(Drs. Said Abdel-Khalik and Minami Yoda, co-advisors)
"Flow Visualization within a Seven-Rod Micro-Bundle"
Single-phase forced convection in microchannels is an effective cooling mechanism which can accommodate the extremely high heat fluxes in such diverse applications as accelerator targets, micro-electronic cooling, compact fission reactor cores, fusion reactor blankets, and micro heat exchangers. Under accident conditions, boiling may take place in the microchannels. Analysis of the thermal-hydraulic performance of such systems requires knowledge of the flow distribution among the channels under normal single phase conditions, as well as the two-phase flow regimes and pressure drop under accident conditions. This research was motivated by the Accelerator Production of Tritium (APT) project at Los Alamos National Laboratory.
A seven-rod micro-bundle with prototypical APT dimensions was constructed from precision ground Pyrex glass rods. Particle tracking velocimetry (PTV) was used to determine the flow distribution within the various sub-channels of the seven-rod micro-bundle. The velocity distribution was compared to predictions of two computer codes: COBRA and Fluent. Additionally, two-phase flow regimes and pressure drop for the bundle were obtained over wide ranges of liquid and gas superficial velocities. Six distinct flow regimes were identified utilizing a stroboscope and high speed video camera. A two-phase (air-water) flow regime map was developed. The micro-bundle flow regime map was compared to prior single microchannel data and models. Two-phase pressure drop data were also collected and compared with predictions of the homogeneous equilibrium model and Friedel's model.
The data obtained in this investigation will provide the means to validate various thermal--hydraulic and safety analysis codes for single and two-phase flow within micro-rod bundles.