• 한국화재소방학회논문지
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• 제23권6호
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• pp.111-115
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• 2009

아세톤 LIF와 Rayleigh 산란법 등 두 가지 레이저 측정 기법을 이용하여 Re수가 1,000 미만의 부력제트 노즐근처에서의 공기 유입을 실험적으로 조사하였다. 아세톤 LIF 실험결과 전체적인 혼합기구는 경계면에서의 불안정성에 의한 거대와구조로 판단되고, Re 수가 커질수록 유입되는 시점이 상류로 이동하며 그 양 또한 증가되었다. 또한 Rayleigh 산란법 결과는 상류에서도 혼합이 제트의 내부까지 이루어지고, 노즐에서 분사방향으로 진행할수록 주위공기의 유입이 제트 내부로 진행되고 있음을 알 수 있다. 이 실험결과로서 기존 등온기체모델에서 제트의 주위공기 유입을 고려하여야 한다는 사실을 입증할 수 있다. 또한, 이상적 플룸식에서 복사열손실을 0.35로 고려하였을 경우에 기존의 연기량 및 온도 예측과 근사한 결과를 얻을 수 있으며, 주위공기 유입효과를 고려하여 보다 간단하면서 정확한 등온기체 모델링 방법을 얻을 수 있다.

• 한국입자에어로졸학회지
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• 제18권4호
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• pp.97-107
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• 2022

The geometry of popular wave plate type mist eliminator for the wet flue gas desulfurization process was improved, fabricated, and experimentally evaluated. A Mist eliminator is a type of inertial particle collector which collection efficiency is proportional to the velocity of the gas phase. However, as the amount of re-entrainment is also proportional to the gas phase velocity, there is a limitation for the gas phase flow rate. Re-entrainment is one of the most important issues in a mist eliminator and is likely to occur as the input of the liquid phase and flow rate of the gas phase increase. In order to resolve this problem, the projection angle of the improved mist eliminator is set to 30° from the conventional one while maintaining the cross-section. With low flow rate conditions, the modified mist eliminator showed a similar pressure drop and overall collection efficiency. However, with conditions in which re-entrainment is obviously occurring, the modified mist eliminator showed better performance in draining droplets than the conventional one. As a result, the modified mist eliminator showed higher overall collection efficiency.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2769-2774
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• 2007

In vacuum ejector-diffuser systems where a finite volume secondary chamber is used, the secondary jet exhibits transient characteristics during start-up. A steady state is achieved after some time in which mass entrainment prevails indefinitely inside the ejector, though there is no flow from the secondary chamber. An attempt is made in this work to study the infinite entrainment of secondary jet into the primary jet from a finite secondary chamber, with the help of a computational fluid dynamics method. The present study is also intended to identify the operating range of vacuum ejector-diffuser systems where the steady flow assumption can be applied without uncertainty. The results obtained show that the only condition in which an infinite mass entrainment is possible is the generation of a re-circulation zone near the primary nozzle exit. The flow in the secondary chamber attains a state of dynamic equilibrium at this point. Steady flow assumption is valid only after this point.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2009년도 춘계학술대회 논문집
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• pp.299-302
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• 2009

The objective of the present study is to analyze the transient flow through theejector system with the help of a computational fluid dynamics (CFD) method. An attempt is made to investigate the interesting and conflicting phenomenon of the infinite entrainment into the primary stream without an infinite mass supply from the secondary chamber. The results obtained show that the one and only condition in which an infinite mass entrainment can be possible in such types of ejectors is the generation of a re-circulation zone near the primary nozzle exit. The flow in the secondary chamber attains a state of dynamic equilibrium of pressures at the onset of the recirculation zone. A steady flow in the ejector system is valid only after this point.

• 한국가시화정보학회지
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• 제16권2호
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• pp.45-52
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• 2018

The tangential and axial cyclones were fabricated using a 3D printer and the total collecting efficiency, cut-diameter, and pressure drop characteristics of the two types of cyclones with the same inlet area were investigated experimentally. The results show that the total collecting efficiency tends to increase as the inlet velocity increases. However, at a 20m/s condition of the tangential cyclone, the collected particles were re-entrained to the ascending vortex flow, resulting in a decrease of the total collecting efficiency. In the axial cyclone, the cross-sectional area is designed to increase at the inlet and the velocity is reduced, so that the re-entrainment effect does not appear in this study. The pressure loss of the tangential cyclone was larger than that of the axial cyclone. The cut-diameter tends to decrease with increasing the inlet velocity in two types of cyclones, except for the 20m/s condition of the tangential cyclone.

• 대한기계학회논문집B
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• 제25권5호
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• pp.611-618
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• 2001

The flow characteristics of a turbulent buoyant jet were experimentally investigated using a single-frame PIV system. The Reynolds number based on the nozzle exit velocity and nozzle diameter was about Re=5$\times$10$^3$. The instantaneous velocity fields in the streamwise plane passing the jet axis were measured in the near field X/D <11 with and without the temperature gradient. By ensemble averaging the instantaneous velocity fields, the spatial distributions of mean velocity, vorticity, and higher-order statistics up to third order were obtained. The temperature difference of 10$\^{C}$ does not affect a significant influence to the flow structure in the near field, but the total entrainment rate is increased slightly. The entrainment rate shows a linear variation with the streamwise distance in the region after X/D=5.0.

• 한국농공학회지
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• 제39권4호
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• pp.82-89
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• 1997

A physically-based soil-water erosion model with simple hydrology and Rose & Hairsine's erosion concept is described, and was implemented in the form of computer program. The model derived from the concept of stream power(Bagnold, 1977) considers settling velocity characteristics of the soil and distinguishes between the processes of entrainment and re-entrainment. It deals separately with rill flow and sheet flow, handles vegetation in terms of soil contact cover, and has the ability to simulate soil movement on nonuniform slopes. The model predicted sediment concentrations reasonably with the results of Mclsaac et al. (1990). It showed a capability to quantitatively predict the movement of soil on uniform and nonuniform slopes. Among the model parameters, soil depositability $({\phi})$ was the most sensitive from the sensitivity analysis.

• 대한기계학회논문집B
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• 제29권5호
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• pp.561-567
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• 2005

The effect of triangular multi-tabs attached at the perimeter of jet nozzle on flow structure in the near field was investigated experimentally. A stereoscopic PIV(SPIV) system was employed to measure three orthogonal velocity components of the 3-D turbulent jet. In this study, two different types of sharp-edged jet nozzle having 4, 8 tabs were tested at the Reynolds number of Re=10,000. SPIV measurements were carried out at 5 cross-sectional planes. Six hundred instantaneous velocity fields were measured for each experimental condition and they were ensemble averaged to get spatial distributions of turbulent statistics such as mean velocity and turbulence intensity. Entrainment rate of surrounding fluid into the tabbed jets was estimated using the measured 3-D velocity field data. The strong vortex structure was induced for the jet flow with 4 tabs, increasing entrainment rate.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.2035-2040
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• 2004

A cone cylinder is used to obtain variable operation conditions for the sonic ejector-diffuser system. The cone cylinder is designed to move upstream and downstream to change the ejector throat area ratio, thus obtaining variable mass flow rates. The present study investigates the effects of ejector throat area ratio and operating pressure ratio on the entrainment of secondary stream for the variable sonic ejector system. In experiment, the ejector throat area is varied in the range from ${\psi}=11.88$ to 66.69, and the operating pressure ratio from $p_{0p}/p_a=1.25$ to 9.0. The results show that the variable sonic ejector system is suitable for a required entrainment ratio of secondary stream by altering the ejector throat area ratio and operating pressure ratio.

• Nuclear Engineering and Technology
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• 제47권4호
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• pp.389-397
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• 2015

The effects of mixing vanes (MVs) attached to a grid spacer on the characteristics of air-water annular flows were experimentally investigated. To know the effects, a grid spacer with or without MV was inserted in a vertical circular pipe of 16-mm internal diameter. For three cases (i.e., no spacer, spacer without MV, and spacer with MV), the liquid film thickness, liquid entrainment fraction, and deposition rate were measured by the constant current method, single liquid film extraction method, and double liquid film extraction method, respectively. The MVs significantly promote the re-deposition of liquid droplets in the gas core flow into the liquid film on the channel walls. The deposition mass transfer coefficient is three times higher for the spacer with MV than for the spacer without MV, even for cases 0.3-m downstream from the spacer. The liquid film thickness becomes thicker upstream and downstream for the spacer with MV, compared with the thickness for the spacer without MV and for the case with no spacer.