증발하는 물방울의 계면활성제에 의한 열모세관 유동 억제

윤성찬(Sungchan Yun),김태권(Tae Kwon Kim),임희창(Hee Chang Lim),강관형(Kwan Hyoung Kang),임근배(Geunbae Lim) 대한기계학회 2013 大韓機械學會論文集B Vol.37 No.7

본 논문은 비이온의 계면 활성제에 의해 증발하는 물방울의 열모세관 유동(마랑고니 유동)이 억제되는 것을 실험적으로 검증한다. 물방울이 소수성 표면 위에서 증발할 때, 액적 내부의 마랑고니 유동을 관찰하였고, 계면 활성제 농도에 따라 이 유동이 억제되는 것을 조사하였다. 초기 계면 활성제 농도가 증가하면, 마랑고니 유동의 속도와 수명이 감소한다. 이 결과는 계면 활성제에 의해 액적계면에서 점착 경계 조건이 성립됨을 보여주는데, 이것은 계면 점착 현상과 관련된 기존의 모델에 기초하여 설명되었다. 또한 액적의 초기 계면 활성제 농도가 임계 농도 이하일 때, 증발 초기 접촉선 비고정 현상을 발견했는데, 이것은 마랑고니 유동이 접촉각의 이력 현상을 감소시키기 때문이다. The suppression of a thermocapillary flow (Marangoni flow) by a nonionic surfactant is experimentally investigated for evaporating pure water droplets on hydrophobic substrates. The experiment shows that as the initial concentration of the surfactant increases, the velocity and lifetime of the flow monotonically decrease. The result confirms the no-slip boundary condition at a liquid-air interface, which is explained on the basis of the previous model regarding the effect of surfactants on the no-slip condition. Interestingly, at an initial concentration much less than a critical value, it is found that depinning of the contact line occurs during the early stage of evaporation, which is ascribed to a reduction in the contact angle hysteresis owing to the presence of the Marangoni flow.

고온 고압기류중을 비행하는 파라핀계 연료액적의 증발에 관한 연구

정성식,川口修 대한기계학회 1991 대한기계학회논문집 Vol.15 No.6

본 연구에서는 고온고압의 기류중에 투입된 미소연료액적의 증발에 관한 정보 를 구하여 분무연소기구의 해명을 위한 기초테이터를 제공하려 시도한다. Evaporation rate constant, obtained by in this experimental study, of freely falling liquid fuel droplet on the condition of hot and pressurized environment are converted to critical evaporation constant according to Eq. of Ranz and Marshall. Critical evaporation constant, on constant environment pressuire, actively increase almost linearly with environment temperature increasing, but, on constant temperature, increases more or less with pressure increasing. Multycomponent droplet mixed with the fine fuel having a different of boiling point evaporate in order to boiling point, and each evaporation rate constant of mixed fuel equal to each fuel.

주변난류유동이 단일액적의 증발에 미치는 영향에 대한 수치적 연구

박정규,Park, Jung Kyu 대한기계학회 1995 대한기계학회논문집 Vol.19 No.10

This investigation reports on the study of the ambient turbulent effects on the droplet vaporization in the fuel spray combustion. For tractability, this discussion considers a single droplet in an infinite turbulent flow. In this numerical study, the low-Reynolds-number version of k-.epsilon. turbulence model was used to represent the turbulence effects. The set of two-dimensional conservation equations which describe the transport phenomena in turbulent flow using the mean flow quantities including the droplet internal laminar motion, are solved numerically with the finite difference procedure of Patankar(SIMPLER). The evaluation of the computational model is provided by two limiting cases: turbulent flow over the solid sphere and the laminar flow over a liquid drop. The results show that the turbulence effects are noticeable for the vaporization at high turbulence intensity (10-50%) which is encountered in a typical spray. The magnitude of turbulence effects mainly depends on the turbulent intensity. These effects are not sensitive to the Reynolds number in the range of 50 to 200, ambient temperature in the range of 700 to 1000.deg. K and the volatility.

산질화 표면에서 액적의 증발열전달 특성

김대윤 ( Dae Yun Kim ),이성혁 ( Seong Hyuk Lee ) 한국분무공학회 2016 한국액체미립화학회지 Vol.21 No.1

The present study aims to experimentally investigate the evaporative heat transfer characteristics of Oxi-nitriding SPCC surface. Moreover, the heat transfer coefficient was examined with respect to surface temperature during droplet evaporation. In fact, the nitriding surface showed significant enhancement for anticorrosion performance compared to bare SPCC surface but the thermal resistance also increased due to the formation of compound layer. From the experimental results, the evaporative behavior of sessile droplet on nitriding surface showed similar tendency with the bare surface. Total evaporation time of sessile droplet on the nitriding surface was delayed less than 5%. The difference in heat transfer coefficient increased with the surface temperature, and the maximum difference was estimated to be around 11% at 80℃ surface. Thus, this nitriding surface treatment method could be useful for seawater heat exchanger industries.

계면활성제를 첨가한 액적의 증발냉각

유갑종,방창훈,김현우,Riu, Kap-Jong,Bang, Chang-Hoon,Kim, Hyun-Woo 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.4

The evaporation cooling phenomenon of a droplet containing a surfactant on a heated surface has been studied experimentally. The two kinds of heater modules made of brass and Teflon$^{TM}$ were tested to investigate the cooling characteristics of droplet. Solutions of water containing Sodium Lauryl Sulfate(0 ppm, 100 ppm, 1000 ppm) were tested in the experiments. The results showed that the contact angle decrease as the concentration of surfactant increases. The tendency did not very with different heated solid materials. As initial temperature of the heated surface becomes high, time averaged heat flux increases and evaporation time decreases with the denser concentration of surfactant. Therefore, water with denser concentration of surfactant could be effective to cool flammable materials. However, the effect of surfactant becomes low as the material temperature is higher than the boiling temperature of water.

액적 체적이 증발 특성에 미치는 영향에 관한 수치해석 연구

정찬호 ( Chan Ho Jeong ),이형주 ( Hyung Ju Lee ),김홍석 ( Hong Seok Kim ),이성혁 ( Seong Hyuk Lee ) 한국분무공학회 2021 한국액체미립화학회지 Vol.26 No.2

This study aims to investigate the influence of the droplet volume on the evaporation characteristics of the sessile droplet. In particular, the effect of the free convection in the vapor domain on the evaporation rate was analyzed through the numerical simulation. The commercial code of the ANSYS Fluent (V.2020 R2) was used to simulate the heat transfer in the liquid-vapor domain. Moreover, we used the diffusion model to estimate the evaporation rate for the different droplet volume under the room temperature. It was found that the evaporation rate significantly increases with the droplet volume because of the larger surface area for the mass transfer. Also, the effect of free convection on the evaporation rate becomes significant with an increment of droplet volume owing to the increase in the droplet radius corresponding to the characteristic length of the free convection.

액적 증발의 계산시간 단축에 관한 수치적 연구

홍성진(S. Hong),손기헌(G. Son),심우섭(W. Shim) 한국전산유체공학회 2018 한국전산유체공학회지 Vol.23 No.3

Numerical study on reducing computation time is performed for sessile droplet evaporation. The conservation equations of mass, momentum and vapor concentration are solved by employing the level-set method which is modified to include the effect of phase change. One of the major difficulties in computing the whole period of droplet evaporation arises from the fact that the surface tension term in the momentum equation causes a serious time step restriction for stable computation. In this work, the time step constraint is avoided by simplifying the droplet shape as a spherical cap whose curvature is spatially uniform so that the surface tension term is treated as a part of the pressure term. The droplet surface is calculated geometrically and then the level-set function is reconstructed from the droplet surface. The numerical result for sessile droplet evaporation in stationary air shows good agreement with the experimental data reported in the literature. The effects of external flow velocity, temperature and contact angle on the droplet evaporation rate are quantified.

진동하는 유동장하에서 내부 순환 유동을 고려한 액적의 증발에 관한 수치적 연구

하만영,Ha, Man-Yeong 대한기계학회 1996 大韓機械學會論文集B Vol.20 No.5

The two-dimensional, unsteady, laminar conservation equations for mass, momentum, energy and species transport in the gas phase and mass, momentum and energy in the liquid phase are solved simultaneously in spherical coordinates in order to study heating and vaporization of a droplet entrained in the oscillating flow. The numerical solution gives the velocity and temperature distribution in both gas and liquid phase as a function of time. When the gas flow oscillates around an vaporizing droplet, the liquid flow circulates in the clockwise or counterclockwise direction and the temperature distribution in the liquid phase changes its shapes, depending on the gas fow direction. When the gas flow changes its direction of circulating liquid flow is opposite to the gas flow, forming two vortex circulating in the opposite direction. During the heating period, the difference in the maximum and minimum temperature is large, followed by the almost uniform temperature slightly below the boiling temperature. The mass and heat transfer from the droplet depend on the droplet temperature, droplet diameter and the magnitude of relative velocity, giving the droplet lifetime different from the d$^{2}$-law.

고압 유동장에서의 액적증발 특성 해석

유용욱,김용모,You, Yongwook,Kim, Yongmo 대한기계학회 1998 大韓機械學會論文集B Vol.22 No.8

The present study is numerically investigated for the high-pressure effects on the vaporization process in the convection-dominating flow field. Numerical results agree well with the available experimental data. The fuel droplet vaporization characterization is parametrically studied for the wide range of the operating conditions encountered with the high-pressure combustion process of turbocharged diesel engines.

고온벽면에서의 액적연료의 증발 및 착화에 관한 연구

송규근 한국마린엔지니어링학회 2002 한국마린엔지니어링학회지 Vol.26 No.1

Recently, impinging spray is used for atomization of diesel engine, but it bring on adhesion of fuel. Therefore, we studied about droplet behavior on high temperature plate changing the size of droplet, surface temperatures, and surface roughness of plate. In this study, We studied to confirm experimentally about mechanism of evaporation and ignition process of single fuel droplet. We observed evaporation time, evaporation appearance and ignition delay time by the photopraphs of 8mm video camera. Experimental results are summarized as follows: 1. The boiling point of fuel affect a evaporation and ignition process. 2. The surface roughness affect a evaporation time. 3. The ignition delay time relate to evaporation characteristic.