• Journal of Advanced Marine Engineering and Technology
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• v.41 no.1
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• pp.8-14
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• 2017

Due to the financial crisis in 2008, the world economy collapsed leading to an increase in oil prices and a decrease in freight by shipping. To overcome this crisis, major shipping companies ordered larger ships, changed their trading route and improved operating of ships to overcome deficits. In particular, low-speed navigation was much favored by many companies so that it can reduce fuel consumption. However, the long-term operation of high-speed optimized engines in low-speeds has affected the jacket cooling fresh water (J.C.F.W.) system as they fail to maintain the normal operational temperature. The temperature of J.C.F.W. system dropped leading to low temperature corrosion. As a result, when the engine is operating at minimal load the functioning of existing J.C.F.W cooler is decreased and the use of fresh water generator is substantially limited. Therefore, an improvement in the functioning of J.C.F.W. system is necessary. In this paper, in order to review the improvements required for the operation of J.C.F.W. of low-speed operating marine diesel, an experiment was conducted by comparing and analyzing the results of the main engine J.C.F.W. system of a Panamax class bulk carrier 82k and a Cape class bulk carrier 180k by installing and uninstalling the J.C.F.W. Cooler. Thus, this paper proposed an improved design of the J.C.F.W. system that is suitable for the present low-speed operation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.4
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• pp.639-647
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• 2019

Recently, as the semiconductor integration technology due to miniaturization and high density of electronic equipment have developed, it is importantly recognized the application of thermal control system in order to release inner heat generated from chips, modules, In this study, we considered the heat transfer and pressure drop characteristics in a horizontal channel with four blocks using k-${\omega}$ SST turbulence model During CFD (Computational Fluid Dynamics) analysis, the parameters applied block width, block height, heat source and turbulence generator placement etc. As the boundary conditions of analysis, the channel inlet temperature and flow velocity were respectively 300 K and 3.84 m/s, the heat flux was $358W/m^2$. As a result, the heat transfer performance was decreased as the block width ratio (w/h) was increased, while it was increased as the block height ratio (h/w) was increased. In addition, as the arrangement of heat source size was increased to high heat flux from low heat flux, it was influenced by heat source size and the heat transfer coefficient showed a tendency to increase, When the turbulence generator was installed in the upper part of block No. 1 position the closely to the channel entrance, the heat transfer characteristics was greatly influenced on the whole of four heating blocks. and in oder to consider the pressure drop characteristics, we are able to select the most appropriate turbulence generator's position.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 1996.11a
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• pp.116-121
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• 1996

An image of future power system which has introduced superconducting generator, cable, transformer, fault current limiter, SMES and so on is presented. Conceptual designs of each SC machines and devices are carried out. The SC cable and SFCL utilize the high Tc superconductor(HTS) cooled by liquid $N_2$Other devices use low temperature superconducting cooled by He. The SC power system models are proposed detailedly. In viewpoint of the operation and control SC power system, The concrete design direction and effective role of each SC apparatus are investigated. In this paper, it is pointed that superconducting fault limiters(SFCLs) should play an important part of the quenching current level coordination to prevent the other SC devices from quenching. Finially, SFCL are also expected to he very effective to introduce flexibility of power system configuration and operation due to their possibility to enhance transient stability and reduce short circuit current.

• 전기의세계
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• v.25 no.5
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• pp.79-87
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• 1976

This paper is to investigate the A.C generation of MHD engine, converting directly the kinetic energy of conductive gas in high temperature to electric power by the effect of magnetic field. It is known that there are at least two kinds of method in A.C MHD power generation; one, by sending stationary plasma flow in an alternating or rotating magnetic field and the other, by transmission of pulse type plasma flow in uniform and constant magnetic field, former method is adopted here. In order to raise the total efficiency of close cycle in combination with nuclear power and MHD genertaion, an argon plasma jet is utilized as heat source, which is not mixed with the seed material, and the design data are obtained for A.C MHD generation in small capacity, but induced voltage and power output have the maximum values, 15 voltages and 7.5W respectively due to plasma flow with low conductivity and weak magnetic field.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.8
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• pp.806-811
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• 2004

1-Hydroxy-4-(2-naphthalenesulfonyloxy) cyclohexane(1), 1,4-di-(2-naphthalenesulfonyloxy) cyclohexane(2), 1-hydroxy-4-(2-thiophenesulfonyloxy) cyclohexane(3), 1,4-di-(2-thiophenesulfonyloxy) cyclohexane(4) were synthesized and evaluated for their performance as novel acid amplifiers for 193 nm photoresists. These acid amplifiers(1-4) showed reasonable thermal stability at the usual resist-processing temperature, 9$0^{\circ}C$-12$0^{\circ}C$. And estimated by the sensitivity curve, (1)-(4) enhanced the sensitivity of poly(tert-butyl methacrylate) film by 1.2-1.4 times, compared to poly(tert-butyl methacrylate) film whithout acid amplifiers, in the presence of a photoacid generator.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.5
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• pp.570-578
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• 1999

An experimental study has been performed on heat and mass transfer in a falling film absorber with a strong lithium bromide solution in small-sized household absorption chiller/heater. Components were concentrically arranged in a cylindrical form. from the center, low temperature generator, absorber and evaporator. This arrangement of helical-typed heat exchangers allows to make the machine much more compact than conventional one. Experimental measurements were conducted with a helical absorber and the obtained data were compared with data in the literatures. The comparison revealed that the helical absorber tube provides a similar performance to existing tube bundle absorber in heat and mass transfer. As a result, the heat and mass transfer characteristics of helical type absorber showed the possibility of the reduction in size and weight of small] capacity absorption chiller/heater.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.16 no.4
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• pp.281-292
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• 2016

The proposed scheme is based on the modified perturb and observe (P&O) algorithm combined with the sliding mode technique. A modified P&O algorithm based sliding mode controller is developed to study the effects of partial shade, temperature, and insolation on the performance of maximum power point tracking (MPPT) used in photovoltaic (PV) systems. Under partially shaded conditions and temperature, the energy conversion efficiency of a PV array is very low, leading to significant power losses. Consequently, increasing efficiency by means of MPPT is particularly important. Conventional techniques are easy to implement but produce oscillations at MPP. The proposed method is applied to a model to simulate the performance of the PV system for solar energy usage, which is compared to the conventional methods under non-uniform insolation improving the PV system utilization efficiency and allowing optimization of the system performance. The modified perturb and observe sliding mode controller successfully overcomes the issues presented by non-uniform conditions and tracks the global MPP. Compared to MPPT techniques, the proposed technique is more efficient; it produces less oscillation at MPP in the steady state, and provides more precise tracking.

• Nuclear Engineering and Technology
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• v.29 no.3
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• pp.229-239
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• 1997

To investigate the realistic behavior of mass and energy release and resultant containment response during large break Loss of Coolant accident (LOCA), analyses are performed for Yonggwang (YGN) 3&4 nuclear power plants by using a merged version of RELAP5/CONTEMPT4 computer code. Comparative analyses by using conservative design computer codes are also peformed. The break types analyzed are the double-ended guillotine breaks at the cold leg and hot leg. The design analysis resulted in containment peak pressure during post-blowdown phase for the cold leg break. However, the RELAP5/CONTEMPT4 analyses show that the containment pressure has a peak during blowdown phase, thereafter it decreases monotonously without the second port-blowdown peak. For the hot leg break, revised design analysis shows much lower pressure than that reported in YGN 3&4 final safety analysis report. The RELAP5/CONTEMPT4 analysis shoos similar trend and confirmed that the bypass flow through the broken loop steam generator during post-blowdown is negligibly small compared to that of cold leg break. The low pressure and temperature predicted tv realistic analysis presented in this paper suggest that the design analysis methodology contains substantial margin and it can be improved to provide benefit in investment protection, such as, relaxing plant technical specifications and reducing containment design pressure.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.5
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• pp.432-438
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• 2003

This paper describes a modified Roebuck compression device as a potential compression device of a rotating cryogenic refrigeration system in superconducting machine such as generator or motor. The conventional cryogen transfer method from stationary refrigeration system to rotating system can be eliminated by an on-board cryogenic refrigeration system that utilizes well-designed multi-stage modified Roebuck compression device. This paper shows basic thermodynamic analysis of modified Roebuck compression device and its application for compressing neon at 77 K with substantial pressure ratio when the rotor diameter is 0.8 m with rotating speed of 3600 rpm. The device does not require any moving part in rotating frame, but two separate thermal reservoirs to convert thermal energy into mechanical compression work. The high temperature thermal reservoir is atmospheric environment at 300 K and the low temperature thermal reservoir is assumed as a liquid nitrogen bath at 77 K. The concept of the compression device in this paper demonstrates its usefulness of generating high-pressure neon at 77 K for rotating J-T neon refrigeration cycle of superconducting rotor.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2524-2527
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• 2007

Solid propellant gas generators (SPGG) play a role as a turbopump starter in liquid propellant propulsion systems by supplying pressurized gas to power turbines for engine start. For such a purpose, the propellants should burn with a relative low flame temperature and the combustion gas should not contain corrosive constituents such as chlorine compounds. In accordance with these requirements, stabilized AN-based propellants have been usually used as the most appropriate oxidizer for propellant compositions. However, the burning area of the propellant intends to increase to satisfy the required mass flux because of its low burning rate. Consequently the burning area incensement brings on the SPGG size augmentation. A flow restriction such as filters is applied to decrease the SPGG size by rising up the combustion pressure resulting in increasing the burning rate. The feasibility of the size reduction of SPGG by the employment of filters have been studied. The preliminary results of this study show that the considerable reduction of SPGG size would be achievable just by installing a filter with relatively high pressure loss coefficient.