Effect of Heater Material and Thickness on the Steady-State Flow Boiling Critical Heat Flux

Steady-state internal flow boiling experiments were conducted on various materials, including accident tolerant fuel cladding material Fe–12Cr–6Al (C26M2) alloy, Zircaloy, and metal-based materials, at atmospheric pressure (84 kPa), 10°C inlet subcooling, and 200 kg/m²‧s mass flow entering the test tubes until critical heat flux (CHF) was reached. The clad thickness effects on flow boiling CHF were evaluated showing a negative relation between CHF and clad thickness up to 0.711 mm. An approach was established to mechanistically understand the measured CHF differences among the tested materials using thermal effusivity, activity, diffusivity, and surface thermal economy. No clear relations were observed within the range of thermal properties of the tested materials. Compared to past CHF data for a mass flux of 300 kg/m²‧s, the CHF data for 200 kg/m²‧s showed increased relative differences among materials. This result implies that higher mass flux may further decrease apparent material sensitivity to CHF.