Effects of nanoparticle size on surface dynamics and thermal performance in film boiling of Al<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si171.svg" display="inline" id="d1e1028"><mml:msub><mml:mrow/><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:math>O<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si172.svg" display="inline" id="d1e1036"><mml:msub><mml:mrow/><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:math> water-based nanofluids

Abstract

This study investigates the impact of nanoparticle diameter on film boiling in Al2O3 water-based nanofluids along a vertical cylinder, focusing on nanoparticle sizes of 5 nm, 10 nm, 30 nm, and 50 nm. Employing a Continuous-Species-Transfer method within a Computational Multi-Fluid Dynamics framework, it simulates the behavior of nanoparticles in liquid and vapor states, emphasizing Brownian motion and thermophoretic effects. A 2D axisymmetric analysis reveals how nanoparticle sizes influence temperature gradients, deposition patterns, and thermophysical properties, with a particular focus on the Nusselt number for assessing heat transfer efficiency. Findings indicate that smaller nanoparticles accumulate on surfaces more over time because of increased Brownian motion. Additionally, nanofluids with smaller particles improve thermal conductivity and concentration near the heat source, which decreases surface tension in the vapor phase. In contrast, larger nanoparticles lead to reduced fluid viscosity. Interestingly, nanofluids with 30 nm and 50 nm nanoparticles perform similarly, indicating a size threshold beyond which further increases do not significantly improve boiling heat transfer. In contrast, nanofluids containing 5 nm and 10 nm nanoparticles exhibit markedly superior thermal removal efficiency, underscoring the critical role of nanoparticle size in optimizing film boiling performance.

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