• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.1
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• pp.50-58
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• 2003

An analytical study was carried out to investigate the performance of an oil pumping system of a variable speed compressor using a commercial CFD program. The simulations for the oil supplying system with the oil and air mixture were performed by varying compressor speed from 40 Hz to 90 Hz. Comparing the predicted with the measured data on the modified scroll compressor validated the simulation model. The predicted results were consistent with the test data with a maximum deviation of 12.8%. The oil flow rate significantly increased with a rise of compressor speed due to a higher oil flow rate from the swing pump and a greater centrifugal force on oil gallery.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.3142-3147
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• 2008

A simple transient simulation of ground source heat pump system was carried out to investigate the effects of ground thermal conductivity on its performance. The TRNSYS code with a simple water to water heat pump model was used to compare the COP variation of the system. A new ground heat exchanger called by semi-closed loop was proposed and constructed in the real site. The effective thermal conductivity was measured using the test equipment developed by according to the line source model. The simulation results showed that highly efficient thermal conductivity of the grout material could increase the performance of the heat pump system very well. And the new ground heat exchanger showed the increased effective thermal conductivity as the penetration water flow rate(PWFR) was increased. Therefore, the performance improvement of the heat pump system using the proposed ground heat exchanger can be expected.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.6
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• pp.928-936
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• 1999

An experimental study was performed to investigate characteristics of an inverter driven water-to-water refrigeration system with a variation of compressor frequencies and expansion devices. The frequency of a compressor varied from 30Hz to 75Hz, and performance of the systems applying three different expansion devices such as capillary tube, thermostatic expansion valve(TXV), and electronic expansion valve(EEV) were measured. The load conditions were altered by varying the temperature of the secondary fluid entering condenser and evaporator with a constant flow rate. When the test conditions were deviated from the standard value(rated value), TXV and EEV showed better performance than capillary tube due to optimum control of mass flow rate and superheat. In the present study, it was observed that the variable area expansion device had better performance than constant area expansion device in an inverter refrigeration system due to active control of flow area with a change of compressor frequency and load conditions.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.8
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• pp.21-28
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• 1997

This paper presents the influence of the process parameters on the change in dynamic behavior of a lathe turning system. With variation of feed rate, depth of cut, direction of tool motion, cutting speed and tool location along the workpiece, the dynamic characteristics of stable cutting, chatter transition and fully developed chatter regions are demonstrated. The workpiece vibration during machining is continuously measured at different tool locations along the workpiece and quantitatively analyzed. Complex linear behavior due to change of process parameter values as well as fundamental wystem nonlinearity due to change of process configuration indicated by a tool path dependence of the locations of chatter onset and disappearance are described. Finally, the structural characteristics of the turning system which can have large and nonlinear effects on system behavior are presented.

• Journal of the Korean GEO-environmental Society
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• v.9 no.2
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• pp.31-37
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• 2008

Diffused Aeration System (DAS) is one of the remediation methods used for removing contaminants in groundwater and this method brings air bubbles in contact with contaminated water, afterwards transferring contaminants in liquid phase into air phase. In this study, three applicability tests using DAS were conducted in two highly contaminated sites. For these tests, diffused air bubbles are generated with a in-flow rate of 17.1, 44.8 and 76.5 (1/min), respectively. The concentrations of TCE in grounwater and air phase were measured during the tests. The measured results showed that TCE concentration hit the highest value after 6~8 min and afterwards decreased gradually. Also, it was observed that the TCE concentration in air phase changed depending on the rate of diffused aeration. In addition, $K_La$ values from liquid to air phase were calculated based on the test results and those of three tests (test 1, 2 3) were 0.444, 1.158 and 1.836(1/hr), respectively. From the comparison of $K_La$ values, the faster air in-flow rate is, the higher the efficiency of the DAS is.

• KIPS Transactions on Computer and Communication Systems
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• v.9 no.12
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• pp.333-338
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• 2020

This paper proposes an augmented reality-based electronic circuit education system as a way for electronic circuit education, which is the basis of ICT convergence technology field. It consists of a hardware module that can identify the actual circuit and a mobile educational content that can check the current flow, input, output, and measured value by applying augmented reality technology. An experiment was conducted on image recognition, which is the main performance, for the purpose of stable operation of the system, and as the experimental method the recognition rate was measured by changing the distance between the hardware module and the mobile device to a certain interval. As a result of the experiment, the recognition rate was 100 percent at a distance of 25[Cm] or higher, and it was confirmed that the recognition rate decreased by 12% at a distance below 25[Cm], which can be said to be the effect of an error that results in image loss taken due to close distance. In the future, we plan to apply the education system presented in this paper to classes, which increases the efficiency of classes and improve students' interest and understanding of the subject.

• Resources Recycling
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• v.29 no.6
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• pp.104-113
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• 2020

Bubble size in froth flotation has long been recognized as a key factor which affects the bubble residence time, the bubble surface area flux (Sb) and the carrying rate (Cr). This paper presents method of bubble size measurement, relationship between operating variables and gas dispersion properties in flotation column. Using high speed camera and image analysis system, bubble size has been directly measured as a function of operating parameters (e.g., superficial gas rate (Jg), superficial wash water rate (Jw), frother concentration) in flotation column. Relationship compared to measured and estimated bubble size was obtained within error ranges of ±15~20% and mean bubble size was 0.718mm. From this system the empirical relationship to control the bubble size and distribution has been developed under operating conditions such as Jg of 0.65~1.3cm/s, Jw of 0.13~0.52cm/s and frother concentration of 60~200ppm. Surface tension and bubble size decreased as frother concentration increased. It seemed that critical coalescence concentration (CCC) of bubbles was 200ppm so that surface tension was the lowest (49.24mN/m) at frother concentration of 200ppm. Bubble size tend to increase when superficial gas rate (Jg) decreases and superficial wash water rate Jw and frother concentration increase. Gas holdup is proportional to superficial gas rate as well as frother concentration and superficial wash water rate (at the fixed superficial gas rate).

• Journal of Korean Society on Water Environment
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• v.28 no.1
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• pp.94-101
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• 2012

The performance data for eight years from a free-surface-flow constructed wetland system receiving agricultural tailwater were used to analyze denitrification rate and nitrogen treatment characteristics according to season and wetland design. Seasonal difference between growing season (March~November) and winter season (December~February) was shown in the concentration of all nitrogen species. Seasonal nitrogen treatment has similar trend with temperature and measured denitrification rate. The highest denitrification rate was measured in July, but treatment efficiency was most higher in May and June. Nitrogen absorption of vegetation could affect to these wetland performances, therefore dense population of wetland vegetation might be helpful. According to design of wetland, at least 25~50 m of wetland length was needed to decrease effluent T-N concentration to background concentration in growing season. In winter season, wetland needed much longer distance to reduce T-N concentration. Mass removal rate was continuously high through whole year because runoff coefficient was low in winter season. Applicability of constructed wetland was observed for the total maximum daily load that control T-N load.

• Proceedings of the KSRS Conference
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• 2005.10a
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• pp.561-563
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• 2005

From the IF (Intermediated Frequency) loop-back test, BER (Bit Error Rate) degradation of processed data, HRIT (High Rate Information Transmission), is estimated by proposed measurement configuration. The specific parameters, likely data rate, FEC (Forward Error Correction), and modulation method, are based on the outcomes of SRR (System Requirements Review) which was held on 13-14 June 2005, in Toulouse. The proposed measurement procedure is that combined 70MHz modulated signal and noise is connected to the spectrum analyzer and receiver. The former measures the C/No (Carrier to Noise density ratio) and the latter estimates BER of FEC decoded data. Implementation loss can be obtained by subtracting measured BER from calculated BER which is also subtracted data rate from measured C/No. This test procedure is very simple and can be applied to assess the implementation loss of dedicated receiver for HRIT in the future.

• Journal of the Korea Institute of Military Science and Technology
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• v.18 no.2
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• pp.109-114
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• 2015

A method to compensate a bias hysteresis error of the ring laser gyro using the rate of temperature is proposed in this paper. Until now, we generally have measured and compensated the error of gyro and accelerometer using the temperature. However, we utilize the measured values of the temperature dependent error elements on the temperature rate in navigation system level. We show through experiments that the proposed method can improve the navigation performance and be very effective.