• 제목/요약/키워드: Transfer resistance

검색결과 1,288건 처리시간 0.035초

온침소재의 열전달특성에 관한 연구 (Study on the Heat Transfer Characteristics of Warm Needle Materials in Korean Medicine)

  • 여수정;정지현;김영곤;구성태;이민규;임사비나
    • Korean Journal of Acupuncture
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    • 제31권3호
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    • pp.125-135
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    • 2014
  • Objectives : Warm needling is the method combining the effects of acupuncture and moxibustion. In modern clinics, warm needling is only affected by treatment time or frequency. We need to study the physical characteristics of warm needles currently used in clinics in order to develop more efficient and economical treatments. Methods : We collected various warm needle specimens and analyzed chemical constitutions, measured heat transfer velocity, micro Vicker's hardness and specific resistance. We studied the relationship between heat transfer velocity and micro Vicker's hardness as well as that between heat transfer velocity and specific resistance. Results : The heat transfer velocity of the Silver_HL was 3.3 mm/sec, of the Au alloy group was 1.3~2.6 mm/sec, and Silver_IN, Silver_ZK and SS groups was less than 0.3 mm/sec. We therefore concluded that the needle composed of Ag has the best heat transfer velocity. In the Micro Vicker's hardness test, Vicker's hardness of the Au alloy group was 159~170 Hv, of Silver_HL was 181 Hv, and of the Silver_IN, Silver_ZK, SS group was 450.8~519 Hv. In the Silver_IN, Silver_ZK and SS groups, hardness was inversely proportial to thermal conductivity. In the specific resistance test, the specific resistance of Silver_HL was the lowest, that of the Au alloy group was the second lowest, and that of the Silver_IN, Silver_ZK, SS groups were the highest. Conclusions : We concluded that the needle composed of Ag has the best heat transfer velocity, highest electric conductivity and thermal conductivity, therefore the needle composed of Ag is suitable for warm needling.

관 내부 냉매비등이 있는 수직관 외부 얼음 형성 연구 (Ice Formation on the Outer Surface of a Vertical Tube with Inside Refrigerant Boiling)

  • ;이근식
    • 대한기계학회논문집B
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    • 제35권2호
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    • pp.129-135
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    • 2011
  • 얼음 제조와 잠열 저장 등에서 수직관 내부를 저온의 냉매를 흘려, 관 외부의 물을 얼리는 과정에서 내부 냉매의 비등열저항과 외부 얼음열저항이 얼음형성에 미치는 영향에 대하여 조사되었다. 상변화 및 비등 열전달 관계식들이 도입되어 얼음두께와 관련변수들이 해석되었으며, 작동유체로는 냉매 22 와 냉매 134a가 사용되었다. 이들의 건도는 0-0.8 범위이다. 해석결과, 최초 약 30 분까지는 내부냉매의 대류저항이 얼음의 전도저항에 비하여 높으나, 그 이후 얼음의 두께 증가에 따른 얼음전도저항의 현저한 증가로 인하여 냉매에 공급되는 열플럭스가 감소되므로 냉매 측 건도와 비등 및 대류열전달계수도 현저히 감소함을 알 수 있었다. 냉매 22 는 대류열전달계수가 냉매 134a 보다 높아서 단위 면적 당 더 많은 얼음을 생성할 수 있음을 알 수 있었다.

원통형 다전극식 정전용량-전기전도도 센서를 이용한 연료전지 차량용 냉각수의 유전특성 평가 (Evaluation about Dielectric Property of Heat Transfer Fluids for Fuel Cell Vehicle using Cylindrical Multi-Terminal Capacitive-Conductive Sensor)

  • 김재훈;김주한;김윤형;최강월;한상옥;용기중
    • 전기학회논문지
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    • 제59권6호
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    • pp.1087-1094
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    • 2010
  • We have developed a cylindrical multi-terminal capacitive-conductive sensor that could be attached to the internal surface of cooling system pipe to evaluate capacitance and conductivity of heat transfer fluid. It was used as measuring system to diagnose insulating condition, by which was kept a insulating resistance of inner stack and at the same time was cooled electrochemical heat of reaction of FCEV(fuel cell electric vehicle) stack that used a compressed hydrogen gas reacting with oxygen in accordance with variation on thermal degradation of nonconductive heat transfer fluid. Also to assess diagnosis characteristics of heat transfer fluid, i.e. coolant, we have performed accelerated aging test using developed sensor attached to cooling system. Consequently, it was measured dielectric and electric resistance of coolant to estimate and analyse for dielectric properties by degradation condition.

Temperature Dependent Behavior of Thermal and Electrical Contacts during Resistance Spot Welding

  • Kim, E.
    • International Journal of Korean Welding Society
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    • 제2권1호
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    • pp.1-10
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    • 2002
  • The thermal contact conductance at different temperatures and with different electrode forces and zinc coating morphology was measured by monitoring the infrared emissions from the one dimensionally simulated contact heat transfer experiments. The contact heat transfer coefficients were presented as a function of the harmonic mean temperature of the two contacting surfaces. Using these contact heat transfer coefficients and experimentally measured temperature profiles, the electrical contact resistivities both for the faying interface and electrode-workpiece interface were deduced from the numerical analyses of the one dimension simulation welding. It was found that the average value of the contact heat transfer coefficients for the material with zinc coating (coating weight from 0 g/$mm^2$to 100 g/$mm^2$) ranges from 0.05 W/$mm^2$$^{\circ}C$ to 2.0 W/$mm^2$$^{\circ}C$ in the temperature range above 5$0^{\circ}C$ harmonic mean temperature of the two contacting surfaces. The electrical contact resistivity deduced from the one dimension simulation welding and numerical analyses showed that the ratio of electrical contact resistivity at the laying interface to the electrical contact resistivity at the electrode interface is smaller than one far both bare steel and zinc coated steel.

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Shear behavior of exposed column base connections

  • Cui, Yao
    • Steel and Composite Structures
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    • 제21권2호
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    • pp.357-371
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    • 2016
  • Column base connections are critical components in steel structures because they transfer axial forces, shear forces and moments to the foundation. Exposed column bases are quite commonly used in low- to medium-rise buildings. To investigate shear transfer in exposed column base plates, four large scale specimens were subjected to a combination of axial load (compression or tension) and lateral shear deformations. The main parameters examined experimentally include the number of anchor rod, arrangement of anchor rod, type of lateral loading, and axial force ratio. It is observed that the shear resisting mechanism of exposed column base changed as the axial force changed. When the axial force is in compression, the resisting mechanism is rotation type, and the shear force will be resisted by friction force between base plate and mortar layer. The specimens could sustain inelastic deformation with minimal strength deterioration up to column rotation angle of 3%. The moment resistance and energy dissipation will be increased as the number of anchor rods increased. Moreover, moment resistance could be further increased if the anchor rods were arranged in details. When the axial force is in tension, the resisting mechanism is slip type, and the shear force will be resisted by the anchor rods. And the shear resistance was reduced significantly when the axial force was changed from compression to tension. The test results indicated that the current design approach could estimate the moment resistance within reasonable acceptance, but overestimate the shear resistance of exposed column base.

축력비 조건에 따른 철근콘크리트기둥의 내화성능에 관한 연구 (A Study on the Fire Resistance Performance of Reinforced Concrete Columns according to Axial Load Ratio)

  • 황규재;조범연;여인환
    • 한국화재소방학회논문지
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    • 제27권6호
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    • pp.26-31
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    • 2013
  • 본 연구의 목적은 성능적 내화설계를 기반으로 한 철근콘크리트 기둥의 내화성능 평가를 최종 목표로 철근콘크리트 기둥의 열전달 해석을 통한 온도분포와 재하가열실험을 통한 수축량으로 적정 축력비를 도출하여 성능설계를 위한 기초 자료로 활용하고자 하는데 있다. 편심이 전혀 없는 순수축력을 기준으로 축력비 0.30, 0.35, 0.40, 0.47을 재하한 결과, 0.40 이상의 축력비를 확보하여야 내화성능을 만족할 수 있다고 판단하였다.

Thermal characteristics of defective carbon nanotube-polymer nanocomposites

  • Unnikrishnan, V.U.;Reddy, J.N.;Banerjee, D.;Rostam-Abadi, F.
    • Interaction and multiscale mechanics
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    • 제1권4호
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    • pp.397-409
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    • 2008
  • The interfacial thermal resistance of pristine and defective carbon nanotubes (CNTs) embedded in low-density polyethylene matrix is studied in this paper. Interface thermal resistance in nanosystems is one of the most important factors that lead to the large variation in thermal conductivities in literature and the novelty of this paper lies in the estimation of the interfacial thermal resistance for defective nanotubes-systems. Thermal properties of CNT nanostructures are estimated using molecular dynamics (MD) simulations and the simulations were carried out for various temperatures by rescaling the velocities of carbon atoms in the nanotube. This paper also deals with the mesoscale thermal conductivities of composite systems, using effective medium theories by considering the size effect in the form of interfacial thermal resistance and also using the conventional micromechanical methods like Hashin-Shtrikman bounds and Wakashima-Tsukamoto estimates.

단순 선형열원 모델을 이용한 지중 유효 열전도도와 보어홀 유효 열저항 산정 (Evaluation of Ground Effective Thermal Conductivity and Borehole Effective Thermal Resistance from Simple Line-Source Model)

  • 손병후
    • 설비공학논문집
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    • 제19권7호
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    • pp.512-520
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    • 2007
  • The design of a ground-source heat pump system includes specifications for a ground loop heat exchanger where the heat transfer rate depends on the effective thermal conductivity of the ground and the effective thermal resistance of the borehole. To evaluate these heat transfer properties, in-situ thermal response tests on four vertical test boreholes with different grouting materials were conducted by adding a monitored amount of heat to circulating water. The line-source method is applied to the temperature rise in an in-situ test and extended to also give an estimate of borehole effective thermal resistance. The effect of increasing thermal conductivity of the grouting materials from 0.818 to $1.104W/m^{\circ}C$ resulted in overall increases in effective thermal conductivity by 15.8 to 56.3% and reductions in effective thermal resistance by 13.0 to 31.1%.

A Study on the Heat Transfer Enhancement of Miniature loop Heat Pipes by Using the Cu Nanofluids

  • Kim, Young-Sik;Jeong, Hyo-Min;Chung, Han-Shik;Tanshen, Md.Riyad;Lee, Dae-Chul;Ji, Myoung-Kuk;Bae, Kang-Youl
    • 동력기계공학회지
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    • 제17권2호
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    • pp.70-77
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    • 2013
  • An experimental study was carried out to understand the heat transfer performance of a miniature loop heat pipes using water-based copper nanoparticles suspensions as the working fluid. The suspensions consisted of deionized water and copper nanoparticles with an average diameter of 80 nm. Effects of the cupper mass concentration and the operation pressure on the average evaporation and condensation heat transfer coefficients, the critical heat flux and the total heat resistance of the mLHPs were investigated and discussed. The pressure frequency also depends upon the evaporator temperature which has been maintained from $60^{\circ}C$ to $90^{\circ}C$. The Investigation shows 60% filling ratio gives the highest inside pressure magnitude of highest number pressure frequency at any of setting of evaporator temperature and 5wt% results the lowest heat flow resistance.

Investigation of contact resistance between metal electrodes and amorphous gallium indium zinc oxide (a-GIZO) thin-film transistors

  • Kim, Woong-Sun;Moon, Yeon-Keon;Lee, Sih;Kang, Byung-Woo;Kwon, Tae-Seok;Kim, Kyung-Taek;Park, Jong-Wan
    • 한국정보디스플레이학회:학술대회논문집
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    • 한국정보디스플레이학회 2009년도 9th International Meeting on Information Display
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    • pp.546-549
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    • 2009
  • In this paper, we investigated the effects of different source/drain (S/D) electrode materials in thin film transistors (TFTs) based on indium-gallium-zinc oxide (IGZO) semiconductor. A transfer length and effective resistances between S/D electrodes and amorphous IGZO thin-film transistors were examined. Intrinsic TFT parameters were extracted by the transmission line method (TLM) using a series of TFTs with different channel lengths measured at a low drain voltage. The TFTs fabricated with Cu S/D electrodes showed the lowest contact resistance and transfer length indicating good ohmic characteristics, and good transfer characteristics with a field-effect mobility (${\mu}_{FE}$) of 10.0 $cm^2$/Vs.

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