액적의 증발에 미치는 수증기 농도의 영향

김용우,이명준,이상석,정성식,하종률 동아대학교 생산기술연구소 1999 生産技術硏究所硏究論文集 Vol.4 No.1

This study is to investigate the influences of water vapor on evaporation of single droplet. We obtained the time histories of droplet diameter from droplets image taken by a CCD camera. Droplets of water-soluble ethanol and water-insoluble paraffin hydrocarbon droplets were exposed in temperature, 473K and atmospheric pressure as the ambient condition. The following are results about evaporation of single droplet which exposure in the field of water vapor of high temperature. There is almost none which water vapor concentration affect on water droplet. But, ethanol droplet had significant influence. In the case of n-heptane has the boiling point which is lower than the boiling point of water, a evaporation rate increase with water vapor concentration. The evaporation rate of n-hexadecane which is higher than the boiling point of water and water-insoluble paraffin hydrocarbon droplet also increased in the high moisture environment.

Ignition and Combustion of a Single Emulsion Fuel Droplet

( Hyemin Kim ) 한국액체미립화학회 2017 한국액체미립화학회 학술강연회 논문집 Vol.2017 No.-

Emulsion fuel is the mixture of two liquids which are immiscible each other. Generally, hydrocarbon fuels and water are used for making emulsion fuel. The distinctive feature of emulsion fuel in combustion process is a micro-explosion. When the droplet is heated, the water droplets inside the fuel change to vapor, while the base fuel maintains the liquid phase. It is because of the difference of boiling temperature. In this circumstance, water vapor blow out from the droplet surface, this called micro-explosion or puffing. In the present research, the ignition and combustion characteristics of a single emulsion droplet were examined. Also, the effect of ambient temperature and water volume ratio were experimentally analyzed. Emulsion fuel was produced by ultrasonically mixed with n-decane and pure water. Small amount of surfactant (Span 80) was added for producing stable mixture. The emulsion fuel droplet was suspended at the tip of fin thermocouple (50㎛), and electric furnace dropped from the top to generate high ambient temperature around the droplet. Images of droplet were achieved via high speed camera, and inner droplet temperature was measured by using thermocouple. The results showed typical feature of emulsion fuel combustion during the experiment, including puffing and flame distortion. Puffing at the droplet surface firstly observed, and after that the droplet ignited far from the droplet surface. Ignition of droplet occurred only when the ambient temperature exceeded 600 ℃, and the ignition delay of droplet increased with water volume ratio in the emulsion fuel. Puffing at the droplet surface was observed both before the droplet ignition and during the droplet combustion.

Water droplet-driven triboelectric nanogenerator with superhydrophobic surfaces

Lee, Jeong Hwan,Kim, SeongMin,Kim, Tae Yun,Khan, Usman,Kim, Sang-Woo Elsevier 2019 Nano energy Vol.58 No.-

<P><B>Abstract</B></P> <P>A bouncing water droplet not only contains mechanical energy, but also electrostatic energy due to the triboelectric charges on its surface that are generated by its contacts with the surrounding environment. Here, we report development of contact electrification-based water droplet-driven triboelectric nanogenerator (Wd-TENG) for harvesting energy from the water-droplet bouncing between two superhydrophobic surfaces. The Wd-TENG consists of polytetrafluoroethylene balls on the bottom and zinc oxide nanosheets on the top; two surfaces of the device obtain electric energy during the contact electrification from the bouncing water, and additionally, maximize the bouncing motions of the droplets. The device produced a short-circuit current and an open-circuit voltage of 1.3 μA and 1.4 V, respectively. Besides, power-generating performances of the Wd-TENG at various angles of inclination were also investigated, and it showed voltage outputs of 5.5 V, 16 V, 9.8 V, and 6.8 V at the inclination angles of 52°, 58°, 64°, and 70°, respectively. These results demonstrate that the Wd-TENG is potentially a strong candidate for scavenging energy from raindrops.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We report development of contact electrification-based water droplet-driven triboelectric nanogenerator (Wd-TENG). </LI> <LI> The Wd-TENG consists of polytetrafluoroethylene balls and zinc oxide nanosheets to effectively harvest from dropping water. </LI> <LI> It is suggested that Wd-TENG is potentially a strong candidate for scavenging energy from raindrops. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>We report development of contact electrification-based water droplet-driven triboelectric nanogenerator (Wd-TENG) for harvesting energy from the water-droplet bouncing between two superhydrophobic surfaces. The Wd-TENG consists of polytetrafluoroethylene balls on the bottom and zinc oxide nanosheets on the top; two surfaces of the device obtain electric energy during the contact electrification from the bouncing water, and additionally, maximize the bouncing motions of the droplets. It is suggested that the potential of the Wd-TENG demonstrated in this study for harvesting raindrop energy is promising.</P> <P>[DISPLAY OMISSION]</P>

가습연소 폐열회수 보일러의 물분사 설계모델 구축에 관한 연구

신재훈 ( Jaehun Shin ),문석수 ( Seoksu Moon ) 한국분무공학회 2021 한국액체미립화학회지 Vol.26 No.2

In order to improve the overall efficiency and meet the emission regulations of boiler systems, the heat exchanging methods between inlet air and exhaust gas have been used in boiler systems, named as the waste-heat-recovery condensing boiler. Recently, to further improve the overall efficiency and to reduce the NOx emission simultaneously, the concept of the water injection into the inlet air is introduced. This study suggests the models for the optimized design parameters of water injection for waste-heat-recovery condensing boilers and performs the analysis regarding the water injection amount and droplet sizes for the optimized water injection. At first, the required amount of the water injection was estimated based on the 1^st law of thermodynamics under the assumption of complete evaporation of the injected water. The result showed that the higher the inlet air and exhaust gas temperature into the heat exchanger, the larger the amount of injected water is needed. Then two droplet evaporation models were proposed to analyze the required droplet size of water injection for full evaporation of injected water: one is the evaporation model of droplet in the inlet air and the other is that on the wall of heat exchanger. Based on the results of two models, the maximum allowable droplet sizes of water injection were estimated in various boiler operating conditions with respect to the residence time of the inlet air in the heat exchanger.

초고압 환경에서 분무되는 액적의 확산 및 지면 영향 분석

한준희 ( Jun Hee Han ),이소영 ( Soyeong Lee ),이정희 ( Jung Hee Lee ),김창완 ( Chang Wan Kim ),이성혁 ( Seong Hyuk Lee ) 한국액체미립화학회 2016 한국액체미립화학회 학술강연회 논문집 Vol.2016 No.-

This study aims to examine the near-wall effect on dispersion characteristics of water droplets under the ultra-high injection pressure conditions. We used the commercial computation fluid dynamics code (ANSYS FLUENT Ver. 17.0) for three-dimensional turbulent flow and the water droplet dispersion. We used SST k-w model for turbulent flow analysis and DPM(Discrete phase model) break up model for injection of the water droplet. The water droplets are injected to air with 175 m/s and the external air flow is present with 3 m/s. We compared and analyzed the characteristics of dispersion of water droplets with the consideration of the change in injection height ranging from 0.5 m to 2.5 m. The numerical analysis shows that the near-wall effect becomes significant on the water droplet dispersion.

다공성 수침-평판전극간의 수적 방출 특성

정재승(Jae-Seung Jung),이우석(Woo-Seok Lee),문재덕(Jae-Duk Moon) 대한전기학회 2009 전기학회논문지 Vol.58 No.10

Water droplet ejection characteristics of a point-to-plate airgap, with a wet porous point as a corona electrode, has been investigated. And the water droplet traces, charge, mass and number were measured experimentally. More particles are observed with wet porous point than metal point because the corona-discharging wet porous point can eject a number of water droplets. The water droplets ejected from the positive-corona-discharging wet porous point showed very fine traces as compared with those from the negative-corona-discharging wet porous point. Moreover, the water droplets ejected from the AC-corona-discharging wet porous point showed granular-like larger traces. It was shown that the weak corona discharge can eject smaller water droplets with larger ratio of mass-to-charge than the intense corona discharge.

Detection and Study of Single Water/Oil Nanoemulsion Droplet by Electrochemical Collisions on an Ultramicroelectrode

Hoang, Nhung T.T.,Ho, Thy L.T.,Park, Jun Hui,Kim, Byung-Kwon Elsevier 2017 ELECTROCHIMICA ACTA Vol.245 No.-

<P><B>Abstract</B></P> <P>Herein, for the first time, research on water-in-oil (water/oil) emulsion droplets by electrochemical analysis has been reported. When the water/1,2-dichloroethane emulsion droplets collided with an ultramicroelectrode (UME), the blocking property of the droplets resulted in a “staircase” current decrease. Each “staircase” current decrease is associated with the collision of an emulsion droplet with the UME surface. The experimental collision frequency was proportional to the concentration of the emulsion droplet. In addition, the size of each water droplet was estimated from the magnitude of the “staircase” current decrease and the simulation data. Results obtained from the collision signals provide information about the size of each single droplet (nano- to micro-) and the pM level concentrations of the water droplets in the organic continuous phase.</P>

AUTO-IGNITION AND MICRO-EXPLOSION BEHAVIORS OF DROPLET ARRAYS OF WATER-IN-FUEL EMULSION

정인철,이경환 한국자동차공학회 2008 International journal of automotive technology Vol.9 No.6

The characteristics of auto-ignition and micro-explosion behaviors of one-dimensional arrays of fuel droplets suspended in a chamber with high surrounding temperature were investigated experimentally with various droplet spacings, numbers of droplet and surrounding temperatures. The fuels used were pure n-decane and emulsified n-decane with varied water contents ranging from 10 to 30%. All experiments were performed under atmospheric conditions with high surrounding temperatures. An imaging technique using a high-speed camera was adopted to measure ignition delay, flame lifetime, and flame spread speed. The camera was also used to observe micro-explosion behaviors. As the droplet array spacing increased, the ignition delay also increased, regardless of water content. However, the lifetime of the droplet array decreased as the droplet spacing increased. The micro-explosion starting time remained unchanged regardless of the number of the droplets or the droplet spacing; however, it tended to be delayed slightly as the water percentage and droplet spacing increased.

Autoignition and combustion behavior of emulsion droplet under elevated temperature and pressure conditions

Won, Jonghan,Baek, Seung Wook,Kim, Hyemin Elsevier 2018 ENERGY Vol.163 No.-

<P><B>Abstract</B></P> <P>In this study, experiments were conducted to investigate the combustion characteristics of an water-in-oil W/O emulsion droplet under elevated temperature and pressure conditions. The base fuel used was n-decane, and total volume ratios of 10, 20, and 30% of distilled water were mixed for producing the emulsion fuel. Span 80 with a volume ratio of 2% was added as a surfactant, and the emulsion fuel was homogeneously mixed via ultrasonication. The combustion process of an emulsion droplet was divided into five stages: droplet heating, classical combustion, puffing, secondary classical combustion, and surfactant combustion. The ignition delay decreased with elevated ambient temperatures, whereas an increase in the ambient pressure and water volume ratio resulted in longer ignition delays. The droplets did not ignite in 500 °C or 600 °C conditions at 1 bar because of the significant Stefan flow of fuel vapor. After droplet ignition, the droplet combustion process, including classical combustion, puffing, and surfactant combustion, followed. The average burning rate increased with ambient pressure, but it was insensitive to ambient temperatures and water volume ratios. After flame extinction, a secondary flame reappeared because of the combustion of surfactant and residues.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Combustion of a water/n-decane fuel emulsion droplet at high pressure and temperature condition was studied. </LI> <LI> Changes of ignition delay and combustion stage of emulsion fuel droplet were observed. </LI> <LI> The changes of average burning rate in experimental conditions were discussed. </LI> </UL> </P>

Numerical Analysis of Liquid Droplet Impingement on Pitted Material Surface with Water Pool of Various Depth

Hirotoshi Sasaki,Yuka Iga 한국유체기계학회 2019 International journal of fluid machinery and syste Vol.12 No.4

Liquid droplet impingement erosion occurs at the elbows in steam pipes where droplets impinge at high speed. In the actual pipe wall which numerous droplets always impinge, it is predicted that both a liquid film exists on a pipe wall surface and, on the other hand, this surface is also eroded by repeated droplet impingement. Therefore, the liquid film and roughness on the material surfaces are considered to exist mixed on the actual impinged point of droplets. In this study, by using an in-house fluid/material two-way coupled numerical method that considers reflection and transmission on the fluid/material interface, the numerical analysis of the phenomenon of liquid droplet impingement on a pitted surface with a water pool is conducted. From the analysis results, the impinged pressure at the moment of impingement is reduced by a water pool. However, as the cavitation bubbles are generated in the bottom and top of the droplet after the impingement and then the cavitation bubble of the bottom side collapses, the collapse pressure which greatly exceeds the pressure of the droplet impingement occurs, and the equivalent stress also increases greatly there. Therefore, this analysis result may indicate one reason why the erosion progresses deeply at the pit part in an actual pipe wall thinning.