• 한국항공우주학회지
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• 제38권10호
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• pp.966-972
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• 2010

본 연구에서는 연소불안정 현상을 제어하는 수동적 기구의 하나인 음향공을 적용하여, 음향공의 설계 변수(오리피스 길이와 지름)와 가진 음압에 따른 감쇠 효과를 선형음향해석과 상온 음향시험을 통하여 연구하였다. 오리피스의 길이가 짧고, 지름이 클수록 감쇠효과가 증가하는 것을 확인하였으며 실험과 선형 음향 해석 결과가 서로 동일한 경향을 보이는 것을 확인하였다. 또한, 가진 음압의 크기가 110 dB 이상에서 감쇠 능력이 비선형적으로 감소하는 것을 확인하였으며, 음향공 오리피스의 단면적이 증가할수록 감소량이 감소하는 것으로부터 비선형 구간에서는 오리피스 단면적을 증가시키는 것이 유리함을 확인하였다.

• 한국분무공학회지
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• 제9권4호
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• pp.31-37
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• 2004

This paper presents spray and combustion characteristics of hydrocarbon fuel injected from pressure-swirl nozzles. Three commercial nozzles with orifice diameters of 0.256, 0.308 and 0.333mm and injection pressures ranging from 0.7 to 1.3 MPa were selected f9r the experiments. Spray characteristics such as breakup length. spray angle and drop size (SMD) were analyzed using photo image analyses and Malvern Panicle Size Analyzer. The drop size was measured with and without a blower at the same measuring locations. The flame length and width were measured using photo image analyses. The temperature distribution along the axial distance and the gas emission such as CO, $CO_2\;and\;NO_x$ were studied. The breakup length decreased with an increase in injection pressure for each nozzle but increased with an increase in nozzle orifice diameter. The spray angle increased and SMD decreased with an increase in injection pressure. The flame with an increased linearly with an increase in injection pressure and in nozzle orifice diameter. The flame temperature increased with an increase in injection pressure but decreased along the axial distance. The maximum temperatures occurred closer to the burner exit and flame at axial distance of 242mm from the diffuser tip. The experimental results showed that the level of CO decreased while that of $CO_2\;and\;NO_x$ increased with an increase in injection pressure and nozzle orifice diameter.

• 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.

• 대한기계학회논문집B
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• 제24권7호
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• pp.957-966
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• 2000

The effect of rotation on the discharge coefficient of orifices with various length-to-diameter ratios and two different inlet corner radii was studied. Length-to-diameter ratios of the orifices range from 0.2 to 10, while the inlet shapes are square edged, or round edges of radius-to-diameter ratio of 0.5. From the experiment, we found that rotational discharge coefficient and Rotation number, when based on ideal exit velocity of the orifice considering momentum transfer from the rotor, describe the effect of rotation very well. In this study, the discharge coefficients of rotating orifices are shown to behave similar to those of the well-known non-rotating orifices. For both rotating and non-rotating orifices, the discharge coefficients increase with the length-to-diameter ratio until a maximum is reached. The flow reattachments in the relatively short orifices are responsible for the increase. The coefficient then decreases with the length-to-diameter ratio due to the friction loss along the orifice bore. The length-to-diameter ratio that yields maximum discharge coefficient, however, increases with the Rotation number because the increased flow-approaching angle requires larger length-to-diameter ratio for complete reattachment. The length-to-diameter ratio for complete reattachment is shorter for round edged orifices than that of square edged orifices by about a unit length-to-diameter ratio.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2009년도 제33회 추계학술대회논문집
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• pp.329-334
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• 2009

형상에 따른 오리피스의 동특성을 확인하기에 앞서 정상 상태에서의 성능에 대한 연구가 선행되어야 한다. 이를 위해 수치해석을 통해 개도, 두께, 팽창각에 따른 오리피스의 성능을 예측하였다. 유동 해석 알고리듬은 SIMPLEC을 사용하였고, 차분 기법은 PRESTO, QUICK 기법을 사용하였으며, 난류 모델은 $k-{\omega}$ STS를 사용하였다. 오리피스의 개도가 증가하면서 유량계수는 급격하게 증가하였고, 두께가 증가하면서 유량계수는 급격하게 증가하였다가 서서히 감소한다. 팽창각이 45도일 때 유량계수가 가장 작게 나타났다.

• 대한기계학회논문집B
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• 제24권11호
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• pp.1506-1512
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• 2000

Control of shock may be important in the hydraulic system and necessary to avoid failure and to improve the efficiency of operation. This study addresses the design and use of an orifice to provide the desired control of the hydraulic actuator system. The experimental apparatus is an idealization of an automobile shift system. Control is accomplished by installing three different types of orifices at appropriate locations in the system. Experimental results show that the orifice can be used to obtain the control of shock and control level depends on the orifice size, orifice type, operating pressure and flow rate.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1996년도 추계학술발표회논문집(1)
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• pp.295-300
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• 1996

To investigate the effects of the side-orifice on the pressure drop for single-phase flow, a series of experiments have been carried out with 16 different downstream test sections with various combinations of side-orifice shapes, different numbers of side-orifices, and different arrangements of the side-orifice using water as a working fluid. From the measurements of the pressure drop and the flow rate, the pressure loss coefficient of the side-orifice(s) has been evaluated. Based on the total number of 529 present data, an empirical correlation for the pressure loss coefficient has been developed in terms of Reynolds number and geometric parameters, such as area ratio, equivalent diameter, leading edge, and average width of side-orifice.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.79-82
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• 2002

Three-dimensional pipe flows with elbows and tees for few different pipe fittings are calculated to estimate the effect of swirling flow on measuring accuracy of orifice flow meter. It is evaluated how the pressure difference across the orifice is dependent on the length of upstream straight pipe in a branch and how swirl intensity, swirl angel and axial velocity distribution affect the measuring error of orifice flowmeter. From the results, it is found that, regardless of flow rate specified in this calculation, the effect of the straight pipe length can be neglected for the lengths larger than thirty diameters although there still remain significant swirl at the orifice

• 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.