Solar-thermal conversion performance of heterogeneous nanofluids

Nanofluids have excellent optical and thermal properties and show great potential for applications in direct absorption solar collectors (DASCs). However, due to the preparation process or force interaction, the nonuniform distribution of NP radii (r) and volume fraction (fv) in heterogeneous nanofluids may affect the solarthermal conversion performance. In this work, we established a multiscale model based on the finite element method (FEM) coupled with the Monte Carlo (MC) method to investigate the solar-thermal conversion performance of heterogeneous nanofluids. Results show that the non-uniform distribution of r has little effect on the solar-thermal conversion performance due to the weak scattering and strong absorption properties of NPs in dilute nanofluids. The non-uniform distribution of fv has great effect on the local heating flux distribution in the heterogeneous nanofluid, which would affect the collector efficiency (ricol) due to the different surface heat losses. And a superior ricol can be achieved at a downward-gradient distribution of r and fv compared with uniform or upward-gradient distributions. This work develops an effective method to evaluate the solar-thermal conversion performance of heterogeneous nanofluids and provides a promising strategy by tuning the distribution of r and fv to enhance the solar collector performance.