Experimental investigations of material-conjugated subcooled flow boiling.

Experimental investigations into accident-tolerant fuel and conventional claddings are conducted across a wide range of flow boiling conditions. Two key thermal-hydraulic performances of these claddings, heat transfer coefficients, and critical heat flux, are characterized for their dependence on thermophysical properties, wall thicknesses and surface morphology. Materials that are investigated in this study include Zircaloys, FeCrAl alloys, Inconels, and stainless steels. Relevant experimental results demonstrate that the impact of thermophysical properties and wall thicknesses on heat transfer coefficients is significant and challenging to resolve using current predictive models. This difference caused by the cladding material is only appreciable under weak heat convection conditions. Increasing the mass flow rate and/or liquid subcooling can significantly reduce or even eliminate this difference in flow boiling heat transfer coefficient. To further analyze these experimental results mechanistically, material-conjugated quenching and evaporative heat fluxes are developed to understand the underlying mechanisms related to cladding properties. Similarly, the flow boiling critical heat flux exhibits a noticeable dependence on cladding material properties, including wall thickness, thermophysical properties, and surface morphology, particularly at low mass fluxes and low inlet subcoolings. However, this critical heat flux dependence on material side factors weakens with increasing mass flow rate and/or inlet subcooling. This suggests that convection-dominated heat transfer becomes increasingly dominant compared to quenching and evaporative mechanisms in determining both heat transfer coefficients and critical heat flux. [Display omitted] • Flow boiling characteristics of various claddings are obtained using subcooled water. • Material-related factors are appreciable under weak heat convections. • Gradual increasing of mass flux and/or inlet subcooling reduces the impacts from materials. • The role of cladding properties can be rationalized by heat flux partitioning model. • ATF-loaded LWR cores can be assessed by present CHF databases under nomimal operation condidtions. [ABSTRACT FROM AUTHOR]