• 설비공학논문집
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• 제27권12호
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• pp.652-658
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• 2015

The Bubble Jet Loop Heat Pipe (BJLHP) is designed to operate in the horizontal orientation. The motion of the bubble generated by boiling working fluid on a heater surface in the evaporating section of the BJLHP helps the working fluid transfer heat to the condensing portion. In this study, we changed the position of the heater in the evaporating section from concentric to eccentric. The concentric heater is located at the center of the tube in the evaporating part, and the eccentric heater is located at the bottom of the inner surface of the same tube. We used R-134a as the working fluid, and the charging ratio was 50%vol. We measured the temperatures of the evaporating and condensing sections by changing the input electric power from 50 W to 200 W, measuring every 50 W. The results of the experiment show that the effective thermal conductivity of BJLHP using an eccentric heater is four times higher than the BJLHP obtained using a concentric heater. Additionally, we conducted a visualization experiment on the evaporating portion of BJLHP to determine why the effective thermal conductivity was higher. The working fluid was water, and we took pictures of the flow visualization for BJLHP. Nucleate boiling with the eccentric heater was more intense and generated more bubbles. Therefore, the eccentric heater was more saturated by the liquefied working fluid.

• 분석과학
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• 제12권6호
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• pp.490-497
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• 1999

불활성기체용융-열전도도 측정법의 수소분석기를 개조하여 글로브박스에 설치했으며 조사핵연료피복관의 수소분석에 사용했다. Zr과 Ti 매질의 수소표준물질로 용융조제인 주석을 사용하지 않고도 수소함량 $3{\mu}g$까지 분석가능하였다. 시료의 크기가 작을수록 수소 회수율이 높았으며 지르칼로이 시료의 수소분석시 Ti 매질의 표준물질을 사용할 수 있음을 확인하였다. 수소분석에 사용한 실제 조사핵연료피복관의 평균 방사능은 10 mR/hr였으며 평균수소농도는 130 ppm이었다.

• 대한건축학회논문집:구조계
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• 제34권3호
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• pp.87-93
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• 2018

Ground source heat pump(GSHP) system is one of the high efficiency heat source systems which utilizes the constant geothermal energy of a underground water or soil. However, the design of conventional GSHP system in the domestic market is dependent on the experience of the designer and the installer, and it causes increase of initial installation cost or degradation of system performance. Therefore, it is necessary to develop a guideline and the optimal design method to maintain stable performance of the system and reduce installation cost. In this study, in order to optimize the GSHP system, design factors according to ground heat exchanger(GHX) type have been examine by simulation tool. Furthermore, the design factors and the correlation of a single U-tube and a double U-tube were analyzed quantitatively through sensitivity analysis. Results indicated that, the length of the ground heat exchanger was greatly influenced by grout thermal conductivity for single U-tube and pipe spacing for double U-tube.

• 접착 및 계면
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• 제11권4호
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• pp.174-180
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• 2010

다중벽탄소나노튜브를 표면처리하여 polymethylmethacrylate (PMMA) 기재에 첨가하여 제조한 고분자 복합재료에서 탄소나노튜브의 표면처리가 계면 및 열전도도에 미치는 효과를 고찰하였다. Coagulation 방법과 atomic transfer radical polymerization (ATRP) 방법을 사용하여 탄소나노튜브를 표면 처리 하여 사용하였으며, ATRP 방법을 적용하여 제조한 복합재료는 coagulation 방법을 사용하여 제조한 복합재료보다 높은 열전도도와 투과도를 가졌다. 순수 PMMA의 열전도도가 0.21 W/mK인데 비하여 ATRP 방법으로 처리한 1 wt%의 탄소나노튜브를 첨가하였을 경우 0.38 W/mK로 열전도도가 향상되었다. 탄소나노튜브와 PMMA기재의 계면을 주사전자현미경을 이용하여 관찰한 결과 탄소나노튜브의 표면처리에 의해 기재 내에 분산이 향상되고 고분자기재-탄소나노튜브 계면에서의 접촉이 용이해져 포논산란이 감소되어 광 투과성을 가지면서 열전도도가 향상된 것으로 보인다.

• 태양에너지
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• 제7권2호
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• pp.86-97
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• 1987

Natural convection in the annulus between a horizontal conducting tube and a cylinder with spacers has been studied by 2-dimensional numerical method with finite difference techniques. The effects of Rayleigh number, conductivities of conducting tube and spacer, and position of spacers were studied analytically. In case of vertical spacers, the maximum local Nusselt number appears at ${\theta}{\approx}50^{\circ}$ in a conducting tube and ${\theta}{\approx}30^{\circ}$ in an outer cylinder, The local Nusselt numbers show positive values on the lower spacer, but negative values on the surface of the upper spacer. In case of horizontal spacers, the flow over the spacer is more active than that of under the spacer as the Rayleigh number increases. The maximum local Nusselt appeares at ${\theta}=180^{\circ}$ in a conducting tube and at ${\theta}=0^{\circ}$ in an outer cylinder. The local Nusselt numbers show positive values on the upward surface, but negative values on the downward surface of spacer. As the dimensionless conductivity increases, the mean Nusselt number remarkably increases at $K_w/K_f<48$ and show almost even at $K_w/K_f{\ge}48$. The mean Nusselt number of a conducting tube with vertical spacers is 5.12 percent less and with horizontal spacers is 11.33 percent less than that of a conducting tube without spacer at $Ra=10^4$, Pr = 0.7 and $K_w/K_f=48$.

• 한국세라믹학회지
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• 제53권6호
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• pp.659-664
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• 2016

Ash deposition of heat exchange boiler, caused mainly by accumulation of particulate matter, reduces heat transfer of the boiler system. Heat and mass transfer through porous media such as ash deposits mainly depend on the microstructure of deposited ash. Therefore, in this study, we investigated microstructural and thermal properties of the ash deposited on the boiler tube. Samples for this research were obtained from the fuel economizer tube in an industrial waste incinerator. To characterize microstructures of the ash deposit samples, scanning electron microscope (SEM), energy-dispersive spectroscopy (EDS), inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray diffraction (XRD) and BET analysis were employed. The results revealed that it had a porous structure with small particles mostly of less than a few micrometers; the contents of Ca and S were 19.3, 22.6% and 18.5, 18.7%, respectively. Also, the results showed that it consisted mainly of anhydrite ($CaSO_4$) crystals. - The thermal conductivities of the ash deposit sample obtained from the economizer tube in industrial waste incinerator were measured to be 0.63 and 0.54 W/mK at $200^{\circ}C$, which were about 100 times less than the thermal conductivity (61.32 W/mK) of the boiler tube itself, indicating that ash deposition on the boiler tube was closely related to a decrease in boiler heat transfer.

• 한국산학기술학회논문지
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• 제18권4호
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• pp.21-26
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• 2017

본 연구에서는 이중관형 열회수 환기장치의 제품 적용 가능성을 검토하기 위해 성능 시험을 수행하였으며 이중관의 내측관의 재질에 변경에 따른 검토를 하기 위해 종이관, 알루미늄관, 폴리머관을 제작하여 동일한 급/배기 풍량을 인가하여 측정하였다. 온도 교환 효율은 모든 경우에서 알루미늄관의 경우가 가장 큰 값을 나타냈으며 종이관과 폴리머관은 비슷한 결과를 보였다. 이는 내측관으로 사용된 재료의 열전도율과 두께의 차이 때문인 것으로 판단된다. 습도 교환 효율은 모든 경우에서 종이관의 경우가 가장 큰 값을 나타냈으며 알루미늄관과 폴리머관은 비슷한 결과를 보였다. 이는 종이 재질은 습도 교환이 가능하지만 알루미늄과 폴리머재질은 습도 교환이 불가능하기 때문인 것으로 판단된다. 습도 교환과 온도 교환의 두 값을 포함하는 전열 교환 효율은 종이관의 경우가 가장 큰 값을 나타냈으며 알루미늄관과 폴리머관은 비슷한 결과를 보였다. 에너지계수(COE)는 현열과 잠열교환이 동시에 일어나는 종이관의 경우 전열에너지계수 값을 현열교환만 일어나는 알루미늄관과 폴리머관은 현열에너지계수를 비교해 보면 종이관의 에너지계수가 가장 큰 값을 나타냄을 알 수 있었다. 본 연구를 통하여 이중관형 열회수 환기장치의 내부관 재질에 따른 성능을 비교 분석 하였으며 환기장치로 적용이 가능한 것을 알 수 있었다.

• Bulletin of the Korean Chemical Society
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• 제30권9호
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• pp.1978-1980
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• 2009

A mesostructured form of carbon was fabricated from a template of mesostructured silica by using pentane, an aliphatic hydrocarbon precursor. To synthesize the mesostructured silica, a buffered (pH of 6.5) mixture of nonionic Pluronic P123 surfactant, sodium silicate, and acetic acid were used. The impregnated silica with Fe$(CO)_5$ (wt 5%) and pentane was placed in a quartz tube, treated with pentane vapor at 800 ${^{\circ}C}$ for two hours to synthesize the mesostructured carbon. The XRD patterns of the carbon replica in the low/wide angle regions, its TEM images, and nitrogen adsorption-desorption isotherm revealed that the long-range framework order of mesostructure with the pore size centered on 2.8 nm was maintained to some extent mainly due to some portions of mesophase carbon that work as a support to fix the hexagonal frameworks by anchoring on the pore surface with an improved graphitic character. The dc conductivity of the mesostructured carbon in pressed powder form at 6.0 MPa was 2.08 S/cm.

• Journal of Biosystems Engineering
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• 제23권1호
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• pp.21-30
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• 1998

A theoretical model was developed to evaluate the effects of soil and airflow characteristics on the soil-air heat exchanger performances. The model, which includes three-dimensional transient energy and mass equilibrium-equation, was solved by using a computer program that uses Finite Difference Methods and Gauss-Seidel iteration computation. Energy gains, heat exchange efficiencies, and outlet air temperature are presented including the effects of soil moisture content, soil conductivity, soil thermal diffusivity, and soil initial temperature. Also, data related to the effects of airflow rate and inlet air temperature on the thermal performance of the system are presented. The results indicated that energy gains depend on soil conductivity, soil thermal diffusivity, and soil initial temperature. Heat exchange efficiencies relied on air mass flow rate and soil moisture content.

• 한국인쇄학회지
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• 제23권2호
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• pp.93-101
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• 2005

The measured plasma temperature of Ar hollow cathode discharge for several metal cathodes are about $620\;{\sim}\;780K$ at discharge current of $7\;{\sim}\;10mA$. The optogalvanic signals were measured using hollow cathode discharge tube with argon as buffer gas at change of discharge currents. A change of ionization rate due to electron collision causes an increase or decrease of the electric conductivity. This change in electric conductivity generates the optogalvanic signal. We conclude that optogalvanic signal has close relation with the lowest metastable atoms density at low current.