumps determined the send-out amount in LNG receiving terminal. So it is main equipment at LNG production process and should be maintained on best conditions. In this paper, to find out the cause of high beat vibration at cryogenic pumps, vibration and motor current signal analysis have been performed. High vibration of cryogenic pumps could be reduced due to the modification of motor rotor.

• Journal of Environmental Science International
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• v.16 no.9
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• pp.1039-1049
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• 2007

This study analyzed two dimensions hydraulic characteristic for actual flood events in steep meandering channel. It could get analysis results as follows; A water level difference of downstream more great than one of upstream at inner and outer of meandering channel. It judged that a significance of downstream level could appear more greatly in meandering channel bank, hydraulic structure and flood inundation analysis. As velocity and depth analysis was shown that much amount flow passing fast velocity happened in meandering channel, it could help establishment of meandering channel bank. In this study, the results of two dimension hydraulic analysis results could help a counterpaln establishment for the flood inundation and bank collapse.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.776-779
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• 2005

Liquefied Natural Gas takes up six hundredths of the volume of natural gas, which makes storage and transportation much easier. To send out natural gas via a pipeline network across the nation, high pressure LNG pumps supply highly compressed LNG to high-pressure vaporization facilities. The Number of high Pressure LNG pumps determined the send out amount in LNG receiving terminal. So it is main equipment at LNG production process and should be maintained on best conditions. In this paper, to find out the cause of high beat vibration at cryogenic pumps, vibration and motor current analysis have been performed. And high beat vibration of cryogenic pumps could be reduced due to the modification of motor rotor.