Experimental Investigation of Flow Boiling Heat Transfer in Different Flow Regimes

This study presents an experimental investigation of flow boiling heat transfer using the low-GWP refrigerant R1233zd(E) across three distinct flow regimes: slug, intermittent, and annular flow. A dedicated test section was first validated through single-phase liquid convection experiments, confirming its thermal reliability through close agreement with the wellestablished Gnielinski correlation. Flow boiling measurements were then conducted with flow regimes identified using the Wojtan (and Barbieri) flow map and visualized through highspeed imaging. The heat transfer coefficient was found to vary significantly with the flow regime. Results reveal that annular flow consistently delivers superior heat transfer performance due to its stable liquid film dynamics. The (lower) heat transfer coefficient corresponding to the intermittent flow regime increases with applied power, which can be explained by the nucleate boiling contribution to the heat transfer.