• Journal of Mechanical Science and Technology
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• 제17권12호
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• pp.2066-2077
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• 2003

The time-dependent behavior of unsteady condensation of moist air through the Ludwieg tube is investigated by using a computational fluid dynamics (CFD) work. The two-dimensional, compressible, Navier-Stokes equations, fully coupled with the condensate droplet growth equations, are numerically solved by a third-order MUSCL type TVD finite-difference scheme, with a second-order fractional time step. Baldwin-Lomax turbulence model is employed to close the governing equations. The predicted results are compared with the previous experiments using the Ludwieg tube with a diaphragm downstream. The present computations represent the experimental flows well. The time-dependent unsteady condensation characteristics are discussed based upon the present predicted results. The results obtained clearly show that for an initial relative humidity below 30% there is no periodic oscillation of the condensation shock wave, but for an initial relative humidity over 40% the periodic excursions of the condensation shock occurs in the Ludwieg tube, and the frequency increases with the initial relative humidity. It is also found that total pressure loss due to unsteady condensation in the Ludwieg tube should not be ignored even for a very low initial relative humidity and it results from the periodic excursions of the condensation shock wave.

• 설비공학논문집
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• 제19권3호
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• pp.228-234
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• 2007

Opening an ancient tomb interior can deal fair damage for preservation in long period because of high moisture. In this study, a duct-type HVAC system was installed to preserve an ancient tomb and temperature and humidity was measured to analyze heat environment. Armhole was measured to search whether an ancient tomb receives effects of vibration caused by a duct-type HVAC system. According to the measured data, temperature in an ancient tomb is kept adaptively in conservation regardless of a duct-type HVAC system installation when it rains in summer. The other side, humidity is kept adaptively in conservation when installed duct-type HVAC system. But when it is in natural state, a lot of humidity by dew condensation phenomena. So it needs a duct-type system for an ancient tomb conservation. In the case of vibration, measurement value of 3 satisfy control but Germanic DIN 4150 does not satisfy. Therefore, equip must be such that it can prevent vibration for safety.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2828-2833
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• 2008

Water management is one of many operating parameters, which influences the performance and stability of a proton exchange membrane fuel cell (PEMFC). Local humidity condition including liquid water saturation has profound impacts on the distributions of overpotentials, current density, and membrane water content. Computational fluid dynamics simulations were conducted to investigate the effect of the inlet humidity variation on the performance of a PEMFC of $9\;cm^2$ active cell area with serpentine flow fields. The results showed that the performance of the simulated PEMFC remained at an almost same level when the cathode inlet humidity was changed from 100% to 60%, while reaching its maximum at air humidity of 80%. However, further decrease in the cathode inlet humidity below 40% started to significantly deteriorate the performance of the PEMFC. The variations of overpotentials, membrane water content, etc. due to the change in the cathode inlet humidity were also discussed.

• 대한설비공학회지:설비저널
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• 제21권5호
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• pp.402-417
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• 1992

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.161-162
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• 2002

This study concerns the tribological behaviors of ultra-thin DLC coating with 3 nm thickness deposited in a mixed gas of argon + 20 % hydrogen as a function of humidity. Reciprocating wear tests employing a micro wear tester were performed under various normal loads and relative humidity in air environment. The chemical composition of the original and worn surfaces were studied by Auger electron spectroscopy (AES). It showed that the ultra-thin DLC coating exhibited low friction with enough wear stability at low normal load (0.18 N) and its tribological behavior was strongly dependent on the humidity. The sample surfaces before and after the test were examined using atomic force microscopy (AFM). Capillary force and meniscus areas were discussed in order to explain the influence of humidity on the friction force.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 하계학술발표대회 논문집
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• pp.1225-1230
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• 2008

Recently the building material have been developed with the concept of controlling the indoor environment as well as the concept of emitting contaminants less. So, a lot of products with humidity control characteristics put it on the market. However, objective evaluation to these products doesn't work out. Thus consumers cannot obtain accurate information to these products. Therefore, we selected inorganic paint in the functionality materials and evaluated its humidity control characteristic in this research. We divided by four stages and evaluated this inorganic paint. The 1st and 2nd third experiments were executed on a natural condition and the fourth experiment was executed with humidity had been raised by using the humidifier.

• Current Applied Physics
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• 제18권11호
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• pp.1375-1380
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• 2018

Atmospheric-pressure plasma has a great potential in many applications due to its simplicity rather than low pressure plasmas. In material processing, biomedical applications, and many other applications, the input power, gas flow rate, and the geometry of electrode have been mainly considered and studied as important external parameters of atmospheric-pressure plasma control. Besides, since the atmospheric-pressure plasmas are typically generated in an open air, the relative humidity is difficult to control and can change day by day. Therefore, the relative humidity cannot be ignored for plasmas. Thus, in this work, the atmospheric-pressure plasma jet was characterized by changing relative humidity, and it was found that the increase in electron density and OH radicals are due to Penning ionization between helium metastable and water vapors at higher humidity condition.

• 한국대기환경학회지
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• 제33권6호
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• pp.616-625
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• 2017

Measurements using five real-time particle samplers were compared to measurements using three NRM (National Reference Method system) filter-based samplers(Gravimetric method) at Incheon, Korea, between May and August, 2014. The purpose of this study was to suggest the quality assurance/quality control (QA/QC) method of each instrument for use in a real-time continuous particle sampler to measure the mass of airborne particles with an aerodynamic diameter less than $2.5{\mu}m$ ($PM_{2.5}$). Five real-time particle samplers of BAM1020, FH62C_14, TEOM, PM-711 and SPM-613 were evaluated by comparing its measured 23 hr average $PM_{2.5}$ concentrations with those measured with NRM filter-based samplers simultaneously. The parameters(e.g. Inlet heating condition, Slope factor, Film response, Intercept, Background, Span value) of the real-time samplers were optimized respectively by conducting test performance evaluation during 7 days in field sampling. For example, inlet heating temperature of TEOM sampler controls $35{\sim}40^{\circ}C$ to minimize the fluctuation of the real-time measurement data and background value of BAM1020 is the key factor affecting the accuracy of $PM_{2.5}$ mass concentration. We classified the $PM_{2.5}$ concentration according to relative humidity (80%) to identify water absorbed in aerosols by measuring the ${\beta}$-ray samplers(BAM1020, FH62C_14) and TEOM. ${\beta}$-ray samplers were not strongly affected by relative humidity that the difference of the average $PM_{2.5}$ concentration was about 5%. On the other hand, The TEOM sampler overestimated $PM_{2.5}$ mass concentration about 15% at low relative humidity (<80%).

• 한국환경보건학회지
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• 제22권4호
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• pp.43-48
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• 1996

Indoor air quality(IAQ) in museum is very important for protection of cultural properties. In our study, we measured air pollutants($NO_x, NH_3, SO_2, O_3$, CO, $CO_2$, TSP), temperature and humidity to evaluate IAQ of national central museum. Indoor carbon dioxide and TSP concentrations were higher than outdoor concentrations. Temperature, huinidity and TSP had large deviation depending on air conditioning operates or not. Indoor gas phase pollutants except $CO_2$ were lower than outdoor concentrations, but $SO_2$ concentration was high in storage. $CO_2$ and TSP were influenced by the number of spectators.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.241-242
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• 2002

Wear behavior or SiC-particle reinforced aluminum matrix composites (MMC) were investigated by pin-on-disk tests in vacuum with various pressures, argon, and air with various levels of humidity. The wear rate of 2024Al and MMC increased in the following order: in a vacuum at $5.0{\times}10^{-4}$ Pa, at 1.0Pa, in argon at 0% RH, in argon at 60% RH, in argon at 90% RH, in air at 0% RH, in air at 60% RH and in air at 90% RH. In other words, the influence or environment on wear becomes stronger in the following order: moisture, oxygen, and a combination of moisture and oxygen. In various environments, the difference of the wear rate of 2024Al and MMC was compared. In argon and air at 0% RH, the wear rates of MMC were higher than that of 2024Al. In contrast, in argon and air at 60, 90% RH, the wear rates of MMC were lower than that of 2024Al.