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Advanced Energy Technology Group Seminar Series


20 November 2003
10:00 AM
479 EBU-II, UC San Diego

Experimental and numerical study of transient condensation of lithium and beryllium fluoride excited vapors for IFE systems

Pattrick Calderoni
Mechanical and Aerospace Engineering Dept.
University of California, Los Angeles

ABSTRACT:

UCLA has constructed and operated an experimental facility to study the transient cooling and condensation of excited vapors generated from the ablation of IFE prototypical materials. The work is part of the effort to provide an experimental feasibility assessment of the application of liquid blankets to inertial fusion energy systems.

The presentation summarizes the results obtained during the year 2003. At first the excited vapor where generated by ablation of a solid sleeve of pure lithium fluoride crystals in a high-current electrical discharge, and injected in an expansion chamber under hard-vacuum conditions. The diagnostic system employed to study condensation includes uniform chamber pressure monitoring, excited gas emission spectroscopy, optical time-of-flight technique and mass spectroscopy of the residual gases. The preliminary results showed that the condensation of LiF vapor is compatible with the stringent requirements of IFE systems repetition rates. But the vapor source design was characterized by the generation of a high amount of non-condensable gases due to the inherent fragility of the LiF crystals. Although the presence of non-condensable gases did not seem to influence the condensation rate, it did inhibit the complete condensation of LiF at the end of the transient process. Because of this, a different configuration of the vapor source was used with flibe. The main difference is that the ablated material is now the surface of a liquid pool of flibe that is held by a cup of nickel that functions both as a crucible for melting and as a anode for the electrical discharge. The results show that the pressure drop associated with the condensation of flibe vapors is well fitted by an exponential decay. The condensation rate can be related to the decay constant, which for the two experiments obtained at 1.44 kJ and 2.56 kJ discharge energy was respectively 4.22 ms and 4.27 ms. SEM analysis of collecting plates showed evidence of micron and sub-micron aerosol formation and impingement on the plate perpendicular to the velocity of the vapors, while the plate parallel to the vapor velocity was characterized by film condensation.

A numerical module has been coupled with the numerical code Tsunami, developed at UCB to simulate gas dynamics in the chamber of IFE systems, to account for condensation at the boundaries of the numerical domain. Results of the application of the code to the geometry and conditions of the experiments showed that the simulation overestimates the condensation rate by one order of magnitude even after the presence of a non-condensable component in the gas mixture was considered.

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