Heat Transfer Enhancement of Nanofluids with Non-Spherical Nanoparticles: A Review

This article reviews the heat transfer enhancement of nanofluids with non-spherical nanoparticles. We divided the non-spherical nanoparticles suspended in nanofluids into three categories based on the dimension of geometric particle structure. Based on the measured data in experimental studies, we then evaluated the shape effect of non-spherical nanoparticles on thermal conductivity and convective heat transfer enhancement of nanofluids. Recent studies explored the numerical predictions and related heat transfer mechanisms. Due to large aspect ratios, thermal conductivity is abnormally enhanced only for nanofluids with carbon nanotubes/nanofibers/nanowires. The approximate enhancement effect exerted by three types of non-spherical nanoparticles on thermal conductivity was 4.5:2.5:1. Thermal conductivity enhancement per concentration was larger for nanorods/ellipsoids with small aspect ratios. The convective heat transfer coefficient was increased by suspending non-spherical nanoparticles in the base fluid. Consequently, no significant thermohydraulic performance was discovered for convective heat transfer of non-spherical nanoparticle nanofluid flow, specifically for turbulent flows, due to increased pumping power. However, the temperature and particle concentration effect on convective heat transfer remains unclear. In addition, no perfect model for predicting the thermal conductivity and convective heat transfer of non-spherical nanoparticle nanofluids has been reported.

Automated summary

This article reviews the heat transfer enhancement of nanofluids with non-spherical nanoparticles. The authors categorized the non-spherical nanoparticles into three types based on their geometric structures and evaluated their effects on the thermal conductivity and convective heat transfer of nanofluids using experimental data. The research found that non-spherical nanoparticles with large aspect ratios, such as carbon nanotubes/nanofibers/nanowires, exhibited abnormally enhanced thermal conductivity. The enhancement effect on thermal conductivity was approximately 4.5:2.5:1 for the three types of non-spherical nanoparticles. Non-spherical nanoparticles with small aspect ratios, such as nanorods/ellipsoids, showed larger enhancement in thermal conductivity per concentration. The convective heat transfer coefficient was increased by suspending non-spherical nanoparticles in the base fluid, but no significant thermohydraulic performance was observed, particularly for turbulent flows, due to increased pumping power.