共查询到17条相似文献,搜索用时 125 毫秒
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采用VOF(Volume of Fluid)自由表面捕捉方法对盐水液滴蒸发过程中气液界面进行追踪,建立了降压环境下单个盐水液滴的蒸发模型,并通过盐水液滴蒸发的实验数据验证了此模型。通过对盐水液滴在相变过程中的形态变化以及传热传质特性的分析,研究了液滴内部温度、速度、蒸汽分布以及液滴形态等随时间的变化情况,分析了影响盐水液滴降压蒸发过程的主要因素。结果表明:在降压蒸发过程中液滴形态变化和环境中蒸汽的分布会随速度场的变化而变化;蒸发过程中初始盐组分质量浓度越大的液滴蒸发速率越缓慢,最终能达到的液滴最低中心温度越高,且液滴中心温度回升速度越慢、回升时间也越晚;液滴初始温度对蒸发速率影响较大,初始温度越高,表面蒸发速率越快,液滴中心温度回升速度越快。 相似文献
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引入相平衡理论建立了DME-LPG-N2三元气、液高压相平衡,获得了液滴表面各组分的物质的量分数.建立了混合液滴超临界蒸发的计算模型,计算了二甲醚(DME)/液化石油气(LPG)双燃料液滴的蒸发过程,考察了液滴的初始直径、初始组分、环境温度和环境压力对蒸发过程的影响.结果表明:环境压力、温度越大,环境介质(N2)在液滴中的溶解越明显;液滴初始直径越小,蒸发寿命越短;液滴中DME越多,亚临界蒸发过程中的液滴蒸发寿命越长,而超临界蒸发过程中液滴蒸发寿命越短;环境温度越高,液滴蒸发寿命越短;在研究的温度范围内,环境压力越高,在亚临界条件下液滴蒸发寿命越短,而在超临界条件下液滴蒸发寿命越长. 相似文献
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建立在高频感应热等离子体环境下单个溶液液滴的运动蒸发模型,采用数值计算的方法模拟了液滴在等离子体射流中的运动和传热过程,分析了不同操作参数对液滴运动蒸发过程的影响.结果表明:液滴初始入射尺寸越小,表面溶质质量分数达到饱和状态所用时间越短;初始入射速度越快,表面溶剂蒸发速度越快,溶质结晶析出时间越短;入射角较大时,液滴会被反向涡流卷吸,表面浓度达到饱和状态的时间较长. 相似文献
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基于格子玻尔兹曼方法(Lattice Boltzmann Method, LBM)对固着在加热基板上的液滴铺展及蒸发过程进行模拟,主要研究重力场、基板润湿性以及初始环境温度对液滴铺展及蒸发过程的影响。通过预测蒸发过程中液滴与基板的接触直径变化和液滴剩余质量变化,分析液滴形状及体积变化。研究结果发现,液滴形貌及蒸发过程受重力影响较大,重力作用下液滴铺展现象明显且蒸发加快。基板的接触角越小,液滴铺展现象越明显,其接触直径越大,蒸发越快。当环境温度与基板温度相差较大时,液滴内部出现涡流,强化换热使蒸发过程加快。 相似文献
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利用开发的计算模型对壬烷液滴在氮气中的蒸发过程进行了数值计算,研究了超临界环境条件下环境压力、环境温度以及液滴初始温度对液滴蒸发特性的影响.结果表明:环境压力越高,在蒸发过程中液滴表面温度的升温速度越快;并在蒸发初期液滴直径的增大越显著,同时液滴表面发生迁移的时刻越早.环境温度越高液滴的蒸发寿命越短,液滴表面发生迁移的时刻越早,并且在蒸发初期液滴直径的增大越不明显.随着液滴初始温度的升高液滴的蒸发寿命和迁移时刻几乎均呈线性趋势逐渐减小,液滴初始温度的高低只会使液滴的蒸发过程整体上提前或延后. 相似文献
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用格子Boltzmann方法中的伪势模型对两个液滴的合并过程进行了数值模拟。详细研究了两液滴能否合并临界尺寸和液滴合并过程中液桥的形成与演化的关系,并研究了表面张力对合并速度的影响。研究结果发现当两个液滴之间距离小于2倍界面厚度时,两个液滴在不受外力的作用下能够自动合并;液桥的宽度与演化时间有一定的指数关系;表面张力越大,合并速度越快,这个结果与前人的理论预测和实验结果一致。 相似文献
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为了研究不同碰撞速度以及不同换热方式对连续液滴撞击热壁面传热特性的影响,以8滴去离子水和铜板为试验材料,设置了速度分别为0.63 m/s、0.77 m/s、0.89 m/s、0.99 m/s的8滴去离子水液滴在膜态蒸发(铜板温度60℃)和核态沸腾(铜板温度110℃)两种换热方式下的液滴撞击热铜板试验,探究铜板热流密度值的变化。结果表明:膜态蒸发换热方式下,液滴撞击热壁面速度越大,铜板的最大热流密度值越大,液滴与壁面之间的换热效果越好。核态沸腾换热方式下,以0.89 m/s的速度值为转折点,当连续液滴撞击热壁面速度小于0.89 m/s时,液滴撞击速度越大,铜板热流密度值越大;当连续液滴撞击热壁面速度大于0.89 m/s时,随着液滴撞击速度的增大,铜板的热流密度值减小。 相似文献
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C. Maqua G. Castanet F. Grisch F. Lemoine T. Kristyadi S.S. Sazhin 《International Journal of Heat and Mass Transfer》2008,51(15-16):3932-3945
Results of experimental studies and the modelling of heating and evaporation of monodisperse ethanol and acetone droplets in two regimes are presented. Firstly, pure heating and evaporation of droplets in a flow of air of prescribed temperature are considered. Secondly, droplet heating and evaporation in a flame produced by previously injected combusting droplets are studied. The phase Doppler anemometry technique is used for droplet velocity and size measurements. Two-colour laser induced fluorescence thermometry is used to estimate droplet temperatures. The experiments have been performed for various distances between droplets and various initial droplet radii and velocities. The experimental data have been compared with the results of modelling, based on given gas temperatures, measured by coherent anti-stokes Raman spectroscopy, and Nusselt and Sherwood numbers calculated using measured values of droplet relative velocities. When estimating the latter numbers the finite distance between droplets was taken into account. The model is based on the assumption that droplets are spherically symmetrical, but takes into account the radial distribution of temperature inside droplets. It is pointed out that for relatively small droplets (initial radii about 65 μm) the experimentally measured droplet temperatures are close to the predicted average droplet temperatures, while for larger droplets (initial radii about 120 μm) the experimentally measured droplet temperatures are close to the temperatures predicted at the centre of the droplets. 相似文献
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I.G. Gusev P.A. Krutitskii S.S. Sazhin A.E. Elwardany 《International Journal of Heat and Mass Transfer》2012,55(7-8):2014-2021
Two new solutions to the equation, describing the diffusion of species during multi-component droplet evaporation, are suggested. The first solution is the explicit analytical solution to this equation, while the second one reduces the solution of the differential transient species equation to the solution of the Volterra integral equation of the second kind. Both solutions take into account the effect of the reduction of the droplet radius due to evaporation, assuming that this radius is a linear function of time. The analytical solution has been incorporated into a zero dimensional CFD code and applied to the analysis of a bi-component droplet evaporation. The case of an initial 50% ethanol–50% acetone mixture and droplets with initial diameter equal to 142.7 μm moving in air at atmospheric pressure has been considered. To separate the effect of the moving boundary on the species diffusion equation from a similar effect on the heat conduction equation inside droplets, described earlier, a rather artificial assumption that the droplet temperature is homogeneous and fixed has been made. It has been pointed out that the effect of the moving boundary slows down the increase in the mass fraction of ethanol (the less volatile substance in the mixture) and leads to the acceleration of droplet evaporation. 相似文献
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Guillaume Castanet Bruno Frackowiak Cameron Tropea Fabrice Lemoine 《International Journal of Heat and Mass Transfer》2011,54(15-16):3267-3276
The temperature field within evaporating ethanol droplets is investigated, relying on the two-color laser induced fluorescence (LIF) measurement technique and on a Direct Numerical Simulation (DNS). The configuration studied corresponds to a monodisperse droplet stream in a diffusion flame sustained by the droplet vapor. An experimental probe volume, small compared to the droplet size, is used to characterize the temperature field within the droplets, whereas DNS takes into account key aspects of the droplet heating and evaporation such as the non-uniform and transient stress, and the mass and heat transfer coefficients at the droplet surface. These investigations reveal that the frictional stresses are strongly reduced due to the small spacing between the droplets. They also show that the Marangoni effect has a significant influence on the internal motion and hence on the internal temperature field. 相似文献
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《能源学会志》2020,93(4):1473-1480
In this work, evaporation experiments of multiple droplets are carried out in a stagnant hot atmospheric environment (573, 673 and 773 K) using high-speed backlit image technique. Three fuel droplets with nearly same initial diameter are suspended at intersections of two 0.1 mm quartz fibers. The normalized droplet spacing (s/d0) of three droplets is 2.25. The results show that the evaporation process of single, edge and central fuel droplet containing three stage: initial heating, unsteady evaporation and quasi-steady evaporation stage. Classical d2 law is still suitable for edge and central droplet at quasi-steady evaporation stage. The third stage of edge and central droplet accounts for more than 60% of droplet lifetime at low temperatures and about 50% at high temperatures. The evaporation rate constant of edge and central droplet increases and droplet lifetime decreases with increasing ambient temperature. The evaporation time of edge and central droplet at first and third stage is higher than single droplet, but lower than single droplet in the second stage. More importantly, the evaporation interactions between droplets is significant at low temperature. Compared with single droplet, the lifetime of central droplet is increased by 31.8%, 18.6% and 25.9%, respectively. 相似文献
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Aiming at improving efficiency in combustion systems, the study on droplet behavior and its trajectory is of crucial importance.
Vortex engine is a kind of internal combustion engine which uses swirl flow to achieve higher combustion efficiency. One of
the important advantages of designing vortex engine is to reduce the temperature of walls by confining the combustion products
in the inner vortex. The scopes of this investigation are to study vortex engine flow field as well as effective parameters
on fuel droplet behavior such as droplet diameter, droplet initial velocity and inlet velocity of the flow field. The flow
field is simulated using Reynolds Stress Transport Model (RSM). The Eulerian-Lagrangian method and the one-way coupling approach
are employed to simulate two phase flow and dispersed phase in the chamber, respectively. A new method, based on computing
pressure force exerted on the droplet surface, is introduced to determine the distinction between using one-way and two-way
coupling approaches. The results showed that the droplets with smaller diameter are more likely to follow the flow stream
lines than bigger droplets, thus evaporate completely in the chamber. Moreover, droplets with greater initial velocity have
higher evaporation rate, yielding the existence of evaporation and combustion in the inner vortex. Additionally, the higher
inlet velocity of continuous phase results in higher centrifugal force, leads droplets in question to deviate towards the
wall faster. 相似文献