• Journal of Sensor Science and Technology
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• v.10 no.4
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• pp.222-231
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• 2001

The material properties of $SnO_2$ were investigated as a function of the amount of $Fe_2O_3$, the partial pressure of oxygen, the concentration of CO gas, and temperature. $Fe_2O_3$-doped $SnO_2$ thick films were prepared by the screen printing technique on alumina substrate. The specimens sintered at $700^{\circ}C$ for 6 hours showed little difference of the grain size and narrow distribution with the content of $Fe_2O_3$. The electrical conductance of undoped $SnO_2$ is high at low firing temperature and at low partial pressure of oxygen. The electrical conductance of $Fe_2O_3-$-doped $SnO_2$ is increased with measurement temperature, but decreased with the content of $Fe_2O_3$. The dependence of oxygen partial pressure is decreased with dopant addition. The highest sensitivity and the good properties of response speed and repeatability for CO gas were observed on the specimen with 0.1 mol% $Fe_2O_3$ at $350^{\circ}C$.

• Journal of Sensor Science and Technology
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• v.4 no.4
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• pp.16-22
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• 1995

Catalytic combustion type gas sensor was fabricated by using ${\gamma}-Al_{2}O_{3}$, Pd catalyst and some binders for metane and propane detection. Using the gas sensor, digital gas meter was manufactured and tested for sensing performance. The fabricated sensor had power consumption of 700mW with applied voltage of dc 2V and the output voltage of the sensor was about 700mV for propane of 1,000ppm and 500mV for methane of 1,000ppm. In 10 cycle injection of the gases of 2,400ppm, The digital meter showed good sensitivity, linearity, and reproductivity with precision of ${\pm}25ppm({\pm}1%)$.

• Journal of the Korean Physical Society
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• v.73 no.10
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• pp.1437-1443
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• 2018

In this work, $SnO_2$ modified with reduced graphene oxide (rGO) and carbon nanotubes (CNTs) separately and combined sensitized by using the co-precipitation method and their sensing behavior toward ethanol vapor at room temperature were investigated. An interdigitated electrode (IDE) gold substrate is very expensive compared to a fluorine doped tin oxide (FTO) substrate; hence, we used the latter to reduce the fabrication cost. The structure and the morphology of the studied materials were characterized by using differential thermal analyses (DTA) and thermogravimetric analysis (TGA), transmission electron microscope (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Brunauer-Emmett-Teller surface area and Barrett-Joyner-Halenda (BJH) pore size measurements. The studied composites were subjected to ethanol in its gas phase at concentrations from 10 to 200 ppm. The present composites showed high-performance sensitivity for many reasons: the incorporation of $SnO_2$ and CNTs which prevents the agglomeration of rGO sheets, the formation of a 3D mesopourus structure and an increase in the surface area. The decoration with rGO and CNTs led to more active sites, such as vacancies, which increased the adsorption of ethanol gas. In addition, the mesopore structure and the nano size of the $SnO_2$ particles allowed an efficient diffusion of gases to the active sites. Based on these results, the present composites should be considered as efficient and low-cost sensors for alcohol.

• Korean Chemical Engineering Research
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• v.53 no.6
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• pp.818-823
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• 2015

In this study, FT reaction in a microchannel was simulated using computational fluid dynamics(CFD), and sensitivity analyses conducted to see effects of channel geometry variables, namely, process channel width, height, gap between process channel and cooling channel, and gap between process channels on the channel temperature profile. Microchannel reactor considered in the study is composed of five reaction channels with height and width ranging from 0.5 mm to 5.0 mm. Cooling surfaces is assumed to be in isothermal condition to account for the heat exchange between the surface and process channels. A gas mixture of $H_2$ and CO($H_2/CO$ molar ratio = 2) is used as a reactant and operating conditions are the following: GHSV(gas hourly space velocity) = $10000h^{-1}$, pressure = 20 bar, and temperature = 483 K. From the simulation study, it was confirmed that heat removal in an FT microchannel reactor is affected channel geometry variables. Of the channel geometry variables considered, channel height and width have significant effect on the channel temperature profile. However, gap between cooling surface and process channel, and gap between process channels have little effect. Maximum temperature in the reaction channel was found to be proportional to channel height, and not affected by the width over a particular channel width size. Therefore, microchannels with smaller channel height(about less than 2 mm) and bigger channel width (about more than 4 mm), can be attractive design for better heat removal and higher production.

• Journal of Energy Engineering
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• v.14 no.1
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• pp.54-61
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• 2005

The APR1400 is an Advanced Pressurized Water Reactor with 3983 MWt power, 2×4 loops, and direct vessel injection system. The Fluidic Device (FD) is adopted to regulate the safety injection flow rate in a Safety Injection Tank (SIT) of APR1400. The performance of a newly designed fluidic Device is evaluated by analyzing a Large Break Loss-of-Coolant Accident (LBLOCA) using TRAC-M/F90, version 3.782. The analysis results show that the TRAC-M code reasonably predicts the important phenomena of blowdown, refill and reflood phases of LBLOCA. The sensitivity studies about gas/water volume changes in a SIT and K factor changes in a SI system were also done to understand the important phenomena with a Fluidic Device in APR1400.

• Korean Journal of Metals and Materials
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• v.47 no.6
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• pp.372-377
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• 2009

We report on hysteresis behavior in the electrical resistance-hydrogen concentration of Pd thin films. The variation of the electrical resistance has been investigated during the process of absorption and desorption of hydrogen gas ($H_{2}$) as a function of thickness of Pd thin films. The hysteresis behavior in the electrical resistance with $H_{2}$ concentration was found for Pd thin films and consists of $\alpha$ phase, ${\alpha}+{\beta}$ phase, and $\beta$ phase regions. The sensitivity of Pd thin films with $H_{2}$ concentration was found to follow Sieverts' law in the $\alpha$ phase region. However, the sensitivity was observed to increase abruptly with $H_{2}$ concentration in the ${\alpha}+{\beta}$ phase co-exist region. This is because Pd-H interaction is stronger in the $\beta$ phase than in the $\alpha$ phase and needs a higher concentration gradient as a driving force to desorb. The formation of the $\beta$ phase also was observed to cause the structural change because of the lattice expansion during absorption. The hysteresis height and the trace of structural change were affected by the thickness of the Pd film. As the film becomes thinner, the hysteresis height becomes lower and the amount of delamination on the surface becomes smaller. For films thinner than 20 nm in thickness, the delamination was not found but electrical resistance hysteresis was still observed.

• Journal of Energy Engineering
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• v.6 no.1
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• pp.104-113
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• 1997

This study aims to develop an analysis model using a commercial process simulator-ASPEN PLUS for an IGCC (Integrated Gasification Combined Cycle) system consisting a dry coal feeding, oxygen-blown entrained gasification process by Shell, a low temperature gas clean up process, a General Electric MS7001FA gas turbine, a three pressure, natural recirculation heat recovery steam generator, a regenerative, condensing steam turbine and a cryogenic air separation unit. The comparison between those results of this study and reference one done by other engineer at design conditions shows consistency which means the soundness of this model. The greater moisture contents in Illinois#6 coal causes decreasing gasifier temperature and the greater ash and sulfur content hurt system efficiency due to increased heat loss. As the results of sensitivity analysis using developed model for the parameters of gasifier operating pressure, steam/coal ratio and oxygen/coal ratio, the gasifier temperature increases while combustible gases (CO＋H2) decreases throughout the pressure going up. In the steam/coal ratio analysis, when the feeding steam increases the maximum combustible gas generation point moves to lower oxygen/coal ratio feeding condition. Finally, for the oxygen/coal ratio analysis, it shows oxygen/coal ratio 0.77 as a optimum operating condition at steam/coal feeding ratio 0.2.

• Korean Journal of Soil Science and Fertilizer
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• v.44 no.6
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• pp.1195-1206
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• 2011

This study was conducted to apply LCA (Life cycle assessment) methodology to lettuce (Lactuca sativa L.) production systems in Namyang-ju as a case study. Five lettuce growing farms with three different farming systems (two farms with organic farming system, one farm with a system without agricultural chemicals and two farms with conventional farming system) were selected at Namyangju city of Gyeonggi-province in Korea. The input data for LCA were collected by interviewing with the farmers. The system boundary was set at a cropping season without heating and cooling system for reducing uncertainties in data collection and calculation. Sensitivity analysis was carried out to find out the effect of type and amount of fertilizer and energy use on GHG (Greenhouse Gas) emission. The results of establishing GTG (Gate-to-Gate) inventory revealed that the quantity of fertilizer and energy input had the largest value in producing 1 kg lettuce, the amount of pesticide input the smallest. The amount of electricity input was the largest in all farms except farm 1 which purchased seedlings from outside. The quantity of direct field emission of $CO_2$, $CH_4$ and $N_2O$ from farm 1 to farm 5 were 6.79E-03 (farm 1), 8.10E-03 (farm 2), 1.82E-02 (farm 3), 7.51E-02 (farm 4) and 1.61E-02 (farm 5) kg $kg^{-1}$ lettuce, respectively. According to the result of LCI analysis focused on GHG, it was observed that $CO_2$ emission was 2.92E-01 (farm 1), 3.76E-01 (farm 2), 4.11E-01 (farm 3), 9.40E-01 (farm 4) and $5.37E-01kg\;CO_2\;kg^{-1}\;lettuce$ (farm 5), respectively. Carbon dioxide contribute to the most GHG emission. Carbon dioxide was mainly emitted in the process of energy production, which occupied 67~91% of $CO_2$ emission from every production process from 5 farms. Due to higher proportion of $CO_2$ emission from production of compound fertilizer in conventional crop system, conventional crop system had lower proportion of $CO_2$ emission from energy production than organic crop system did. With increasing inorganic fertilizer input, the process of lettuce cultivation covered higher proportion in $N_2O$ emission. Therefore, farms 1 and 2 covered 87% of total $N_2O$ emission; and farm 3 covered 64%. The carbon footprints from farm 1 to farm 5 were 3.40E-01 (farm 1), 4.31E-01 (farm 2), 5.32E-01 (farm 3), 1.08E+00 (farm 4) and 6.14E-01 (farm 5) kg $CO_2$-eq. $kg^{-1}$ lettuce, respectively. Results of sensitivity analysis revealed the soybean meal was the most sensitive among 4 types of fertilizer. The value of compound fertilizer was the least sensitive among every fertilizer imput. Electricity showed the largest sensitivity on $CO_2$ emission. However, the value of $N_2O$ variation was almost zero.

• Atmosphere
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• v.17 no.4
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• pp.365-379
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• 2007

Global warming may shift the properties and dynamics of ENSO. We study the changes in ENSO characteristics in a coupled general circulation model, ECHO-G/S. First, we analyse the mean state changes by comparing present day simulation and various high $CO_2$ climates. The model shows a little El Nino-like changes in the sea surface temperature and wind stress in the eastern tropical Pacific. As the mean temperature rises, the ENSO amplitude and the frequency of strong El Ninos and La Nina decrease. The analysis shows that the weakening of the oceanic sensitivities is related to the weakening of ENSO. In addition to the surface changes, the remote subsurface sea temperature response in the western Pacific to the wind stress in the eastern Pacific influences the subsequent ENSO amplitude. However, ENSO amplitude does not show linear response to the greenhouse gas concentrations.

• Korean Journal of Materials Research
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• v.13 no.7
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• pp.442-446
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• 2003

Tin dioxide ($SnO _2$) thin films were deposited at $375^{\circ}C$ on alumina substrate by metal-organic chemical vapor deposition. A few hillocks like a cauliflower were observed and the number of hillock on thin film surface increased with annealing temperature in air atmosphere. The oxygen content and the binding energy during air annealing at$ 500^{\circ}C$ came to close the stoichiometric $SnO_2$. The cauliflower hillocks seem to be the result of the continuous migration of the tiny grains to release the stress of an expanded grain. Sensitivity of CO gas depended on annealing temperature and increased with increasing annealing temperature.