(Drs. Said I. Abdel-Khalik and Sheldon M. Jeter, co-advisors)

"Onset of Flow Instability in Horizontal, Uniformly-Heated Annuli"

Abstract

The tungsten target of the Accelerator Production of Tritium (APT) project, currently under development at Los Alamos National Laboratory, consists of horizontal, concentric annuli. Under normal conditions, the target is cooled by single-phase forced convection of heavy water through 1 mm thick concentric annular channels between the tungsten annuli. Under accident or transient conditions, however, boiling and two-phase flow may take place in the coolant channels. To prevent Ledinegg flow excursions in the boiling channels, limits are imposed on the channel power input. The purpose of this research project is to experimentally determine the effect of various operational parameters on the onset of flow instability (OFI) in heated, horizontal annuli with prototypical APT dimensions. Additionally, the effect of uncertainties in coolant channel gap thickness due to manufacturing tolerances on OFI is investigated.

Six annular configurations with gap thicknesses between 0.724 mm and 1.001 mm, which simulated the innermost annular channel within the peak power rung of the prototypical APT target, were tested in the Georgia Tech Microchannel Test Facility (GTMTF). Water at a controlled flowrate, exit pressure , inlet temperature, and dissolved non-condensable gas concentration was delivered to the test section. Power was provided to both the inner and outer surfaces of the annulus to produce a wide range of heat fluxes and inner-to-outer surface heat flux ratios. A total of 138 OFI experiments were run. For each set of operating conditions and power inputs, the demand curves for the channel were generated. The demand curves were then used to determine the mass flux corresponding to the onset of flow instability. The data were compared to predictions of OFI correlations developed previously for circular channels and triangular rod bundle subchannels. A new OFI correlation based on the data obtained in this investigation was developed.