Experiments on Preplanetary Dust Aggregation
Experiments on Preplanetary Dust Aggregation
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行星前尘埃聚集实验
DOI：
10.1006/icar.1998.5891
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发表时间：
1998
期刊：
影响因子：
3.2
通讯作者：
J. Blum
中科院分区：
文献类型：
--
作者：
G. Wurm;J. Blum
为了研究早期太阳星云中的低速尘埃相互作用，我们进行了两组实验。在第一类实验中，我们研究了嵌入稀薄湍流气体环境中的尘埃云的颗粒质量演化，在该环境中，最初单分散的球形SiO_2颗粒(直径为1.9μm)迅速聚集。对聚集体结构的分析表明，团簇是由弹道团簇聚集形成的，没有重组，遵循m∝a Dfg形式的质量-尺寸关系，其中Df≈1.91是质量为m的聚集体的分维，a g是质量为m的聚集体的回转半径。与模型计算的比较表明，平均碰撞速度vc落在0.07m S−1≲vc≲0.5m S−1区间。在第二组实验中，通过从涡轮分子泵中提取分形聚集体并将其注入悬浮管中，我们能够观察到聚集体之间的个别碰撞。这些类型的模拟是在实验室进行的，因此碰撞的主要来源是相对沉积。在碰撞速度为0.001 m S≈1−v c≲0.01m S≲1的范围内，我们研究了单体数在i=1和i−100之间的28个聚集体之间的碰撞。我们的观察表明，对于上述集合体质量和碰撞速度，粘合效率为βc=1，没有颗粒重组的迹象。由于我们重视我们的实验室实验与太阳星云的情况之间的相似性，例如，颗粒大小和成分、碰撞速度和摩擦制度，我们的研究结果直接适用于太阳星云的模拟，并可用于对太阳系早期聚集生长的时间尺度估计。我们的实验表明，由气体阻力效应(如沉积、径向漂移或气体湍流)引起的碰撞自相互作用的尘埃颗粒集合将采用钟形质量分布。这种演化导致了分维低于或接近Df=2的分维聚集体。
Abstract For the study of low-velocity dust interactions in the early solar nebula, we have performed two sets of experiments. In the first type of experiments, we studied the grain-mass evolution of a dust cloud embedded in a rarefied turbulent gas environment in which the initially monodisperse spherical SiO 2 grains (1.9 μm diameter) rapidly aggregate. The analysis of the resulting aggregate structures revealed that the clusters were formed by ballistic cluster–cluster aggregation without restructuring and follow a mass–size relation of the form m ∝ a D f g , where D f ≈ 1.91 is the fractal dimension and a g is the radius of gyration of an aggregate with the mass m . A comparison with model calculations shows that the mean collisional velocity v c falls into the interval 0.07 m s −1 ≲ v c ≲ 0.5 m s −1 . By extraction of the fractal aggregates from the turbomolecular pump and injection into a levitation tube in the second set of experiments, we were able to observe individual collisions between the aggregates. These types of simulations were performed in the laboratory so that the dominant source of the collisions was relative sedimentation. We investigated 28 collisions between aggregates with monomer numbers between i = 1 and i ≈ 100 in the collision velocity range 0.001 m s −1 ≲ v c ≲ 0.01 m s −1 . Our observations show a sticking efficiency of β c = 1 for the above-mentioned aggregate masses and collision velocities with no signs of grain restructuring. As we have attached importance to the similarity between our laboratory experiments and the situation in the solar nebula, e.g., grain size and composition, collision velocities, and friction regime, the results of our investigations are directly applicable to the solar nebula modeling and may be used for time-scale estimations of the aggregate growth in the early Solar System. Our experiments suggest that an ensemble of dust grains which is collisionally self-interacting caused by gas drag effects, such as sedimentation, radial drift, or gas turbulence, will adopt a bell-shaped mass distribution. This evolution results in fractal aggregates with fractal dimensions below or close to D f = 2.
影响因子：
3.2
作者：
V. Mannings;A. Boss;S. Russell
通讯作者：
V. Mannings;A. Boss;S. Russell