• Korea-Australia Rheology Journal
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• 제21권4호
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• pp.269-280
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• 2009

The drop formation dynamics of a shear thinning, elastic, yield stress ($\tau_o$) fluid (Carbopol 980 (poly(acrylic acid)) dispersions) in silicone oil has been investigated in a flow-focusing microfluidic channel. The rheological character of each solution investigated varied from Netwonian-like through to highly non-Newtonian and was varied by changing the degree of neutralization along the poly (acrylic acid) backbone. We have observed that the drop size of these non-Newtonian fluids (regardless of the degree of neutralisation) showed bimodal behaviour. At first we observed increases in drop size with increasing viscosity ratio (viscosity ratio=viscosity of dispersed phase (DP)/viscosity of continuous phase (CP)) at low flowrates of the continuous phases, and thereafter, decreasing drop sizes as the flow rate of the CP increases past a critical value. Only at the onset of pinching and during the high extensional deformation during pinch-off of a drop are any differences in the non-Newtonian characteristics of these fluids, that is extents of shear thinning, elasticity and yield stress ($\tau_o$), apparent. Changes in these break-off dynamics resulted in the observed differences in the number and size distribution of secondary drops during pinch-off for both fluid classes, Newtonian-like and non-Newtonian fluids. In the case of the Newtonian-like drops, a secondary drop was generated by the onset of necking and breakup at both ends of the filament, akin to end-pinching behavior. This pinch-off behavior was observed to be unaffected by changes in viscosity ratio, over the range explored. Meanwhile, in the case of the non-Newtonian solutions, discrete differences in behaviour were observed, believed to be attributable to each of the non-Newtonian properties of shear thinning, elasticity and yield stress. The presence of a yield stress ($\tau_o$), when coupled with slow flow rates or low viscosities of the CP, reduced the drop size compared to the Newtonian-like Carbopol dispersions of much lower viscosity. The presence of shear thinning resulted in a rapid necking event post onset, a decrease in primary droplet size and, in some cases, an increase in the rate of drop production. The presence of elasticity during the extensional flow imposed by the necking event allowed for the extended maintenance of the filament, as observed previously for dilute solutions of linear polymers during drop break-up.

• 대한환경공학회지
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• 제35권10호
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• pp.710-716
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• 2013

대기 오염, 기후 변화 등 환경 문제와 자원 고갈로 인해 화석 연료를 대체할 에너지에 많은 관심이 집중되고 있다. 폐바이오매스의 에너지화 분야에서도 다양한 연구가 이루어지고 있다. 폐목질계 바이오매스의 급속열분해는 바이오매스 에너지화 기술 중 하나로 액상 연료를 생산할 수 있다. 바이오매스의 급속열분해에는 주로 기포유동층 반응기가 쓰이고 있으며, 기포유동층 급속열분해 반응기에서는 반응물에 열을 효과적으로 전달하기 위하여 고체입자의 유동매체를 이용한다. 이러한 기포유동층 반응기에서 유동층 내 고체 입자의 움직임과 혼합은 기포의 거동에 영향을 받는다. 이로 인해 열전달 현상이 달라지고 결과적으로는 폐목질계 바이오매스의 급속열분해 반응 속도가 변한다. 따라서 본 연구에서는 기포유동층 반응기 내부의 수력학적 특성과 폐목질계 바이오매스 급속열분해 반응에 관한 연구를 수행하였다. 반응기내의 기체-고체 유동에 대해 Eulerian-Granular 방법을 사용하여 반응기를 시뮬레이션 하였으며, two-stage semi-global reaction model로 폐바이오매스의 급속 열분해반응을 모사하였다. 결과를 살펴보면, 유동층 내에서 기포들이 생성되고 상승하면서 크기가 증가한다. 이러한 기포의 거동에 의해 기포 주위의 고체 입자는 여러 방향으로 움직이게 된다. 고체 입자상의 활발한 움직임으로 바이오매스 입자가 유동층에 골고루 퍼져 일차 반응이 유동층 전반에서 일어난다. 그리고 일차 반응 중 타르가 생성되는 반응 속도가 가장 높게 나타난다. 그 결과 기체상 생성물 중 타르가 약 66 wt.%로 가장 많이 발생한다. 반면 이차 반응은 유동층에서보다 freeboard에서 더 많이 일어난다. 따라서 기포의 거동이나 입자의 움직임에 의한 영향은 일차 반응보다 상대적으로 적을 것으로 판단된다.

• 암석학회지
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• 제25권1호
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• pp.39-50
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• 2016

제주도 현무암에 산출되는 첨정석 페리도타이트 포획암에 $CO_2$-유체포유물이 포획되어 있다. 이 $CO_2$-유체포유물들은 규칙적인 결정면으로 둘러싸여 있으며 세립의 네오블라스트 결정에는 일차포유물로, 조립의 반상쇄성에는 이차포유물로 산출된다. 냉각/가열 실험에서 $CO_2$-유체포유물의 삼중점은 $-57.1^{\circ}C$(${\pm}0.9^{\circ}C$)로서 대체로 균질하다. 이는 이 $CO_2$-유체포유물들이 거의 순수하게 $CO_2$로 이루어져 있음을 의미한다. 그러나 균질화 온도는 $-39^{\circ}C$(${\rho}=1.12g/cm^{3)}$)에서 $23^{\circ}C$(${\rho}=0.82g/cm^{3)}$)로 넓은 범위에 걸쳐 나타나며, 이는 많은 유체포유물이 포획된 이후 재평형 되어졌음을 반영한다. 일차/이차포유물과 균질화온도 사이에 체계적인 차이는 없다. 가장 낮은 균질화온도(즉, 가장 높은 밀도)를 보이는 유체포유물에서 계산된 포획 압력은 ${\approx}0.9GPa$이다. 제주 페리도타이트와 $CO_2$-유체포유물의 조직적 특성과 낮은 균질화 온도는 $CO_2$-유체가 맨틀기원의 유체로서 상부 맨틀암석권에서 페리도타이트의 재결정화 작용 동안 존재하던 유체로 해석된다. $CO_2$-유체의 포획은 제주 페리도타이트의 진화과정에서 후기의 사건이며, 상부맨틀 암석권의 상부(천부)에서 일어났음을 지시하고 있다.

• 대한소아치과학회지
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• 제30권3호
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• pp.459-464
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• 2003

함치성 낭종이란 퇴축법랑상피와 법랑질 표면 사이에 체액이 축적되어 치관이 내강의 안쪽에 있으며 치근은 바깥쪽에 위치하는 매복치 치관을 둘러싸는 치원성 낭을 의미한다. 함치성 낭종의 치료법으로는 적출술, 조대술, 감압술 및 외과적 절제술이 있다. 본 증례는 하악 제2유구치의 만기잔존을 주소로 내원한 환아들을 검사하였다. 두 환아에서 해당 제2유구치의 협측부에서 팽융을 관찰하였다. 두 환아, 모두 방사선사진상 하악 제2소구치의 치관을 포함한 단방성의 방사선투과상이 보였으며 조직검사 결과 함치성 낭종으로 진단되었다. 본 증례에서 발치와를 통한 조대술을 시술하였다. 제2유구치를 발거하고 바세린 거즈로 발치와를 보호한 후 익일에 보격장치를 겸한 obturator를 장착해 주었다. 시술 후 매복된 영구치는 정상 맹출속도보다 빠르게 맹출하는 양상을 보이고 있다.

• 대한기계학회논문집B
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• 제26권6호
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• pp.850-858
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• 2002

The present study investigates in detail the combined effects of the Coriolis force and centrifugal force on the development of turbulent flows in a square-sectioned U-bend rotating about an axis parallel to the center of bend curvature. When a viscous fluid flows through a curved region of U-bend, two types of secondary flow occur. One is caused by the Coriolis force due to the rotation of U-bend and the other by the centrifugal force due to the curvature of U-bend. For positive rotation, where the rotation is in the same direction as that of the main flow, both the Coriolis force and the centrifugal force act radially outwards. Therefore, the flow structure is qualitatively similar to that observed in a stationary curved duct. On the other hand, under negative rotation, where these two forces act in opposite direction, more complex flow fields can be observed depending on the relative magnitudes of the forces. Under the condition that the value of Rossby number and curvature ratio is large, the flow field in a rotating U-bend can be represented by two dimensionless parameters : $K_{TC}$ =Re $\sfrac{1}{4}$√λand a body force ratio F=λ/Ro. Here, $K_{TC}$ has the same dynamical meaning as $K_{TC}$ =Re√λ for laminar flow.

• 대한기계학회논문집
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• 제16권10호
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• pp.1979-1989
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• 1992

본 연구에서는 말굽와류에 대한 전반적인 사항을 고찰하는 한편, 실린더의 기 하학적 형상이 말굽와류에 미치는 영향을 정성적으로 고찰하는 데 있다. 그러므로 본 실험에서는 먼저 경계층이 형성되어 있는 평판에 원형 실린더를 설치하여, 말굽와 류에 의한 3차원 유동현상을 고찰하고, 또한 동일한 평판에 쐐기형상의 실린더를 설치 하여, 그 주위에서 발생하는 3차원 유동현상과 원형 실린더 주위에서 일어나는 3차원 유동현상과의 정성적인 비교를 통하여, 말굽와류에 의한 3차원 유동손실을 줄일 수 있 는 가능성을 제시하고자 한다.

• Archives of Plastic Surgery
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• 제43권1호
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• pp.40-45
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• 2016

Background Bioabsorbable plates and screws are commonly used to reduce maxillofacial bones, particularly in pediatric patients because they degrade completely without complications after bone healing. In this study, we encountered eight cases of a delayed foreign body reaction after surgical fixation with bioabsorbable plates and screws. Methods A total of 234 patients with a maxillofacial fracture underwent surgical treatment from March 2006 to October 2013, in which rigid fixation was achieved with the Inion CPS (Inion, Tampere, Finland) plating system in 173 patients and Rapidsorb (Synthes, West Chester, PA, USA) in 61 patients. Their mean age was 35.2 years (range, 15-84 years). Most patients were stabilized with two- or three-point fixation at the frontozygomatic suture, infraorbital rim, and anterior wall of the maxilla. Results Complications occurred in eight (3.4%) of 234 patients, including palpable, fixed masses in six patients and focal swelling in two patients. The period from surgical fixation to the onset of symptoms was 9-23 months. Six patients with a mass underwent secondary surgery for mass removal. The masses contained fibrous tissue with a yellow, grainy, cloudy fluid and remnants of an incompletely degraded bioabsorbable plate and screws. Their histological findings demonstrated a foreign body reaction. Conclusions Inadequate degradation of bioabsorbable plates caused a delayed inflammatory foreign body reaction requiring secondary surgery. Therefore, it is prudent to consider the possibility of delayed complications when using bioabsorbable plates and surgeons must conduct longer and closer follow-up observations.

• Journal of Korean Neurosurgical Society
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• 제48권3호
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• pp.244-250
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• 2010

Objective : Adequate management of increased intracranial pressure (ICP) is critical in patients with traumatic brain injury (TBI), and decompressive craniectomy is widely used to treat refractory increased ICP. The authors reviewed and analyzed complications following decompressive craniectomy for the management of TBI. Methods : A total of 89 consecutive patients who underwent decompressive craniectomy for TBI between February 2004 and February 2009 were reviewed retrospectively. Incidence rates of complications secondary to decompressive craniectomy were determined, and analyses were performed to identify clinical factors associated with the development of complications and the poor outcome. Results : Complications secondary to decompressive craniectomy occurred in 48 of the 89 (53.9%) patients. Furthermore, these complications occurred in a sequential fashion at specific times after surgical intervention; cerebral contusion expansion ($2.2{\pm}1.2$ days), newly appearing subdural or epidural hematoma contralateral to the craniectomy defect ($1.5{\pm}0.9$ days), epilepsy ($2.7{\pm}1.5$ days), cerebrospinal fluid leakage through the scalp incision ($7.0{\pm}4.2$ days), and external cerebral herniation ($5.5{\pm}3.3$ days). Subdural effusion ($10.8{\pm}5.2$ days) and postoperative infection ($9.8{\pm}3.1$ days) developed between one and four weeks postoperatively. Trephined and post-traumatic hydrocephalus syndromes developed after one month postoperatively (at $79.5{\pm}23.6$ and $49.2{\pm}14.1$ days, respectively). Conclusion : A poor GCS score ($\leq$ 8) and an age of $\geq$ 65 were found to be related to the occurrence of one of the above-mentioned complications. These results should help neurosurgeons anticipate these complications, to adopt management strategies that reduce the risks of complications, and to improve clinical outcomes.

• 대한핵의학회지
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• 제24권2호
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• pp.279-285
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• 1990

Simultaneous presence of ascites and pleural effusion has been documented in patients with cirrhosis of the liver, renal disease, Meigs' syndrome and in patients undergoing peritoneal dialysis. Mechanisms proposed in the formation of pleural effusion in most of the above diseases are lymphatic drainage and diaphragmatic defect. But sometimes, hepatic hydrothoraxes in the absence of clinical ascites and pleural effusion secondary to pulmonary or cardiac disease are noted. It is not always possible to differentiate between pleural effusion caused by transdiaphragmatic migration of ascites and by other causes based soly on biochemical analysis. Authors performed radionuclide scintigraphy after intraperitoneal administration of $^{99m}Tc-labeled$ colloid in 23 patients with both ascites and pleural effusion in order to discriminate causative mechanisms responsible for pleural effusion. Scintigraphy demonstrated the transdiaphragmatic flow of fluid from the peritoneum to pleural cavities in 13 patients correctly. In contrast, in 5 patients with pleural effusion secondary to pulmonary, pleural and cardiac diseases, radiotracers fail to traverse the diaphragm and localize in the pleural space. Ascites draining to mediastinal lymph nodes and blocked passage of lymphatic drainage were also clarified, additionaly. Conclusively, radionuclide peritoneal scintigraphy is an accurate, rapid and easy diagnostic tool in patients with both ascites and pleural effusion. It enables the causes of pleural effusion to be elucidated, as well as providing valuable information required when determining the appropriate therapy.

• 한국산업융합학회 논문집
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• 제25권1호
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• pp.61-70
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• 2022

Fire damage time in high-rise buildings and wildland fire increasing every year. The use of high-pressure fire pumps is required to effectively extinguish fires. Reflecting the curvature effect of the fire hose occurring at the actual fire fighting site, this study provides a database of pressure drop, discharge velocity and maximum discharge height through C FD numerical analysis and it can provide using standards for fire extinguishing. Two Reynolds numbers of 200000 and 400000 were numerically analyzed at 0° -180° bending with water of 25℃ as a working fluid in hoses with a diameter of 65mm, a length of 15m, and a radius of curvature of 130mm. Realizable k-ε turbulence model was used and standard wall function was used. The pressure drop increases as the bending angle increases, and the maximum value at 90° and then decreases. The increasing rate is greater than the decrease. The velocity of the secondary flow also decreases after having the maximum value at 90°. The decreasing rate is greater than the increase. The turbulent kinetic energy increases to 120° and decreases with the maximum value. Pressure drop, velocity of the secondary flow, and turbulence kinetic energy are measured larger in the second bending region than in the first bending region.