• Proceedings of the KSME Conference
• /
• 2000.04b
• /
• pp.154-161
• /
• 2000

As a mass flow controller is widely used in many manufacturing processes for controlling a mass flow rate of gas with accuracy of 1%, several investigators have tried to describe the heat transfer phenomena in a sensor tube of an MFC. They suggested a few analytic solutions and numerical models based on simple assumptions, which are physically unrealistic. In the present work, the heat transfer phenomena in the sensor tube of the MFC are studied by using both experimental and numerical methods. The numerical model is introduced to estimate the temperature profile in the sensor tube as well as in the gas stream. In the numerical model, the conjugate heat transfer problem comprising the tube wall and the gas stream is analyzed to fully understand the heat transfer interaction between the sensor tube and the fluid stream using a single domain approach. This numerical model is further verified by experimental investigation. In order to describe the transport of heat energy in both the flow region and the sensor tube, the Nusselt number at the interface between the tube wall and the gas stream as well as heatlines is presented from the numerical solution.

• Membrane Journal
• /
• v.12 no.3
• /
• pp.143-150
• /
• 2002

Electrodialysis(ED) is a reliable and effective process for the separation and concentration of ionic compounds. However, commercial uses of ED are often hindered by the cost of the stack that mainly resulted from the ion-exchange membrane cost. In order to minimize the membrane cost, it is desired to operate ED at the highest practicable current density. In an actual ED system the high current operation is limited by the concentration polarization phenomenon. This article illustrates the transport phenomena of ions through ion exchange membranes using current-voltage relations as a characterizing method. Also recent studies on electroconvection and water-spitting phenomena caused by concentration polarization were reviewed.

• Korean Journal of Medicinal Crop Science
• /
• v.7 no.2
• /
• pp.129-137
• /
• 1999

The structure of amyloplasts and intercellular transport in the old and new bulbs of Frjtillaria pallidiflora were observed by means of electron microscope. The structure of internal membrane system was different between new and old amyloplasts. The active intercellular transport was observed in both new and old bulbs. The phenomena of encytosis and exocytosis always could be found in the cell membrane, and plasmodesmata established a symplasmic pathway for intercellular transport. Groups of vesicles often located at the ends of plasmodesmata, showing that they participated in the intercellular transport. These results laid a foundation for the further study on the mechanism of growth and development in Fritillaria pallidiflora.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.25 no.6
• /
• pp.405-411
• /
• 2013

A sediment transport calculation considering cohesive force is proposed to deal with the transport phenomena of cohesive sediment. In the proposed calculation, each sand particle is assumed to be surrounded by a thin layer of mud. The critical Shields parameter and bed-load sediment transport rate are modified to include the cohesive force acting on the sand particle. The proposed calculation is incorporated into a two-way coupled fluid-structure-sediment interaction model, and applied to wave-induced topographic change of artificial shallows. Numerical results show that an increase in the content ratio of the mud, cohesive resistance force per unit surface area and water content cause increases in the critical Shields parameter and decreases in the bed-load sediment transport rate, reducing the topographic change of the shallow without changing its trend. This suggests that mixing mud in the pores of the sand particles can reduce the topographic change of shallows.

• Journal of the Korean Chemical Society
• /
• v.28 no.3
• /
• pp.163-169
• /
• 1984

The transport rates of $K^+$ion through CHCl$_3$ liquid membrane containing dibenzo-18-crown-6(DBC) as a carrier molecule have been determined at $25^{\circ}C$. The transport rates depend highly on the ion concentration and on the nature of anion. It is concluded that $K^+$ions are transported in the form of ion-pair. In the case of potassium picrate, however, it is found that the transport proceeds with the formation of the incomplete ion-pair in the concentration less than 1.0 ${\times}10^{-3}$M of picrate, while with the complete formation of ion-pair in the concentration more than 1.0 ${\times}10^{-3}$M of picrate. Seven steps of the transport process are suggested and they can be illustrated in terms of energy barrier model as a function of the position of ionic species in the membrane.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.28 no.6
• /
• pp.403-407
• /
• 2015

Generally, MWCNT, with thermal, chemical and electrical superiority, is manufactured with CVD (chemical vapor deposition). Using MWCNT, it is comonly used as gas sensor of MOS-FET structure. In this study, in order to repeatedly detect gases, the author had to effectively eliminate gases absorbed in a MWCNT sensor. So as to eliminate gases absorbed in a MWCNT sensor, the sensor was applied heat of 423[K], and in order to observe how the applied heat was diffused within the sensor, the author interpreted the diffusion process of heat, using COMSOL interpretation program. In order to interpret the diffusion process of heat, the author progressed modeling with the structure of MWCNT gas sensor in 2-dimension, and defining heat transfer velocity($u={\Delta}T/{\Delta}x$), accorded to governing equation within the sensor, the author proposed heat transfer mechanism.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.7 no.1
• /
• pp.27-40
• /
• 1997

The heat in Czochralski method is transfered by all transport mechanisms such as convection, conduction and radiation and convection is caused by the temperature difference in the molden pool, the rotations of crystal or crucible and the difference of surface tension. This study delvelops the simulation model of Czochralski growth by using the finite difference method with fixed grids combined with new latent heat treatment model. The radiative heat transfer occured in the surfce of the system is treated by calculating the view factors among surface elements. The model shows that the flow is turbulent, therefore, turbulent modeling must be used to simulate the transport phenomena in the real system applied to 8" Si single crystal growth process. The effects of a cusp magnetic field imposed on the Czochralski silicon melt are studied by numerical analysis. The cusp magnetic field reduces the natural and forced convection due to the rotation of crystal and crucible very effectively. It is shown that the oxygen concentration distribution on the melt/crystal interface is sensitively controlled by the change of the magnetic field intensity. This provides an interesting way to tune the desired O concentration in the crystal during the crystal growing.

• Proceedings of the KIEE Conference
• /
• 2011.07a
• /
• pp.1582-1583
• /
• 2011

Recently, it has been found that trifluoroiodomethane ( $CF_3I$) gas can replace $SF_6$ gas as a prospective substitute gas. For quantitative understanding of gas discharge phenomena, we should know electron collision cross sections and electron transport coefficients. Using electron collision cross sections of $CF_3I$ and Xe, we calculated elecron drift velocity, longitudinal coefficient, effective ionization coefficient in $CF_3I$-Xe mixtures using a two-term approximation of the Boltzmann equation. We also compared the electron transport coefficients in pure gas and those of 10%, 20%, 50%, and 70% $CF_3I$-Xe mixture gases. The present data may be showed appropriate ratios of $CF_3I$-Xe mixture gas for replacing the $SF_6$ gas.

• Transactions of the Korean Society of Machine Tool Engineers
• /
• v.16 no.3
• /
• pp.133-140
• /
• 2007

A 2-D model of fluid flow, mass transport and electrochemistry is analysed to examine the effect of current density at the current collector depending on active layer thickness of catlyst in polymer elecrolyte fuel cells. The finite element method is used to solve the continuity, potential and Maxwell-Stefan equations in the flow channel and gas diffusion electrode regions. For the material behavior of electrode reactions in the active catalyst layers, the agglomerate model is implemented to solve the diffusion-reaction problem. The calculated model results are described and compared with the different thickness of active catalyst layers. The significance of the results is discussed in the viewpoint of the current collecting capabilities as well as mass transportation phenomena, which is inferred that the mass transport of reactants dictates the efficiency of the electrode in the present analysis.

• Journal of Korean Society for Atmospheric Environment
• /
• v.12 no.5
• /
• pp.593-596
• /
• 1996

The encironmental consequences of airborne mercury (Hg) release from waste incineration system are wellperceived. To provide some insights into those phenomena, we have assessed annual emission rates of Hg for several major incineration systems in Korea following the procedures developed abroad. The results of our computation, derived on the basis of dividing the whole amounts of annually incinerated wastes into municipal solid Wastes (MSW), and medical solid wastes (MDW), indicate that the extent of Hg release may be significant nationwide, possibly approaching a few tonnes of Hg per year basis. Knowing that the airborne transport and the resulting deposition of Hg can exert serious pollutions to the aquatic ecosystems, of particular fisheries, we are obliged to establish a stringent measure to confine the amount of Hg released via incineration.