• 제목/요약/키워드: Thermal wave

검색결과 538건 처리시간 0.027초

자성 페라이트 용사피막의 전자파 차폐 특성 (Electromagnetic Wave Shield Characteristics of Thermal Sprayed Ferrite Coatings)

  • 정태식;김태형;박경채
    • Journal of Welding and Joining
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    • 제20권1호
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    • pp.76-82
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    • 2002
  • In these days, many advanced nations have enforced import restrictions against things emitting electromagnetic wave which has report that it is so harmful. In general, electromagnetic wave is composed of electric wave and magnetic wave. The reflection of electromagnetic wave is mainly reflected by conductive materials and the magnetism loss is generated by magnetic ferrite. The magnetism loss of ferrite is separated by eddy current loss, residual magnetism loss and hysteresis loss. Thermal sprayed coating is intended to manufacture because of simple processes and high efficient electromagnetic wave shielding. The high efficient thermal sprayed coatings were made from the magnetic ferrite materials that characterizes absorption of electromagnetic wave, and the electric conductive materials that characterize emitting of electromagnetic wave. This study was manufactured thermal sprayed coatings to improve absorption-efficiency, and measured the electromagnetic wave shielding efficiency. As the experimental results, high electromagnetic wave shield efficiency was obtained at wave frequency 2GHz to thermal sprayed ferrite coatings manufactured by size distribution range of spray powders, $38~88\mu\textrm{m}$.

용사에 의한 페라이트 자성재료 코팅의 .전자파 차폐특성 (Characteristic of Electromagnetic Wave Shielding Coatings by Thermal Spray)

  • 정태식;박경채
    • 대한용접접합학회:학술대회논문집
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    • 대한용접접합학회 2000년도 특별강연 및 추계학술발표대회 개요집
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    • pp.240-242
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    • 2000
  • This study was investigated absorption properties of electromagnetic wave in thermal sprayed Sr-ferrite coatings. The experiment of this study was ; manufactured thermal spraying powder for improving absorption-efficiency, processed for increasing strength of thermal spray coatings, and measured the electromagnetic wave shielding efficiency. This study was obtained excellent absorption-efficiency by thermal sprayed Sr-ferrite coatings.

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유한한 평판에서 포물선형 및 쌍곡선형 열전도 방정식과 파동 방정식의 비교 해석 (Comparative Analysis of the Parabolic and Hyperbolic Heat Conduction and the Damped Wave in a Finite Medium)

  • 박상규;이용호
    • 동력기계공학회지
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    • 제3권3호
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    • pp.14-21
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    • 1999
  • The wave nature of heat conduction has been developed in situations involving extreme thermal gradients, very short times, or temperatures near absolute zero. Under the excitation of a periodic surface heating in a finite medium, the hyperbolic and parabolic heat conduction equations and the damped wave equations in heat flux are presented for comparative analysis by using the Green's function with the integral transform technique. The Kummer transformation is also utilized to accelerate the rate of convergence of these solutions. On the other hand, the temperature distributions are obtained through integration of the energy conservation law with respect to time. For hyperbolic heat conduction, the heat flux distribution does not exist throughout all the region in a finite medium within the range of very short times(${\xi}<{\eta}_l$). It is shown that due to the thermal relaxation time, the hyperbolic heat conduction equation has thermal wave characteristics as the damped wave equation has wave nature.

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열 펌으로 형성된 웨이브 모발의 거칠기 분석 (Analysis of roughness of wave hair formed by thermal perm)

  • 박장순;임순녀
    • 한국융합학회논문지
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    • 제12권7호
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    • pp.235-241
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    • 2021
  • 헤어미용을 통한 외모 관리는 미용산업의 근간(根幹)을 이루면서 열을 이용한 퍼머넌트 웨이브는 헤어살롱에서 많이 시술되고 있지만, 열 퍼머넌트 웨이브 시술로 인한 모발 손상은 불가피한 현실이다. 따라서 모발 웨이브 형성력을 더욱 높일 수 있고 고객의 모발 손상을 최소화할 수 있는 열 퍼머넌트 웨이브에 대한 효율적인 방안을 제시할 목적으로 본 연구를 진행하였다. 후두부의 버진 헤어를 채취하여 thermal rod pretreatment and thermal permanent wave treatment를 한 후, Atomic Force Microscope를 통한 모발 거칠기 분석과 3D-image를 연구하였다. 연구 결과 평균 거칠기(Ra)와 십점 평균 거칠기(Rz) 모두 4구간이 각각 223nm와 853nm로 산출되면서 가장 높은 수치를 나타냈다. 실험 데이터의 표본이 적은 한계성을 지니고 있으나 본 연구를 통해 웨이브 형성력을 더욱 상승시킬 수 있으며, 고객 모발의 큐티클 보호와 함께 모발 손상을 최소화할 수 있는 열 퍼머넌트 웨이브에 대한 객관적인 방안 제시가 현실적으로 가능해질 것으로 판단한다.

Experimental Study Shock Waves in Superfluid Helium Induced by a Gasdynamic Shock Wave Impingement

  • Yang, Hyung-Suk;Nagai, Hiroki;Murakami, Masahide;Ueta, Yasuhiro
    • 한국초전도저온공학회:학술대회논문집
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    • 한국초전도저온공학회 2000년도 KIASC Conference 2000 / 2000년도 학술대회 논문집
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    • pp.43-47
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    • 2000
  • Two modes of shock waves, a compression shock wave and a thermal shock wave, propagating in He II have been investigated. The shock waves are at a time generated by the impingement of a gasdynamic shock wave onto a He II free surface in the newly developed superfluid shock tube facility. Superconductive temperature sensors, piezo-type pressure transducers and visualization photograph were used for the measurement of them and the phenomena induced by them were investigated in detail. It is found that the compression by a compression shock wave in He II causes temperature drop because He II has negative thermal expansion coefficient. the thermal shock wave is found to be of a single triangular waveform with a limited shock strength. The waveform is similar to that generated by stepwise strong heating from an electrical heater for relatively long heating time. In the experiments at the temperatures near the lambda temperature, no thermal shock wave is sometimes detected in shock compressed He II. It can be understood that shock compression makes He Ii convert to He I in which no thermal shock wave is excited.

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Detection and Quantification of Defects in Composite Material by Using Thermal Wave Method

  • Ranjit, Shrestha;Kim, Wontae
    • 비파괴검사학회지
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    • 제35권6호
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    • pp.398-406
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    • 2015
  • This paper explored the results of experimental investigation on carbon fiber reinforced polymer (CFRP) composite sample with thermal wave technique. The thermal wave technique combines the advantages of both conventional thermal wave measurement and thermography using a commercial Infrared camera. The sample comprises the artificial inclusions of foreign material to simulate defects of different shape and size at different depths. Lock-in thermography is employed for the detection of defects. The temperature field of the front surface of sample was observed and analysed at several excitation frequencies ranging from 0.562 Hz down to 0.032 Hz. Four-point methodology was applied to extract the amplitude and phase of thermal wave's harmonic component. The phase images are analyzed to find qualitative and quantitative information about the defects.

주사탐침열파현미경을 이용한 1 차원 나노구조체의 정량적 열전도도 계측기법 (Quantitative Method to Measure Thermal Conductivity of One-Dimensional Nanostructures Based on Scanning Thermal Wave Microscopy)

  • 박경배;정재훈;황광석;정의한;권오명
    • 대한기계학회논문집B
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    • 제38권12호
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    • pp.957-962
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    • 2014
  • 본 연구에서는 나노스케일의 공간 해상도를 가지는 주사탐침열파현미경(scanning thermal wave microscopy, STWM)을 이용하여 1 차원 나노구조체의 열전도도를 정량적으로 계측하는 방법을 제시한다. 먼저, 1 차원 나노구조체의 열확산도를 계측하기 위한 STWM 의 원리를 설명한 후, 정량적인 열확산도 계측을 위한 이론적 해석 과정을 설명한다. STWM 을 이용한 본 계측기법은 열파가 이동한 거리에 따른 상대적인 위상지연만을 가지고 열확산도를 계측하여 열전도도를 구하기 때문에 탐침과 나노구조체 사이의 열접촉저항 및 나노구조체와 열원간의 열접촉저항의 영향을 받지 않으며, 나노구조체에 인가되는 정확한 열유속을 구할 필요가 없다. 따라서 기존의 측정 기법들에 비해 계측이 매우 단순하면서도 정량적인 계측이 가능하다.

Stress wave법에 의한 열적 열화된 목재의 휨탄성계수 예측 (Estimating MOE of Thermal Degraded Wood by Stress Wave Method)

  • 이전제;김정원
    • Journal of the Korean Wood Science and Technology
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    • 제26권3호
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    • pp.9-15
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    • 1998
  • The strength and stiffness of structures would be weakened by thermal degradation of wood members which are exposed to a variety of heat including a fire. For this reason, thermal degraded wood members can't pertinently support the load. However, it is easy to repair or rehabilitate wood structures. So, the degraded wood members which can't support the load can be replaced with new members. For the sake of this advantage, there is a need for nondestructive evaluation(NDE) technique, which is very effective to assess wood members in service. In this paper, it was considered whether the stress wave method is adequate to estimate static bending MOE of thermal degraded wood. As the result, the relationship between static bending MOE and MOEsw in elevated temperature was found out significant. Therefore, the application of stress wave method for estimating static bending MOE of thermal degraded zzwood would be possible. However, it is thought that further research for the effects of exposure temperature, time, and thermal degradation on the relationship between static bending MOEb and MOEsw would be needed.

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단일굴곡 및 이중굴곡 판 형상을 갖는 직교류 공랭식 판형열교환기의 전열특성에 대한 실험적 연구 (Experimental Investigation of an Cross-Flow Air-Cooled Plate Heat Exchanger with Single-Wave and Double-Wave Plates)

  • 김민성;백영진;;박성룡;나호상;정재훈;임혁
    • 설비공학논문집
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    • 제21권6호
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    • pp.347-354
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    • 2009
  • Experimental study on a cross-flow air-cooled plate heat exchanger (PHE) was performed. Two types of PHEs were manufactured either with single-wave plates or with double-wave plates in parallel. Cooling air flows through the PHEs in a crosswise direction against internal hot water. The heat exchanger aims to substitute open-loop cooling towers with closed-loop water circulation, which guarantees cleanliness and compactness. In this study, prototype single-wave and double-wave PHEs were designed and tested in a laboratory scale experiments. From the tests, the double-wave PHE shows approximately 50% enhanced heat transfer performance compared to the single-wave PHE. However, the double-wave PHE costs 30% additional pressure drop. For the commercialization, a wide channel design for air flow would be essential for performance and reliability.

Laser Lock-in Thermal Wave Imaging for Nondestructive Evaluation

  • An, Yun-Kyu;Sohn, Hoon;Kim, Ji Min
    • 비파괴검사학회지
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    • 제33권4호
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    • pp.317-322
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    • 2013
  • This paper presents a new laser lock-in thermography (LLT) technique for nondestructive evaluation. LLT utilizes a modulated continuous wave laser beam as a heat source to obtain high fidelity thermal wave images even at the presence of background heat disturbances. The thermal waves propagating along the surface and through-the-thickness directions of a structure are visualized using newly developed laser lock-in amplitude and phase images, enhancing the detectability of surface and subsurface defects. The LLT technique is numerically investigated and experimentally validated using thermal images obtained from a steel specimen with low emissivity.