b'Figure 4. Selected results from UNM-led project: Summary of material-dependent CHF with respect to different flow boiling conditions including selected results. Inlet subcooling is 10 C for subfigure (a) and the mass flux is 500 kg/m2s for subfigure (b).concepts to investigate the impact ofThe cladding surface temperature cladding surface characteristics in CHFwas precisely evaluated using a high under normal and anticipated off- spatial/temporal resolution optical-normal conditions. Figure 5 presentsfiber (~2.5 mm, ~100 Hz) and the selected results of surface effectsresults show that most temperature studies and flow boiling studies aspeaks occurred at 80~95% of the total well as void fraction measurements.length (~470mm) on ATF materials. This project also aims at investigatingCHF was slightly reduced as wettability the evolution of the surface charac- decreases for the ATF materials in flow teristics and surface chemistry underboiling heat transfer under atmo-testing conditions. The team evidencedspheric pressure. This is thought to be the effect of surface roughness andcaused by a lower liquid supply on wettability on critical heat flux (CHF)the cladding due to the lower wetting through the CHF tests in the UW-flowcharacteristics of the surface, resulting boiling facility under atmosphericin the early-formation of vapor film pressure. Some results are shown inwhich induces CHF. The change in Figure 6 shows for surface effectswetting characteristics was mainly seen studies along with an overview ofon Cr-coated Zr-4 by PVD where a flow boiling test facilities and results.decrease of ~10% over bare Zr-4 was 42 2020|AFC ACCOMPLISHMENTS'