• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.1
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• pp.45-54
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• 1996

An experimental investigation on the two-phase flow through tube orifices was performed with the refrigerant mixture of R32/125/134a(30/10/60). A series of tests were conducted to generate wide range of data at varying operation conditions with four short tubes. The tests include both single and two-phase flow conditions at the inlet of the short tube with different oil concentrations. Experimental data were presented as a function of major operating parameters and short tube diameter. Based on test results and data analysis, a semi-empirical flow model was developed to predict the mass flow rate through short tube orifices with a given set of conditions. The flow model was formed to cover both single and two-phase flow at the inlet of short tube with considering the effects of oil concentration.

• Bulletin of the Korean Chemical Society
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• v.34 no.1
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• pp.139-142
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• 2013

A study was carried out to evaluate the solid phase micro-extraction (SPME) for formaldehyde emission analysis of uncoated plywood. In SPME, formaldehyde was on-fiber derivatized through headspace extraction and analyzed by gas chromatography coupled with mass spectrometry (GC/MS). The SPME was compared with desiccators (DC-JAS 233), small-scale chamber (SSC-ASTM D6007) and liquid-liquid extraction (LLE-EPA 556) methods which were performed in accordance with their respective standards. Compared to SSC (RSD 4.3%) and LLE (RSD 5.0%), the SPME method showed better repeatability (RSD 1.8%) and not much difference from DC (RSD 1.4%). The SPME has proven to be highly precise (at 95% confidence level) with better recovery (REC 102%). Validation of the SPME method for formaldehyde quantitative analysis was evidenced. In addition, the SPME by air sampling directly from plywood specimens (SPME-W) correlated best with DC ($r^2$ = 0.983), followed by LLE ($r^2$ = 0.950) and SSC ($r^2$ = 0.935).

• Journal of Korean Society on Water Environment
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• v.21 no.6
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• pp.624-629
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• 2005

The purpose of this study is to investigate the performance of nitrogen removal using autotrophic microorganism in the Membrane-Attached Biofilm Reactor (MABR). The treatment system consists of an aerobic MABR (R1) for nitrification and an anaerobic MABR (R2) for hydrogenotrophic denitrification. Oxygen and hydrogen were supplied through the lumen of hollow-fiber membranes as electron acceptor and donor, respectively. In phase Ι, simultaneous organic carbon removal and nitrification were carried out successfully in R1. In phase II, to develop the biofilm on the hollow-fiber membrane surface and to acclimate the microbial community to autotrophic condition, R1 and R2 were operated independently. The MABRs, R1 and R2 were connected in series continuously in phase III and operated at HRT of 8 hr or 4 hr with $NH_4{^+}-N$ concentration of influent, from 150 to 200 mgN/L. The total nitrogen removal efficiency reached the maximum value of 99% at the volumetric nitrogen loading rate of $1.20kgN/m^3{\cdot}d$ in the combined MABR system with R1 and R2. The results in this study demonstrated that the combined MABR system could operate effectively for the removal of nitrogen in wastewater not containing organic materials and can be used stably as a high rate nitrogen removal technology.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.27 no.1
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• pp.3-15
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• 2001

The bilayer forming ability of pseudo-ceramide PC104 in octanoic acid/water/n-octyl $\beta$-D-glucoside mixtures was investigated through the phase diagram. Because of its low solubility in water and of its crystallization, pseudoceramide PC104 was dissolved in octanoic acid, which is nontoxic additive for foods and cosmetics. The mixtures formed four different phases (L1, L2, LC and two phases). Depending on the concentration of PC104 in octanoic acid, the region of each phase was extended or contracted. On the contrary to the region of L2, regions of lamellar phase and L1 phase were expanded. The bilayer-forming ability of PC104 was explained on the basis of concentration of PC104 at interface and interaction between PC104 and octanoic acid. From FT-IR results, it was found that the interactions of PC104’s polar head group with octanoic acid increased as the amount of PC104 in octanoic acid increased. Also emulsion size and size distribution have been studied depending upon the emulsification path. droplets of emulsion prepared from lamellar phase were smaller and more homogeneous compared to those of emulsions formed from L2 phase.

• Journal of Mechanical Science and Technology
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• v.17 no.8
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• pp.1211-1218
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• 2003

The present study investigated two-phase flow distribution and phase separation of R-22 refrigerant through various types of branch tubes. The key experimental parameters were the orientation of inlet and branch tubes (horizontal and vertical), diameter ratio of branch tube to inlet tube (1 and 0.61), mass flux (200-500 kg/㎡s), and inlet quality (0.1-0.4). The predicted local pressure profile in the tube with junction was compared and generally agreed with the measured data. The local pressure profile within the pressure recovery region after the junction has to be carefully investigated for modeling the pressure drop through the branch. The equal flow distribution case can be found by adjusting the orientation of the inlet and branch tubes and the diameter ratio of the branch tube to the inlet tube. The T-junction with horizontal inlet and branch tubes showed the nearly equal phase distribution ratio. The quality at the branch tube varied from 0 to 1 as the orientation of the branch tube changed, while it varied within${\pm}$50% as the orientation of the inlet tube changed.

• The Transactions of the Korean Institute of Power Electronics
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• v.28 no.1
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• pp.22-29
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• 2023

A grid-connected inverter can be used in grid-connected or stand-alone modes. Generally, a grid-connected inverter operates in a grid-connected mode, but the inverter operates in stand-alone mode if grid faults occur. In the stand-alone mode, the grid-connected inverter must supply electric power to a critical load that needs to receive stable power even though grid faults occur. Generally, three-phase loads are used as critical loads, but a single phase is configured in some cases. In these conditions, the critical load is required to unbalance the load power consumption, which makes the three-phase load voltage unbalancd. This unbalanced voltage problem can cause fatal problems to the three-phase critical loads, and thus must be addressed. Hence, this paper proposes an algorithm to solve this unbalanced voltage problem by the individual phase current control. The proposed method is verified using Psim simulation and experiments.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2002.09a
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• pp.367-369
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• 2002

We have designed ramp profile excitation pulse based on the Shinnar-Le Roux (SLR) algorithm. The algorithm provides many advantages to pulse designers. The first advantage is the freedom of deciding the amplitudes, frequencies, and ripple sizes of stopband, passband, and transition band of pulse profile. The second advantage is the freedom of deciding the pulse phase, more specifically, minimum phase, linear phase, maximum phase, and any phase between them. The minimum phase pulse is the best choice in the case of 3D TOF, because it minimizes the echo time, which implies the best image quality in the same MR examination condition. In addition, the half echo technique is slightly modified in our case. In general, using the half echo technique means that the acquired data size is half and the rest part can be filled with complex conjugate of acquired data. But in our case, the echo center is just shifted to left, which implies the reduction of echo time, and the acquired data size is the same as the one without using the half echo technique. In this case, the increase of right part of data leads to improvement of the resolution and the decrease of left part of data leads to decrease of signal to noise ratio. Since in the case of 3D TOF, the signal to noise ratio is sufficiently high and the resolution is more important than signal to noise ratio, the proposed method appears to be significantly affective and gives rise to the improved high resolution angiograms.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.22 no.8
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• pp.1076-1082
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• 2018

This paper describes interferometer direction finder which measures the angle of arrival based on calculation of the phase difference of received radio signal from different antennas. Modern Electronic Warfare direction finder uses digital phase difference measuring techniques which have less effect on temperature variation and better performance under low Signal to Noise Ratio environment. In this paper, we analyze acceptable phase difference error for requirement of system's direction finding accuracy and introduce digital phase difference calculation techniques. We have investigated quantitative analysis on phase difference calculation according to sample number, SNR, interference injection. Through the simulation, frequency domain measurement technique is better performance than the time domain one at the environment of low SNR and interference injection. Proposed method can be used to determine the performance of interferometer direction finder.

• Proceedings of the KIEE Conference
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• 1997.11a
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• pp.630-633
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• 1997

This paper describes a design of a single phase PWM converter for high speed train. Parallel operation and control method of four Quadrant PWM converters are described. Simulation and modelling of the converters is performed. Capacity of the converter/inverter and power circuit for high speed traction system designed. And harmonic contents of AC line current's are analyzed. The results of the simulation are presented.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.347-352
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• 2000

The pressure drop characteristics of R-22 and R-410A(a mixture of 50wt% R-32 and 50wt% R-125) flowing in a small diameter tube with 1.77[mm] inner diameter and 3.14[mm] outer diameter was investigated experimentally. the mass fluxes of refrigerants are ranged from 450 to $1050[kg/(m^2{\cdot}s)]$ and the qualites are varied from 0.05 to 0.95. The main experimental results were summarized as follows; The single-phase liquid friction factors for small diameter tubes are higher than those predicted by the Blasius equation. In case of two-phase flow, the pressure gradient of the small diameter tube increases with increasing mass velocity and vapor quality. The experimental data are not well correlated by predictions which were proposed for the large diameter tube.