• Proceedings of the KWS Conference
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• 2002.10a
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• pp.396-401
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• 2002

A practical method for evaluating the possibility of the occurrence of cracking in actual thick-plate T-joint weldments is presented in this study. Systematic experiments based on the method of the design of experiment are conducted in order to investigate the crack tendency in relation to typical welding parameters such as diffusible hydrogen, restraint intensity, preheating temperature and so on. The elastic analysis using the [mite element techniques is employed to quantify the restraint intensities of the specimens. The defined restraint intensities are treated in numerical way for the sake of considering the most uncertain factor among some major factors that govern the cracking phenomena due to welding. The critical plane for judgment of the crack occurrence or crack density is presented as a function of typical welding parameters including determined restraint intensities. The results of numerical estimation by the proposed method for the experimental specimens show the usefulness as a practical tool in welding induced crack problem having extensive uncertainties.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.74-77
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• 2009

Ignition performance tests were performed to develop a catalytic ignitor which used hydrogen peroxide and kerosene. Ignition characteristics were investigated by exit area of the catalytic bed, shape of kerosene injector and lead time of purge gas. The results showed that exit area of catalytic bed must be enough for non chocking condition and kerosene must be sprayed with swirl in the middle of catalytic bed. Also in case without preheating of catalytic bed, hydrogen peroxide must be leaded by 3sec, and purge gas must be supplied simultaneously or lately with kerosene.

• KIEAE Journal
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• v.5 no.2
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• pp.19-26
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• 2005

Every site has a different given geometrical and climatic condition, which influenced not only the lifestyle of the humanbeings but also the regional architecture. For example, on a cold region, the reduction of the energy loss is necessary, like an igloo, which has a littlest energy loss at hemisphere. Or on a warm region, the house must be protected thermally from the overheating at the sunshining. like a huge shading. An architectural interpretation in the (extreme) moderate climate, like Korea, has always tried to satisfy the both opposite demands simultaneously. A facade, which divides out- and inside, has an ideal position to lead the regulated regional climatic conditions into the room. The Double Facade System(DFS) is well known as an innovative solution in the european countries, like Germany. It provides an reasonable alternative, which can achieve these goals at the same time. A Double Facade System provides an effective sunshade, which means a cooling energy reduction at the warm season. In addition, it enables a natural ventilation at the cold season with the preheating at the system as well as spring and autumn. An ordinary Single Facade System with a inside or outside sun blind provides a solution just for a specified season, like a summer or winter. But the Double Facade System can deal with the various climatic conditions in the moderate climate.

• Journal of the Korean Ceramic Society
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• v.34 no.4
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• pp.343-350
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• 1997

To fabricate the ceramic/metal(SiC/ Al alloy) composite, SiC preform was prepared by Pressureless Powder Packing Forming Method and 6061 Al alloy was infiltrated into the preform. Uniform compact having an average pore size of 10 ${\mu}{\textrm}{m}$ and narrow pore size distribution was prepared. Phenolic resin solution(40 wt%) was penetrated into the SiC compact, and then the compact was preheated at the temperature of 120$0^{\circ}C$. The pore size distribution and the microstructure of the preform were not changed by preheating. An uniform microstructure without any crack in the preform was obtained in SiC-Al alloy composite. The infiltration of 6061. Al alloy into the preform began at the temperature of 130$0^{\circ}C$ and the amount of infiltration increased in proportion to the infiltration temperature and the soaking time. The increasement rate of the infiltration amount decreased after 3 h. As a result of the infiltration at 140$0^{\circ}C$ for 4 h, Al alloy was well distributed in the interparticle channels and the relative density of the composite was above 98%. The strength and the fracture toughness of the composite were 303 MPa and 21.65 MPam1/2, respectively.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.4
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• pp.481-488
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• 1998

In recently, lots of researcher have been attached to develope various alternative fuels and to use renewable fuels for solution of the exhaust emission problems. In this study, the usability of used vegetable oil as alternative fuel for diesel engines has been investigated. This paper was compared with the exhaust emissions and performance in diesel engine with used vegetable oil and conventional diesel fuel. Since the vegetable oil includes oxygen of about 10%, it influenced the combustion process strongly. So, the smoke emissions of used vegetable oil were exhausted to be lower than those of diesel fuel. Also, the used vegetable oil was much the same cycle to cycle variation with diesel fuel except $P_{(dP}$d.theta.)max/, but the cycle to cycle variation of used vegetable oil was reduced significantly by preheating of the fuel and swirling of the intake air. It was concluded that used vegetable oil could be utilized effectively as renewable fuel for diesel engine.e.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.65-70
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• 2001

OH radical and NOx have been measured in a methane-air partially premixed flame using PLIF technique to define preheated air combustion characteristics. The temperature of mixture is determined by 300K, 400K, 600K and 800K below the auto-ignition temperature respectively. Flame height increases as equivalence ratio increased. As initial enthalpy is supplied, the radius of flame was increased and much amount of yellow flame in rich equivalence ratio was observed. This is due to the faster burning velocity. Also initial oxidization begins earlier as the initial temperature of mixture increased. It means that height of premixed flame front decreased. This phenomenon can be observed OH PLIF image. The qualitative analysis of OH concentration in the PLIF image shows that overall OH concentration increases with equivalence ratio and the initial temperature of mixture increased. At the preheating temperature goes up, axial gradient of OH concentration is less steep than that of lower temperature condition. This may identify that combustion reacts continuously, so preheated air combustion can evade the local heating and make high temperature indiscriminately in the overall reaction zone.

• Journal of the Korean Society for Precision Engineering
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• v.31 no.2
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• pp.119-123
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• 2014

Recently, laser processing technologies have been developed in many different industrial fields. The laser processing technologies are widely being applied such as laser assisted machining, cladding, heat treatment and coating. In the laser modules of the laser assisted machining system, laser lens is very important for accuracy and productivity of product. As the laser beam size, shape and focusing distance change, heat input energy of preheating point can be changed, the laser module of the laser assisted machining system should be equipped with various lenses differing beam size, beam shape and focusing distance. In this study, the rotary and linear laser modules are suggested. The finite element analysis is carried out to certify the static and dynamic stabilities of the developed laser modules. Finally, the rotary and linear laser modules have been fabricated successfully using the analysis results.

• Journal of Welding and Joining
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• v.20 no.4
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• pp.517-524
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• 2002

An overlaying of the seating surfaces of engine valves by OAW, GTAW or PTA weldings are common practice. The OAW method of a lower torch energy density compared to GTAW and PTA methods produces smoother deposits but the pain size at the vicinity of the interface is increased remarkably up to $30~50{\mu\textrm{m}}$ (that of base metal is about $10\mu\textrm{m}$). It's grain coarsening and the solute dilution are related to the decarburizing during OAW could be minimized by reducing the preheating temperature and by maintaining the carbide precipitates in base metal prior to welding. The formation of columnar structures and carbide precipitation zone in the vicinity of the GTAW welded interface, because of the high heat concentration, causes weakened zone on the valve seat face. The width of the reaction boundary zone is about $50\mu\textrm{m}$ for PTA and GTAW overlaying, and about $150\mu\textrm{m}$ for OAW welding. The smaller width of the reaction boundary zone is the less the solute-dilution rate. Thereby PTA welding may be recommended for overlaying of the seating surfaces.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.1112-1113
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• 2015

In the end of 2014, Changwon National University and TECHSTEEL Co., Ltd. had initiated a project on the development of a 300 kW-class HTS DC Induction Furnace(HTS DC IF) for preheating non-ferrous metal billets funded by the Korea Institute of Energy Technology Evaluation and Planning for 3 years. This is the one of the most realistic commercial machines applying the coated conductors. In this paper, the development progress of a 300 kW-class HTS DC IF was introduced. The major characteristics of the furnace including its capacity, structure and operation scheme were presented. For ensuring the successful design, a pre-validation study was performed through the electromagnetic, heat transfer and solid mechanical analysis using a multi-physics FEM tool. The aluminum billet was heated up to $540^{\circ}C$ under 1 T of the magnetic flux density at the center of the billet, and the simulation results were described in detail.

• Journal of the Korean Society of Safety
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• v.32 no.2
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• pp.7-13
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• 2017

An experimental study was conducted to identify the quantitative measurement bias for the bare-bead thermocouple (TC), which was widely used for measuring temperature in fire experiments. To this end, an apparatus could be controlled individually gas flow rate, preheating temperature and incident radiative heat flux was developed to simulate the thermal environments of fire. A relative measurement bias of bare-bead TC was evaluated with the comparison of double-shield aspirated TC. As a result, the relative measurement bias of bare-bead TC was gradually increased with the increase in radiative heat flux with constant gas temperature. The relative bias was also significantly increased with the decrease in gas temperature. Quantitatively, at the gas temperature of $20^{\circ}C$, the bare-bead TC had the relative bias of approximately 400% with the radiative heat flux of $20kW/m^2$ corresponding to thermal radiation level of the flashover. The present study was intend to provide fire researchers with methodologies for the reanalyses of temperature measured using bare-bead TC, radiation corrections, and validation of fire modeling.