• Proceedings of the Acoustical Society of Korea Conference
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• 1994.06a
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• pp.764-769
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• 1994

The impedance of an electro-acoustic transducer can be controlled by motional feedback, and the noise in a duct can be reduced actively by adjusting the impedance using an additional sound. In this paper, two approaches for active noise control using motional feedback (MFB) loudspeaker are described. First configuration uses an external sensor to pickup of source directly. In this configuration, the adaptation of controller is necessary to compensate the change of transfer function from noise source to control poing. The second configuration uses a new adaptive algorithm specialized for peridic noise. Because this configuration does not require any reference input and the error sensor couples very tightly with control loudspeaker, this MFB system itself is independent of the duct condition. No microphone are required in both configurations, so that a more reliable and stable active control system can be realized under severe conditions such as high pressure, high temperature, dust, flow and so on.

• Nuclear Engineering and Technology
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• v.39 no.4
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• pp.249-256
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• 2007

Light water reactors operated under supercritical pressure conditions have been selected as one of the promising future reactor concepts to be studied by the Generation IV International Forum. Whereas the steam cycle of such reactors can be derived from modem fossil fired power plants, the reactor itself, and in particular the reactor core, still need to be developed. Different core design concepts shall be described here to outline the strategy. A first option for near future applications is a pressurized water reactor with $380^{\circ}C$ core exit temperature, having a closed primary loop and achieving 2% pts. higher net efficiency and 24% higher specific turbine power than latest pressurized water reactors. More efficiency and turbine power can be gained from core exit temperatures around $500^{\circ}C$, which require a multi step heat up process in the core with intermediate coolant mixing, achieving up to 44% net efficiency. The paper summarizes different core and assembly design approaches which have been studied recently for such High Performance Light Water Reactors.

• Nuclear Engineering and Technology
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• v.51 no.5
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• pp.1381-1389
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• 2019

Stress corrosion cracking (SCC) widely found in both primary and secondary sides of steam generator (SG) tubing in pressurized water reactors (PWR) has become an important safety issue. Using eddy-current tests (ECTs), non-destructive evaluations are performed for the integrity management of SG tubes against intergranular SCC. To enhance the reliability of ECT, this study investigates the effects of oxide films on ECT's detection capabilities for SCC in laboratory-degraded SG tubing in high temperature and high pressure aqueous environment.

• Korean Journal of Pharmacognosy
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• v.52 no.3
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• pp.157-162
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• 2021

The heat-mediated reflux apparatus extraction of Paeonia lactiflora Pall. has been widely used as a traditional extraction method. In this paper, the microwave apparatus extraction method of Paeonia Radix was performed and the active ingredients and functional constituents were compared with the reference extraction method. The most effective extraction condition of albiflorin using the microwave was 120℃ in 50% methanol, and paeoniflorin was maximally extracted at 60℃. The reduced level of paeoniflorin molecule at high-pressure and high-temperature extraction condition was caused by the molecular instability. Additionally, the microwave extraction of 50% methanol extracts at 150℃ showed the highest functional constituents determined by in vitro DPPH radical scavenging activity, polyphenol concentration, and tyrosinase inhibition assay. The microwave apparatus was adapted as a rapid, low-cost, and environmentally friendly method to extract active ingredients and the practical extraction conditions of Paeonia Radix can be used in industrial applications.

• Nuclear Engineering and Technology
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• v.54 no.2
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• pp.546-553
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• 2022

Narrow rectangular channels are employed in nuclear research reactors that use plate-type nuclear fuels, high heat-flux compact heat exchangers, and high-performance micro-electronics cooling systems. Two-phase flow in narrow rectangular channels is important, and it needs to be better understood because it is considerably different than that in round tubes. In this study, mechanistic models were developed for the flow regime transition criteria for various flow regimes in co-current air-water two-phase flow for vertical downward flow inside a narrow rectangular channel. The newly developed criteria were compared to a flow regime map of downward air-water two-phase flow inside a narrow rectangular channel with a 2.35-mm gap width under ambient temperature and pressure conditions. Overall, the proposed model showed good agreement with the experimental data.

• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.1
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• pp.88-94
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• 2012

One of the effective ways to reduce both $NO_x$ and PM at the same time in a diesel CI engine is to operate the engine in low temperature combustion (LTC) regimes. In general, two strategies are used to realize the LTC operation-dilution controlled LTC and late injection LTC - and in this study, the former approach was used. In the dilution controlled regime, LTC is achieved by supplying a large amount of EGR to the cylinder. The significant EGR gas increases the heat capacity of in-cylinder charge mixture while decreasing oxygen concentration of the charge, activating low temperature oxidation reaction and lowering PM and $NO_x$ emissions. However, use of high EGR levels also deteriorates combustion efficiency and engine power output. Therefore, it is widely considered to use increased intake pressure as a way to resolve this issue. In this study, the effects of intake pressure variations on performance and emission characteristics of a single cylinder diesel engine operated in LTC regimes were examined. LTC operation was achieved in less than 8% $O_2$ concentration and thus a simultaneous reduction of both PM and $NO_x$ emission was confirmed. As intake pressure increased, combustion efficiency was improved so that THC and CO emissions were decreased. A shift of the peak Soot location was also observed to lower $O_2$ concentration while $NO_x$ levels were kept nearly zero. In addition, an elevation of intake pressure enhanced engine power output as well as indicated thermal efficiency in LTC regimes. All these results suggested that LTC operation range can be extended and emissions can be further reduced by adjusting intake pressure.

• Progress in Superconductivity and Cryogenics
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• v.20 no.3
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• pp.21-27
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• 2018

It is difficult to fabricate and maintain moving parts of expander at cryogenic temperature. This paper describes numerical analysis and experimental investigation on a cryogenic reciprocating expander without moving piston. An intake valve which takes high-pressure gas, and an exhaust valve which discharges low-pressure gas, are connected to a tube. The inside pressure of the tube is pulsated for work production. This geometric configuration is similar to that of pulse tube refrigerator but without regenerator. An orifice valve and a reservoir are installed to control the phase of the mass flow and the pressure. At the warm end, a heat exchanger rejects the heat which is converted from the produced work of the expanded gas. For the numerical analysis, mass conservation, energy conservation, and local mass function for valves are used as the governing equations. Before performing cryogenic experiments, we carried out the expander test at room temperature and compared the performance results with the numerical results. For cryogenic experiments, the gas is pre-cooled by liquid nitrogen, and then it enters the pulse tube expander. The experiments are controlled by the opening of the orifice valve. Numerical analysis also found the expander conditions that optimize the expander performance by changing the intake pressure and valve timing as well as the opening of the orifice valve. This paper discusses the experimental data and the numerical analysis results to understand the fundamental behavior of such a newly developed non-mechanical expander and elucidate its potential feature for cryogenic application.

• Journal of the Korean Society for Heat Treatment
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• v.33 no.1
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• pp.20-24
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• 2020

Single crystal diamonds are in great demand in such fields as mechanical, electronic applications and optoelectronics. Large area single crystal diamonds are attracting attention in future industries for mass production and low cost. In this study, hot filament CVD (HFCVD) is used to grow large area single crystal diamond. However, the growth rate of large area single crystal diamond using HFCVD is known to be very low. The goal of this study is to use single crystal diamond substrates in HFCVD with methane-hydrogen gas mixtures to increase the growth rate of single crystal diamond and to optimize the conditions by analysing the effects of deposition conditions for high quality crystallinity. The deposition pressure, the ratio of CH₄/H₂ gas, the substrate temperature and the distance between the filament and the substrate were optimized. The sample used a 4×4 (mm²) size single crystal diamond substrate (100), the CH₄/H₂ gas ratio was fixed at 5%, the substrate temperature was synthesized to about 1000℃. At this time, the deposition pressure was changed to three types of 50, 75, 85 Torr and deposited. Finally, optimization was investigated under pressure conditions to analyse the growth rate and quality of single crystal diamond.

• Nuclear Engineering and Technology
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• v.53 no.8
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• pp.2616-2628
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• 2021

The results of effective irradiation swelling in a wide range of burnup levels are numerically obtained for an inert matrix fuel, which are verified with DART model. The fission gas swelling of fuel particles is calculated with a mechanistic model, which depends on the external hydrostatic pressure. Additionally, irradiation and thermal creep effects are included in the inert matrix. The effects of matrix creep strains, external hydrostatic pressure and temperature on the effective irradiation swelling are investigated. The research results indicate that (1) the above effects are coupled with each other; (2) the matrix creep effects at high temperatures should be involved; and (3) ranged from 0 to 300 MPa, a remarkable dependence of external hydrostatic pressure can be found. Furthermore, an explicit multi-variable mathematic model is established for the effective irradiation swelling, as a function of particle volume fraction, temperature, external hydrostatic pressure and fuel particle fission density, which can well reproduce the finite element results. The mathematic model for the current volume fraction of fuel particles can help establish other effective performance models.

• Tribology and Lubricants
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• v.22 no.3
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• pp.137-143
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• 2006

The sliding contact interface of machine components such as bearings, gears frequently operates in lubrication at the inception of sliding failure under high loads, speed and slip. The surface temperature at the interface of bodies in a sliding contact is one of the most important factors influencing the behavior of machine components. Most surface failure in sliding contact region result from frictional heat generation. However, it is difficult to measure temperature rise experimentally. So the calculation of the surface temperature at a sliding contact interface has long been an interesting and important subject for tribologist. The surface temperature rise is related in contact pressure, sliding speed, material properties and lubrication thickness. Though roughness, load, ect all of the condition, are same, film thickness varies with velocity. In this study, surface temperature rise due to frictional heating in lubrication is calculated with various velocities. Surface film shearing and dry solid asperity contact are used to simulate the change of frictional heat in lubricated contact