共查询到17条相似文献,搜索用时 156 毫秒
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为探究闪蒸喷雾冷却的微观机理, 设计并搭建了液滴悬挂式真空闪蒸实验装置, 利用可视化窗口探究Tween20 液滴闪蒸过程中的闪蒸特性及气泡生长机理. 液滴在快速降压过程中形态会经历气泡成核、气泡生长、伴随气泡生长、爆裂这四个阶段的变化, 并反复循环这一过程直至液滴稳定蒸发. 对于液滴温度的变化, 闪蒸室的终态压力起到了决定性的作用, 并且其终态温度随压力的升高明显上升. 同时通过液滴闪蒸过程形态图分析发现, 液滴在剧烈爆炸阶段其温度也发生明显下降; 在稳定蒸发阶段, 其温度也将开始稳定不变. 因此可知液滴的剧烈爆炸会带走其自身的大量热量. 而 Tween20 浓度对液滴温度的影响微乎其微, 但其会使液滴内气泡的初始成核时间发生明显滞后, 并抑制液滴内的气泡发生破裂. 相似文献
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本文利用自组装技术制备了铜基十八烷基硫醇疏水表面(SAM),通过红外热像仪分析了低压条件下液滴表面和换热表面的温度分布以及液滴脱落引起的温度分布演变。实验结果表明:低压蒸汽冷凝条件下,冷凝表面局部温度分布不均匀;单个液滴表面温度呈中心高边缘低的凸型分布;随着液滴半径的增加,液滴表面温度升高;相同操作压力下,随着过冷度的增加,液滴表面温度降低。在液滴脱落过程中,液滴表面温度逐渐升高,同时裸露出的换热表面局部过冷度增大,局部表面温度呈现出中心低周围高的凹型温度分布,随之恢复到液滴脱落前的温度。随着蒸汽压力降低,冷凝临界过冷度增加,导致裸露表面上具有更低温度的中心区域核化点密度高,最终加剧了整个换热表面液滴尺寸分布的非均匀程度。 相似文献
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设计搭建了电场作用下燃油液滴燃烧实验装置,对比了不同电压下生物柴油液滴的形态演变、变形程度、子液滴等行为,分析了不同电压下液滴火焰形貌演变、火焰尺寸等燃烧特性及最高液滴温度变化。结果表明,电压为3 k V和4 k V的电场会诱发生物柴油液滴产生锥射流,其破碎生成子液滴,尺寸范围为20~120μm,速度基本低于2.5 m·s-1;受电场对火焰和液滴的综合影响,火焰变化主要表现为高度减小、宽度增大,纵横比减小;电压为1 k V和2 k V的电场降低了最高液滴温度,而当电压增加至3 k V和4 k V时最高液滴温度增加。 相似文献
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The freezing and melting process of a small water droplet on a superhydrophobic cold surface was investigated using the Laser Induced Fluorescence (LIF) technique. The superhydrophobic surface was prepared using a sol-gel method on a red copper test plate. From the obtained fluorescence images, the phase transition characteristics during the freezing and melting process of a water droplet were clearly observed. It was found that, at the beginning of the droplet freezing process, liquid water turned into ice at a very fast rate. Such phase transition process decreased gradually with time and the volume of frozen ice approached a constant value at the end of the icing process. In addition, the freezing time was found to reduce with the decrease of the test plate temperature. Besides, when the test plate temperature is relatively high, the effect of droplet volume on the freezing time is very significant. Over all, we provide some tentative insights into the microphysical process related to the icing and melting process of water droplets. 相似文献
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Guowei Xiao Kai H. Luo Xiao Ma Shijin Shuai 《Proceedings of the Combustion Institute》2019,37(3):3219-3227
Evaporation processes of a fuel droplet under sub- and supercritical ambient conditions have been studied using molecular dynamics (MD) simulations. Suspended n-dodecane droplets of various initial diameters evaporating into a nitrogen environment are considered. Both ambient pressure and temperature are varied from sub- to supercritical values, crossing the critical condition of the chosen fuel. Temporal variation in the droplet diameter is obtained and the droplet lifetime is recorded. The time at which supercritical transition happens is determined by calculating the temperature and concentration distributions of the system and comparing with the critical mixing point of the n-dodecane/nitrogen binary system. The dependence of evaporation characteristics on ambient conditions and droplet size is quantified. It is found that the droplet lifetime decreases with increasing ambient pressure and/or temperature. Supercritical transition time decreases with increasing ambient pressure and temperature as well. The droplet heat-up time as well as subcritical to supercritical transition time increases linearly with the initial droplet size d0, while the droplet lifetime increases linearly with . A regime diagram is obtained, which indicates the subcritical and supercritical regions as a function of ambient temperature and pressure as well as the initial droplet size. 相似文献
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As realistic objects in the Universe, the black holes are surrounded by complex environment. By taking the effect of thermal environment into account, we investigate the evaporation process and the time evolutions (page curves) of the entanglement entropies of Hawking radiation of various types of black holes. It is found that the black holes with the thermal environments evaporate slower than those without the environments due to the environmental contribution of the energy flux in addition to Hawking radiation. For Schwarzschild black hole and Reissner-Nordström black hole in flat spaces, when the initial temperature of the black hole is higher than the environment temperature, the black holes evaporate completely and the Hawking radiation is eventually purified. For Schwarzschild-AdS black hole, it will evaporate completely and the Hawking radiation is purified when the environment temperature is lower than the critical temperature. Otherwise, it will reach an equilibrium state with the environment and the radiation is maximally entangled with the black hole. Our results indicate that the final state of the black hole is determined by the environmental temperature and the temporal evolution and the speed of the information purification process characterized by the page curve of the Hawking radiation is also influenced by the thermal environment significantly. 相似文献
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Norbert Roth Klaus Anders Arnold Frohn 《Particle & Particle Systems Characterization》1994,11(3):207-211
Two independent optical diagnostic techniques for studying the evaporation and freezing of optically levitated droplets are described. In the first technique the size of the droplet is determined by evaluation of the fringe spacing of the light scattered in the forward hemisphere at a scattering angle of 45°. The other technique evaluates the oscillations of optically leviated droplets caused by fluctuations in the radiation pressure. The frequency of these fluctuations is a direct measure for the change of radius with time. In both methods the signals change drastically when freezing of the droplet occurs. Hence the moment of freezing can easily be detected. 相似文献
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利用三维分子动力学模拟方法,研究了纳米尺度水滴撞击冷壁面的结冰过程.数值模拟中,统计系统采用微正则系综,势能函数选用TIP4P/ice模型,温度校正使用速度定标法,牛顿运动方程的求解采用文莱特算法,水滴内部结冰过程则通过统计垂直方向水分子温度分布来判定.研究发现,当冷壁面温度降低时,水滴完全结冰的时间减小,但水滴降至壁面温度的时间却增大;同时随着壁面亲水性降低,水滴内部热传递速度减慢(尤其是冷壁面与水滴底端分子层间),水滴内部温度趋于均匀,但水滴完全结冰时间延长. 相似文献