• 한국전기전자재료학회논문지
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• 제30권10호
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• pp.631-636
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• 2017

The degradation mechanism of $Mo_xW_{1-x}Si_2$ ultrahigh-temperature heating elements fabricated by self-propagating high-temperature synthesiswas investigated. The $Mo_xW_{1-x}Si_2$ specimens (with and without post-annealing) were subjected to ADTs (accelerated degradation tests) at temperatures up to $1,700^{\circ}C$ at heating rates of 3, 4, 5, 7, and $14^{\circ}C/min$. The surface loads of all the specimen heaters were increased with the increase in the target temperature. For the $Mo_xW_{1-x}Si_2$ specimens without annealing, many pores and secondary-phase particles were observed in the microstructure; the surface load increased to $23.9W/cm^2$ at $1,700^{\circ}C$, while the bending strength drastically reduced to 242 MPa. In contrast, the $Mo_xW_{1-x}Si_2$ specimens after post-annealing retained $single-Mo_xW_{1-x}Si_2$ phases and showed superior durability after the ADT. Consequently, it is thought that the formation of microcracks and coarse secondary phases during the ADT are the main causes for the degraded performance of the $Mo_xW_{1-x}Si_2$ heating elements without post-annealing.

• 생물환경조절학회지
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• 제22권3호
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• pp.220-227
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• 2013

본 연구는 온실 운영에 필요한 전력량을 확보함으로서 온실경영비 절감을 목적으로 태양광발전시스템을 온실에 인접한 건물의 옥상에 설치하여 일사량에 따른 발전량을 실험적으로 검토하였다. 연구결과를 요약하면 다음과 같다. 실험기간 동안 수평면 일사량의 최대, 평균 및 최소값은 각각 $26.1MJ{\cdot}m^{-2}$, $14.0MJ{\cdot}m^{-2}$ 및 $0.6MJ{\cdot}m^{-2}$ 정도였고, 일일 전력량은 각각 약 6.1kWh, 3.7kWh 및 0.01kWh 이었다. 그리고 누계 일사량과 전력량은 각각 약 $4,378.2MJ{\cdot}m^{-2}$ 및 1,163.2kWh 정도이었다. 그리고 부하에 의해 소비된 적산전력량의 최대, 평균 및 최소값은 각각 4.5kWh, 2.4kWh 및 0.0kWh 정도이었고, 누계전력량은 739.2kWh 정도로서 발생 전력량의 약 63.5%에 해당하였다. 본 실험에 사용된 시스템의 평균 소비전력량을 기준으로 보면, 온풍기의 용량 및 작동시간이 작은 경우는 충분하지만 큰 경우는 부족한 것으로 나타났다. 어레이 표면온도가 상대적으로 높아지면 일사량에 비례해서 발생 전력이 증가하지 않은 것으로 나타났지만, 두 인자 간에 상관계수는 0.851 정도로서 상관관계가 높은 것으로 나타났다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.205.2-205.2
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• 2016

The emission test a domestic fabricated cathode is conducted using an easy-replaceable-emitter-type test bench. A simple cylindrical button type cathode is dropped vertically into a cathode cup holder. The cathode is heated by a tungsten wire heater located around the cup holder. The cathode temperature is measured by an optical pyrometer. A high voltage pulse power supply gives the anode-cathode gap voltage up to 20 kV with the pulse width of 15 us. The emitted current from the cathode is captured at a faraday cup and is measured using current transformer and oscilloscope. The test bench is installed in the vacuum chamber with easy access door and, therefore, the cathode can be easily replaceable. We confirmed the emission current density of $15A/cm^2$ and $80A/cm^2$ with a domestic fabricated B-type cathode and a Scandate cathode, respectively. The detailed test result for the cathode will be presented.

• 한국해양공학회지
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• 제28권4호
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• pp.351-355
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• 2014

Today, carbon fibers are used as heating elements. Carbon fibers are generally used to reinforce composite materials because they are lightweight and have a high strength and modulus. Carbon fiber reinforced composite materials are used for aerospace, automobile, and wind turbine blade applications. This work explored the possibility of using carbon fiber reinforced composite materials as self heating materials. The temperatures of the carbon fiber reinforced composites were measured. These results verified that the carbon fiber reinforced composite materials could be used as heating elements. A glass fiber was laminated using various methods. The thermal characteristics of the composites were evaluated. This confirmed that the generation of heat varied according to the lamination thicknesses of the carbon fiber and glass fiber. As the number of carbon fiber laminations increased, the heat-generating temperature increased. In contrast, as the number of glass fiber laminations increased, the amount of heat decreased. The generation of heat and ability to remain warm could be controlled by controlling the carbon fiber and glass fiber laminations.

• 한국농공학회지
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• 제21권1호
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• pp.78-85
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• 1979

In order to obtain the basic data for designing optimum flat plate solar air heaters, which can be operated with relatively low temperature for drying farm products, 8 different treatment of solar air heaters were devised and tested for their heating performances and efficiencies. The results were analised and summarized as follows. 1. The primary factors, structure of air path (C), black coating materials (A) and bottom coating methods (B) showed very high significant effect of far above 1% level. With respect to the mutual multiplying effect of secondary factors, 1% level of significance was found with coating materials and methods (AB), and 5% level of significance was found with coating materials and air path structure (AC). 2. The heating performance of the air heaters with winding air path showed about twice those with straight air path. 3. The Korean black ink which is less expensive than dim oil paint showed 3-4% better heating efficiencies as the black coating material of flat plate solar air heaters. 4. The heating efficiencies of the solar air heaters whose bottoms were not black coated were 2-3% higher than those with black coated bottoms. 5. The highest heating efficiency of solar air heater among 8 different treatment was found in the plot of Korean black ink-bottom not coated-winding air path showing 29.0-34.5%

• 한국연소학회:학술대회논문집
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• 한국연소학회 1999년도 제19회 KOSCO SYMPOSIUM 논문집
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• pp.111-115
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• 1999

In order to enhance the burner performance of household gas fired absorption chiller/heaters, the operating condition(excess air $\approx$ 10%) of the burner currently being used was required to be optimized. In this regard, we examined where the $CO_{\min}$. emission limit was located between blow off and yellow tip limit and how much amount of excess air was exhausted by means of observing blow off and yellow tip limit. It was found that the $CO_{\min}$ limit(excess air ${\approx}$ 4%) was determined near the yellow tip limit. The effect of exhaust pressure on the $CO_{\min}$. limit was that, if exhaust pressure was higher than that in steady condition, higher air blower fan rpm is demanded to maintain the $CO_{\min}$ limit. Therefore, it was necessary to optimize the operating condition of burner in terms of a thermal efficiency and safety.

• 대한기계학회논문집B
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• 제28권1호
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• pp.81-88
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• 2004

In this study, heat and mass transfer characteristics of five components solution (LiBr＋Lil＋LiNO$_3$＋LiCl＋$H_2O$) which could be substituted for commonly used LiBr solution are tested using a helical absorber. The arrangement of helical-typed heat exchangers allows to make the system more compact as compared to conventional one. The effects of experimental parameters, such as the solution flow rate, cooling water, solution temperature, solution concentration and surfactant have been investigated in view of the heat and mass transfer. The results of the experiment of heat and mass transfer performance show that five components solution should have 2％ higher concentration fur equal absorption capacity of LiBr solution. But considering that five components solution have higher solubility than LiBr solution about 4％ high concentration, five components solution could be applied to a small sized water cooled or air cooled absorption chiller/heater. The increase of heat and mass transfer coefficient by surfactant addition is about 25∼30％ and 23∼40％ respectively.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1491-1498
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• 2003

Droplet evaporation can be used to transfer large amounts of energy since heat is transferred across a thin liquid film. Spreading the drop over a larger area can enhance this heat transfer. One method of accomplishing this is to dissolve gas into the liquid. When the drop strikes the surface, a gas bubble nucleates and can grow and merge within the liquid, resulting in an increase in the droplet diameter. In this study, time and space resolved heat transfer characteristics for a single droplet striking a heated surface were experimentally investigated. The local wall heat flux and temperature measurements were provided by a novel experimental technique in which 96 individually controlled heaters were used to map the heat transfer coefficient contour on the surface. A high-speed digital video camera was used to simultaneously record images of the drop from below. The measurements to date indicate that significantly smaller droplet evaporation times can be achieved. The splat diameter was observed to increase with time just after the initial transient dies out due to the growth of the bubble, in contrast to a monotonically decreasing splat diameter for the case of no bubbles. Bursting of the bubble corresponded to a sudden decrease in droplet heat transfer.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 추계학술대회 논문집
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• pp.386-394
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• 2007

Due to the transportability problems, long rail shall be from base rail unit, which is normally 100m for regular rail and 300m for high speed rail. After these rail units are transported from the fabricator to the site, the field weld would be performed.axial stresses in the long rail is mainly from the temperature differences at various locations the long rail. Also the gaps between each welds cause secondary axial stresses in the rail. In addition to these, re-welds the fractured rails, rail buckling, irregular rail vibration, rail twist also result innonuniform axial stresses in the rail. To obtain the rail buckling stability, the rail stresses shall be released due to the resetting of CWR. Traditionally two resetting of CWR methods have been applied, the one is rail heater and the other is rail tenser. these methods, the latter has been recommended because it has less limitation in the rail length and it is easier to minimized the force differences. But even in this method, the calculation is cumbersome and is not easy to find out the rail stress distribution itself.refined methodsxial stress resetting in the long rail is studied and this study be easily applied in the real construction. From this approach, more rational rail maintenance system can be expected.

• 대한기계학회논문집B
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• 제25권12호
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• pp.1748-1755
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• 2001

The shell and tube heat exchangers were introduced to apply to a big capacity condenser and a high pressure feed water heater for power plant in the beginning of 1990s. Design and manufacturing technology fur shell and tube heat exchangers have been developed until now. But it is very difficult to calculate the expected performance characteristics of the shell and tube heat exchanger, because there are many design parameters to be considered according to internal structure and the shell side heat transfer mechanism complicately related to the design parameters. Design parameters to be considered in the design stage of shell and tube heat exchanger are shell and tube side fluids, flow rate, inlet and outlet temperature, physical properties, type of heat exchanger, outer diameter, thickness, length of tube, tube arrangement, tube pitch, permissive pressure loss on both sides, type of baffle plate, baffle cutting ratio. The propose of study is an analysis TEMA(Tubular Exchanger Manufacturers Association) E shell and tube heat exchanger performance with changing a number of baffles(3, 5, 7, 9, 11) and tubes(16, 20) and determined optimal baffle spacing.