Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000cem..conf...34d&link_type=abstract
Catastrophic Events and Mass Extinctions: Impacts and Beyond, p. 34
Astronomy and Astrophysics
Astrophysics
Nucleation, Thermodynamic Equilibrium, Vapors, Hypervelocity Impact, Asteroid Collisions, Cometary Collisions, Mathematical Models, Iron Meteorites, Supercooling, Kinetic Equations, Equations Of State
Scientific paper
In hypervelocity impacts of asteroids or comets on the surface of a planetary body, depending on the impact velocity, part or all of the projectile material and some of the target material can be vaporized and expands as a dense gas cloud. Purely hydrodynamic treatment using an equation of state valid for thermodynamic equilibrium does not cover the case when the vapor is quenched into a metastable state before condensation sets in. During the expansion, density and pressure fall by many orders of magnitude, making it difficult to treat the process with conventional hydrodynamic algorithms. Here, for expansion into vacuum, an analytical solution due to Zeldovich and Raizer is used to approximate hydrodynamics. In the presence of an atmosphere, a numerical solution based on a second-order accurate Godunov method with van der Waal's equation of state is constructed. After the pioneering work of Raizer who investigated the fate of condensation products of an iron meteorite expanding into vacuum, only few authors have studied the problem of condensation in impacts. Qualitatively, the main theoretical results of Raizer stayed unchanged. The conventional view of the order of events during condensation is as follows: (1) the adiabate of the vapor reaches the coexistence curve, the vapor becomes saturated, further expansion along the gas adiabate leads to supercooling; (2) at some critical degree of supercooling, the nucleation rate becomes high enough that a large number of critical nuclei of the new phase forms; (3) nucleation terminates, and clusters grow into droplets of macroscopic dimensions, the gas pressure drops; and (4) at some moment, the flux of molecules at the surface of the droplets is so low that the degree of condensation freezes, a non-zero mass fraction of gas remaining. In this work, a numerical solution of the kinetic equations for moments of the size distribution of growing droplets and of the energy equation is presented. It is demonstrated that the above order of events is a too simplistic scenario and that nucleation events in impact-generated vapor appear several times at different temporal and spatial scales. The degree of supercooling follows a complicated oscillating pattern on a logarithmic time scale. In this way, several generations of droplets are formed, with very different final dimensions. The distribution of sizes such is no more dominated by a single scale, but rather characterized by several generations of droplets of different characteristic sizes (each time a new generation appears, the r.m.s. size of droplets decreases, because the older and large drops are outnumbered by finer, newly-formed droplets. Additional information is contained in the original extended abstract.
No associations
LandOfFree
Multi-Scale Condensation in Impact-Produced Vapor Clouds does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Multi-Scale Condensation in Impact-Produced Vapor Clouds, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Multi-Scale Condensation in Impact-Produced Vapor Clouds will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1253570