• Title/Summary/Keyword: Heat Input

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A Study on temperature behavior of pulsating heat pipe with different diameter in evaporator (증발부 내경 변화에 따른 진동형 히트파이프의 온도 거동에 관한 연구)

  • Kim, Jihoon;Park, Chulwoo;Shah, Syed Abdullah;Kim, Daejoong
    • Journal of the Korean Society of Visualization
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    • v.17 no.1
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    • pp.10-18
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    • 2019
  • In this study, the temperature behavior of Pulsating Heat Pipe (PHP) according to the diameter change were studied by limiting the diameter change to only the evaporator. To investigate operation of PHP in various heat input, heat input power was increased from 10 to 120 W. The results show operation can be divided into 3 regimes by temperature behavior. Thermal resistance was increased before start-up and decreased with increasing heat input. At 110 W heat input, thermal conductivity of 2 mm PHP was 8 .times higher compare to thermal conductivity of copper. Further, to investigate details of temperature behavior in higher heat input, FFT analysis was conducted. Based on the results, when the deviation of peak frequency in each section is lowest, the thermal resistance has lowest value.

Evaporation Cooling of Droplet due to Surface Roughness under Radiative Heat Input Condition (복사가열조건에서 표면 거칠기에 따른 액적의 증발 냉각)

  • Bang Chang-Hoon;Kwon Jin-Sun;Yea Yong-Taeg
    • Journal of the Korean Society of Safety
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    • v.19 no.3
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    • pp.14-19
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    • 2004
  • The objective of the present work is to examine evaporation cooling of droplet due to surface roughness under radiative heat input condition. The surface temperatures varied from $80\~160^{\circ}C$ on aluminum alloy (AL 2024) and surface roughness was $0.18{\mu}m,\;1.36{\mu}m$. The results are as follows; Regardless of surface roughness under radiative heat input condition, as droplet diameter is larger, the in-depth temperature of solid decreases and evaporation time increases. In the case of $0.18{\mu}m\;and\;1.36{\mu}m$ of surface roughness, the larger the surface roughness is, the less the evaporation time is and the larger the temperature within the solid is. In the case of $Ra=0.18{\mu}m$ evaporation time and time averaged heat flux for radiative heat input case is shorter than for the conductive case.

A Study of Arc Modeling and Heat Input Distribution on the Surface during Torch Weaving in Gas Metal Arc Welding (가스 메탈 아크 용접에서 토치 위빙 중 아크 모델링 및 표면 입열 분포 해석에 관한 연구)

  • Kim, Yong-Jae;Rhee, Se-Hun
    • Journal of the Korean Society for Precision Engineering
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    • v.18 no.1
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    • pp.162-170
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    • 2001
  • In torch weaving in arc welding on V groove, the heat input distribution on groove surface is a main factor determining the bead shape and the weld quality with and without the weld defects such as undercut, overlap, etc. In this study, we calculate the heat input varying with the welding current, arc voltage, welding speed and the touch weaving condition using numerical method. And we investigate the heat input distribution on groove surface while applying the various grooves having 2 dimensional heat sources.

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The Arc Brazing by Variable Polarity AC Pulse MIG Welding Machine (극성가변 AC 펄스 MIG용접기를 이용한 아크 브레이징)

  • 조상명;공현상
    • Journal of Welding and Joining
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    • v.21 no.4
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    • pp.56-62
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    • 2003
  • MIG brazing is used for many parts without melting base metal because of high productivity. Pulsed MIG brazing can be used to further reduce heat input and to improve the process stability. However, a significant amount of zinc in galvanized sheet steel is burned off in the area of brazes. Therefore, the brazing method to reduce the heat input is needed. In the brazing for galvanized sheet steel, variable polarity AC pulse MIG arc brazing can be applied to more decrease the heat input by setting EN-ratio adequately. In this research, we studied for the variable polarity AC pulse MIG arc brazing to decrease the heat input by using ERCuSi-A wire. As the result of increasing EN-ratio, melting ratio of base metal and burning off of zinc were reduced in galvanized sheet steel.

Modeling of Welding Heat Input for Residual Stress Analysis (용접 잔류응력 해석을 위한 Heat Input Model 개발)

  • 심용래;이성근
    • Journal of Welding and Joining
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    • v.11 no.3
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    • pp.34-47
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    • 1993
  • Finite element models were developed for thermal and residual stress analysis for the specific welding problems. They were used to evaluate the effectiveness of the various welding heat input models, such as ramp heat input function and lumped pass models. Through the parametric studies, thermal-mechanical modeling sensitivity to the ramp function and lumping techniques was determined by comparing the predicted results with experimental data. The kinetics for residual stress formation during welding can be developed by iteration of various proposed mechanisms in the parametric study. A ramp heat input function was developed to gradually apply the heat flux with variable amplitude to the model. This model was used to avoid numerical convergence problems due to an instantaneous increase in temperature near the fusion zone. Additionally, it enables the model to include the effect of a moving arc in a two-dimensional plane. The ramp function takes into account the variation in the out of plane energy flow in a 2-D model as the arc approaches, travels across, and departs from each plane under investigation. A lumped pass model was developed to reduce the computation cost in the analysis of multipass welds. Several weld passes were assumed as one lumped pass in this model. Recommendations were provided about ramp lumping techniques and the optimum number of weld passes that can be combined into a single thermal input.

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Evaluation and Comparison of Weldabilities with Various Welding Processes on TMCP Steels (TMCP강의 용접 공정별 입열량에 따른 용접부 물성 평가 및 비교)

  • Choi, Chul Young;Ji, Chang Wook;Kim, Hyoung Chan;Nam, Dae-Geun;Kim, Joungdon;Kim, Soon Kook;Park, Yeong-Do
    • Journal of Welding and Joining
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    • v.32 no.1
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    • pp.6-14
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    • 2014
  • This paper has an aim to evaluate microstructure and fracture toughness of TMCP steel weldment applied for off-shore wind tower with the focus on the effect of heat input on the weldment with various welding processes; FCAW(13kJ/cm and 30kJ/cm), SAW(62kJ/cm), and EGW(177kJ/cm). Based on experimental results developed from this study, it was found that the impact toughness of top side for TMCP steel weldments with heat input up to 62 kJ/cm satisfied the required minimum value except the EGW(177kJ/cm). The heat input and microstructure are the main factors of impact toughness. The heat input of 13kJ/cm on back side with low heat input increased the amount of grain boundary ferrite which has low impact toughness, and heat input of 177kJ/cm on top side is significant enough to produce the austenite grain growth. The compositions and sizes of inclusions which are the dominant factors for the formation of acicular ferrite were analyzed by OM and EDS. As the heat input increased, the inclusions also grew and a nucleation site decreased. The size of nonmetallic inclusions and the crack width was nearly similar, therefore the inclusions were related with the crack propagation.

Effect of Welding Heat Input and PWHT Cooling Rate on Mechanical Properties of Welded Region at SAW of 1.25Cr-0.5Mo Steel for Pressure Vessel (압력용기용 1.25Cr-0.5Mo 강의 Submerged Arc Welding시 입열 및 PWHT 냉각속도가 용접부 기계적 성질에 미치는 영향)

  • Lee Dong-Hwan;Park Jong-Jin
    • Journal of Welding and Joining
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    • v.22 no.5
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    • pp.26-31
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    • 2004
  • In order to propose the optimum welding condition for field application, the effects of welding heat input and cooling rate at PWHT on the mechanical properties were investigated. Submerged arc welding of 1.25Cr-0.5Mo steel for pressure vessel was conducted at welding heat inputs of 15.2kJ/cm, 30.9kJ/cm, and 44.8kJ/cm, and cooling rates of 184$^{\circ}C$/hr, 55$^{\circ}C$/hr, and 2$0^{\circ}C$/hr at PWHT. From the test results, as the welding heat input increase up to 30.9kJ/cm, the changes of microstructure and impact toughness were small. At the heat input of 44.8kJ/cm, however, toughness decreased obviously due to the coarsening of coarse-grained HAZ and formation of ferrite at bainite grainboundary of weld metal. On the other hand, cooling rates at PWHT did not effect on the changes in microstructure and mechanical properties. Even though tensile strength and impact toughness at all welding conditions of this study were above the minimum specification requirement, it was confirmed that heat input of 30.9kJ/cm was the optimum welding condition to improve welding performance by higher heat input.

A STUDY ON THE FORMATION OF IMPERFECTIONS IN CW $CO_2$ LASER WELD OF DIAMOND SAW BLADE

  • Minhyo Shin;Lee, Changhee;Kim, Taiwoung;Park, Heedong
    • Proceedings of the KWS Conference
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    • pp.639-643
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    • 2002
  • The main purpose of this study was to investigate the formation mechanisms of imperfections such as irregular humps, outer cavity and inner cavity in the laser fusion zone of diamond saw blade. Laser beam welding was conducted to join two parts of blade; mild steel shank and Fe-Co-Ni sintered tip. The variables were beam power and travel speed. The microstructure and elements distributions of specimens were analyzed with SEM, AES, EPMA and so on. It was found that these imperfections were responded to heat input. Irregular humps were reduced in 10.4∼17.6kJ/m heat input range. However there were no clear evidences, which could explain the relations between humps formation and heat input. The number of outer cavity and inner cavity decreased as heat input was increased. Considering both possible defects formations mechanisms, it could be thought that outer cavity was caused by insufficient refill of keyhole, which was from rapid solidification of molten metal and fast molten metal flow to the rear keyhole wall at low heat input. More inner cavities were found near the interface of the fusion zone and sintered segment and in the bottom of the fusion zone. Inner cavity was mainly formed in the upper fusion zone at high heat input whereas was in the bottom at low heat input. Inner cavity was from trapping of coarsened preexist pores in the sintered tip and metal vapor due to rapid solidification of molten metal before the bubbles escaped.

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The Effect of Ferrite Ratio on the Properties of PWHT Overlaid Welds (Duplex SS 육성 용접부의 물성에 미치는 열처리전 페라이트 함량의 영향)

  • Seong, Hui-Jun;Kim, Yeong-Il;Seo, Chang-Gyo
    • Proceedings of the KWS Conference
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    • pp.294-296
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    • 2005
  • Several duplex overlaied-weldments which have different ferrite ratio were prepared by changing welding heat input ant post weld heat treatment were carried out to understand the effect of the ferrite ratio on the precipitation during post weld heat treatment. High heat input weldment indicated low ferrite ratio, while low heat input weldment has high ferrite ratio. Low ferrite ratio weldment showed much and faster precipitation. But high ferrite ratio weldment showed less and slower precipitation.

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Effects of Heat Input and Interpass Temperature on the Strength and Toughness of Multipass Weld Metal (철골 다층 용접금속 강도 및 인성에 미치는 입열 및 패스간 온도의 영향)

  • Byeon, Ji-Cheol;Bang, Guk-Su;Jang, Ung-Seong;Park, Cheol-Gyu;Jeong, U-Hyeon
    • Proceedings of the KWS Conference
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    • pp.162-164
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    • 2005
  • 570MPa grade weldable steels were $CO_{2}$ welded with various heat input and interpass temperature using flux cored wires. Effects of heat input and interpass temperature on the strength and toughness of weld metal were investigated and interpreted in terms of microstructural change, recovery of alloying elements, and the amount of reheated weld metal.

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