• Title/Summary/Keyword: External Heat Input

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Analytical Study of heat Transfer in Evaporative Cooling of a Porous Layer (다공층의 증발냉각 열전달에 관한 해석적 연구)

  • 김홍제;이진호
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.16 no.1
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    • pp.104-111
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    • 1992
  • In this study, the heat transfer characteristics of the evaporative transpiration cooled system is analytically investigated considering the occurrence of the two-phase evaporation zone. Under the condition of the external heat input, analytical solutions of the three regions (i.e., vapor, liquid and two-phase evaporation zone) are respectively obtained using the matching conditions for the steady-state problem where properties are constant. As results, the length of the evaporation zone increases with increasing heat input and with decreasing mass flow rate. It also increases with increasing particle size, system porosity, thermal conductivity of material, inlet temperature and latent heat of coolant. The position of the lower interface of the evaporation zone have a lot of efforts on the evaporation zone length, the position of the upper interface penetrates deeper into the porous layer with lower thermal conductivity of porous material, higher system porosity and larger particle size.

CONE CALORIMETER STUDIES OF WOOD SPECIES

  • Grexa, Ondrej;Horvathova, Elena;Osvald, Anton
    • Proceedings of the Korea Institute of Fire Science and Engineering Conference
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    • 1997.11a
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    • pp.77-84
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    • 1997
  • Cone calorimeter measurements can be used for the calculation of effective material properties, which can be used as input parameters in modeling of fire. Main parameter measured in Cone calorimeter is heat release rate. Some other parameters as time to ignition, effective heat of combustion, mass loss rate or total heat released is also measured in Cone calorimeter. Total heat released is important from the point of view of total energy available in material in Fire situation. Cone calorimeter. measurements were done on several wood species (oak, beech, spruce, poplar). Measurements were provided at external irradiances 30, 50 and 65 ㎾/$m_2$ in horizontal orientation. Heat release rate data were evaluated and compared as a function of external irradiance for various species of wood. furthermore the influence of external irradiance on effective heat of combustion and total heat release was also evaluated for the period of flame combustion.

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Analysis of unsteady temperature distribution in a cylinder for rifle barrel disign (원통형 용기의 비정상온도해석)

  • ;;;Lee, Hung Joo
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.3 no.4
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    • pp.173-180
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    • 1979
  • Temperature distriburion in a hollow chlinder has been analyzed mathematically. Unsteady condition considered assumed a constant heat flux input from the inside. The results are compared with experimental results of surface temperature rise of a gun barrel during continuous firing. Their agreements are acceptable. Effects of various dimensionless parameters on the surface temperature rise are discussed. For small Biot numbers, the external survface temperature approaches more rapidly to the steady temperature. Temperature difference between internal and external surfaces becomes greater for small Biot number. Steady solution assumed that the gas temperature inside the cylinder varies periodically. Relative amplitude and phase angles between the gas temperature and the internal or external surface temperature are obtained. Phase angles become smaller for large radiancy of gas temperature variation, small external Biot number, or large internal biot number. Relative amplitudes become samller as radiancy of gas temperature variation and internal Biot number become smaller. or external Biot number becomes larger. The solution obtained in this paper can be applied to gun barrels, heat pipes used in heat excangers, and reciprocation engines.

Burning Characteristics of Wood-based Materials using Cone Calorimeter and Inclined Panel Tests

  • Park, Joo-Saeng;Lee, Jun-Jae
    • Journal of the Korean Wood Science and Technology
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    • v.30 no.3
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    • pp.18-25
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    • 2002
  • Research to discuss the fire performance of materials requires tools for measuring their burning characteristics and validated fire growth models to predict fire behavior of the materials under specific tire scenarios using the measured properties as input for the models. In this study, burning characteristics such as time to ignition, weight loss rate, flame spread, heat release rate, total heat evolved, and effective heat of combustion for four types of wood-based materials were evaluated using the cone calorimeter and inclined panel tests. Time to ignition was affected by not only surface condition and specific gravity of the tested materials but also the type and magnitude of heat source. Results of weight loss rate, measured by inclined panel tests, indicated that heat transfer from the contacted flame used as the heat source into the inner part of the specimen was inversely proportional to specific gravity of material. Flame spread was closely related with ignition time at the near part of burning zone. Under constant and severe external heat flux, there was little difference in weight loss rate and total heat evolved between four types of wood-based panels. More applied heat flux caused by longer ignition time induced a higher first peak value of heat release rate. Burning characteristics data measured in this study can be used effectively as input for fire growth models to predict the fire behavior of materials under specific fire scenarios.

Fabrication and Characteristics Test of Micro Heat Pipe Array for IC Chip Cooling (IC 칩 냉각용 초소형 히트 파이프의 제작 및 성능 평가)

  • 박진성;최장현;조형철;조한상;양상식;유재석
    • The Transactions of the Korean Institute of Electrical Engineers C
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    • v.50 no.7
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    • pp.351-363
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    • 2001
  • This paper presents an experimental investigation on the heat trensfer characteristic of micro pipe (MHP) array with 38 triangular microgrooves. A heat pipe is an effective heat exchanger operating without external power. The heat pipe transfers heat by means of the latent heat of vaporization and two-phase fluid flow driven by the capillary force. The overall size of the MHP array can be put undermeath a microelectonic die and integrated into the electrronic package of a microelectronin device to dissipate the heat from the die. The MHP array is fabricated by micromachining with a silicon wafer and a glass substrate. The MHP was filled with water and sealed. The experimental results show the temperature decrease of 12.1$^{\circ}C$ at the evaporator section for the input power of 5.9 W and the improvement of 28% in the heat transfer rate.

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STUDY ON THE EFFECT OF RESIDUAL STRESS ON THE EXTERNALLY LOADED WELDED STRUCTURE

  • Rajesh S.R.;Bang Han Sur;Joo Sung Min;Kim In Sik
    • Proceedings of the KWS Conference
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    • v.43
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    • pp.58-60
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    • 2004
  • In the field of welding the behavior of a welded structure under consideration may be predicted via heat transfer and residual stress analysis. In order to facilitate the industrial applications of welding, numerical modeling of heat transfer and residual stress in weldment has been carried out applying Finite Element Method (FEM) and the analysis with the external load including this residual stress due to welding has been done. The present work includes the specialized finite element codes for the calculation of nonlinear heat transfer details and residual stress redistributed along with the external load in the welded structures. A basic interface, which allows models, built in commercial preprocessing package access to the data necessary to build standard input decks for these specialized FEM codes, which are not supported by commercial package. The results from the FEM codes are imported back into commercial package for visualization. In addition the residual stress values are exported to commercial package (such as ANSYS, PATRAN etc.) for further analysis with the external loads, which make the FEM codes fully applicable to the industrial purpose.

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A Study on the Characteristics of Repair Welding for Mold Steel using Continuous Wave Nd:YAG Laser (연속파형 Nd:YAG 레이저를 이용한 금형강의 보수용접 특성에 관한 연구)

  • Yoo, Young-Tae;Shin, Ho-Jun
    • Journal of the Korean Society for Precision Engineering
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    • v.27 no.11
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    • pp.7-16
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    • 2010
  • In this study, wire was used as the filler material for the laser repair welding, and the phenomenon in which the supplied filler material was melted and beaded down into the specimen was examined with varying laser powers and welding speeds. The optimal processing condition was found to be the laser power of 1,300 W, the welding speed and feed wire supply speed of 0.5 ml/in and the defocused distances of +2mm. At this time, the heat input(E) was $65{\sim}75\;J/mm^2$, and no internal defect occurred. When repair welding was carried out as the optimal processing for the part that had an external defect with the radius of 2mm, the filler metal was melted, resulting in the volume smaller than the defect part and thus causing the part unfilled. Therefore, it was found to be necessary to carry out repair welding two to three times by multiple passes rather than does it only once by single pass.

A Study on Welding Distortion and Residual Stress for Tubular Welded Joint (튜브 용접부의 용접변형 및 잔류응력에 관한 연구)

  • Jin, Hyung-Kook;Shin, Sang-Beom;Lee, Dong-Ju;Park, Dong-Hwan
    • Journal of Welding and Joining
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    • v.30 no.5
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    • pp.51-56
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    • 2012
  • The purpose of this study is to evaluate the distortion and the residual stress of GTA tubular welds between tube and head. In order to do it, the heat input model for GTA welding process was first developed by experiment and FE analyses. The welding distortion and the residual stress distribution of the tubular welds according to welding pass and various restraint degrees were evaluated by using FEA with the heat input model. From FEA results, it was found that the residual stress and the radial distortion at the weld toe of tube part decrease with a decrease in the number of welding pass. However, the maximum residual stresses in each direction of tubular welds are almost constant regardless of the external restraint degree. It was mainly due to the high internal restraint of the welds.

Characteristics of Hot-Film Type Micro-Flowsensors Fabricated on SOI Membrane and Trench Structures (SOI 멤브레인과 트랜치 구조상에 제작된 발열저항체형 마이크로 유량세선의 특성)

  • 정귀상;김미목;남태철
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.14 no.8
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    • pp.658-662
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    • 2001
  • This paper describes on the fabrication and characteristics of hot-film type micro-flowsensors integrated with Pt-RTD(resistance thermometer device) and micro-heater on the SOI(Si-on-insulator) membrane and trench structures, in which MGO thin-film was used as medium layer in order to improve adhesion of Pt thin-film to SiO$_2$ layer. Output voltages increased due to increase of heat-loss from sensor to external. The output voltage was 250 nV at N$_2$ flow rate of 2000 sccm/min, heating power of 0.3 W. The response time($\tau$:63%) was about 42 msec when input flow was step-input. The results indicated that micro-flowsensors with the SOI membrane and trench structures have properties of a high-resolution and ow consume power.

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Fabrication of Micro-heaters Using MgO as Medium Layer and It`s Application for Micro-Flowsensors (매개층 산화마그네슘막을 이용한 백금박막 미세발열체의 제작과 마이크로 유량센서에의 응용)

  • 홍석우;조정복;정귀상
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 1999.11a
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    • pp.358-361
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    • 1999
  • This paper describes on the fabrication and characteristics of hot-film type micro-flowsensors integrated with Pt-RTD\`s and micro-heater on the Si substrate, in which MgO thin-films were used as medium layer in order to improve adhesion of Pt thin-films to SiO$_2$ layer The MgO layer improved adhesion of Pt thin-films to SiO$_2$` layer without any chemical reactions to Pt thin-films under high as gas flow rate and its conductivity increased due to increase of heat-loss from sensor to external. Output voltage was 82 mV at N2 flow rate of 2000 sccm/min, heating power of 1.2W. The respons time was about 100 msec when input flow was step-input

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