Molecular dynamics study on boiling characteristics of liquid sodium under different wall temperature: Incipient boiling superheat, heat transfer performance and mechanism

DD Su and XB Li and HN Zhang and FC Li, APPLIED THERMAL ENGINEERING, 264, 125475 (2025).

DOI: 10.1016/j.applthermaleng.2025.125475

The phase change of liquid sodium is crucial for the heat transfer performance of sodium heat pipes, the safe operation of sodium-cooled fast reactors, etc., where the boiling characteristics and mechanism are still not well understood. This molecular dynamics (MD) study aims to investigate the phase change characteristics of liquid sodium and the underlying dynamics at various wall temperatures. The boiling of liquid sodium is simulated on a platinum (Pt) solid substrate, with wall temperature ranging from 1500 K to 1700 K. It is revealed that as the wall temperature increases from 1500 K to 1550 K, the phase change of liquid sodium shifts from being primarily driven by surface evaporation and bubble nucleation to one dominated by surface evaporation, bubble nucleation, and explosive boiling. When the wall temperature rises from 1550 K to 1700 K, the onset of explosive boiling advances from 17.59 ns to 0.45 ns. And there is always a layer of solid-like sodium on the solid substrate during the boiling. For the bubble nucleation in the liquid film, as the wall superheat increases, the pressure in the vapor region decreases, accompanied by a decrease in thermal resistance at the solid-liquid interface. On the contrary, for the explosive boiling, the pressure in the vapor region significantly increases as the wall superheat decreases, and the thermal resistance at the solid-liquid interface increases. At 1700 K, the interface thermal resistance reached 1.32 x 10- 8 K center dot m2/W (at onset of explosive boiling). Also, as explosive boiling progresses, atoms in the solid-like sodium layer rise, as the supercooled atoms being replenished. This study provides a microscopic understanding for the development of the liquid sodium phase change cooling technology.

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