• Journal of Fisheries and Marine Sciences Education
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• v.26 no.3
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• pp.639-646
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• 2014

A heat exchanger using two-phase loop thermosyphons was developed as a waste heat recovery system. An experimental study was carried out on the heat transfer characteristics of two-phase loop thermosyphons heat exchanger and the results from the experiments were used to see the possibility which the two-phase loop thermosyphons could be an alternate solution for waste heat recovery system. In the present work, R134a has been used as the working fluid and the filling rate do working fluid and heat flux have been used as the experimental parameters. The results show that the filling rate of working fluid and heat flux are very important factors for the operation of two-phase loop thermosyphons. The experimental results showed the provisional results as a waste heat recovery system.

• Nuclear Engineering and Technology
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• v.36 no.1
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• pp.12-23
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• 2004

In the present study a new measurement technique has been developed, which uses an ultrasonic transmission signal in order to identify the vertical two phase flow pattern. The ultrasonic measurement system developed in the present study not only provides the information required for the identification of vertical two phase flow patterns but also makes real time identification possible. Various vertical two phase flow patterns such as bubbly, slug, churn, annular flow etc. have been accurately identified with the present ultrasonic measurement system under atmospheric condition. In addition, the present test apparatus can practically simulate the ultrasonic propagation characteristics under high temperature and high pressure systems. Therefore, it is expected that the present ultrasonic flow pattern identification technique could be applicable to the vertical two phase flow systems under high temperature and high pressure conditions.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.6
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• pp.446-454
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• 2008

The purpose of this paper is to analyze two-phase flows of the hydrogen recirculation system. Two-phase flow modeling is one of the great challenges in the classical sciences. As with most problems in engineering, the interest in two-phase flow is due to its extreme importance in various industrial applications. In hydrogen recirculation systems of fuel cell, the changes in pressure and temperature affect the phase change of mixture. Therefore, two-phase flow analysis of the hydrogen recirculation system is very important. Two-phase computation fluid dynamics (CFD) calculations, using a commercial CFD package FLUENT 6.2, were employed to calculate the gas-liquid flow. A two-phase flow calculation was conducted to solve continuity, momentum, energy equation for each phase. Then, the mass transfer between water vapor and liquid water was calculated. Through an experiment to measure production of liquid water with change of pressure, the analysis model was verified. The predictions of rate of condensed liquid water with change of pressure were within an average error of about 5%. A comparison of experimental and computed data was found to be in good agreement. The variations of performance, properties, mass fraction and two-phase flow characteristic of mixture with resepct to the fuel cell power were investigated.

• Journal of Microbiology and Biotechnology
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• v.9 no.4
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• pp.498-503
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• 1999

Protease produced from Bacillus sp. FSE-68 was isolated from Meju, a Korean fermented soybean starter, and was purified by a two-consecutive aqueous two-phase system. The change of partition coefficient (K) in the polyethylene glycol (PEG)/potassium phosphate buffer (PPB) aqueous two-phase system was measured at different pHs (6.0- 9.2), PPB concentrations (8-12%), and temperatures (4 and $20^{\circ}C$). As the PPB concentration in the aqueous two-phase system increased, the protease concentration in the top phase (PEG-rich phase) increased, thereby enhancing the partition coefficient. The minimum partition coefficient of the protease was achieved at pH 7.0, whereas that of the total protein was at pH 6.0. The biggest difference in partition coefficients of total protein and protease occurred at pH 6.0. It was interesting to note that the partition coefficient of protease decreased as the temperature increased. The optimum condition of the primary aqueous two-phase extraction of Bacillus sp. FSE-68 was pH 6.0, 14% (w/w) PPB, and 16% (w/w) PEG at $4^{\circ}C$, and the crude enzyme concentration in this system was 50% (w/w). The protease, which was concentrated in the top phase, was further mixed with 15% (w/w) PPB (pH 7.0) in the ratio of 1:1 at $20^{\circ}C$ to elute the bottom phase (PPB-rich phase). Using these steps, the purification fold achieved was 9.2 with a 44.7% yield.

• Journal of Power Electronics
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• v.3 no.4
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• pp.249-258
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• 2003

This paper presents a high-efficient and cost effective three-phase AC/DC-DC/AC power conversion system with a single two-switch type active Auxiliary Resonant DC Link (ARDCL) snubber circuit, which can minimize the total power dissipation. The active ARDCL snubber circuit is proposed in this paper and its unique features are described. Its operation principle in steady-state is discussed for the three phase AC/DC-DC/AC converter, which is composed of PWM rectifier as power factor correction (PFC) converter, sinewave PWM inverter. In the presented power converter system not only three-phase AC/DC PWM rectifier but also three-phase DC/AC inverter can achieve the stable ZVS commutation for all the power semiconductor devices. It is proved that the proposed three-phase AC/DC-DC/AC converter system is more effective and acceptable than the previous from the cost viewpoint and high efficient consideration. In addition, the proposed two-switch type active auxiliary ARDCL snubber circuit can reduce the peak value of the resonant inductor injection current in order to maximize total system actual efficiency by using the improved DSP based control scheme. Moreover the proposed active auxiliary two-switch ARDCL snubber circuit has the merit so that there is no need to use any sensing devices to detect the voltage and current in the ARDCL sunbber circuit for realizing soft-switching operation. This three-phase AC/DC-DC/AC converter system developed for UPS can achieve the 1.8% higher efficiency and 20dB lower conduction noise than those of the conventional three-phase hard-switching PWM AC/DC-DC/AC converter system. It is proved that actual efficiency of the proposed three-phase AC/DC-DC/AC converter system operating under a condition of soft switching is 88.7% under 10kw output power.

• Journal of Microbiology and Biotechnology
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• v.7 no.5
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• pp.345-351
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• 1997

An aqueous/organic two-phase reaction system was applied to the production of catechol using immobilized resting cells of Pseudomonas putida CY 400. Water/ethyl ether system was used because of high partition coefficient of catechol and thus to reduce the product inhibition and degradation. Among the tested immobilization carriers, polyacrylamide gel gave the highest catechol productivity. The immobilization seemed to protect the cells against solvent toxicity. From the simulation of reaction conditions based on two-phase models, it was found that there was an optimum acetate concentration at fixed benzoate and cell concentrations for the catechol productivity. A lower phase volume ratio (lower fraction of organic phase) gave a higher productivity. However, the substrate conversion was low at low phase volume ratio.

• 한국생물공학회:학술대회논문집
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• 2000.11a
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• pp.73-76
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• 2000

A novel, continuous bioreactor system combining a bubble column (absorption section) and a two-phase bioreactor (degradation section) has been designed to treat a gas stream containing benzene. The bubble column contained hexadecane as an absorbent for benzene, and was systemically chosen considering physical, biological, environmental, operational and economic factors. This solvent has infinite solubility for benzene and very low volatility. After absorbing benzene in the bubble column, the hexadecane served as the organic phase of the two-phase partitioning bioreactor, transferring benzene into the aqueous phase where it was degraded by Alcaligenes xylosoxidans Y234. The hexadecane was then continuously recirculated back to the absorber section for the removal of additional benzene. All mass transfer and biodegradation characteristics in this system were investigated prior to operation of the integrated unit, and these included: the mass transfer rate of benzene in the absorption column, the mass transfer rate of benzene from the organic phase into the aqueous phase in the two-phase bioreactor, the stripping rate of benzene out of the two-phase bioreactor, etc. All of these parameters were incorporated into model equations, which were used to investigate the effects of operating conditions on the performance of the system. Several experiments were conducted to show the feasibility of this system. This process is believed to be very practical for the treatment of high concentrations of gaseous pollutants.

• Nuclear Engineering and Technology
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• v.53 no.4
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• pp.1304-1310
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• 2021

Two-phase flow, especially gas-liquid two-phase flow, has a wide application in industrial field. The diagnosis of two-phase flow parameters, which directly determine the flow and heat transfer characteristics, plays an important role in providing the design reference and ensuring the security of online operation of two-phase flow system. Computer tomography (CT) is a good way to diagnose such parameters with imaging method. This paper has proposed a novel image reconstruction method for thermal neutron CT of two-phase flow with improved simulated annealing (ISA) algorithm, which makes full use of the prior information of two-phase flow and the advantage of stochastic searching algorithm. The reconstruction results demonstrate that its reconstruction accuracy is much higher than that of the reconstruction algorithm based on weighted total difference minimization with soft-threshold filtering (WTDM-STF). The proposed method can also be applied to other types of two-phase flow CT modalities (such as X(𝛄)-ray, capacitance, resistance and ultrasound).

• Journal of the Korean Society of Visualization
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• v.15 no.1
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• pp.11-18
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• 2017

A two-phase flow observed in a heat exchanger or nuclear power generation often has a profound effect on undesirable noise or flow characteristics. Void fraction, which refers to the ratio of gas (or liquid) to the total fluid, affects heat transfer coefficient, vibration and so forth. In other words, void fraction is one of most important parameters in two-phase flow since it contributes to comprehend the characteristics of two-phase flow. We developed a two-phase flow visualization system to measure cross-sectional and volumetric void fractions by using quick closing valves and image processing software. With this system, we could observe the plug, slug, and stratified flow patterns of two-phase flow and measure a myriad of void fractions. As a consequence of the experiment, we found that the estimated void fractions were largely coincident with the predictive values by Chisholm model.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.41-45
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• 1997

To design a control system, it is a elementary point that the stability of the system should be guaranteed. Also, the phase of the system plays an important role for its frequence performance. In this paper, we present two stability criterion of repetitive control system with phase-lead and lag compensator. First, the stability criterion for the servo control system with phase-lead and lag compensator is shown by using small-gain theorem. Second, for the repetitive control system with the compensator, the stability criterion, also, is determined by using small-gain theorem. Two stability criterions show the same results that the stability depends on a coefficient of the phase-lead and lag compensator under some condition in servo control system and repetitive control system.