Measurement of the heat transfer coefficient and viscous pressure loss for mercury flowing in narrow channels

The Spallation Neutron Source (SNS) is a new linear accelerator that is being designed for neutron scattering experiments. The SNS will supply pulses of high-energy protons to a flowing liquid mercury target. The spallation reaction resulting from the bombardment of the protons on the mercury target produces 1.3 MW of thermal power, which must be absorbed by the mercury and structural materials. To prevent excessive temperatures and thermal stresses in the structural materials, the liquid mercury must also serve as a coolant in addition to being the source of neutrons. To provide additional cooling to the target container, cool mercury flows in narrow, rectangular channels around the nose of the target container. This area is directly exposed to the proton beam. Three test sections are used in the Mercury Thermal Hydraulic Loop (MTHL) to investigate heat transfer in the window-cooling channels. The Water-Cooled Test Section is used to detect nonwetting spots. The Electrically-Heated Straight Test Section provides high quality data on the heat transfer coefficient and friction factor for flow velocities from 1 to 4 m/s and heat fluxes from 192 kW/m² to 1.14 MW/m² at mercury bulk temperatures ranging from 67 to 143 °C. Finally, A Curved Electrically Heated Test Section provides investigation of the effect of curvature on the heat transfer and friction factor performance. Results from the experiments indicate that no non-wetting spots appeared. Observed friction factors are slightly lower than those obtained from a Moody Curve for a smooth pipe, but they agree well at the SNS nominal velocity. Inferred heat transfer coefficients lie well with world tube data when compared on a Nusselt vs. Peclet number plot. Due to fabrication difficulties with the Curved Electrically Heated Test Section, no effects of curvature are discernable.