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The heat transfer characteristics of CO₂ and CO₂-oil mixture in tubes
Rin Yun(윤린) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11
The heat transfer characteristics of CO₂ and CO₂-oil mixture in tubes including convective flow boiling, gas cooling, and condensation are investigated. Two-phase flow patterns are thoroughly investigated based on physical phenomena, which show the early flow transition to intermittent or annular flow especially for small diameter tube. The physical phenomena for nucleate boiling of CO₂ follow the same trends with other organic fluids under the same reduced pressure. The gas cooling heat transfer is critically dependent on the turbulent diffusivity related with buoyancy force due to the large density difference. Under the oil presence conditions, the interaction of oil rich layer and bubble formation is the physical mechanism for the CO₂-oil mixture convective boiling. Besides, the gas cooling phenomena with oil should be investigated based on the flow patterns formed by CO₂ and oil, and the oil rich layer, whose thickness are depends on the solubility of CO₂ to oil explains the physical mechanisms of heat transfer. The thermodynamic properties of CO₂-oil were estimated by the general model based on EOS, and they are utilized to estimate the properties for oil rich layer and oil droplet vapor core. Through these predicted properties, the convective boiling and gas cooling heat transfer coefficients and pressure drop theoretically estimated. Condensation of CO₂ is not so different from the existing one, so the heat transfer coefficients and pressure drop are well estimated by the existing one developed for other fluids.
CHP Capacity Optimizer를 이용한 건물 열병합 시스템의 경제성 평가
윤린(Rin Yun) 대한설비공학회 2008 설비공학 논문집 Vol.20 No.5
This paper presents and analyzes the effects of on-grid electricity cost, fuel price and initial capital cost of a CHP system, on the optimum DG and AC capacity and NPV, by using the ORNL CHP Capacity Optimizer, which was applied to a library in a university. By considering the current domestic energy cost and initial capital cost, it is shown that the installation and operation of the CHP system is not economical. However, with the current domestic CHP installation cost and fuel price, the NPV achieved by the installation of CHP system is greater when the on-grid electricity price is a factor of x1.5 the present value. Regarding the initial capital cost of the CHP system, the reduction of the DG cost is much more economical than that of the AC cost, with respect to NPV. Electricity cost and fuel price have opposite effects on NPV, and NPV is more sensitive to an increase of the electricity cost than an increase of the fuel price.
낮은 오일 농도에서 CO₂-PEC9 혼합물의 밀도와 점성예측
윤린(Rin Yun) 대한설비공학회 2008 설비공학 논문집 Vol.20 No.11
Due to environmental concerns CO₂ has been reintroduced as a potential candidate to replace HFCs in refrigeration systems. Oils are always required in a vapor-compression cycle, and thus it is necessary to precisely estimate the thermodynamic mixture properties of CO₂-lubricant oil. In the present study, the density and the viscosity of the mixture was calculated by the Redlich and Kwong type EoS and the modified Peng and Robinson type viscosity EoS, respectively. The viscosity model was based on the similarity between P-v-T and T-u-P relationships. The predicted results were compared with the experimental data of Pensado et al. whose test conditions were 100~650 bar of pressure and 303 K ~353 K of temperature with the CO₂-POEs mixtures under 92.2 wt.% and 83.3 wt.% of CO₂ concentration. The mean deviations of the mixture density were 7.93% and 8.32% for 92.2 wt.% and 83.3 wt.% of CO₂ concentration, respectively. Concerning the viscosity, the mean deviations were 4% and 10% for 92.2 wt.% and 83.3 wt.% of CO₂ concentration under the Pensado et al.'s test conditions.
첨가물이 존재하는 CO₂ Hydrate 형성의 CFD 모델링
윤린(Rin Yun),Benedict Prah,이광빈(Kwangbin Lee) 대한설비공학회 2021 설비공학 논문집 Vol.33 No.12
CO₂ hydrate formation with additives in the pipeline was simulated by the CFD tool of the COMSOL Multiphysics. The length and diameter of the pipeline for the hydrate formation simulation were 1 m and 0.0347 m, respectively. The 3D axis-symmetric geometric structure was implemented. The Eulerian multiphase flow model was introduced for the modelling of the hydrate formation processes composed of complex multi-physical phenomena such as mass transfer, heat transfer, and phase change. The validity of the simulation results was proved by comparing them with previous experimental data in terms of hydrate formation rate. As a result, hydrate velocity and volume fraction along length direction were calculated. The average hydrate mass fraction increased from 8% to 12% by additive.
Kyoung-Yun Kim,Ha-Rin Moon,Jung-Mi Yun 한국식품영양과학회 2021 한국식품영양과학회 학술대회발표집 Vol.2021 No.10
Metabolic syndrome (MetS) is a complex metabolic disorder and is a high-risk condition for type 2 diabetes and cardiovascular disease. Rapid screening of at-risk individuals using accurate and time-saving tools is effective in disease management. Using the KNHANES data, we collected data of 2,234 subjects suitable for the study design, of which 974 (43.6%) were men and 1,260 (56.4%) were women. We used ROC analysis to estimate the sex-specific neck circumference (NC) optimal cut-off point to predict MetS risk. In addition, in order to analyze the risk of MetS according to the estimated NC, logistic regression analysis was performed by correcting confounding factors. As a result of ROC analysis, the optimal neck cut point for predicting the risk of MetS was in men 38.25 cm (AUC: 0.759, 95% CI: 0.729-0.790) and in women 33.65 cm (AUC: 0.811, 95% CI: 0.782-0.840). In above this neck cut point, the risk of MetS was associated with increasing by 1.872-fold (P=0.004) in men and 4.639-fold (P<0.001) in women. It is suggested that more studies should be conducted to analyze the disease prediction effect of the combined application of anthropometric indicators currently in use and NC.