• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.7 s.94
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• pp.1823-1832
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• 1993

CWS(coal-water slurry) is used for application in power plants, boilers, industrial furnaces. A single coal-water slurry droplet ignition has been examined to reveal the basic nature of their evaporation, volatilization and heating processes. The interior droplet temperature distribution has been considered. The effect of coal thermal conductivity, droplet size, water fraction in the slurry, gas temperature and velocity and radiation on the ignition phenomena were also studied. Either increasing the velocity and gas temperature or decreasing the droplet size and water fraction in the slurry may reduce the time for evaporation and ignition delay time.

• Bulletin of the Korean Chemical Society
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• v.12 no.1
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• pp.97-101
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• 1991

Gas-phase pyrolyses of carbonate esters, ${\alpha}$- and ${\beta}$-hydroxy esters and ${\beta}$-hydroxy ketones have been studied theoretically by the AM1 MO method. Carbonate esters were found to decompose by two types of processes; in the reaction pathway involving an intermediate, the decomposition of the intermediate was rate-limiting, but direct pyrolyses were also possible via a six-membered cyclic transition state in which the methoxy oxygen attacks a hydrogen atom on the ${\beta}$-carbon. The hydroxy esters and ketones were found to decompose in a concerted process involving a six-membered cyclic transition state. Successive methylation on the ${\alpha}$- and ${\gamma}$-carbon led to an increase in the reactivity in agreement with experiments.

• Journal of Sensor Science and Technology
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• v.33 no.5
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• pp.255-258
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• 2024

Exhaled breath analysis has emerged as a non-invasive and cost-effective approach in medical diagnostics, particularly for detecting biomarkers such as acetone. This study presents the synthesis and characterization of Cr-doped ε-WO₃ spheres designed to improve gas-sensing performance. These spheres were synthesized via ultrasonic spray pyrolysis, resulting in a material with a complex composition exhibiting high sensitivity and selectivity towards acetone over ethanol (response ratio = 13.2 at 325℃). The enhanced acetone sensitivity of the Cr-doped WO₃ sensor is attributed to the strong interaction between the spontaneous electric dipole moment of ε-WO₃ and the significant dipole moment of acetone. This sensor can detect exhaled acetone, facilitating effective monitoring of a ketogenic diet.

• Journal of the Korean Institute of Gas
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• v.17 no.5
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• pp.28-36
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• 2013

The underground coal which is buried in the ground will have a lot of attention to overcome energy crisis as an energy resources standpoint. Many studies of underground coal gasification have been also conducted because of its advantage which does not require mining. In this study, the simulation of underground coal gasification process was carried out with Aspen Plus. This study was executed by Rock Mountain 1 Underground Coal Gasification project in the United States in the late 1980s as a reference. Sensitivity analysis proceeded to investigate synthesis gas characteristics following different injection condition of oxidizing agent. The underground coal gasification model has been implemented. That is divided into drying, pyrolysis, char gasification and the simulation results was confirmed by the production gas flow, yield of synthesis gas and amount of gasified carbon from results of the actual experimental data.

• Journal of the Korean Wood Science and Technology
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• v.44 no.3
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• pp.350-359
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• 2016

We performed fast pyrolysis of empty fruit bunch (EFB) in the range of temperature from $400{\sim}550^{\circ}C$ and 1.3 s of residence time. The effect of temperature on the yields and physicochemical properties of pyrolytic products were also studied. Elemental and component analysis of EFB showed that the large amount of potassium (ca. 8400 ppm) presents in the feedstock. Thermogravimetric analysis suggested that the potassium in the feedstock catalyzed degradation of cellulose. The yield of bio-oil increased with increasing temperature in the range of temperature from $400{\sim}500^{\circ}C$, while that of gas and biochar decreased and showed monotonous change each with increasing temperature. When the EFB was pyrolyzed at $550^{\circ}C$, the yield of bio-oil and char decreased while that of gas increased. Water content of the bio-oils obtained at different temperatures was 20~30% and their total acid number were less than 100 mg KOH/g oil. Viscosity of the bio-oils was 11 cSt (centistoke), and heating value varied from 15 to 17 MJ/kg. Using GC/MS analysis, 27 chemical compounds which were classified into two groups (cellulose-derived and lignin-derived) were identified. Remarkably the concentration of phenol was approximately 25% based on entire chemical compounds.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.04b
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• pp.93-93
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• 2009

In order to overcome the lack of reactivity with hydrogen gas ($H_2$) and utilize unique properties of Carbon Nano Tubes (CNTs) for the application to hydrogen sensors, there have been intensive works on the surface functionalization of CNTs with various types of nanoparticles including Pd. In the present work, we have investigated the effect of dendrimers and Pd nanoparticles to the hydrogen sensing properties of CNTs by comparing three types of samples: Pd/SWNTs (Sample I), Pd/dendrimer/SWNTs (Sample II) and heat-treated Pd/dendrimers/SWNTs (Sample III). As a result of IV measurement under the $H_2$ and air, sample I was found to have a high sensitivity (25%) to $H_2$, but to have a very slow response time (324 s) and recovery rate. On the other hand, Sample II was found to show much faster response time (3 s) and good recovery rate but lower sensitivity (8.6%) than Sample I which is due to induced dipole moments in the dendrimers. Interestingly, Sample III showed both fast response time (7 s) and high sensitivity (25%), indicating that the pyrolysis of the dendrimers during heat treatment which reduce the distance between the surface of the SWNTs and the functionalized Pd nanoparticles plays a key role in improving the sensitivity. The pyrolysis of the dendrimers in Pd nanoparticle-dendrimer-SWNTs was found to enable a significant electrical conductance modulation upon exposure to extremely low concentrations (10 ppm) of $H_2$ in air. Our results demonstrate that the Pd Nanoparticle-Grafted Single-Walled Carbon Nanotubes(SWNTs) with Dendrimers can be used to detect hydrogen, makingoutstanding properties such as fast response, and recovery time, high sensitivity, low detection limit at room temperature compared with other types of hydrogen sensors.

• Journal of the Korean Electrochemical Society
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• v.6 no.1
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• pp.6-12
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• 2003

Plasma carbon black(PB) which prepared by plasma pyrolysis of methane was treated at 800, 1300 and $2100^{\circ}C$ under $2\times10^{-2}$ torr. Four different samples including raw PB were added to $LiCoO_2$, cathode active material of lithium secondary battery, to investigate effects of properties of plasma black as conductors on electrochemical characteristics. Based on our experimental results, PB conductors with low amount of surface functional groups and high electrical conductivity enhanced the cyclability and the initial discharge capacity. However, deterioration of rate capability and cyclability were observed (or the plasma black treated at $2100^{\circ}C$ For the plasma black conductor prepared from plasma pyrolysis, the effects of properties of carbon black on electrochemical characteristics were combined results of changes in electrical conductivity and structural properties such as agglomeration of plasma black. The conductivity of plasma black increased with treatment temperature, while dispersion of plasma black decreased. As a result, the high cyclability of cell was observed at $800^{\circ}C$ of heat treatment temperature.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.1
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• pp.12-18
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• 2019

The spherical $SiO_2$ powders were synthesized by the scaled-up ultrasonic pyrolysis (USP). The aqueous $SiO_2$ sol, which contained 20~30 nm $SiO_2$ particles, was used as a precursor for the scaled-up USP. The effects of the USP operating conditions and precursor conditions were systematically investigated, including reaction temperature, gas flow rate, and the concentration of $SiO_2$ sol on the morphologies of synthesized $SiO_2$ particles. the synthesized $SiO_2$ particle showed a pseudo-crystal phase, spherical morphology, and a smooth surface. The size of the spherical $SiO_2$ particle decreased as both reaction temperature increased and precursor concentration decreased. In addition, the synthesized $SiO_2$ particle size was increased by increasing the gas flow rate. Lastly, the scaled-up USP was compared with the lab-scale USP based on the same process conditions. Due to a short retention time in the reaction tube during the USP process, the $SiO_2$ particle synthesized via the lab-scale USP showed a larger particle size.

• Journal of Korea Foundry Society
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• v.43 no.4
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• pp.187-193
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• 2023

Shell core making is an excellent process in terms of formability and desanding, but when the molten aluminum comes into con- tact with the shell core, gas generation by pyrolysis of the resin is inevitable. In addition, when the ventilation is inadequate, pores will remain inside the casting, which can directly lead to defects of the casting. While studies on the gas generation behavior of shell core making have been reported, the modeling of gas generation has not been extensively investigated. We will develop a gas evolution analysis method that considers the relationship between temperature and gas quantity for the core to be developed. We then use the developed method to analyze the flow and solidification behavior of metal molten metal during core mold design and low-pressure casting of cylinder head products, and predict the occurrence of casting defects to derive a casting method that min- imizes the occurrence of defects.

• Korean Chemical Engineering Research
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• v.50 no.3
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• pp.511-515
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• 2012

In this study, we used a commercial simulator to investigate the gasification characteristics of Roto coal in the partitioned fluidized-bed gasifier, which consists of 4 parts such as coal pyrolysis, char gasification, tar/oil gasification and char combustion. The heating medium was exchanged between the combustion part and the gasification part in order to supply the energy needed for pyrolysis and gasification. The correlation model from experimental data in relation to the reaction temperatures, the reaction gases and the coal feed rates was derived for the coal pyrolysis. The equilibrium model was used for the gasification and the combustion model for the char combustion. In order to compare the reaction behavior of the partitioned fluidized-bed gasifier, the single-bed gasifier was also simulated. The cold gas efficiency of both partitioned fluidized-bed gasifier and single-bed gasifier was almost the same. The $H_2$ and $CH_4$ contents of the syngas in the partitioned fluidized-bed gasifier slightly increased and the CO and $CO_2$ contents slightly decreased, compared with the singlebed gasifier. In order to verify the model, ten cases of the single-bed gasification experiment have been simulated. The contents of CO, $CO_2$, $CH_4$ in the syngas from the simulation corresponded with the experimental data while those of $H_2$ was slightly higher than experimental data, but the tendency of $H_2$ content in the syngas was similar to the experiments. In the coal conversion, the simulation results were higher than the experiments since equilibrium model was used for the gasification so that the residence time and contact time in the model is different from the experiments.