SUMMARY

The primary purpose of this investigation was to experimentally determine the effect of operational parameters on the onset of flow instability (OFI) in narrow, uniformly heated, vertical, rectangular channels. The geometry investigated was a 9.0 cm long rectangular channel with a 1.0mm by 1.3cm cross section. This geometry closely matches the coolant channel geometry in an accelerator target. Nitrogen-saturated subcooled water was used as the coolant, with mass fluxes ranging from 250 to 1336 kg/m^2 s, and an inlet temperature of 26ºC for the OFI experiments. The exit pressures investigated ranged from 275kPa to 620kPa, while the heat flux ranged from 0.729 to 2.236 MW/m^2. The primary data collected from these experiments were used to develop two correlations for the heat flux and mass flux at OFI. Wall temperature data were also collected in order to develop a Nusselt number correlation for the single-phase regime. This correlation is valid for the Reynolds number range of 6x103 to 1.7x104. The data obtained in this investigation will aid designers of high-power-density systems establish design limits to prevent over heating and possible damage due to the onset of flow instability.