M.S. Thesis Presentation by Ryan M. Stoddard
Monday, April 10, 2000

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

"Onset of Flow Instability and Critical Heat Flux in Horizontal, Thin, Uniformly-Heated Annuli"


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 using heavy water through 1 mm thick concentric annular channels.  Under accident or transient conditions, however, boiling may take place in the coolant channels, which can lead to two-phase flow instabilities or burnout within the channels.  Therefore, the purpose of this investigation was to study the effects of various operational and design parameters on the onset of Ledinegg flow instability (OFI) and critical heat flux (CHF) in horizontal, thin, uniformly-heated annuli.

Thirteen different experimental setups were employed in the Georgia Tech Microchannel Test Facility (GTMTF) to determine the OFI and CHF behavior of annular channels with thickness on the order of one millimeter.  The OFI data were compiled and used to create two correlations; one comparing OFI heat flux to saturation heat flux and the other comparing OFI mass flux to saturation mass flux.  The CHF data acquired were compared with several empirical CHF correlations available in the literature and used to demonstrate that OFI, rather than CHF, is the limiting phenomenon in microchannel heat transfer.  The data obtained in this investigation provided the basis for quantifying the thermal margins for the proposed APT target bundle geometry under both normal and accident conditions.