• 동력기계공학회지
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• 제19권6호
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• pp.54-59
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• 2015

This paper is a numerical study on the correlation of leakage by the variation of operating temperature and orifice diameter applying to hydrostatic bearing in hydraulic actuator. Compared with Brackbill and Kandlikar experimental paper to verify the validity of the numerical analysis technique of the present study, we derive the result that the results of experiments and numerical analysis to match very well. CFD analysis program were analyzed using a commercial code FLUENT V14.5. Inlet and outlet, were applied pressure conditions, the main variables of the analysis is temperature and the orifice inner diameter. The analysis results, pressure value has decreased as the oil temperature and the orifice diameter increases.

• 한국분무공학회지
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• 제8권2호
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• pp.7-15
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• 2003

The effects of fuel density and fuel viscosity on spray characteristics were investigated under two different gas turbine fuels and various fuel supply pressure conditions through measurement of SMD, number density and volume flux by using PDPA system in dual orifice injector for gas turbine engines. In this study, we found out that the droplet size and spray structure are strongly depend on fuel density for dual orifice injector. The spray characteristics of high density fuel in dual orifice injector are similar with the characteristics of low density fuel in single orifice injector. The shear region between primary main fuel stream and secondary main fuel stream is examined in low density fuel condition but not exist in high density fuel condition, then this shear region is very important in quality of gas turbine spray. There are worth consideration for the effect of fuel density on spray characteristics in frontal device design to improve combustion efficiency.

• 설비공학논문집
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• 제18권2호
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• pp.186-191
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• 2006

In this study, five experiments were carried out, with an orifice located downstream of a fan in case I where upstream duct length is 6 D, and that in the downstream is 4 D and different downstream distance to the fan in the rest, so as to determine the optimal location of the orifice and reduce the duct length of airflow measurement device. The resulting flow rate-pressure drop correlations were found to satisfy the limitation of SMACNA standard, which specified an error of $\pm7.5\%$ based on the real flow rate. Also, the best one of five. cases was achieved with the orifice located midway of the orifice duct four times its diameter long.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.2151-2156
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• 2004

In this study, five experiments were carried out, with an orifice located downstream of a fan in case I and upstream distance to the fan in the rest cases(case $II{\sim}$), so as to determine the optimal location of the orifice and reduce the size of airflow measurement device. The resulting flow rate-pressure drop correlations were found to satisfy the limitation of SMACNA standard, which specified an error of ${\pm}7.5%$ based on the real flow rate. The best outcome was achieved with the orifice located midway of the orifice duct 4 times its diameter long.

• International Journal of Aeronautical and Space Sciences
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• 제3권1호
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• pp.1-8
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• 2002

A numerical analysis was performed on the fluid flow in injector orifice of a liquid rocket engine. The present computational code was verified against the published data for turbulent flow in a pipe with a sudden expansion-contraction. Considered were the parameters for the flow analysis in an injector orifice: Reynolds number, ratio of mass flow rate of the injector orifice and inlet flow rate, and slant angle of the injector orifice. The discharge coefficient increased slightly as the Reynolds number increased. The slant angle of the injector changed critically the discharge coefficient. The discharge coefficient increased by 7% when the slant angle changed from $-30^{\circ}$ to $30^{\circ}$ The ratio of mass flow rate had relatively little impact on the discharge coefficient.

• Journal of Chest Surgery
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• 제21권4호
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• pp.757-760
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• 1988

Double mitral valve orifice is an unusual congenital abnormality, and is rarely of clinical importance. That abnormality not produce hemodynamic deficits, but it has been associated with other congenital heart diseases, especially atrioventricular canal defects, and so it is surgically important condition. After the first report by M.S. Greenfield in 1876, there are only a few reported cases all over the world. We experienced two cases of double mitral valve orifice with atrioventricular canal defect. The small accessory mitral orifice was placed in anterior mitral leaflet as a hole type in both cases. The A-V canal defects are corrected with a one patch technique, but the accessory orifices are left unclosed because there were no mitral regurgitations through the orifice. On the 4th postoperative day, the patients have been performed echocardiography; both had no mitral regurgitation. Both of patients are now being follow-up and we find no specific problems. A small accessory mitral orifice may be left unclosed and rarely produce significant regurgitation, conclusively.

• 설비공학논문집
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• 제11권5호
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• pp.647-657
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• 1999

An experimental study has been peformed to investigate the heat transfer characteristics of impinging jets with multiple orifice nozzles. Four different shapes of multiple orifice nozzle were tested to improve the heat transfer characteristics of impinging jet. Heat transfer coefficients were obtained by using transient and steady method based on the liquid crystal thermography, and both methods showed very similar results. The effects of multiple orifice nozzles on the heat transfer characteristics of impinging jets were discussed in detail. The results showed that multiple orifice nozzles improved the heat transfer characteristics of impinging jet. Especially, heat transfer coefficients around stagnation region of impinging jets were highly increased.

• Nuclear Engineering and Technology
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• 제53권11호
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• pp.3643-3652
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• 2021

Sizing the tube inlet orifice of a Once-Through Steam Generator (OTSG) is important to protect the integrity of the tubes from thermal cycling and vibration wear. In this study, a new sizing criterion is proposed for the tube inlet orifice to suppress the parallel channel instability in an OTSG. A perturbation method is used to capture the essential parts of the thermal-hydraulic phenomena of the parallel channel instability. The perturbation model of the heat transfer regime boundaries is identified as a missing part in existing models for sizing the OTSG tube inlet orifice. Limitations and deficiency of the existing models are identified and the reasons for the limitations are explained. The newly proposed model can be utilized to size the tube inlet orifice to suppress the parallel channel instability without excessive engineering margin.

• 대한기계학회논문집B
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• 제27권2호
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• pp.197-205
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• 2003

A cascade impactor is a multistage impaction device used to separate airborne particles into aerodynamic size classes. A micro-orifice impactor uses micro-orifice nozzles to extend the cut sizes of the lower stages to as small as 0.05 ${\mu}{\textrm}{m}$ in diameter without resorting to low pressures or creating excessive pressure drops across the impactor stages. In this work, the phenomenon of particle clogging in micro-orifice nozzles was experimentally investigated for a commercial micro-orifice uniform deposit impactor (MOUDI). It was observed, using an optical microscope, that the micro-orifice nozzles of the final stages were partially clogged due to particle deposition during the aerosol sampling. Therefore the pressure drops across the nozzles were higher than the nominal values given by the manufacturer. To examine the effect of particle clogging in micro-orifice nozzles, the particle collection efficiency of the MOUDI was evaluated using an electrical method for fine particles with diameters in the range of 0.1-0.6 ${\mu}{\textrm}{m}$. The monodisperse liquid dioctyl sebacate (DOS) particles were used as test aerosols. A faraday cage was employed to measure the low-level current of the charged particles upstream and downstream of each stage. It was found that the collection efficiency curves shifted to correspond to smaller orifice sizes, and the 50-% cutoff sizes were much smaller than those given by the manufacturer for the three stages with nozzles less than 400 ${\mu}{\textrm}{m}$ in diameter.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2003년도 제20회 춘계학술대회 논문집
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• pp.72-75
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• 2003

본 연구에서는 인젝터 형상에 따른 캐비테이션과 같은 유동 현상이 수직 분사된 액체 제트의 분열에 미치는 영향을 살펴보고자 하였다. 오리피스의 지름과 길이대 지름비(L/d) 및 입구의 형상이 다른 인젝터에서 압력을 변화시켜가며 내부 유동 변화를 살피고 수직분사 시 액주의 분열 거리와 궤적을 구하여 기존의 연구 결과와 비교하고 분석하였다. 실험 결과 곡률이 없는 경우(sharp edged)의 오리피스에서는 어느 정도 이상의 압력에서 모두 캐비테이션이 발생하였고 곡률이 없는 경우 중 길이대 지름비가 작은 오리피스에선 더 높은 압력에서 캐비테이션 성장에 의한 수력튀김(hydraulic flip)현상도 관찰할 수 있었다. 수직분사 시 곡률이 있는 경우와 없는 경우 모두 동일한 모멘텀 플럭스 비(q)에 대해 거의 같은 궤적 형상을 보였으나 캐비테이션이 일어날 경우 교란에 의해 액주의 분열 거리는 감소하였고 수력튀김 또한 제트 단면적의 감소 및 제트의 확산으로 분열거리가 감소하였다.