Seok Min Hong

High-temperature CO2 sorption on Na2CO3-impregnated layered double hydroxides

Layered double hydroxide (LDH), one of representative high-temperature CO2 sorbents, has many advantages, including stable CO2 sorption, fast sorption kinetics, and low regeneration temperature. However, CO2 sorption uptake on LDH is not high enough for practical use; thus it is usually enhanced by impregnation with alkali metals such as K2CO3. In this study, LDH was impregnated with Na2CO3, and analyses based on scanning electron microscopy, N2 gas physisorption, in situ X-ray diffraction, and Fourier transform infrared spectroscopy were carried out to elucidate the characteristics of sorbents and the mechanism of CO2 sorption. Although the surface area of LDH decreased after Na2CO3 impregnation, CO2 sorption uptake was greatly enhanced by the additional basicity of Na2CO3. The crystal structure of Na2CO3 in the Na2CO3-impregnated LDH changed from monoclinic to hexagonal with increasing temperature, and the sorbed-CO2 was stored in the form of carbonate. Thermogravimetric analysis was used to measure CO2 sorption uptake at 200–600 °C. The sample of Na2CO3: LDH=0.35: 1 weight ratio had the largest CO2 sorption uptake among the tested sorbents, and the CO2 sorption uptake tended to increase even after 400 °C.

CO2 capture in the sustainable wheat-derived activated microporous carbon compartments

Microporous carbon compartments (MCCs) were developed via controlled carbonization of wheat flour producing large cavities that allow CO2 gas molecules to access micropores and adsorb effectively. KOH activation of MCCs was conducted at 700 °C with varying mass ratios of KOH/C ranging from 1 to 5, and the effects of activation conditions on the prepared carbon materials in terms of the characteristics and behavior of CO2 adsorption were investigated. Textural properties, such as specific surface area and total pore volume, linearly increased with the KOH/C ratio, attributed to the development of pores and enlargement of pores within carbon. The highest CO2 adsorption capacities of 5.70 mol kg−1 at 0 °C and 3.48 mol kg−1 at 25 °C were obtained for MCC activated with a KOH/C ratio of 3 (MCC-K3). In addition, CO2 adsorption uptake was significantly dependent on the volume of narrow micropores with a pore size of less than 0.8 nm rather than the volume of larger pores or surface area. MCC-K3 also exhibited excellent cyclic stability, facile regeneration, and rapid adsorption kinetics. As compared to the pseudo-first-order model, the pseudo-second-order kinetic model described the experimental adsorption data methodically.

Development of porous carbon nanofibers from electrospun polyvinylidene fluoride for CO2 capture

Highly porous carbon nanofibers (CNFs) are successfully prepared for CO2 capture from the carbonization of electrospun polyvinylidene fluoride (PVDF). In the CNF preparation, different temperatures in the range 300–1000 °C are applied for carbonization, and the effect of temperature is investigated. Well-developed porosities and enhanced CO2 adsorption uptakes are achieved by applying a large degree of carbonization at temperatures of 400 °C or above. In the carbonization at high temperatures, narrow micropores (<0.7 nm) are predominantly developed in the PVDF-based CNFs, contributing to an increase of specific surface area and pore volume up to 1065 m2 g−1 and 0.61 cm3 g−1, respectively. The highest CO2 adsorption uptake of 3.1 mol kg−1 is measured at 30 °C and ∼1 atm for PVDF-based CNF carbonized at 1000 °C. PVDF-based CNFs also display excellent recyclability and rapid adsorption–desorption kinetics, which make PVDF-based CNFs promising adsorbents for CO2 capture.

Solvent-assisted amine modification of graphite oxide for CO2 adsorption

Amine-modified graphite oxides (GAs) for CO2 adsorption were prepared using 3-aminopropyl-triethoxysilane. Graphite was first oxidized using highly concentrated acid, and then modified with the amine using a solvent-assisted method. Ethanol and water were used as the solvents, and the solvent effects were investigated. The morphological changes, functionalities, and compositions of the GAs were characterized by scanning electron microscopy, Fourier-transform infrared and X-ray photoelectron spectroscopies, and elemental analysis. The CO2 adsorption behavior was evaluated by thermogravimetric analysis at 30 °C under atmospheric pressure. The GA prepared in water (GA-W) had a higher CO2 adsorption uptake (1.64 mol kg−1) than did the GA prepared in ethanol (1.31 mol kg−1). The amine loading was predominantly influenced by the solvent, and water was an effective solvent for amine modification. GA-W also showed good regenerability in repeated adsorption–desorption cycles with high adsorption/desorption rates.

Enhanced Lithium- and Sodium-Ion Storage in an Interconnected Carbon Network Comprising Electronegative Fluorine

Fluorocarbon (CxFy) anode materials were developed for lithium- and sodium-ion batteries through a facile one-step carbonization of a single precursor, polyvinylidene fluoride (PVDF). Interconnected carbon network structures were produced with doped fluorine in high-temperature carbonization at 500-800 °C. The fluorocarbon anodes derived from the PVDF precursor showed higher reversible discharge capacities of 735 mAh g-1 and 269 mAh g-1 in lithium- and sodium-ion batteries, respectively, compared to the commercial graphitic carbon. After 100 charge/discharge cycles, the fluorocarbon showed retentions of 91.3% and 97.5% in lithium (at 1C) and sodium (at 200 mA g-1) intercalation systems, respectively. The effects of carbonization temperature on the electrochemical properties of alkali metal ion storage were thoroughly investigated and documented. The specific capacities in lithium- and sodium-ion batteries were dependent on the fluorine content, indicating that the highly electronegative fluorine facilitates the insertion/extraction of lithium and sodium ions in rechargeable batteries.

A study on cooling performance and exergy analysis of desiccant cooling system in various regeneration temperature and outdoor air conditions

Desiccant cooling system is an air conditioning system that uses evaporative cooler to cool air and it can perform cooling by using heat energy only without electrically charged cooler. Thus, it can solve many problems of present cooling system including the destruction of ozone layer due to the use of CFC[chloro fluoro carbon] affiliated refrigerants and increase of peak power during summer season. In this study, cooling performance and exergy analysis was conducted in order to increase efficiency of desiccant cooling system. Especially, using exergy analysis based on the second law of thermodynamics can resolve the issue related to system efficiency in a more fundamental way by analyzing the cause of exergy destruction both in whole system and each component. The purpose of this study is to evaluate COP[coefficient of performance], cooling capacity and exergy performance of desiccant cooling system incorporating a regenerative evaporative cooler in various regeneration temperature and outdoor air conditions. Corresponding Author, ydchoi@korea.ac.kr 2014 The Korean Society of Mechanical Engineers C 이장일 홍석민 변재기 최영돈 이대영 414  유용도 :   엑서지 파괴율 :  엑서지 효율 :  추기율 : CC 냉방용량 :  외기온도 :  외기습도 :

Prediction of Thermal and Elastic Properties of Honeycomb Sandwich Plate for Analysis of Thermal Deformation

* Dept. of Mechanical Engineering, Korea Univ. (Received December 9, 2013 ; Revised December 31, 2013 ; Accepted January 19, 2014)Key Words: Honeycomb(허니컴), Sandwich(샌드위치), Composite(복합재), Heat Transfer(열전달), Thermal Deformation(열변형), Thermal Conductivity(열전도계수), Coefficient of Thermal Expansion(열팽창계수), Elastic Properties(탄성 물성치), Thermal Properties(열 물성치), Anisotropy(이방성)초록: 전자장치들의 소형화 및 박형화가 됨에 따라 전자장치의 수명과 직결되는 열적문제가 중요해지고 있다. 열적문제를 해결하기위해 열확산과 단열을 통한 열적 안정성 연구가 필요하다. 허니컴 샌드위치 평판은 이방성의 열전도계수를 갖는다. 허니컴 샌드위치 평판이 적용된 시스템에 대해 온도분포와 열변형을 해석하기 위하여 열 및 탄성 물성치가 필요하다. 본 연구에서는 허니컴 코어의 크기, 두께 그리고 구성된 재료에 따라 허니컴 샌드위치 평판의 물성치가 변하기 때문에 허니컴 샌드위치 평판의 열전도계수, 열팽창계수, 탄성계수, 전단탄성계수, 푸아송비와 같은 열 및 탄성 물성치를 예측하였다.Abstract: Thermal problems that are directly related to the lifetime of an electronic device are becoming increasingly important owing to the miniaturization of electronic devices. To solve thermal problems, it is essential to study thermal stability through thermal diffusion and insulation. A honeycomb sandwich plate has anisotropic thermal conductivity. To analyze the thermal deformation and temperature distribution of a system that employs a honeycomb sandwich plate, the thermal and elastic properties need to be determined. In this study, the thermal and elastic properties of a honeycomb sandwich plate, such as thermal conductivity, coefficient of thermal expansion, elastic modulus, Poissons ratio, and shear modulus, are predicted. The properties of a honeycomb sandwich plate vary according to the hexagon size, thickness, and material properties.o resp n d ig Aut h, y c@ ka .