Experimental study of natural convection heat transfer and gaseous dynamics from dual-channel circulation loop

This research focuses on establishing a range of scaled separate and integral effects experiments for studying thermal-hydraulic behavior occurring within a component or region of the prismatic very high-temperature reactor (VHTR) such as plenum-to-plenum heat transfer and gaseous dynamics during natural circulation. Natural circulation of the coolant is the leading capability for VHTR to transport the decay heat from the core to the reactor vessel during accident scenarios. To address this need, a scaled-down facility is designed and developed with only two channels with upper and lower plena. The emphasis is placed on high-resolution and high-fidelity experimental data for local heat transfer and gaseous dispersion measurements utilizing sophisticated techniques under different operating conditions. These techniques are 1) non-invasive flush wall mounted heat transfer coefficient probe to measure reliably the heat flux and surface temperature along the flow channels, and by measuring simultaneously these two variables and the flowing fluid, the heat transfer coefficient can be obtained, 2) radial temperature sensor adjuster to measure radial temperature variations of the coolant along the flow channels, and 3) advanced gaseous tracer technique to accurately measure the residence time distribution (RTD) in an of flow systems by injecting pulse change gas tracer and then monitoring its concentration at the exit. The measured RTD is utilized to quantify the gas dispersion and identify the degree of mixing in the system. The obtained local heat transfer and gaseous dispersion data in this study will provide high spatial and temporal resolutions benchmarking data for validating heat transfer and gaseous dispersion computations and correlations that are integrated with CFD simulations --Abstract, page iv