• Journal of Korean Society for Atmospheric Environment
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• v.1 no.1
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• pp.33-41
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• 1985

In order to investigate the Phenomenon of Acid Precipitation, pH value and Anions of Fluroide, chloride, nitrite, phosphate, bromide, nitrate and sulfate were measured from the acid precipitations sampled around 7 districts over seoul area during period of 9 months from January till September, in 1985. From the distribution of pH value gatnered, acid precipitations were noticed during period from January till Aprill, and from as of April 22nd, situation gradually recovered. The average pH value till April showed comparatively low, ranging 4.0-5.0. The pH value of 4.5-5.6 in average over whole year reaches to similar level of those in Japan. Anion analysis revealed that the main factor of pH value in Seoul district attribute mainly to the sulfate ion and nitrate ion. Moreover, these Phenomena of acid precipitation in Seoul area appeared to concentrate on certain districts, and they are slowly moving toward other directions due to such factors as wind-velocity and directions.

• Journal of the korean Society of Automotive Engineers
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• v.14 no.3
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• pp.109-114
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• 1992

The purpose of this study is to experimentally research the effects of polymer additives on turbulent transition of Couette flow between concentric cylinders when outer one is rotating and inner one is at rest; the diameter ratio being 0.2. Aqueous polymer solution generate the degradation phenomena in machine forming work, but this is not effected in about 10 minute at 5ppm. aqueous polymer solution testing. The Reynolds number, referred to the gap distance and rotation velocity of the outer cylinder, of turbulent transition is about 20000 for water flow. In the laminer region, the torque value is as same as theoretical one in the region of low Reynolds number, but becomes high with an increase in the Reynolds number. The polymer additives reduce the Reynolds number for turbulent transtition. In the turbulent region, the torque is remarkably reduced by the polymer additives, soluble polymer take down effect of turbulent transition boundary torque.

• International Journal of Aeronautical and Space Sciences
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• v.1 no.1
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• pp.36-47
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• 2000

Three-dimensional compressible turbulent flow fields within the passage of a diffusing S-duct have been simulated by solving the Navier-Stokes equations with SIMPLE scheme. The average inlet Mach number is 0.6 and the Reynolds number based on the inlet diameter is $1.76{\times}10^6$ The extended $k-{\varepsilon}$ turbulence model is applied to modeling the Reynolds stresses. Computed results of the flow in a circular diffusing S-duct provide an understanding of the flow structure within a typical engine inlet system. These are compared with experimental wall static-pressure, total-pressure fields, and secondary velocity profiles. Additionally, boundary layer thickness, skin friction values, and streamlines in the symmetric plane are presented. The computed results depict the interaction between the low energy flow by the flow separation and the high energy flow by the reversed duct curvature. The computed results obtained using the extended $k-{\varepsilon}$ turbulence model.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.25 no.1
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• pp.78-84
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• 2011

Using sensors to detect current or voltage of motors is disadvantaged because motor is exposed to vibration, impacts, corrosion, high temperature and humidity in the machinery structure like HEV. In the case of IPMSM, position information is included not only in the flux or EMF term but also in the rotator inductance because of its saliency. To solve this problem, a new mathematical model of IPMSMs on fixed frame is proposed and an extended EMF includiing rotating position information is defined to estimate extended EMF. A strong low-pass filter through the variable cut-off frequency using velocity function was proposed. This makes it is possible to estimate extended EMF by least order disturbance observer. The proposed method was proved through the experiment.

• Journal of the Korean Society for Heat Treatment
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• v.19 no.1
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• pp.20-29
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• 2006

Wear behaviour of B.390 aluminum alloy with different particle sizes of primary Si against a SM45C counterface was studied as a function of wear load and sliding velocity, using pin-on-disk apparatus under dry condition. The wear rate of specimen with fine primary Si particles showed increased wear resistance at high wear load, on the other side wear resistance of coarse primary Si particle size was improved at low wear load. As the compressive residual stress in the matrix increased remarkably by liquid nitrogen(LN) treatment, wear resistance of the LN treated specimen was more excellent than that of T6 treated specimen.

• Journal of Korean Society for Atmospheric Environment
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• v.19 no.5
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• pp.541-549
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• 2003

A basic experimental study was conducted in order to find the optimum combustion control technology to decrease the thermal NO$_{x}$, by applying the catalytic combustion method with natural gas. NO$_{x}$ emission increased with increasing space velocity due to temperature rising in the furnace. In order to overcome the low resistance to high temperature, secondary air was supplied to the CST combustor. The following secondary fuel formed combustible mixture in part, which resulted in steep increase of the exiting temperature of the 2nd catalyst bed. It led to the more generator of NO$_{x}$, 30∼60% of the 1 st catalyst bed. It might be due to the potential increase of thermal NO$_{x}$.

• Journal of Microbiology and Biotechnology
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• v.2 no.4
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• pp.268-272
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• 1992

Alcohol dehydrogenase activity of Clostridium acetobutylicum ATCC 4259 was studied for its specificity against substrates in acidogenic and solventogenic cultures. The bacterium reduces propionate, valerate and caproate added to the medium to the corresponding alcohols. Acetaldehyde, propionaldehyde, butyraldhyde, pentanal, and hexanal were used as the substrates by alcohol dehydrogenase, and all were reduced to the corresponding alcohols with varying affinities and reaction velocities. Acetaldehyde showed the lowest affinity and lowest velocity while the other aldehydes showed similar $K_m\;and\;V_max$ values. NADPH was used as the electron donor for the reduction of aldehydes. Alcohol dehydrogenase activity was low in acidogenic culture, and high in solventogenic culture.

• Journal of the Korean Society of Combustion
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• v.8 no.2
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• pp.7-16
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• 2003

The transfer of air pollutants between passenger room and service room in train are investigated by the computational analysis. The effects of service room temperature, inlet velocity, initial concentration and heating are studied. The flow induced by the difference of density between two rooms is found to take the major role in transfer of polluted air. Low temperature of service room enhances the polluted air flow into passenger room along the floor. Exhaust fan above the door between two rooms is not effective for this case. Strong inlet flow is found to suppress polluted air flow from service room. The heating of passenger room can promote air pollution.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.178-181
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• 2011

Recently, micro shock tube is being extensively used in various fields of engineering applications. The flow characteristics occurring in the micro shock tube may be significantly different from that of conventional macro shock tube due to very low Reynolds number and Knudsen number effects which are, in general, manifested in such flows of rarefied gas, solid-gas two-phase, etc. In these situations, Navier-Stokes equations cannot properly predict the micro shock tube flow. In the present study, a two-dimensional CFD method has been applied to simulate the micro shock tube, with slip velocity and temperature jump boundary conditions. The effects of wall thermal conditions on the unsteady flow in the micro shock tube were also investigated. The unsteady behaviors of shock wave and contact discontinuity were, in detail, analyzed. The results obtained show much more attenuation of shock wave, compared with macro-shock tubes.

• Magazine of the Korean Society of Agricultural Engineers
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• v.20 no.1
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• pp.4626-4630
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• 1978

The objective of this study is to investigate how the varieties of consistency of fresh concrete influence on the plastic shrinkage in dry condition. The test was conducted under the controlled chamber in which the temperature was kept at 25 ${\pm}$2$^{\circ}C$, the humidity 35 ${\pm}$3%, and the wind velocity 4.0 ${\pm}$0.5m/sec. The results obtained from the test are as follow. 1) The rate of evaporation was highest at 2-3 hour after casting, and decreased gradually. 2) The plastic shrinkage was increased as to the slump values. The shrinkage rate was very highest at 2-4 hour and hardly showed any changes after 6 hour. 3) The recommendation for good cloncrete is that slump value should be as low as possible in construction.