Mechanism analysis of the influence of nanoparticles on the convective heat transfer coefficient of traditional fluids

With the continuous progress of science and technology, the heat transfer performance of electronic chips and internal combustion engine pistons is increasingly required by industry. The traditional pure liquid can hardly meet the current heat transfer requirements, and it is known that the heat transfer performance of solids is always better than that of fluids. Therefore, adding solid particles to the fluid has a positive effect on the heat transfer performance of the fluid. In this paper, an experimental system is established to study the heat transfer performance of SiO2-water nanofluids, and the variation of each physical parameter and convective heat transfer coefficient of SiO2-water nanofluids flowing in a circular tube at different volume fractions is measured. The microscopic mechanism of the enhanced heat transfer of nanofluids is also analyzed from the perspective of nanoparticle's micro-motion by numerical simulation. The results show that the convective heat transfer coefficients of nanofluids gradually increase with increasing volume fraction of nanoparticles under the same conditions. The convective heat transfer coefficients of SiO2-water nanofluids with volume fractions of 0.5 %, 1 %, and 2 % increase by 15.1 %, 25.9 %, and 36.8 %, respectively, compared with pure water. Then the extent of the effect of nanofluid physical parameter changes and nanoparticle micro-motion on the improvement of nanofluid heat transfer performance is analyzed. It is found that the micro-motion of nanoparticles has a greater effect on the enhanced heat transfer of nanofluids compared to the variation of physical parameters. It is also found that the conventional convective heat transfer coefficient formulation for single-phase flow is not applicable to calculate the convective heat transfer coefficient of SiO2-water nanofluids. Therefore, the new formulations based on the convective heat transfer coefficient of SiO2-water nanofluids in different flow regimes are established.