• 한국건설순환자원학회논문집
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• 제8권4호
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• pp.571-580
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• 2020

본 연구에서는 열에너지 저장시스템의 중요한 요소인 저장 매체에 관한 연구를 수행하였다. 열에너지 저장 매체로써 콘크리트는 열적 및 역학적 특성이 우수하며 저렴한 비용으로 인해 다양한 이점을 갖는다. 또한, 강섬유가 혼입된 초고강도 콘크리트는 고인성 및 고강도 특성으로 인해 고온 노출에 우수한 내구성을 나타내며, 강섬유의 높은 열전도율은 축열 및 방열에 유리한 영향을 미친다. 초고강도 콘크리트의 온도분포 특성을 파악하기 위하여 콘크리트 블록을 제작하고 일정한 열사이클을 적용하여 가열실험을 수행하였다. 열유체 흐름에 의한 열전달을 위하여 열전달 파이프를 콘크리트 블록 중심부에 매립하였다. 또한, 열전달 파이프 형상에 따른 온도분포 특성을 비교하기 위하여 핀의 유무에 따라 원형 파이프 및 종방향 핀 부착 파이프를 설정하였다. 열사이클에 따른 온도분포 특성을 분석하고, 이를 토대로 시간에 따른 열에너지 및 누적 열에너지를 산정하여 비교 분석하였다. 열사이클이 반복될수록 강섬유 혼입 초고강도 콘크리트는 고온에 대하여 안정화를 나타내었다. 또한, 온도분포 및 열에너지 산정 결과를 통해 축열 성능을 보유한 것으로 판단되며, 열에너지 저장 매체 역할을 수행할 수 있는 재료로 기대된다.

• 대한치과기공학회지
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• 제34권1호
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• pp.11-21
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• 2012

Purpose: Densification and mechanical properties of dental zirconia ceramics were evaluated by different sintering methods. Materials and Methods: Y-TZP zirconia block(Kavo $Everest^{(R)}$ ZS blank, Kavo dental GmbH, Bismarckring, Germany) was used in this study. Sintering were performed in heat sintering furnace and microwave sintering furnace, and then experimented and analyzed on a change in densification according to the sintering time, a change in densification according to thickness, flexural strength and micro-structure in zirconia specimens. Results: Microwave sintering was very effective in considerable mechanical properties such as flexural strength and bulk density was drastically increased than conventional electric heating method. It is also shown that microwave sintering time was faster and more economical than common method to be present in qualities which equal or exceed. Conclusion: It will be important to seek the accurate sintering condition of dental zirconia by microwave sintering method and the continuous research is necessary for the study of relationship between sintering methods and mechanical properties.

• 자원환경지질
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• 제40권6호
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• pp.833-841
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• 2007

지하수열펌프시스템(GWHP)은 지원열펌프시스템(GSHP)가운데 성능이 가장 우수하며 저온의 천부지하수열을 이용하는 시스템이다. GWHP시스템은 지중연결 열펌프시스템(GCHP)에 비해 최대 블록부하와 전 시스템 성능에 부합되는 지하수유량을 기준으로 하여 설계를 하며 최적 지하수유량은 해당지역의 지하수온도, 판형열교환기의 규격과 전체펌프와 배관류의 전 양정고에 따라 결정한다. 대체적으로 전형적인 빌딩루프순환수의 필요유량은 1RT당 $9.5{\sim}11.4lpm$ 정도인데 비해 GWHP시스템이 필요로 하는 최적 지하수유량은 이보다 꿜씬 적은 $3.8{\sim}9.5lpm$정도이다.

• 한국전기전자재료학회논문지
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• 제21권12호
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• pp.1135-1140
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• 2008

Bismuth-telluride based thin film materials are grown by Metal Organic Chemical Vapor Deposition(MOCVD). A planar type thermoelectric device has been fabricated using p-type $Bi_{0.4}Sb_{1.6}Te_3$ and n-type $Bi_2Te_3$ thin films. Firstly, the p-type thermoelectric element was patterned after growth of $4{\mu}m$ thickness of $Bi_{0.4}Sb_{1.6}Te_3$ layer. Again n-type $Bi_2Te_3$ film was grown onto the patterned p-type thermoelectric film and n-type strips are formed by using selective chemical etchant for $Bi_2Te_3$. The top electrical connector was formed by thermally deposited metal film. The generator consists of 20 pairs of p- and n-type legs. We demonstrate complex structures of different conduction types of thermoelectric element on same substrate by two separate runs of MOCVD with etch-stop layer and selective etchant for n-type thermoelectric material. Device performance was evaluated on a number of thermoelectric devices. To demonstrate power generation, one side of the sample was heated by heating block and the voltage output measured. As expected for a thermoelectric generator, the voltage decreases linearly, while the power output rises to a maximum. The highest estimated power of $1.3{\mu}W$ is obtained for the temperature difference of 45 K. we provide a promising procedure for fabricating thin film thermoelectric generators by using MOCVD grown thermoelectric materials which may have nanostructure with high thermoelectric properties.

• 대한의용생체공학회:의공학회지
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• 제28권3호
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• pp.429-440
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• 2007

A coded excitation has been studied to improve the performance for ultrasound imaging in term of SNR, imaging frame rate, contrast to tissue ratio, and so forth. However, it requires a complicated arbitrary waveform transmitter for each active channel that is typically composed of a multi-bit Digital-to-Analog Converter (DAC) and a linear power amplifier (LPA). Not only does the LPA increase the cost and size of a transmitter block, but it consumes much power, increasing the system complexity further and causing a heating-up problem. This paper proposes an optimized 1.5bit fourth order sigma-delta modulation technique applicable to design an efficient arbitrary waveform generator with greatly reduced power dissipation and hardware. The proposed SDM can provide a required SQNR with a low over-sampling ratio of 4. To this end, the loop coefficients are optimized to minimize the quantization noise power in signal band while maintaining system stability. In addition, the decision level for the 1.5 bit quantizer is optimized for a given input waveform, which results in the SQNR improvement of more than 5dB. Computer simulation results show that the SQNR of a FM(frequency modulated) signal generated by using the proposed method is about 26dB, and the peak side-lobe level (PSL) of its compressed waveform on receive is -48dB.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 추계학술대회 논문집 Vol.21
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• pp.425-425
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• 2008

Bismuth-antimony-telluride based thermoelectric thin film materials were prepared by metal organic vapor phase deposition using trimethylbismuth, triethylantimony and diisopropyltelluride as metal organic sources. A planar type thermoelectric device has been fabricated using p-type $Bi_{0.4}Sb_{1.6}Te_3$ and n-type $Bi_2Te_3$ thin films. Firstly, the p-type thermoelectric element was patterned after growth of $4{\mu}m$ thickness of $Bi_{0.4}Sb_{1.6}Te_3$ layer. Again n-type $Bi_2Te_3$ film was grown onto the patterned p-type thermoelectric film and n-type strips are formed by using selective chemical etchant for $Bi_2Te_3$. The top electrical connector was formed by thermally deposited metal film. The generator consists of 20 pairs of p- and n-type legs. We demonstrate complex structures of different conduction types of thermoelectric element on same substrate by two separate runs of MOCVD with etch-stop layer and selective etchant for n-type thermoelectric material. Device performance was evaluated on a number of thermoelectric devices. To demonstrate power generation, one side of the device was heated by heating block and the voltage output was measured. The highest estimated power of 1.3mW is obtained at the temperature difference of 45K. We provide a promising approach for fabricating thin film thermoelectric generators by using MOCVD grown thermoelectric materials which can employ nanostructures for high thermoelectric properties.

• Fibers and Polymers
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• 제2권2호
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• pp.98-107
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• 2001

The phase transition behavior isothermal micro-phase separation kinetics of polyester-based thermoplastic elastomer were studied using the synchrotron X-ray scattering(SAXS) method. The structural changes occurring during heating period were investigated by determining the changes of the one-dimensional correlation function, interfacial thickness and Porod constant. Based on the abrupt increases of the domain spacing and interfacial thickness, a major structural change occurring well below the melting transition temperature is suggested. Those changes are explained in terms of melting of the thermodynamically unstable hard domains or/and the interdiffusion of the hard and soft segments in the interfacial regions. SAXS profile changes during the micro-phase separation process were also clearly observed at various temperatures and the separation rate was found to be sensitively affected by the temperature. The peak position of maximum scattering intensity stayed constant during the entire course of the phase separation process. The scattering data during the isothermal phase separation process was interpreted with the Cahn-Hilliard diffusion equation. The experimental data obtained during the early stage of the phase separation seems to satisfy the Cahn-Hilliard spinodal mechanism. The transition temperature obtained from the extrapolation of the diffusion coefficient to zero value turned out to be about 147$\pm$$2^{\circ}$, which is close to the order-disorder transition temperature obtained from the Porod analysis. The transition temperature was also estimated from the inveriant growth rate. By extrapolating the inveriant growth rate to zero, a transition temperature of about 145$\pm$$\pm$$2^{\circ}$ was obtained.

• 한국화재소방학회논문지
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• 제11권1호
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• pp.21-35
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• 1997

The natural convection and combined heat transfer induced by fire in a rectangular enclosure is numerically studied. The model for this numerical analysis is partially opened right wall. The solution procedure includes the standard k-$\varepsilon$ model for turbulent flow and the discrete ordinates method (DOM) is used for the calculation of radiative heat transfer equation. In numerical study, SIMPLE algorithm is applied for fluid flow analysis, and the investigations of combustion gas induced by fire is performed by FAST model of HAZARD I program. In this study, numerical simulation on the combined naturnal convection and radiation is carried out in a partial enclosure filled with absorbed-emitted gray media, but is not considered scattering problem. The streamlines, isothermal lines, average radiation intensity and kinetic energy are compared the results of pure convection with those of the combined convection-radiation, the combined heat transfer. Comparing the results of pure convection with those of the combined convection-radiation, the combined heat transfer analysis shows the stronger circulation than those of the pure convection. Three different locations of heat source are considered to observe the effect of heat source location on the heat transfer phenomena. As the results, the circulation and the heat transfer in the left region from heating block are much more influenced than those in the right region. It is also founded that the radiation effect cannot be neglected in analyzing the building in fire. And as the results of combustion gas analysis from FAST model, it is found that O2 concentration is decreased according to time. While CO and CO2 concentration are rapidly increased in the beginning(about 100sec), but slowly decreased from that time on.

• 구강회복응용과학지
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• 제32권2호
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• pp.123-129
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• 2016

의원성의 외상 혹은 감염은 신경 손상의 중요한 원인 중 하나이며, 이는 의사-환자 관계에 매우 큰 영향을 주는 일로 여겨진다. 관련 치과 술식의 예로는 임플란트 시술시 직접적인 혹은 열에 의한 손상, 근관치료시의 약제 유출, 발치시의 외력, 전달국소마취시 바늘에 의한 외상, 악골 수술로 인한 외상 등이 있다. 이러한 신경손상이 발생하지 않도록 위험군 예측 및 시술 시 주의가 필요하며, 신경 손상 시 조기 발견을 통해 제대로 대처하지 않으면 만성적 신경병증으로 발전할 수 있는 가능성이 높아질 수 있으므로 그 징후를 신속히 파악하고 적절히 관리하는 것이 매우 중요하다.

• 공업화학
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• 제21권5호
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• pp.570-574
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• 2010

기존 단열재의 주된 기능은 단지 열전달을 차단하는 기능과 건물로부터 열손실을 줄여주는 기능만을 수행했다. 반면, 축열재는 특정온도 범위 내에서 열에너지를 저장 또는 방출함으로써 건물에너지 사용량을 절감할 수 있다. 축열 건자재는 실내 공기온도 변화주기를 효과적으로 조절하여 일정하게 온도를 유지시킬 수 있다. 결과적으로 냉난방시스템 기능을 효율적으로 향상시킬 수 있다. 본 연구는 건축자재로 많이 이용되고 있는 석고보드에 상변화잠열물질을 축열재로 첨가하여 그 물성과 열환경 특성을 파악하였다. 또한 축열 건자재를 활용할 때 발생가능한 문제점을 확인하였다. 마지막으로 TVOC와 HCHO 함량 분석으로부터 오염물질의 배출가능성을 조사하여 축열 건자재의 환경 친화도를 검토하였다.