• Nuclear Engineering and Technology
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• 제33권3호
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• pp.315-326
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• 2001

Direct ECC bypass phenomena that occur in a reactor vessel downcomer with a Direct Vessel Injection (DVI) system during the reflood phase of a Large Break Loss-of-Coolant Accident (LBLOCA) are experimentally investigated using a transparent l/7.5 scaled down test facility of the Upper Plenum Test Facility (UPTF). A series of separate effect tests are peformed in order to investigate the mechanisms of direct ECC bypass and to find out its scaling parameters. Various flow regimes and phasic distribution in downcomer are identified and mapped, and the fraction of direct ECC bypass is measured under a wide range of air and water injection conditions. From the counterpart test of the UPTF Test 21-D, the dimensionless gas velocity ( $j^{*}$$_{g,eff}$) is derived experimentally, which is believed to be a major scaling parameter for the fraction of direct ECC bypass. And it is found out that the direct ECC bypass is greatly affected by the spreading width of ECC water film and the geometric configuration of the downcomer.r.

• Journal of Chest Surgery
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• 제24권3호
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• pp.253-260
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• 1991

The adequacy of anticoagulation with heparin during cardiopulmonary bypass, and precise neutralization with protamine at the conclusion of cardiopulmonary bypass, were important. In sixty children undergoing cardiopulmonary bypass, ACT and heparin dose-response curve were studied. Total dose of heparin before bypass were 2.80$\pm$0.74 mg/kg and the amount of protamine administered after bypass were 3.0$\pm$1.23 mg/kg. So protamine: heparin ratio was 1.07: l.c After administration of protamine which dose is calculated with heparin dose-response curve, ACTs were returned to normal range[mean 114.8 $\pm$13 second]. The heparin sensitivity and its half-life do not have relationship with age, weight, height, surface area and urine amount during operation. And there are too much individual variations in heparin sensitivity and its half-life. So conventional heparin protocols can overestimate or underestimate the amount of heparin and protamine. Heparin dose-response curve makes it possible to maintain anticoagulation in a safe range during bypass with adequate amount of heparin individually. At the conclusion of bypass, this curve can be used to predict the precise amount of protamine amount of protamine needed for neutralization of the heparin. But heparin dose-response curve to be used clinically, further studies will be needed about relationship between ACT and heparin level in the high range, influence of hemodilution and hypothermia to ACT and discrepancy between true adequate amount of protamine and calculated amount by heparin dose-response curve.

• International Journal of Vascular Biomedical Engineering
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• 제3권1호
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• pp.1-5
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• 2005

Background: Coronary atherosclerosis artery disease is the leading cause of morbidity and mortality. Coronary artery bypass grafting (CABG) which utilizes the saphenous vein graft, has helped in alleviating the suffering of these patients. Newer techniques are being developed to improve upon the techniques. Still there is significant number of failures, leading to re-grafting or re-vascularization. Some studies have helped in identifying the high and low shear stress regions. Further studies based on their realistic models are required. Material, methods and results: we developed the realistic model of fully blocked right coronary with bypass graft placed at angle of $5^0$ with curvature similar to that of artery. Pulsatile flow of birefringent solution through this model by polarized light was visualized. The images of complete flow field in the model were recorded and analyzed. Regions of high flow disturbances which are prone to further changes are identified. Existence of recirculation in the blocked coronary may initiate new blood-tissue interactions deleterious to bypass graft. Conclusion: Our study shows that by selecting the procedure to place bypass graft at minimum angle with curvature similar to that of artery and smooth sutures may improve the life span of the graft. This study also identified that coronary blocked regions contributing by recirculation flow at the proximal and distal regions of bypass which may require further studies.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.539-543
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• 2009

When the suction pressure of compressor decreases under its limit, the compression ratio is increased causing the malfunctions of compressor. As the method to decrease the compression ratio, hot gas bypass system is usually adopted in heat pump system. In the hot gas bypass system, the discharged gas from the compressor is bypassed into the compressor suction, which causes the increase of suction pressure and the decrease of compression ratio. In this study, the characteristics and performances of the hot gas bypass system in heat pump was investigated experimentally with a variation of the bypass flow rate ratio. With the increase of the bypass rate ratio, the compressor suction pressure was increased, even though the total capacity and COP was decreased. From the analysis of the experimental results, the optimum pressure control algorithm was suggested in this study.

• 한국전산유체공학회지
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• 제22권1호
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• pp.67-80
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• 2017

The high-speed bypass effect on the heat exchanger performance has been investigated numerically. The plate-fin type heat exchanger was modeled using two-dimensional porous approximation for the fin region. Governing equations of mass, momentum, and energy equations for compressible turbulent flow were solved using ideal-gas assumption for the air flow. Various bypass-channel height were considered for Mach numbers ranging 0.25-0.65. Due to the existence of the fin in the bypass channel, the main flow tends to turn into the core region of the channel, which results in the distorted velocity profile downstream of the fin region. The boundary layer thickness, displacement thickness, and the momentum thickness showed the variation of mass flow through the fin region. The mass flow variation along the fin region was also shown for various bypass heights and Mach numbers. The volumetric entropy generation was used to assess the loss mechanism inside the bypass duct and the fin region. Finally, the correlations of the friction factor and the Colburn j-factor are summarized.

• Journal of Chest Surgery
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• 제25권12호
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• pp.1399-1403
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• 1992

The evaluation of the effectivess of ongoing cardiopulmonary resucitation efforts is dependent on the commonly used methods, such as the presence of femoral or carotid artery pulsations, arterial blood gas determinations, peripheral arterial pressure and intracardiac pressure monitoring. But recent studies suggest that end-tidal carbon dioxide tension serves as a non-invasive measurement of pulmonary blood flow and therefore cardiac output under constant ventilation. A prospective clinical study was done to determine whether end-tidal carbon dioxide monitoring in open heart surgery under cardiopulmonary bypass could be used as a prognostic indicator of bypass weaning. We monitored end-tidal PCO2 values continuously during cardiopulmonary bypass in 30 patients. "Ohmeda 5210 CO-2 monitor" under infrared absorption method were incorperated into the ventilator circuit by means of a side point adaptor between endotracheal tube and ventilator tubing. 18 patients[Group I ] were res-ucitated from partial bypass followed by aorta cross clamp off and 12 patients[Group II ] from aorta cross clamp off followed by partial bypass. But there was no difference between two groups[p>0.05]. The value of end-tidal carbon dioxide tension during ventricular fibrillation or nearly arrest state was 6.6$\pm$2.9 mmHg, and at the time of spontaneous beating was 19.3$\pm$5.6 mmHg[Mean$\pm$Standard deviation], In conclusion end-tidal carbon dioxide tension monitoring provides clinically useful, continous, noninvasive and supplementary prognostic indicator during cardiopulmonary bypass weaning procedures.rocedures.

• Journal of Mechanical Science and Technology
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• 제15권9호
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• pp.1302-1310
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• 2001

This paper introduces modeling and simulation results for pipeline inspection gauge (PIG) with bypass flow control in natural gas pipeline. The dynamic behaviour of the PIG depends on the different pressure across its body and the bypass flow through it. The system dynamics includes: dynamics of driving gas flow behind the PIG, dynamics of expelled gas in front of the PIG, dynamics of bypass flow, and dynamics of the PIG. The bypass flow across the PIG is treated as incompressible flow with the assumption of its Mach number smaller than 0.45. The governing nonlinear hyperbolic partial differential equations for unsteady gas flows are solved by method of characteristics (MOC) with the regular rectangular grid under appropriate initial and boundary conditions. The Runge-Kuta method is used for solving the steady flow equations to get initial flow values and the dynamic equation of the PIG. The sampling time and distance are chosen under Courant-Friedrich-Lewy (CFL) restriction. The simulation is performed with a pipeline segment in the Korea Gas Corporation (KOGAS) low pressure system, Ueijungboo-Sangye line. Simulation results show us that the derived mathematical model and the proposed computational scheme are effective for estimating the position and velocity of the PIG with bypass flow under given operational conditions of pipeline.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 하계학술대회 논문집 Vol.8
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• pp.25-26
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• 2007

In this paper, we studied the shadow effect which is one of environmental cause for hot-spot phenomenon on PV by considering electrical effects. We fabricated PV module in case of existence and nonexistence of bypass diode. And maximum output power and thermal distribution was analyzed by shadowing solar cell by increase of 5%. From the results, the PV module's(without bypass diode) maximum output power was reduced by hot-spot gradually. But the PV module's(with bypass diode) maximum output power had no reduction by operation of bypass diode, though solar cell is shadowed more than 60%. The solar cell temperature of PV module(without bypass diode) was $10^{\circ}C$ higher compared to module's one. This is a reason for shortening of durability of PV module.

• Journal of Chest Surgery
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• 제37권1호
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• pp.11-18
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• 2004

배경: 태아심장수술이 가능하려면 심폐우회술 시 태반혈류의 유지가 가장 중요하다. 태반 혈관의 수축으로 인한 혈류 감소는 태아에 심한 저산소성 손상을 초래한다. 본 연구에서는 태반혈관 수축 억제를 위한 인도메타신과 완전 척추 마취가 태반 혈류에 미치는 영향을 테스트하였다. 대상 및 방법: 제태기간 120∼150일 되는 20마리의 태아양을 정중흉골절개하에 주폐동맥과 우심방에 각각 12 G, 14∼18 F 크기의 도관을 삽관하여 30분 동안 심폐우회술을 시행하였다 어미양은 케타민 정주를 이용한 전신마취를 시행하였고 태아양에 대하여는 근육이완제만을 사용하였다. 심페우회술은 바이오펌프(Bio-pump, Bio-Medicus 회사제, 미국)와 태반을 산화기로 이용하여 시행하였다. 대조군은 태반을 산화기로 사용하여 체외순환만을 시행하였고(10마리), 실험군은 완전 척추 마취와 인도메타신을 전처치한 후 같은 방법으로 체외순환을 시행하였다 시간 경과에 따른 태아혈역학 및 동맥혈가스소견, 태반혈류 변화를 측정하였다. 결과: 태아양의 평균체중은 3.5 $\pm$ 1.3 (2.2 ∼ 5.2) kg이었다. 대조군에서는 심폐우회 시작 직후 평균 44.7 mmHg에서 14.4 mmHg로 급격한 혈압 강하가 관찰되었고 이때 측정한 혈류는 74.3∼97.0 $m\ell$/kg/min 였다. 동맥혈 가스 소견 역시 동맥혈 이산화탄소분압치가 61.9∼129.6 mmHg이었으며 체외순환 정지 후에는 심실세동으로 혈역학 측정이 불가능하였다. 실험군에서는 심폐우회 시작 직후 혈압이 30∼45.8 mmHg로 의미있게 높게 유지되었다. 태반 혈류는 78.8∼120.2 $m\ell$/kg/min로 대조군보다 높았다. 같은 시간대에 측정한 동맥혈 이산화탄소 분압치는 평균 59.1∼92.3 mmHg였으며 체외순환 정지 후에는 대조군보다 덜 급격하게 심기능 저하를 보여 평균동맥압이 27.3 mmHg였다. 결론: 연구자 등은 본 연구를 통하여, 30분간 심폐우회술을 실시하면서 인도메타신 전처치와 완전 척추 마취군에서 의미있는 태반혈류개선을 관찰하였으나 임상적용이 가능한 태반혈류의 유지에는 어려움을 겪었다. 향후 태아심폐우회술과 관련된 기술적인 측면에서의 개선, 인도메타신 용량의 조절, 순환회로의 최소화, 체외순환을 위한 우회펌프의 개선 등 태아 체외순환의 수정에 관한 지속적인 연구가 요구된다.

• Journal of Chest Surgery
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• 제13권3호
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• pp.174-185
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• 1980

It was my great nohour that I can be exposed to such plenty materials of the coronary bypass surgery. Here, I am summarizing the xoronary bypass surgery, clinically. The material is serial 101 patients who underwent coronary bypass surgery between July 17, 1979 to November 30, 1979 in Shadyside Hospital, University of Pittsburgh. 1. Incidence of the Atherosclerosis is frequent in white, male, fiftieth who are living in industrialized country. It has been told the etiologic factor of the atherosclerosis is hereditary, hyperlipidemia, hypertension, smoking, drinking, diabetes, obesity, stress, etc. 2. The main and most frequent complication of the coronary atherosclerosis is angina pectoris. Angina pectoris is the chief cause of coronary bypass surgery and the other causes of coronary bypass surgery are obstruction of the left main coronary artery, unstable angina, papillary muscle disruption or malfunction and ventricular aneurysm complicated by coronary artery disease. 3. The preoperative clinical laboratory examination shows abnormal elevation of plasma lipid in 82 patint, plasma glucose in 40 patient, total CPK-MB in 24 patient stotal LDH in 22 patient out of 101 patient. 4. Abnormal ECG findings in preoperative examine were 29.1% myocardial infarction, 25.8% ischemia and injury, 14.6T conduction defect. 5. Also we had done Echocardiography, Tread Mill Test, Myocardial Scanning, Vectorcardiography and Lung function test to get adjunctive benefit in prediction of prognosis and accurate diagnosis. 6. The frequency of coronary atherosclerosis in main coronary arteries were LAD, RCA and Circumflex in that order. 7. The patients' main complaints which were became as etiologic factor undergoing coronary bypass surgery were angina, dyspnea, diaphoresis, dizziness, nausea and etc. 8. For the coronary bypass surgery, we used cardiopulmonary bypass machine, non-blood, diluting prime, cold cardioplegic solution and moderate cooling for the myocardial protection. 9. We got the grafted veins from Saphenous and Cephalic vein. Reversed and anastomosed between aorta and distal coronary A. using 5-0 and 7-0 prolene continuous suture. Occasionally we used internal mammary A. as an arterial blood source and anastomosed to the distal coronary A. and to side fashion. 10. The average cardiopulmonary bypass time for every graft was 43.9 min. and aortic clamp time was 23 minute. We could Rt. coronary A. bypass surgery only by stand by the cardiopulmonary machine and in the state of pumping heart. 11. Rates by the noumbers of graft were as follow : 21.8% single, 33.7% double, 26.7% triple, 13.9% quadruple, 3% quintuple and 1% was sixtuple graft. 12. combined procedures with coronary bypass surgery were 6% aneurysmectomy, 3% AVR, 1% MVR, 13% pacer implantation and 1% intraaortic ballon setting. 13. We could see the complete abolition of anginal pain after operation in 68% of patient, improvement 25.8%, no change in 3.1%, and there was unknown in 3%. 14. There were 4% immediate postoperative deaths, 13.5% some kinds of heart complication, 51.3% lung complications 33.3% pleural complications as prognosis.