• 대한기계학회논문집B
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• 제26권4호
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• pp.604-613
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• 2002

Generation characteristics of electrospray droplets for highly viscous liquid have been investigated by measuring size distributions of droplets emitted from the Taylor cone using glycerol solutions with various conductivities. Because of very small volatility of glycerol, droplet sizes can be measured by an aerodynamic size spectrometer (TSI Aerosizer DSP) with negligible evaporation of droplets. For highly conducting and viscous liquid, the sizes of the droplets electrosprayed from the Taylor cone are found to be relatively insensitive to applied voltages and the electrosprays assisted by the corona discharge call produce monodisperse droplets as long as the corona intensity is not too high. Near the minimum flow rate where a liquid cone is stable, the spray tends to consist of a one -peak monodisperse distribution of drop lets. However, at high flow rates, the spray bifurcates into bimodal distributions, which are consistent with the result of the previous study for less viscous liquids than our liquids. For liquid flow rates (Q) below 1 nl/s, the measured droplet diameters by the aerosizer are in the range of 0.30 to 1.2 ${\mu}{\textrm}{m}$ for the glycerol solutions. The diameters of monodisperse droplets scale approximately with $r^*=Q_$\tau$(Q$\tau$){^1/3}$ where $r^*$ is a characteristic length and $\tau$is the electrical relaxation time of the fluid. However, when compared with several represe ntative scaling laws, the droplet diameters are two to six factors greater than those predicted by the scaling laws. This may be closely related to the combined effect of the much higher viscosity and the electrical charge on the jet breakup of glycerol so solution.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제35회 추계학술대회논문집
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• pp.386-392
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• 2010

상용 전산유체해석 프로그램을 사용하여 오리피스형 분사기에서 수직분사 액체 제트의 다상유동을 해석하였다. 본 연구의 목적은 오리피스형 분사기 분무 특성을 이해하고 연소기 내부 위치에 따른 유동조건와 항력계수와의 관계식을 구하는 것이다. 수치해석 결과 모형 램젯 연소기에서 수직분사 유동해석은 난류점성모델인 Realizable $k-{\varepsilon}$ 모델과 다상유동모델인 DPM 모델이 유효함을 확인하였다. 또한 오리피스형 분사기에서 레이저 흡수법을 사용하여 측정한 실험결과(증기농도분포)는 수치해석 결과와 잘 일치하였다.

• 대한기계학회논문집B
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• 제21권5호
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• pp.691-699
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• 1997

The effects of concave hemispherical surface curvature on the local heat transfer from a turbulent round impinging jet were experimentally investigated. The liquid crystal transient method was used for these measurements. This method, which is a variation on the transient method, suddenly exposes a preheated wall to an impinging jet while video recording the response of liquid crystals for the measurement of the surface temperature. The Reynolds number ranges from Re=11,000 to 50,000, the nozzle-to- surface distance from L/d=2 to 10, and the surface curvature from D/d=6 to 12.The present results are also compared to those for the flat plate case. In the experiment, the local Nusselt numbers tend to increase in all regions with an increasing surface curvature. The maximum Nusselt number for all Reynolds numbers occurred at L/d .ident. 6 and a second maximum in the Nusselt number occurred at R/d .ident. 2 for both Re=23,000 and Re=50,000 in the case of L/d=2 and for Re=50,000 only in the case of L/d=4. Meanwhile, as the surface curvature increases, the value of the secondary maximum Nusselt number decreases. All the other cases exhibit monotonically decreasing values of the Nusselt number along the curved surface. The stagnation point Nusselt numbers are well correlated with Re, L/d, and D/d.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.774-778
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• 2004

The atomization process of a circular $SF_{6}$ liquid jet issued into an otherwise quiescent, high-pressure $N_2$ gas was observed to explore the breakup mechanism of liquid ligaments involved in turbulent atomization. Both liquid and gas temperatures were fixed at a room temperature but the gas pressure was elevated to more than twice the critical pressure of $SF_{6}$. Therefore, the liquid surface was in a thermodynamic state close to a critical mixing condition with suppressed vaporization. Since the surface tension and the surface gas density approach zero and the surface liquid density, respectively, phenomena equivalent to those which would appear when a very high speed laminar flow of water were injected into the atmospheric-pressure air can be observed by issuing $SF_{6}$ liquid at low speeds in micro-gravity environment which avoid disturbances due to gravity forces. The instability ob near-critical mixing surface jet was quantitatively characterized using a newly developed device, which could issue a very small amount of $SF_{6}$ liquid at small constant velocity into a very high-pressure $N_2$ gas.

• 한국추진공학회지
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• 제7권1호
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• pp.28-39
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• 2003

본 연구에서는 캐비테이션과 수력튀김과 같은 유동 현상이 수직 분사된 액체 제트의 분열에 미치는 영향을 살펴보았다. 오리피스 지름, 오리피스의 길이대 지름비, 오리피스 입구의 형상 그리고 배출 압력을 변화시켜가며 내부 유동 변화를 살피고 수직분사시 액주의 분열 거리와 제적을 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 캐비테이션 성장에 의한 수력튀김(hydraulic flip)현상도 관찰할 수 있었다 수직분사시 캐비테이션이 성장할수록 그리고 수력튀김 현상이 나타날 때 액주의 분열거리는 상당히 감소한다는 것을 알 수 있었다. 하지만 곡률이 있는 경우와 없는 경우 모두 유량 계수를 고려한 유효지름과 유효 모멘텀 플럭스 비에 대해 거의 같은 궤적 형상을 나타낸다는 것을 알 수 있었다.

• 한국추진공학회지
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• 제22권2호
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• pp.1-10
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• 2018

본 연구에서는 횡단류 공기유동에 수직으로 분사되는 액체제트의 분열거리와 액주궤적에 대한 음향가진의 영향을 살펴보았다. 이를 위해 단공 원형노즐 분사기를 이용하여 동일한 횡단류 공기속도에서 분사압력과 음향가진의 크기를 변화시켜가며 수류실험을 수행하였다. 또한 음향가진 주파수 기준 12개의 위상각에서 분무 이미지를 얻어 위상각 변화에 따른 영향을 확인하였다. 실험결과 분열길이는 비가진 상태에 비해 음향가진 상태에서 전반적으로 감소하였지만 위상각에 따른 변화는 발견되지 않았다. 본 실험 범위 내에서 음향가진은 수직분사 액체제트의 액주궤적에 거의 영향을 주지 못하였다.

• 한국추진공학회지
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• 제13권2호
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• pp.1-8
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• 2009

횡단류로 펄스 분사되는 액체제트의 분무 특성을 연구하기 위하여 35.7 ~ 166.2Hz 범위의 분사 주파수와 횡단류 속도 42 ~ 136 m/s의 조건에서 실험을 수행하였다. 횡단 유동장에서 액체제트의 주된 분열 인자는 압력 펄스 주파수의 영향보다는 횡단류의 항력에 의존하며, 주기적인 압력 진동에 의해 횡단류로 분사된 액체제트는 상하 진동하는 특성을 나타냈다. 또한 액적의 집합체(liquid jet puff)가 횡단류 방향의 액체 제트 표면에 나타났으며, 이러한 두 가지 특성을 통해 유동장의 혼합을 예상할 수 있었다. 압력 펄스 주파수에 의한 SMD 특성은 연속 분사의 층상 구조와 다른 비층상 구조로 나타났으며, 체적 유속은 압력 펄스 주파수가 증가함에 따라 감소하는 경향을 나타내었다.

• 대한기계학회논문집B
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• 제24권2호
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• pp.214-223
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• 2000

In this research, a study on the characteristics of the liquid sheet formed by two impinging jets is presented. Using the interference phenomena of light, the thickness of the liquid sheet, which seems to heavily affect the size of the droplets, is measured and compared with existing theoretical modelings. Thinner liquid sheet is produced with larger impinging angle, smaller orifice diameter, and higher azimuthal angle but the jet velocity doesn't affect the thickness. More viscous liquid produces thicker liquid sheet. The theoretical modelings predict the same trend as the experiments but the thickness values are overestimated at low azimuthal angles. This difference is gradually decreased as the azimuthal angle is increased: The breakup mechanism of the droplets from the liquid sheet is visualized by a high speed camera. The crest around the edge of the liquid sheet is protruded with the accumulation of liquid at the end of protuberance, which contracts into a spherical shape and then becomes detached when the stem breaks down, producing large droplets with a few small size of satellites.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.291-294
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• 2002

This study describes the external spray characteristics of deflector nozzle such as the breakup procedures of liquid sheet, spray angle, discharge coefficient and bubble behaviors of spray and SMD at deflector nozzle. In order to visualize the spray behaviors shadow graphy technique were used. According to the increase of injection pressure, development of the spray passes through the dribbling, distoted jet, closed bubble due to the contraction by surface tension forces, the bubble opens into hollow tulip shape, and the curved surface straightened to form a conical sheet like as the simplex swirl atomizer. Spray cone angle was nearly 90 deg. Variations of SMD were examined in order to describe the dependency of SMD on the injection pressure and orifice diameter. The shape of deflector and oriffice diameter had an effect on the discharge coefficient.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.478-483
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• 2003

This paper describes spray characteristics of a swirl injector which is intended for use in a HCCI engine. Many optical diagnostics such as laser diffraction methods, and high speed camera photography are applied to measure the spray drop diameter and to investigate the spray development process. The effect of fuel properties on the spray characteristics was investigated using three different fuels because HCCI combustion is tolerant of the chemical composition of various fuels. From these results, the HCCI injector formed a hollow cone sheet spray rather than a liquid jet and the atomization efficiency is high for the low-pressure injector. The SMD of test injector was ranged from $15{\mu}m$ ${\mu}m$ We also found that the spray breakup characteristics were dependent on the fuel properties such as density, viscosity, and surface tension.