• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.8 no.6
• /
• pp.1307-1312
• /
• 2007

The flow characteristics of R-134a in a small diameter tube was investigated experimentally. An experimental apparatus was consisted of a magnetic gear pump, an evaporator, a sight-glass, a condenser and a measurement instruments. The sight-glass for flow pattern observations was located at the inlet and outlet of the evaporator. The experiment was carried out to show the flow characteristics of R-134a in a small diameter tube. Mass flux of refrigerants was ranged from 100 to 1000 $kg/m^2s$, the saturation temperature was $30^{\circ}C$. In the flow patterns during evaporation, the annular flow in a 2 mm inner diameter tube occurred at a relatively lower quality and mass velocity, compared to that in a 8 mm inner diameter tube. The evaporation flow pattern in a small diameter tube has been shown major deviations with the Baker, Mandhane and Taitel-Dutler's flow pattern maps but it was similar to the Dobson's flow pattern map.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.41 no.3
• /
• pp.226-232
• /
• 2013

A compact hydrogen generation device of fuel cell system using chemical hydride storage technique was designed to fit the propulsion device requirement of a small unmanned aerial vehicle(SUAV). For high efficient, compact, and lightweight hydrogen generation control device, the Co-B catalyst hydrogen conversion rate by $NaBH_4$ aqueous solution flux is measured so that the proper amount of Co-B catalyst for maximum hydrogen generation of 100W stack was proposed. A compact hydrogen generation device is controlled by pump's on/off using its own internal pressure and consumes fuel in high efficiency through a dead-end type fuel cell. The fuel cell system has stable operation for a planed flight profile. The system operates up to maximum 7 hours and at least 4 hours for tough flight profiles.

• Membrane Journal
• /
• v.21 no.2
• /
• pp.155-162
• /
• 2011

Dense tubular $Ba_{0.5}Sr_{0.5}Co_{0.8}Fe_{0.2}O_{3-{\delta}}$ (BSCF) membranes were prepared by extrusion technique. The phase structure of the $Ba_{0.5}Sr_{0.5}Co_{0.8}Fe_{0.2}O_{3-{\delta}}$ membranes was characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). Relative density of $Ba_{0.5}Sr_{0.5}Co_{0.8}Fe_{0.2}O_{3-{\delta}}$ tubular membrane was 94.10%. Oxygen permeation was measured at difference operating condition of feed side and permeate side in the temperature range from 700 to $950^{\circ}C$. The oxygen permeation flux of dense tubular $Ba_{0.5}Sr_{0.5}Co_{0.8}Fe_{0.2}O_{3-{\delta}}$ membrane reached maximum 1.37 mL/$min{\cdot}cm^2$ at $900^{\circ}C$ exposed to ambient air (feed side) and vacuum pump (permeate side).

• Journal of Korean Society of Environmental Engineers
• /
• v.27 no.11
• /
• pp.1168-1173
• /
• 2005

Pilot scale vertical-type membrane bioreactor was operated to examine the effect of $FeCl_3$ injection on the removal of organics, nitrogen and phosphorous, and additionally trans-membrane pressure (TMP) was observed. The membrane type was hollow fiber membrane with pore size of $0.25\;{\mu}m$, and the material was polytetrafluoroethylene (PTFE). The membrane permeate was continuously removed by a pump under a constant flux ($25\;L/m^2/h$). Air back-flushing technique were adopted to reduce fouling. As a result, TMP was increased more slowly than that of the operation without air back-flushing, During long-term operation, approximately 310 days, the injection of $FeCl_3$ was effective not only in removing phosphorous chemically but also in reducing TMP increase. Furthermore, while the average COD and T-N concentration of the effluent without $FeCl_3$ injection was 14.3 mg/L and 6.0 mg/L respectively, that of effluent with $FeCl_3$ was 11.3 mg/L and 6.0 mg/L respectively, which confirmed the effects of $FeCl_3$.

• Journal of Hydrogen and New Energy
• /
• v.22 no.2
• /
• pp.161-167
• /
• 2011

Proton conductors have attracted considerable attention for solid oxide fuel cell (SOFC), hydrogen pump, gas sensor, and membrane separators. Doped $SrCeO_3$ exhibits appreciable proton conductivity in hydrogen-containing atmosphere at high temperature. However commercial realization has been hampered due to the reactivity of $SrCeO_3$ with $CO_2$. The chemical stability and proton conductivity are dependent on dopant type. The purpose of this work is to investigate chemical stability of $SrCe_{0.95}Gd_{0.05}O_{3-\alpha}-Ce_{0.9}Gd_{0.1}O_{2-\beta}$ composites in $CO_2$ and $H_2$ gases. Thermogravimetric analysis (TGA) was performed in gaseous $CO_2$ and electrical conductivity of the composites were also measured between 500 and $900^{\circ}C$ in air and $H_2$ atmosphere. $SrCe_{0.95}Gd_{0.05}O_{3-\alpha}-Ce_{0.9}Gd_{0.1}O_{2-\beta}$ composite membranes showed good chemical stability of in $CO_2$ atmosphere and high conductivity at hydrogen condition. The hydrogen permeation of $SrCe_{0.95}Gd_{0.05}O_{3-\alpha}-Ce_{0.9}Gd_{0.1}O_{2-\beta}$ composite membranes was investigated as a function of volumetric content of $SrCe_{0.95}Gd_{0.05}O_{3-\alpha}$. The $SrCe_{0.95}Gd_{0.05}O_{3-\alpha}-Ce_{0.9}Gd_{0.1}O_{2-\beta}$(6:4) membrane with a thickness of 1.0 mm showed the highest hydrogen permeability with the flux reaching of 0.12 $ml/min{\cdot}cm^2$ at $800^{\circ}C$ in 100%$H_2/N_2$ as feed gas.

• Progress in Superconductivity
• /
• v.13 no.1
• /
• pp.58-63
• /
• 2011

Recently, superconductor flywheel energy storage systems (SFESs) have been developed for application to a regenerative power of train, a power quality improvement, the storage of distributed power sources such as solar and wind power, and a load leveling. As the high temperature superconductor (HTS) bearings offer dynamic stability without the use of active control, accurate analysis of the HTS bearing is very important for application to SFESs. Mechanical property of a HTS bearing is the main index for evaluating the capacity of an HTS bearing and is determined by the interaction between the HTS bulks and the permanent magnet (PM) rotor. HTS bearing rotor consists of PM and iron collector and the proper dimension design of them is very important to determine a supporting characteristics. In this study, we have optimized a rotor magnet array, which depends on the limited bulk size and performed various dimension layouts for thickness of the pole pitch and iron collector. HTS bearing rotor was installed into a single axis universal test machine for a stiffness test. A hydraulic pump was used to control the amplitude and frequency of the rotor vibration. As a result, the stiffness result showed a large difference more than 30 % according to the thickness of permanent magnet and iron collector. This is closely related to the bulk stiffness controlled by flux pining area, which is limited by the total bulk dimension. Finally, the optimized HTS bearing rotor was installed into a flywheel system for a dynamic stability test. We discussed the dynamic properties of the superconductor bearing rotor and these results can be used for the optimal design of HTS bearings of the 10kWh SFESs.

• Korean Chemical Engineering Research
• /
• v.49 no.6
• /
• pp.804-809
• /
• 2011

Tubular $Ba_{0.5}Sr_{0.5}Co_{0.8}Fe_{0.2}O_{3-${\delta}$}$ membranes were prepared by extrusion. TGA results of green body membrane after extrusion showed three successive weight losses due to decomposition of organic additives and carbonate. Drying shrinkage rate of tubular $Ba_{0.5}Sr_{0.5}Co_{0.8}Fe_{0.2}O_{3-${\delta}$}$ membranes was no change after 68 h and higher in the membrane with large outer diameter. XRD and SEM results showed the sintered membranes were the single phase structure and dense. The stoichiometric molar ratio agreed well with composition ratio calculated by EDS results for $Ba_{0.5}Sr_{0.5}Co_{0.8}Fe_{0.2}O_{3-${\delta}$}$ membrane. Radial crushing strength of tubular $Ba_{0.5}Sr_{0.5}Co_{0.8}Fe_{0.2}O_{3-${\delta}$}$ membrane with 0.95 mm thickness was 5.7 kgf/$mm^2$ and the oxygen permeation rate of same membrane was 146.85 mL/min ($Jo_2$=2.33 mL/$min{\cdot}cm^2$) at $950^{\circ}C$. Therefore, it was known that use of vacuum pump was more effective than that of sweep gas to obtain higher oxygen permeation flux.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.26 no.4
• /
• pp.327-342
• /
• 2021

The global coastal region is considered as a sink for atmospheric CO₂. Since most of the studies in the East Sea focused on the Ulleung Basin, the importance of coastal region for carbon cycle has been overlooked. In this study, we compared the biological pump and CO₂ absorption between the Ulleung Basin and coastal region by surface measurements of biological O₂ supersaturation (𝚫O₂/Ar) and partial pressure of CO₂ (fCO₂). Cold and less saline waters in the coastal regions were in contrast with a warm and saline water in the Ulleung Basin. The coastal waters near Samcheok and Pohang showed higher fluorescence, 𝚫O₂/Ar, and lower fCO₂ than those in the Ulleung Basin, indicating higher primary production and CO₂ absorption in the areas. The average net community production estimated by 𝚫O₂/Ar were 19 ± 6 and 60 ± 9 mmol O₂ m^-2d^-1 in the Samcheok and Pohang, respectively, 2-7 times higher than that of 8 ± 4 mmol O₂ m^-2d^-1 in the Ulleung Basin. Similarly, the average CO₂ flux between the seawater and atmosphere were -17.1 ± 8.9 and -25.8 ± 13.2 mmol C m^-2d^-1 in the Samcheok and Pohang, respectively, 4-5 times higher than that of -4.7 ± 2.5 mmol C m^-2d^-1 in the Ulleung Basin. In the Samcheok and Pohang, degrees of N₂ saturation were lower by 3% than that the ambient waters, suggesting the possibility of nitrogen fixation by primary producers.

• Journal of Soil and Groundwater Environment
• /
• v.21 no.1
• /
• pp.49-60
• /
• 2016

Distribution and behavior of baseline soil CO₂ were investigated in a candidate geologic CO₂ storage site in Pohang, with measuring CO₂ concentrations and carbon isotopes in the vadose zone as well as CO₂ fluxes and concentrations through ground surface. This investigation aimed to assess the baseline CO₂ levels and to build the CO₂ monitoring system before injecting CO₂. The gas in the vadose zone was collected using a peristaltic pump from the depth of 60 cm below ground surface, and stored at gas bags. Then the gas components (CO₂, O₂, N₂, CH₄) and δ¹³C_CO2 were analyzed using GC and CRDS (cavity ringdown spectroscopy) respectively in laboratory. CO₂ fluxes and CO₂ concentrations through ground surface were measured using Li-COR in field. In result, the median of the CO₂ concentrations in the vadose zone was about 3,000 ppm, and the δ¹³C_CO2 were in the wide range between −36.9‰ and −10.6‰. The results imply that the fate of CO₂ in the vadose zone was affected by soil property and vegetations. CO₂ in sandy or loamy soils originated from the respiration of microorganisms and the decomposition of C₃ plants. In gravel areas, the CO₂ concentrations decreased while the δ¹³C_CO2 increased because of the mixing with the atmospheric gas. In addition, the relation between O₂ and CO₂, N₂, and the relation between N₂/O₂ and CO₂ implied that the gases in the vadose zone dissolved in the infiltrating precipitation or the soil moisture. The median CO₂ flux through ground surface was 2.9 g/m²/d which is lower than the reported soil CO₂ fluxes in areas with temperate climates. CO₂ fluxes measured in sandy and loamy soil areas were higher (median 5.2 g/m²/d) than those in gravel areas (2.6 g/m²/d). The relationships between CO₂ fluxes and concentrations suggested that the transport of CO₂ from the vadose zone to ground surface was dominated by diffusion in the study area. In gravel areas, the mixing with atmospheric gases was significant. Based on this study result, a soil monitoring procedure has been established for a candidate geologic CO₂ storage site. Also, this study result provides ideas for innovating soil monitoring technologies.