共查询到19条相似文献,搜索用时 187 毫秒
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通过小型冰风洞开展了发动机整流罩缩比模型即旋转锥体表面积冰可视化实验研究,获得了不同温度、锥体转速和液态水含量条件下不同时刻的霜冰、瘤状冰和刺冰三种类型积冰形貌,并且通过分析单个水滴在锥体表面的受力和传热进行了水滴的运动和凝固分析,结果表明温度越低水滴完全凝固所需的时间越短,当温度较高时,由于转速较大,锥体表面的未完全凝固液滴会在离心力作用下脱离锥面并在脱离的过程中凝固从而形成刺状结冰。 相似文献
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本文采用高速摄像仪对水滴和乙醇液滴撞击加热壁面后的蒸发过程进行了实验观测, 分析了液滴撞击加热壁面后的蒸发特性参数. 实验中, 两种液体初始温度均为20 ℃, 不锈钢壁面初始温度范围为68-126℃. 水滴初始直径为2.07 mm, 撞击壁面时Weber 数为2-44; 乙醇液滴初始直径为1.64 mm, Weber数为3-88. 结果表明, 液滴受到重力、表面张力及流动性的影响, 在蒸发过程的大部分时间内, 水滴高度持续降低而接触直径几乎不变; 蒸发后期, 液滴发生回缩, 水滴的接触直径、高度和接触角出现振荡现象. 乙醇液滴的接触角随时间的增加呈现先减小随后保持不变的趋势, 而接触直径和高度则持续减小, 直到液滴完全蒸发. 液滴蒸发总时长与液体物性和壁面温度有关, 随壁面温度的升高而减小, 与液滴撞击壁面时的Weber 数无关. 同时, 随着壁面温度的升高, 液滴显热部分占总换热量的比重增大, 显热部分能量不可忽略, 本文实验条件下得到水滴的平均热流密度为0.014-0.110 W·mm-2. 相似文献
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温稠密物质是惯性约束核聚变、重离子聚变、Z箍缩动作过程中物质发展和存在的重要阶段. 其热力学性质和辐射输运参数在聚变实验和内爆驱动力学模拟过程中有至关重要的作用. 本文通过建立非理想Saha方程, 结合线性混合规则的理论方法模拟了温稠密钛从10-5-10 g·cm-3, 104 K到3×104 K区间的粒子组分分布和电导率随温度密度的变化, 其中粒子组分分布由非理想Saha方程求解得到. 线性混合规则模型计算温稠密钛的电导率时考虑了包括电子、原子和离子之间的多种相互作用. 钛的电导率的计算结果与已有的爆炸丝实验数据相符. 通过电导率随温度密度变化趋势判断, 钛在整个温度区间, 密度0.56 g·cm-3时发生非金属相到金属相相变. 对于简并系数和耦合系数的计算分析, 钛等离子体在整个温度和密度区间逐渐从弱耦合、非简并状态过渡到强耦合部分简并态. 相似文献
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为了研究不同冷壁面特性上液滴的结晶过程以及凝固速率的规律,利用通过加入对流换热和辐射换热项,使用固相体积分数修正流场的改进的焓-LB方法,使得模型模拟的结果更加精确.分析了液滴在6种不同的壁面特性下,凝固过程平均固相体积分数随时间的变化.分析了凝固后接触角及接触面积与半径的比值随亲疏水性不同的变化.结果表明:壁面的亲水性越好,液滴凝固成核后与壁面的接触角越小,接触面积与半径之间的比值越大;反之,壁面的疏水性越好,液滴凝固成核后与壁面的接触角越大,接触面积与半径之间的比值越小.在超疏水表面存在粗糙元间距较大时,凝固速率最慢,且与粗糙元的接触面积较小,有利于抑霜除霜. 相似文献
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A physical model and a mathematical model of heat transfer in the conditions of inhomogeneous (with a solid inclusion—a carbon particle) liquid droplet evaporation while moving through high-temperature (800–1500 K) gases are formulated. Numerical investigations were performed using, as an example, a spherical inhomogeneous water droplet during heating in the air medium. The most probable mechanism of phase transitions in a water–carbon particle–heated air system is considered (the initial droplet size, radius, varied in the range from 0.5 mm to 1.5 mm, the inclusion radius was 0.1–1 mm). It has been found that in certain conditions, besides water evaporation from the outer (free) droplet surface, intensive vaporization is possible at the liquid–solid inclusion interface. Conditions of realization of these phase transitions in inhomogeneous water droplet–high-temperature gas medium systems are identified. 相似文献
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O. V. Vysokomornaya M. V. Piskunov G. V. Kuznetsov P. A. Strizhak 《Journal of Engineering Thermophysics》2017,26(2):183-196
Thermocouple measurements of temperature have been performed at three main points of heterogeneous water droplet–high-temperature gases system: on the surface and in the depth of a solid inclusion, as well as on the free surface of the water droplet. Investigations have been carried out for water droplets of an initial volume of 5–15 μl with single inclusions of cubic graphite particles of a typical size of 1 mm. The gas temperature varied from 700 K to 1200 K, which corresponds to the main practical applications: thermal purification of water from solid and liquid impurities, fire extinguishing, treatment of heat-loaded surfaces of power equipment, etc. A hypothesis about the dominant role of radiant heat transfer in vaporization within heterogeneous water droplets has been grounded. It has been shown that in a short period (a few seconds), the surface temperature of an opaque solid inclusion within a droplet can reach the boiling point of water. A significant change in the optical properties of water with increasing temperature has been revealed, i.e., water became partially transparent to the infrared radiation. Presence of an opaque heterogeneous inclusion enhances this effect due to intensification of the heating of the water film. The heat and mass transfer characteristics obtained in the experiments were used for designing a model that takes into account the radiative properties of water film and adequately reproduces the results of thermocouplemeasurements. Based on the findings of the investigations, a conclusion has been formulated that models of high-temperature evaporation of water droplets should be developed with due account of changes in the optical properties of water and formation of a vapor buffer layer around inclusions. 相似文献
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凝胶推进剂虽然兼具有液体推进剂流量可控和固体推进剂长期可储存等优点, 但凝胶喷雾液滴蒸发燃烧问题却一直困扰着凝胶推进剂研制及燃烧室设计工作, 阻碍了凝胶推进剂实际工程应用.设计实现了凝胶单液滴蒸发燃烧实验系统, 通过某型有机凝胶偏二甲肼(UDMH)单液滴在四氧化二氮蒸气中的蒸发燃烧实验现象, 进一步深入分析了凝胶液滴蒸发燃烧机理.根据实验中凝胶单液滴在不同阶段的蒸发特性, 建立了有机凝胶喷雾液滴在胶凝剂膜形成、膨胀、破裂三个不同蒸发阶段的多组分蒸发模型, 采用初步选定的模型参数及物性参数对凝胶单液滴在高温气体环境中的蒸发全过程进行了仿真计算, 并与常规液体液滴的仿真结果进行了对比分析.结果表明,凝胶喷雾液滴表面胶凝剂含量在蒸发初期增加比较缓慢, 但在某临界时刻后的极短时间内迅速升高至形成胶凝剂膜的质量分数95%, 导致表面质量流率迅速下降至0,表面温度则快速上升至UDMH推进剂沸点.胶凝剂膜形成后, 液滴半径及表面UDMH蒸气质量分数出现了实验现象中凝胶液滴反复膨胀-破裂的震荡现象, 液滴表面温度维持在略高于沸点的某温度范围内,凝胶液滴内部的沸腾蒸发明显强于液体液滴表面稳态蒸发流率, 使得凝胶喷雾液滴生存时间小于常规液体液滴. 相似文献
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The rate of dropwise evaporation is significantly altered by additives, such as benzene, n-hexane and acetone in water. These additives change some of the thermal and physical properties of the coolants, which have significant impact on various parameters that controls the droplet evaporative cooling, such as sensible, heat extraction period, droplet momentum and contact area. The open literature does not reveal the effects of the aforesaid additives on the dropwise evaporation. Therefore, in the current work, an attempt has been made to investigate the effects of above-mentioned additives on dropwise evaporation rate and reveal the mechanism involved. The droplet evaporative cooling experiments are conducted on a 2 mm thick AISI 304 steel plate (10 × 10 mm). The result shows that with increment in benzene and n-hexane concentration in water, the evaporation time significantly reduces. This is attributed to the decreasing surface tension, specific heat and contact angle. However, in case of acetone, the reduction in evaporation time is achieved only up to a concentration of 300 ppm, beyond which the evaporation time increases. This is because of the significant consumption of time in recoiling of the droplet. In addition to the above, the mechanism for the aforesaid enhancement process is tried to reveal by developing the models. For the validation of the developed equations, experimental results are compared with the numerically computed data. The comparison discloses that the developed model is quite accurate and shows insignificant variation from the experimental results. R2 and RMSE are also calculated for both the developed models and based on minimum recommended RMSE; the best model is also suggested. 相似文献
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低压闪蒸液滴形态和温度变化的研究 总被引:5,自引:0,他引:5
将液滴在常压下突然置于低压环境中,液滴由最初的平衡状态变成过热状态,发生闪蒸.本文实验研究了低压闪蒸液滴内部形态和温度的变化,系统描述了液滴闪蒸过程中的各种形态变化,总结了稳态闪蒸和稳态结冰过程中环境压力和初始温度对温度变化的影响.实验结果表明液滴闪蒸分六种形态.稳态闪蒸中环境压力越低,液滴的最终温度也越低;液滴的初始温度越高,降到最低温度的时间越长.稳态结冰过程中,液滴初始温度增加,液滴结冰温度和结冰回升最高温度也随之增加;液滴的结冰温度和回升最高温度随环境压力的增高而减小. 相似文献
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喷雾蒸发燃烧的研究对指导发动机燃烧系统设计具有重要意义。本文搭建了高速数字全息系统,在线测量乙醇喷雾火焰中液滴的粒径、三维位置、速度及蒸发率。对喷雾火焰中的液滴进行了统计分析,得到液滴粒径及三维空间分布。燃烧喷雾场液滴的平均粒径为68μm;非燃烧火焰测试区液滴数量多且较密集,燃烧火焰测试区液滴数量少且稀疏.追踪单液滴并处理得到湍流火焰中液滴的运动轨迹及速度。通过研究粒径的平方D2随停留时间ts的变化,测得液滴平均蒸发率为-3.343×10-7 m2/s. 相似文献
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Z. Tavassoli G.J. Rodgers 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(1):139-144
We study a single, motionless three-dimensional droplet growing by adsorption of diffusing monomers on a 2D substrate. The
diffusing monomers are adsorbed at the aggregate perimeter of the droplet with different boundary conditions. Models with
both an adsorption boundary condition and a radiation boundary condition, as well as a phenomenological model, are considered
and solved in a quasistatic approximation. The latter two models allow particle detachment. In the short time limit, the droplet
radius grows as a power of the time with exponents of 1/4, 1/2 and 3/4 for the models with adsorption, radiation and phenomenological
boundary conditions, respectively. In the long time limit a universal growth rate as is observed for the radius of the droplet for all models independent of the boundary conditions. This asymptotic behaviour
was obtained by Krapivsky [#!krapquasi!#] where a similarity variable approach was used to treat the growth of a droplet with
an adsorption boundary condition based on a quasistatic approximation. Another boundary condition with a constant flux of
monomers at the aggregate perimeter is also examined. The results exhibit a power law growth rate with an exponent of 1/3
for all times.
Received 19 July 1999 相似文献