• 청정기술
• /
• 제10권4호
• /
• pp.215-220
• /
• 2004

본 연구에서는 초임계 이산화탄소를 역용매로 이용하고, 에탄올을 용매로 하여 마이크로 사이즈의 아세트아미노펜 입자를 제조하였다. 아세트아미노펜/에탄올 용액과 초임계 이산화탄소를 침전조에 주입할 때 이중 노즐을 사용하였다. 반응 온도와 압력, $CO_2$의 유량과 아세트아미노펜/에탄올 용액의 유량의 변화가 입자의 크기와 형상에 미치는 영향에 대해 살펴보았다. 제조된 입자의 크기와 형상은 SEM으로 분석하였다.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2010년도 제35회 추계학술대회논문집
• /
• pp.597-600
• /
• 2010

극저온 액체 질소 제트 유동의 아임계 및 초임계 특성을 파악하기 위한 실험을 수행하였다. 단일 제트 분사기를 고압 챔버 내에 장착하여 제트의 주위기체압력, 분사기 형상 및 유동 조건의 영향을 조사하였다. 실험 결과로부터 아임계 조건과 초임계 조건에서의 제트의 특성 변화를 관찰하였으며, 주위기체압력이 대기압일 경우 유동 내에 섭동이 발생함을 파악하였다. 분사기 형상에 따른 유동 변화 또한 파악하였다.

• 설비공학논문집
• /
• 제14권12호
• /
• pp.1004-1013
• /
• 2002

Turbulent carbon dioxide flows and cooling heat transfers under supercritical state in a straight duct with a square cross-section are numerically analyzed employing low Reynolds number $\kappa-\varepsilon$ model and algebraic stress model. The flow is assumed to be (quasi-incompressible. Predicted Nusselt number and friction factor are compared with the experimental data, Blasius correlation for friction factor and Dittus-Boelter correlation for Nusselt number. Computational results for the Fanning's friction factor agree well with the all Rohsenow and Choi's correlation, Liou and Hwang's experimental data and Blasius correlation. The results obtained by algebraic stress model agree more with the Liou and Hwang's experimental data, while the results obtained by low Reynolds number $\kappa-\varepsilon$ model agree more with Blasius correlation. In the computation of Nusselt number, Dittus-Boelter correlation can not exactly fit the computational results. Therefore we propose the new correlation$Nu=0.053Re^{0.73}Pr^{0.4}$for the turbulent cooling heat transfer of carbon dioxide under supercritical state.

• Biotechnology and Bioprocess Engineering:BBE
• /
• 제10권4호
• /
• pp.315-321
• /
• 2005

Supercritical carbon dioxide extraction was investigated as a method for removing lipids and bad flavor from tuna viscera. To find the optimum conditions, different experimental variables, such as pressure, temperature, flow rate of solvent and sample size, were evaluated for the effective removal of lipids and the undesirable smell. Ethanol was used as the entrainer, with a $3\%$ by vol $CO_2$ flow rate. By increasing the pressure at constant temperature, the efficiency of the lipid removal was improved and the protein was concentrated without denaturalization. The main fatty acids extracted from the tuna viscera were palmitic acid (16:0), heptadecanoic acid (17:1), oleic acid (18:1) and docosahexaenoic acid (22:6). The major amino acids in the tuna viscera treated by supercritical carbon dioxide were glutamic acid, leucine and lysine, and the free amino acids were L-proline, taurine and L-$\alpha$-aminoadipic acid.

• KSBB Journal
• /
• 제26권1호
• /
• pp.69-77
• /
• 2011

In this study, poly (L-lactic acid) (PLLA) microparticles containing gemcitabine hydrochloride were prepared by a supercritical fluid process, called aerosol solvent extraction system (ASES), utilizing supercritical carbon dioxide as antisolvent. The influence of process parameters such as temperature, pressure, $CO_2$ and solution flow rate, solution concentration, and feed ratio of drug to polymer on the morphology and characteristics of the microparticles was studied in detail. The gemcitabine-loaded microparticles exhibited a spherical shape with a smooth surface. The entrapment efficiency of gemcitabine increased with increasing temperature, solution concentration and $CO_2$ flow rate and with decreasing drug/polymer feed ratio. The maximum drug loading obtained from the ASES process was found to be about 11%. The ASES-processed PLLA microparticles containing gemcitabine showed a relatively high initial burst due to the presence of surface pores on the microparticles and the poor affinity between drug and polymer.

• Nuclear Engineering and Technology
• /
• 제53권4호
• /
• pp.1100-1108
• /
• 2021

Supercritical water has great potential as a coolant for nuclear reactor. Its use will lead to higher thermal efficiency of Rankine cycle. However, in certain conditions heat transfer may get deteriorated which may lead to undesirable high clad surface temperature. It is necessary to estimate the operating conditions in which heat transfer deterioration (HTD) will take place, so as to establish thermal margins for safe reactor operation. In the present work, the heat flux corresponding to onset of HTD for vertically upward flow of supercritical water in a pipe is obtained over a wide range of system parameters, namely pressure, mass flux, and pipe diameter. This is done by performing large number of simulations using an in-house CFD code, which is especially developed and validated for this purpose. The identification of HTD is based on observance of one or more peak/s in the computed wall temperature profile. The existing correlations for predicting the onset of HTD are compared against the results obtained by present simulations as well as available sets of experimental data. It is found that the prediction accuracy of the correlation proposed by Dongliang et al. is best among the existing correlations.

• 분석과학
• /
• 제21권5호
• /
• pp.392-396
• /
• 2008

산겨릅나무(Acer tegmentosum)는 지방간, 가염, 간경변증, 간암에 뚜렷한 치료 작용이 있으며, 특히 간에 쌓인 독을 풀고 간세포를 살리는 효능이 있어 약용으로 많이 사용된다. 그러나 산겨릅나무 줄기에는 독성물질이 있어 안전성, 오남용 등의 문제점을 가지고 있다. 그래서 산겨릅나무 줄기의 독성물질을 제거하고 독성 물질에 대한 연구를 활발히 하기 위해 먼저 초임계유체 추출기법(SFE, Supercritical Fluid Extraction)을 이용하였다. 초임계유체 추출에서 최적의 실험 조건은 압력 100 bar, 추출온도 $40^{\circ}C$로 구성하고, 초임계 $CO_2$의 유속 3 mL/min과 modifier인 에탄올의 유속 0.2 mL/min 이다.

• Nuclear Engineering and Technology
• /
• 제39권4호
• /
• pp.273-286
• /
• 2007

This paper presents the research activities performed to date for the development of a supercritical pressure water-cooled reactor (SCWR) in Korea. The research areas include a conceptual design of an SCWR with an internal flow recirculation, a reactor core conceptual design, a heat transfer test with supercritical $CO_2$, an adaptation of an existing safety analysis code to the supercritical pressure condition, and an evaluation of candidate materials through a corrosion study. Methods to reduce the cladding temperature are introduced from two different perspectives, namely, thermal-hydraulics and core neutronics. Briefly described are the results of an experiment on the heat transfer at a supercritical pressure, an experiment that is essential for the analysis of the subchannels of fuel assemblies and the analysis of a system safety. An existing system code has been adapted to SCWR conditions, and the process of a first-hand validation is presented. Finally, the corrosion test results of the candidate materials for an SCWR are introduced.

• Nuclear Engineering and Technology
• /
• 제40권2호
• /
• pp.117-126
• /
• 2008

In this paper, a new reactor core design is proposed on the basis of a mixed core concept consisting of a thermal zone and a fast zone. The geometric structure of the fuel assembly of the thermal zone is similar to that of a conventional thermal supercritical water-cooled reactor(SCWR) core with two fuel pin rows between the moderator channels. In spite of the counter-current flow mode, the co-current flow mode is used to simplify the design of the reactor core and the fuel assembly. The water temperature at the exit of the thermal zone is much lower than the water temperature at the outlet of the pressure vessel. This lower temperature reduces the maximum cladding temperature of the thermal zone. Furthermore, due to the high velocity of the fast zone, a wider lattice can be used in the fuel assembly and the nonuniformity of the local heat transfer can be minimized. This mixed core, which combines the merits of some existing thermal SCWR cores and fast SCWR cores, is proposed for further detailed analysis.

• Korean Chemical Engineering Research
• /
• 제59권1호
• /
• pp.85-93
• /
• 2021

For accurate and reliable process design for phenol oxidation in a plug flow reactor with supercritical water, modeling can be very insightful. Here, the velocity and density distribution along the reactor have been predicted by a numerical model and variations of temperature and phenol mass fraction are calculated under various flow conditions. The numerical model shows that as we proceed along the length of the reactor the temperature falls from above 430 ℃ to approximately 380 ℃. This is because the generated heat from the exothermic reaction is less that the amount lost through the walls of the reactor. Also, along the length, the linear velocity falls to less than one-third of the initial value while the density more than doubles. This is due to the fall in temperature which results in higher density which in turn demands a lower velocity to satisfy the continuity equation. Having a higher oxygen concentration at the reactor inlet leads to much faster phenol destruction; this leads to lower capital costs (shorter reactor will be required); however, the operational expenditures will increase for supplying the needed oxygen. The phenol destruction depends heavily on the kinetic parameters and can be as high as 99.9%. Using different kinetic parameters is shown to significantly influence the predicted distributions inside the reactor and final phenol conversion. These results demonstrate the importance of selecting kinetic parameters carefully particularly when these predictions are used for reactor design.