共查询到19条相似文献,搜索用时 271 毫秒
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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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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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《内燃机工程》2014,(1)
以单一组分液滴在静止环境中的蒸发模型为基础,建立多组分液滴蒸发的折算数学模型,并以二甲醚(DME)/液化石油气(LPG)双燃料液滴作为研究对象,对其亚临界蒸发过程进行了详细的模拟研究。获得了各组分在不同环境温度和环境压力下液滴蒸发的湿球温度,以及组分摩尔分数变化时双组分液滴湿球温度的变化情况。考察了液滴中组分的初始摩尔分数、液滴初始温度、环境温度和压力及混合规则对蒸发过程的影响,结果表明:相同环境条件下,混合物的湿球温度随DME摩尔分数的增大而升高;液滴初始质量相同时,DME初始摩尔分数越大,蒸发的时间越长;初始质量及组分初始浓度一样的多组分液滴,初始温度越接近湿球温度,蒸发时间越短;环境压力越高,液滴湿球温度越高,气体混合物扩散系数越小,液滴生存期内加热期所占的比例明显增加,蒸发时间较长;使用混合规则二,蒸发时间较长。 相似文献
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为了探究脱硫废水液滴的蒸发机理,采用单液滴蒸发实验台研究了中高温环境下脱硫废水液滴的蒸发特性,分析了废水液滴在对流干燥过程中的蒸发特性及干燥温度、水质和初始粒径对其的影响规律;采用集中参数反应工程(L-REA)模型整理数据,建立了基于活化能的废水液滴蒸发动力学模型。结果表明:脱硫废水液滴蒸发期间由于表面溶质富集存在明显成壳与降速蒸发现象,成壳后剩余水分因升温而快速汽化,导致壳层膨胀与部分破碎;升高干燥温度和减小初始粒径有利于废水液滴蒸干,废水液滴中不溶性固体(SS)含量增加会使干燥产物粒径减小;由实验参数得到的L-REA模型能较好地描述废水液滴的蒸发历程,模型预测300℃干燥温度下,单液滴初始粒径50μm的液滴总蒸发时长在0.05 s以内。 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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亚临界和超临界压力下燃料液滴的蒸发特性 总被引:1,自引:0,他引:1
以实际气体状态方程为基础,建立了适用于高压下的导热系数、扩散系数等物性参数的计算方法,并将高压汽液相平衡、混合物临界点以及蒸发焓的概念引入到液滴表面的传热传质过程中,以此为基础建立了单个燃料液滴的高压蒸发模型.研究了亚临界和超临界压力下壬烷液滴在氮气中的蒸发过程及其物理控制因素,重点探讨了超临界压力下液滴蒸发过程中液滴表面自亚临界状态向超临界状态的迁移过程及迁移条件.结果表明,在亚临界压力下,液滴蒸发始终受相变控制.在超临界压力下,当液滴表面由燃料和环境气体组成的混合物达到其临界点时,液滴表面将发生自亚临界状态向超临界状态的迁移.在液滴表面迁移之后,液滴表面消失,燃料自高浓度的燃料核心向远方场的扩散过程不受相变控制.另外,随着环境温度的升高液滴表面发生迁移所需的最低环境压力逐渐降低. 相似文献
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采用标准微电子机械系统(Micro-Electro-Mechanical System,MEMS)加工工艺,设计并加工了一种具有圆柱微结构的超疏水润湿梯度表面,搭建了研究液滴蒸发过程的可视化光学实验平台,同时从不同角度观察了液滴在具有圆柱状微结构超疏水润湿梯度表面的蒸发行为。通过实验研究发现:液滴在具有圆柱状微结构的超疏水润湿梯度表面的蒸发过程中,随着液滴的蒸发,液滴体积、液滴与表面的接触半径均不断减小,蒸发过程遵循混合蒸发模型;液滴边缘的三相线跳跃与移动均只发生在相对疏水的区域一侧;而在相对亲水的一侧,液滴边缘始终处于静止状态,直至液滴完全蒸发;在超疏水润湿梯度表面上的液滴蒸发过程中,液滴质心仅在具有润湿梯度的方向上移动,且液滴质心移动方向与润湿梯度方向相反(朝亲水侧移动)。最后基于液滴蒸发过程中的能量变化理论,解释了出现上述现象的原因。 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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N.S. Dixit N. Venkatramani V.K. Rohatgi 《International Journal of Heat and Mass Transfer》1987,30(12):2617-2625
The electrical conductivity of the working medium of a combustion driven MHD generator is increased by introducing a low-ionization potential additive (seed). This seed is in the form of a fine spray of an aqueous solution of K2CO3 by an atomizer. However, the electrical conductivity depends strongly on the evaporation process and the evaporation in turn depends on the size of droplets. In this paper, the effect of seed droplet size on evaporation (and hence on electrical conductivity and plasma temperature) have been analysed by formulating a single step finite rate evaporation model. Experiments were conducted to measure plasma temperature and conductivity on a potassium seeded combustion plasma system by introducing seed droplets of different sizes. The measured and the predicted values have been compared to substantiate the model. 相似文献
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V.E. Nakoryakov S.Ya. Misyura S.L. Elistratov 《International Journal of Heat and Mass Transfer》2012,55(23-24):6609-6617
The effect of the volume of distillate droplets and temperature of the heated wall on evaporation process was investigated. The strong influence of thermal-physical and geometrical parameters of the wall on droplet evaporation is shown. A change in the ratio of droplet diameter to the wall thickness can lead to a change in evaporation regimes. Distribution of interface temperature along the droplet length is measured. At evaporation the wall temperature under the droplet changes significantly. A new method for measurement of the droplet mass on the heated wall is presented. The regimes of droplet boiling differ significantly from pool boiling. The droplet mass is directly changed in time; evaporation is separated into several stages. 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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G. Miliauskas 《International Journal of Heat and Mass Transfer》2003,46(21):4119-4138
The study presents the mathematical model of unsteady heat transfer in evaporating semitransparent droplets of non-isothermal initial state and the numerical research method, evaluating selective radiation absorption and its influence on the interaction of transfer processes. The relation of the transfer processes inside droplets and in their surroundings and the necessity of thorough research of these processes are substantiated. When modeling the combined energy transfer in water droplets, the evaluation of thermoconvective stability in evaporating semitransparent liquid droplets is presented; the influence of the droplet initial state on its heating and evaporation process is investigated. The influence of heat transfer peculiarities on the change of the evaporating droplet state is indicated. Main parameters, which decide the peculiarities of the interaction of unsteady transfer processes in droplets and their surroundings, are discussed. The results of the numerical research are compared to the known results of the experimental studies of water droplet temperature and evaporation rate. 相似文献