• Korean Journal of Agricultural and Forest Meteorology
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• v.2 no.3
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• pp.80-86
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• 2000

Eddy covariance method is widely used in measuring vertical fluxes of mass and energy between the atmosphere and the biosphere. In this method, scalar concentration is measured with either open-path or closed-path sensors. For the latter, fluctuations of scalar concentration are attenuated as the sample travels through a long tube, resulting in flux loss. To quantify this tube attenuation, water vapor concentrations measured with both closed-path and open-path sensors were analyzed. Our statistical analysis showed that the power spectral density obtained from the closed-path sensor was different from that from the open-path sensor in the frequency range of > 0.5 Hz. The loss of water vapor flux due to tube attenuation was < 5% during midday. At nighttime, however, the flux loss increased significantly because of the low wind speeds and the weak turbulence sources. Theoretical calculation for the tube attenuation showed a small bias in high frequency range probably because of the interaction of sticky water vapor with a tube wall.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.22 no.4
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• pp.323-329
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• 2004

Water vapor is an important parameter in monitoring changes in the Earth's climate and it can be used to improve weather forecasting. However, it haven't observed accurately by reasons of structural and economic problem of observation. GPS meteorology technique for precipitable water vapor measurement is currently actively being researched an advanced nation. Main issue of GPS meteorology is an accuracy of PWV measurement related weighted mean temperature and meteorological data. In this study, the korean weighted mean temperature had been recalculated by a linear regression method based on meteorological observations from 6 radiosonde stations for 2003 year. We examined the accuracy of PWV estimates from GPS observations and Radiosonde observations by new korean weighted mean temperature and others.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.27 no.5
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• pp.535-544
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• 2009

Signals from the Global Positioning System(GPS) satellite are used to retrieve the integrated amount of water vapor or the precipitable water vapor(PWV) along the path between a transmitting satellite and ground-based receiver. In order to retrieve the PWV from GPS signal delay in the troposphere, the actual zenith wet delay, which can be derived by extracting the zenith total delay and subtracting the actual zenith hydrostatic delay computed using surface pressure observing, will be needed. Since it has been not co-located between GPS permanent station and automated weather station, the air-pressure on the mean sea level has been used to determine the actual zenith hydrostatic delay. The directly use of this air-pressure has been caused the dilution of precision on GPS PWV retrieval. In this study, Korean reverse sea level correction method of air-pressure was suggested for the improving of GPS PWV retrieval capability and the accuracy of water vapor estimated by GPS was evaluated through a comparison with radiosonde PWV.

• Journal of Adhesion and Interface
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• v.5 no.1
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• pp.29-35
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• 2004

We have prepared polyster/nanQhybridized polyimide films in the range of 1~9 wt% of organophilic synthetic layered silicate (STN). Firstly, poly(amic acid)/STN nanocomposite solutions were prepared via solution blending method in DMAc or THF/MeOH solution, and then cast on the polyester film followed by imidization reaction, thermal and chemical method repestively. XRD and TEM experiment showed that the STN was fully exfoliated through the polyimide matrix. Surface morphologies of nanohybridized polyimide films were characterized by AFM and thermal, mechanical properties were also confirmed by TGA, DMA and UTM each. And also, the water vapor permeabilities highly depended on the content of STN. The sample from chemical imidization route and THF/MeOH solvent system showed better water vapor barrier properties than thermal one and DMAc system.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.52-53
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• 2005

$Y_2O_3$ film was directly deposited on Ni-3at%W substrate using DC reactive sputtering technique. Metallic yttrium was used for DC sputtering target and water vapor was used for oxidizing the deposited metallic Yttrium atoms on the substrate. The window of the water vapor turned out to be broad. The minimum partial pressure of water vapor was determined by sufficient oxidation of the $Y_2O_3$ film, and the maximum partial pressure of water vapor was determined by the non-oxidation of the target surface. As the sputtering power was increased, The deposition rate increased without narrowing the window. The fabricated $Y_2O_3$ films showed good texture qualities and surface morphologies. The YBCO film deposited directly on the $Y_2O_3$ buffered Ni-3at%W substrate showed $T_c$, $I_c$ (77 K, self field), and $J_c$ (77 K, self field) of 89 K, 64 A/cm and 1.l $MA/cm^2$, respectively.

• Journal of the Korean Institute of Gas
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• v.2 no.4
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• pp.47-52
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• 1998

Water vapor absorption performance of four components solution ($LiBr+LiNO_3+LiC1+H_2O$) which could be substituted for commonly used $LiBr/H_2O$ solution in water cooled abosorption chiller is tested using a vertical tube absorber. Inlet solution concentration, inlet solution temperature, solution flow rate and inlet temperature of cooling water is varied as experimental parameters. The results of the experiment of water vapor absorption performance show that four components solution should have $2\%$ higher concentration for equal absorption capacity of $LiBr/H_2O$. But considering that four components solution have higher solubility than LiBr solution about $3\%$ high oncentration, four components solution ($LiBr+LiNO_3+LiC1+H_2O$) have more absorption capacity than LiBr solution in actual absorption chiller and can be applied to a small or air cooled absorption chiller.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.258-258
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• 2014

Spark discharge in water generates shockwaves which have been utilized to generate mechanical actuation for potential use in pumping application. Discharge pulses of several microseconds generate shockwaves and vapor bubbles which subsequently displace the water for a period of milliseconds. Through the use of a sealed discharge chamber and metal bellow spring, the fluid motion can be used create an oscillating linear actuator. Continuous actuation of the bellow has been demonstrated through the use of high frequency spark discharge. Discharge in water forms a region of high electric field around the electrode tip which leads to the creation of a thermal plasma channel. This process produces fast thermal expansion, vapor and bubble generation, and a subsequent shockwave in the water which creates physical displacement of the water [1]. Previous work was been conducted to utilize the shockwave effect of spark discharge in water for the inactivation of bacteria, removal of mineral fouling, and the formation of sheet metal [2-4]. Pulses ranging from 25 to 40 kV and 600 to 900 A are generated inside of the chamber and the bellow motion is captured using a slow motion video camera. The maximum displacements measured are from 0.7 to 1.2 mm and show that there is a correlation between discharge energy input to the water and the displacement that is generated. Subsequent oscillations of the bellow are created by the spring force of the bellow and vapor in the chamber. Using microsecond shutter speed ICCD imaging, the development of the discharge bubble and spark can be observed and measured.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.28 no.11
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• pp.434-443
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• 2016

The evaporation of water from an aqueous solution is widely used in the food, desalination, pulp, and chemical industries. Usually, a large amount of energy is consumed in the evaporation process to boil off water due to atmospheric pressure. As a way of improving the energy efficiency of the evaporation process, the combination of multiple effect evaporation and thermal vapor recompression has been proposed and has become a successful technique. In this study, 4 multiple-effect falling film type evaporators for sugar solution are designed and the energy efficiency of the system is analyzed in response to the selection of the steam ejector position. Energy efficiency is increased and vapor is more compressed in the steam ejector as the Thermal Vapor Recompression (TVR) is arranged in the rear part of the evaporator system. A simplified 0-dimensional evaporator model is developed using non-linear equations derived from mass balances, energy balances, and heat transfer equations. Steam economy is calculated to compare the evaporation performance of the 4 proposed evaporators. The entrainment ratio, compression ratio, and expansion ratio are computed to check the ejector performance.

• Membrane Journal
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• v.23 no.3
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• pp.237-244
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• 2013

We fabricated several composite membranes with selectively permeable performance designed to facilitate water vapor transport and resist DMMP vapor permeation. Materials for selective permeable membrane were based on polyvinyl alcohol and functional polymer containing basic functional group. With these materials, we characterized selectively permeable performance to identify next-generation material with chemical-biological protective capability. Results showed that polyvinyl alcohol (PVA)/polyethyleneimine (PEI) materials possessed performance with superior water vapor permeation ($2,200{\sim}2,900g/m^2/day$) and protective capability against DMMP vapor ($47g/m^2/day$).

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.4
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• pp.499-509
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• 1998

In the absorption process of water vapor in a liquid film, the composition of the gas phase, in which a non-absorbable gas is combined with the absorbate influences the transport characteristics remarkably. In the present study, the absorption processes of water vapor into aqueous solution of lithium bromide in the presence of non-absorbable gases were investigated analytically. The continuity, momentum, energy and diffusion equations for the solution film and gas phase were formulated in integral forms and solved numerically. It was found that the mass transfer resistance in gas phase increased with the concentration of non-absorbable gas. However the primary resistance to mass transfer was in the liquid phase. As the concentration of non-absorbable gas in the absorbate increased, the liquid-vapor interfacial temperature and concentration of absorbate in solution decreased, which resulted in the reduction of absorption rate. The reduction of mass transfer rate was found to be significant for the addition of a small amount of non-absorbable gas to the pure vapor, especially at the outlet of an absorber where non-absorbable gases accumulated. At higher non-absorbable gas concentration, the decrease of absorption flux was almost linear to the volumetric concentration of non-absorbable gas.