• 한국전산유체공학회지
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• 제2권2호
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• pp.51-58
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• 1997

A reliable computational solver has been developed for the analysis of three-dimensional inviscid compressible flows around a nacelle of a high bypass ratio turbofan engine, The numerical algorithm is based on the modified Godunov scheme to allow the second order accuracy for space variables, while keeping the monotone features. Two step time integration is used not only to remove time step limitation but also to provide the second order accuracy in a time variable. The multi-block approach is employed to calculate the complex flow field, using an algebraic, conformal, and elliptic method. The exact solution of Riemann problem is used to define boundary conditions. The accuracy of the developed solver is validated by comparing its results around the isolated nacelle in the cruise flight regime with the solution obtained using a commercial code "RAMPANT. "

• Nuclear Engineering and Technology
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• 제41권3호
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• pp.295-306
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• 2009

The subchannel grade void distributions in the NUPEC (Nuclear Power Engineering Corporation) BFBT (BWR Full-Size Fine-Mesh Bundle Tests) facility were evaluated with the subchannel analysis code MATRA and the system code MARS. Fifteen test series from five different test bundles were selected for an analysis of the steady-state subchannel void distributions. Two transient cases, a turbine trip without a bypass as a typical power transient and a re-circulation pump trip as a flow transient, were also chosen for this analysis. It was found that the steady-state void distributions calculated by both the MATRA and MARS codes coincided well with the measured data in the range of thermodynamic qualities from 5% to 25%. The results of the transient calculations were also similar and were highly feasible. However, the computational aspects of the two codes were clearly different.

• 설비공학논문집
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• 제15권5호
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• pp.337-345
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• 2003

In the case of heat exchangers operating under frosting condition, the growth of frost layer causes the heat exchanger to increase the thermal resistance and pressure loss of the air flow. In this paper, a transient characteristic prediction model of the heat transfer for multi inverter heat pump with frosting on its surface was presented taking into account the change of the fin efficiency due to the growth of the frost layer. In this dynamic simulation program, which was peformed for a basic air conditioning system model, such as evaporator, condenser, compressor, linear electronic expansion valve (LEV) and bypass circuit. The theoretical model was driven from the obtained heat transfer coefficient and mass transfer coefficient, independently. And we consider heat transfer performance was only affected by a decrease of the wind flow area. The calculated results were compared with some cases of experiments for frosting conditions.

• 설비공학논문집
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• 제16권8호
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• pp.728-740
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• 2004

Heat sink has extended surface area for enhanced heat transfer. The enhanced convection heat transfer has been used widely, such as cooling electronic chips in the electronics industry. Heat sink usually requires an increase in the heat transfer and a decrease in the pressure drop, and must improve the performance in the flow field of industrial plants. In this study, wing fin heat sink was studied and tests were conducted in a rectangular cross sectional channel with wing fin heat sinks. The leading and trailing ends of a wing fin have a sharp edge, simulating the airfoil feature. Empirical correlations have been developed for wing fin heat sink types. And wing fin heat sinks have better cooling performance than elliptic fin and square fin types.

• 항공우주시스템공학회지
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• 제17권5호
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• pp.11-18
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• 2023

The architecture of the Fuel Thermal Management System (FTMS) in a commercial aircraft engine was built to model and simulate the fuel system. The study shows the thermal interactions between the fuel and engine lubrication oil through the mission profile of a high bypass ratio, two-spool turbofan engine. Fuel temperature was monitored as it flowed through each sub-component of the fuel system during the mission. The heat load in the fuel system strongly depended on the fuel flow rate, and was significantly increased for the periods of cruise and descent with decrease of fuel flow rate, rather than for the periods of take-off. Due to the thermal interaction in the pump housing, the fuel temperature at the outlet of the low-pressure pump was increased (4.0, 9.2, and 30.0) % over the case without thermal interaction for take-off, cruise, and descent, respectively.

• Journal of Chest Surgery
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• 제37권1호
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• pp.1-10
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• 2004

배경: 기존에 사용되고 있는 인공심폐기는 비박동성 펌프로 회로 내부에 형성되는 압력이 낮고 혈구 손상이 적어서 표준 인공 심폐기로 선호되고 있다. 그러나 많은 실험적 연구들을 보면 박동성 관류가 혈역학, 대사, 장기의 기능, 미세 순환에 대하여 비박동성 관류보다 유익함을 알 수 있다. 그러나 박동성 인공심폐기는 높은 회로 내부 압력과 혈구손상이 해결되어야 할 문제점으로 개발이 어려웠다. 이 연구의 목적은 국내에서 제작된 이중 박동성 인공심폐기의 안전성 및 유효성을 알아보는 것이다. 대상 및 방법: 6마리의 송아지를 대상으로 이중 박동성 인공 심폐기 실험을 하였으며, 완전체외순환을 시켰다. 체외순환은 상,하 대정맥과 대동맥 사이를 우회하였으며, 막형 산화기를 사용하여 혈액을 산화시켰다. 산화기는 좌우측 펌프 중간에 위치시켰다. 순환 시간은 4시간이었다. 동맥혈가스분석, 혈액검사, 혈장 유리 혈색소를 측정하였으며, 맥압과 회로 내부압력을 관찰하였다. 측정은 인공 심폐기 구동 전과 순환 1, 2, 3, 4시간째에 측정하였다. 결과: 동맥혈 가스분석상 pH, 이산화 탄소분압은 모두 정상 범위였으며, 동맥혈 산소 분압은 100 mmHg 이상의 충분한 산화를 보였다. 혈장 유리혈색소는 완전 체외순환하여 4시간이 경과하면서 15.87 $\pm$5.63 mg/㎗로 점차 증가소견을 보였으나 20 mg/㎗ 이내였다. 혈액검사소견상 뚜렷한 이상소견은 없었다. 순환전 수축기 혈압은 97.5$\pm$5.7 mmHg이었으며 시간 경과하여도 100 mmHg 이상의 혈압을 유지하였다. 확장기 혈압은 72.2$\pm$7.7 mmHg이었으며 시간 경과하여도 잘 유지되었다. 평균 혈압은 순환 전 83$\pm$9.2 mmHg이었으며, 시간 경과 시 증가된 소견을 보였다. 펌프의 유량은 3.3 L/min이상을 유지할 수 있었다. 완전체외순환 동안의 혈압의 변화를 보면 순환 전 심장과 유사한 동맥혈압을 보였다. 결론: 이중 박동 구조를 이용한 박동성 인공심폐기는 효과적인 박동성 혈류를 제공하면서 혈구 세포손상도 적었으며, 혈액학적 및 혈역학적인 면에서도 우수한 결과를 보였다. 따라서 모든 심장수술의 인공심폐기로 사용되어질 경우 말초장기에 생리적이고 안정적인 혈류를 공급할 수 있을 것으로 기대된다.

• 대한핵의학회지
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• 제36권6호
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• pp.357-367
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• 2002

목적: 뇌혈관질환에 있어서 뇌혈류와 뇌혈류예비능을 기저/아세타졸아미드 뇌혈류SPECT로 평가 가능하나 재관류 수술효과를 비교 평가하기 위해서는 정량적인 평가가 필요하다. 대상 및 방법: 12명의 환자($51{\pm}15$세, 남:녀:6:6)의 수술 전후 기저 시와 아세타졸아미드 부하 뇌관류 SPECT를 SPM에서 공간정규화하고 소뇌의 계수를 기준으로 계수정규화한 후 확률뇌지도(statistical probabilistic anatomical map, SPAM)를 이용하여 부위별 혈류를 정량화하였다. 이 결과로부터 수술 전후 및 정상대조군($59{\pm}15$세, 남:녀:10:11)과의 비교를 McNemar test와 Mannwhitney test를 이용하여 비교하였다. 혈류예비능은 기저 시와 부하시의 차이를 기저 시 계수를 기준으로 백분율로 표현하였다. 결과: 수술 후 수술 부위의 기저 시와 아세타졸아미드 부하 시 혈류 그리고 혈류예비능 모두가 유의하게 향상되었다(p<0.05). 정상군과의 비교에 있어서는 기저 시 혈류는 정상군과 차이가 없을 정도로 호전되었으나, 아세타졸아미드 부하시 혈류와 혈류예비능은 수술 후에도 유의한 차이를 보였다(p<0.05). 혈류예비능은 주로 수술부위를 중심으로 향상되었다. 결론: SPM 및 SPAM을 이용하여 기저/아세타졸아미드 뇌혈류 SPECT의 수술 전후결과를 정량적, 객관적으로 쉽게 비교 평가할 수 있다.

• Journal of Mechanical Science and Technology
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• 제15권3호
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• pp.291-299
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• 2001

Recently, severe wear on the shutdown rod cladding of Ulchin Nuclear Power Plant #1, #2 were observed by the Eddy Current Test(E.C.T.). In particular, the wear at the sixth card location was up to 75%. The test results indicated that the Flow Induced Vibration(F.I.V.) might be the cause of the fretting wear resulting from the contact between Rod Cluster Control Assemblies(RCCAs) and their spacing cards(guide plates) arranged in the guide tube. From reviewing RCCAs fretting wear repots and analyzing the general characteristics of F.I.V. mechanism in the reactor, geometric layout and flow conditions around the control rod, it is concluded that the turbulence excitation is the most probable vibration mechanism of RCCA. To identify the governing mechanism of RCCA vibration, an experiment was performed for a representative rod position in which the most serious fretting wear experienced among the six rod positions. The experimental rig was designed and set up to satisfy the governing nondimensional numbers which are Reynolds number and mass damping parameter. The vibration amplitude measurement by the non-contact laser displacement sensor showed good agreements in the frequency and the maximum wearing(vibration) location with Ulchin E.C.T. results and Framatome report, respectively. The sudden increase in the vibration amplitude was sensed around the 6th guide plate with mass flow rate variation. Comparing the similitude rod behaviour with the idealized response of a cylinder in flow induced vibration, it was found that he dominant mechanism of vibration was transferred from turbulence excitation to periodic shedding at the mass flow ate 90ι/min. Also the critical velocity of the vibration in RCCAs was determined and the vibration can be prevented by reducing the bypass flow rate below the critical velocity.

• Journal of Chest Surgery
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• 제37권6호
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• pp.511-516
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• 2004

배경: 관상동맥우회술 시 내유동맥편의 골격화 채취법의 이론적인 장점들의 하나는 골격화 채취가 내유동맥의 채취에 필연적으로 수반되는 흉골로의 혈류 공급의 감소를 최소화시킨다는 것이다. 저자들은 술 전과 술 후 각각 골주사를 통하여 좌측 및 우측 흉골로의 흡수율을 비교 분석하여, 술 후 내유동맥편의 채취 방법에 따른 흉골로의 혈류 감소의 차이를 증명하고자 하였다. 대상 및 방법: 2002년 4월부터 2003년 3월까지 시행한 48예의 관상동맥우회술 환자들 중 술 전 및 술 후 1일째 골주사를 시행한 27예의 환자를 대상으로 하였다. 8예의 환자에서 양측 내유동맥을 모두 사용하였으며(BIMA군), 19예의 환자에서 좌내유동맥만을 사용하였는데(LIMA군), 이 중 골격화 채취를 하여 사용한 환자가 12예(LIMA_skel군), 경상 채취하여 사용한 환자가 7예(LIMA_ped군)였다. 골주사를 시행 후 임의의 정중선을 기준으로 흉골의 좌측 부분에 관심 영역을 그리고 흉골의 반대편에 이 영역의 대칭영상을 만들어 또 하나의 관심 영역을 만든 후 각 관심 영역의 화소 당 평균 계산치를 택하여 좌우비를 산출 하였다. 결과: LIMA군에서 좌우비는 수술 전 94.6$\pm$4.1%에서 술 후 87.9$\pm$6.9%로 감소한 반면(p=0.003), BIMA군에서는 통계적으로 유의한 변화를 보이지 않아 좋은 대조를 보였다. LIMA_skel군 과 LIMA_ped군에서의 좌우비는 각각 수술 전 95.3$\pm$4.2% 및 93.4$\pm$3.9% 에서 술 후 88.3$\pm$7.7% 및 87.4$\pm$5.8%로 감소하였으나 감소 정도를 분율로 표시하였을 때 LIMA_skel군이 -7.44$\pm$7.08, LIMA-ped 군이 -6.17$\pm$9.08로 통계적인 유의성은 없었다. 결론: 술 후 흉골의 골주사 흡수의 감소는 내유동맥의 채취가 채취방법에 상관없이 동측의 흉골의 혈류 공급을 감소시킴을 시사하였다. 내유동맥의 골격화 채취가 비골격화 채취에 비하여 흉골의 혈류 공급의 보존 측면에서 월등한 이점을 보이지는 않았다.

• Journal of Chest Surgery
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• 제18권2호
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• pp.182-192
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• 1985

[here are so many reports that pulsatile blood flow provides physiologic organ perfusions during cardiopulmonary bypass. So, we compared the recent 30 cases undergoing cardiac surgery by Cobe-Stckert pulsatile roller pump with another 30 cases by Polystan nonpulsatile roller pump. Pulsatile flow was applied during aortic-cross clamping period when synchronized to internal EKG simulator, and perfusion mode was changed to continuous nonpulsatile flow after declamping of aorta. Age, sex, weight, and disease entities were comparable and operative techniques were similar between two groups. 1. There were no differences in average ACC time, ECC time, and Operation time. 2. Postoperative artificial respiration time was 6hrs 30mins in nonpulsatile group and 4hrs 48mins in pulsatile group, and detubation time after ventilator weaning was 2hrs 44mins in nonpulsatile group and 1hrs 43mins in pulsatile group. 3. Average pulse pressure was 8mmHg in nonpulsatile group and 55mmHg in pulsatile group, and a mean arterial pressure was 66.0mmHg in nonpulsatile group and 60.7mmHg in pulsatile group. 4. Mean urine-output during ACC;ECC period was 9.717.3;9.913.2ml/kg/hr in nonpulsatile group and 14.215.0;15.817.5 in pulsatile group [p<0, 05], and thereafter progressive decrease of differences in urine output between two groups until POD 2, and lesser amounts of diuretics was needed in pulsatile group during same postoperative period. Serum BUN/Cr level showed no specific difference and urine concentration power was well preserved in both groups. 5. Plasma proteins and other Enzymes showed no differences between two groups, but serum GOT/GPT level was higher in nonpulsatile group till POD 2. 6. Serum Electrolytes showed no differences between two groups. 7. WBC, RBC, Platelet counts, Hgb and Hct were not different and Coagulogram was well preserved in both groups. 8. Plasma free Hgb level was 7.09mg% in pulsatile group compared with 3.48mg% in pulsatile group on POD 1 but was normalized on POD 2. Gross hemoglobinuria after ECC was noted in 6 cases [20%] of pulsatile group and 4 cases [13%] of nonpulsatile group. 9. In both groups, most patients were included in NYHA class III to IV [28 cases;93% in nonpulsatile group, 22 cases;73% in pulsatile group] preoperatively, and well improved to class I to 11[22 cases; 73% in nonpulsatile group, 30 cases; 100% in pulsatile group] postoperatively. There were 7 operative mortalities in nonpulsatile group only, which were 5 cases of TOF with hepatic failure, 1 case of multiple VSDs with low out-put syndrome, and 1 case of mitral valvular heart disease with cardiomyopathy. We concluded that the new, commercially available Cobe-Stckert pulsatile roller pump device was safe, simple, and reliable.