• Advances in nano research
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• 제4권1호
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• pp.1-14
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• 2016

Superparamagnetic iron oxide nanoparticles (Nps), composed of magnetite, $Fe_3O_4$, or maghemite, ${\gamma}-Fe_2O_3$, core and biocompatible polymer shell, such as dextran or chitozan, have recently found wide applications in magnetic resonance imaging, contrast enhancement and hyperthermia therapy. For different diagnostic and therapeutic applications, current attempt is focusing on the synthesis and biomedical applications of various ferrite Nps, such as $CoFe_2O_4$ and $MnFe_2O_4$, differing from iron oxide Nps in charge, surface chemistry and magnetic properties. This study is focused on the synthesis of manganese ferrite, $MnFe_2O_4$, Nps by most commonly used chemical way pursuing better control of their size, purity and magnetic properties. Co-precipitation syntheses were performed using aqueous alkaline solutions of Mn(II) and Fe(III) salts and NaOH within a wide pH range using various hydrothermal treatment regimes. Different additives, such as citric acid, cysteine, glicine, polyetylene glycol, triethanolamine, chitosan, etc., were tested on purpose to obtain good yield of pure phase and monodispersed Nps with average size of ${\leq}20nm$. Transmission electron microscopy (TEM), X-ray diffraction, energy dispersive X-ray spectroscopy (EDX), $M\ddot{o}ssbauer$ spectroscopy down to cryogenic temperatures, magnetic measurements and inductively coupled plasma mass spectrometry were employed in this study.

• 반도체디스플레이기술학회지
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• 제22권3호
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• pp.119-124
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• 2023

In this study, experimental approach of the measurement of condensation and evaporation heat transfer coefficients is discussed for mixed refrigerants using in the ultra low-temperature cooling system for semiconductor etching process. An experimental apparatus was described performing the condensation and evaporation heat transfer measurements for mixed refrigerants. The mixed refrigerant used in this study was composed of the optimal mixture determined in previous research, with a composition of Ar:R14:R23:R218 = 0.15:0.4:0.15:0.3. The experiments were conducted over a temperature range from -82℃ to 15℃ and at pressures ranging from 18.5 bar to 5 bar. The convection heat transfer coefficients of the mixed refrigerant were measured at flow rates corresponding to actual operating conditions. The condensation heat transfer coefficient ranged from approximately 0.7 to 0.9 kW/m2K, while the evaporation heat transfer coefficient ranged from 1.0 to 1.7 kW/m2K. The detailed discussion of the experimental methods, procedures, and results were described in this paper.

• 설비공학논문집
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• 제21권12호
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• pp.715-732
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• 2009

This article reviews the papers published in the Korean Journal of Air-Conditioning and Refrigeration Engineering during 2008. It is intended to understand the status of current research in the areas of heating, cooling, ventilation, sanitation, and indoor environments of buildings and plant facilities. Conclusions are as follows. (1) Research trends in thermal and fluid engineering have been surveyed in the categories of general fluid flow, fluid machinery and piping, new and renewable energy, and fire. Well-developed CFD technologies were widely applied in developing facilities and their systems. New research topics include fire, fuel cell, and solar energy. Research was mainly focused on flow distribution and optimization in the fields of fluid machinery and piping. Topics related to the development of fans and compressors had been popular, but were no longer investigated widely. Research papers on micro heat exchangers using nanofluids and micro pumps were also not presented during this period. There were some studies on thermal reliability and performance in the fields of new and renewable energy. Numerical simulations of smoke ventilation and the spread of fire were the main topics in the field of fire. (2) Research works on heat transfer presented in 2008 have been reviewed in the categories of heat transfer characteristics, industrial heat exchangers, and ground heat exchangers. Research on heat transfer characteristics included thermal transport in cryogenic vessels, dish solar collectors, radiative thermal reflectors, variable conductance heat pipes, and flow condensation and evaporation of refrigerants. In the area of industrial heat exchangers, examined are research on micro-channel plate heat exchangers, liquid cooled cold plates, fin-tube heat exchangers, and frost behavior of heat exchanger fins. Measurements on ground thermal conductivity and on the thermal diffusion characteristics of ground heat exchangers were reported. (3) In the field of refrigeration, many studies were presented on simultaneous heating and cooling heat pump systems. Switching between various operation modes and optimizing the refrigerant charge were considered in this research. Studies of heat pump systems using unutilized energy sources such as sewage water and river water were reported. Evaporative cooling was studied both theoretically and experimentally as a potential alternative to the conventional methods. (4) Research papers on building facilities have been reviewed and divided into studies on heat and cold sources, air conditioning and air cleaning, ventilation, automatic control of heat sources with piping systems, and sound reduction in hydraulic turbine dynamo rooms. In particular, considered were efficient and effective uses of energy resulting in reduced environmental pollution and operating costs. (5) In the field of building environments, many studies focused on health and comfort. Ventilation. system performance was considered to be important in improving indoor air conditions. Due to high oil prices, various tests were planned to examine building energy consumption and to cut life cycle costs.

• 대한화장품학회지
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• 제48권1호
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• pp.55-64
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• 2022

Cleansing foam이라 불리는 지방산 칼륨 cream soap은 crystal gel 구조로 이루어져 있어 유화계와는 달리 전단응력에 약하며 고온의 보관조건에서 쉽게 분리되는 특성을 보여준다. Crystal gel 구조는 지방산의 종류 및 비율, 중화도, polyol의 종류와 사용량에 따라 크게 영향을 받는다. Crystal gel 구조에 미치는 이들의 영향을 조사하기 위해 water/potassium hydroxide (KOH)/fatty acid ternary system에서 실험을 실시하였다. Differential scanning calorimeter (DSC) 측정 결과 myristic acid (MA) : stearic acid (SA) = 3 : 1 비율에서 공융점(eutectic point)를 갖고 이 혼합비가 가장 안전한 삼성분계(ternary system)를 만든다는 것을 발견했다. 점도 측정과 편광현미경 (POM) 관찰 결과 중화도는 75% 부근이 최적이라고 판단된다. 삼성분계의 melting point (T_m)이 보관온도보다 높을 때, 그리고 crystal phase가 lamellar gel phase로 상 전이가 일어날 때 안정하나 지방산 함량의 증가는 안정성에 거의 영향을 미치지 않는다. 삼성분계에 polyol의 첨가는 T_m을 변화시키고 상전이를 일으키는데 중요한 역할을 한다. 클렌징폼의 구조는 저온 주사전자현미경 (Cryo-SEM), 소각 및 광각 X-선 산란 (SAXS, WAXS) 분석으로 규명하였다. Butylene glycol (BG), propylene glycol (PG), dipropylene glycol (DPG)은 T_m을 낮추어주며 lamellar gel phase 형성을 어렵게 하는 반면 glycerin, PEG-400, sorbitol은 T_m을 상승시키고 lamellar gel phase 형성을 용이하게 하며 안정한 삼성분계를 만든다.