An empirical investigation on the thermal conductivity of a hybrid nanofluid ( MgO ‐ ZnO /ethylene glycol) and proposal of a novel multivariate correlation

Abstract

Recently, new research studies on nanofluids are increasingly focusing on hybrid nanofluids with enhanced thermophysical properties to overcome the limitations imposed by single‐component nanofluids. This work experimentally investigated the thermal conductivity of a novel hybrid nanofluid consisting of a mixture of MgO–ZnO and ethylene glycol (EG). Three significant variables were tested to investigate the performance of the new hybrid nanofluid: volume fraction (0.2%–1%, at a constant mixture of 50–50 ratio), temperature (set to 25–50°C with high accuracy), and nanoparticle diameter (set to 20, 55, and 90 nm). From the experimental study, it was identified that the maximum enhancement of the thermal conductivity was 11.48%, which was at the smallest nanoparticle diameter (20 nm), highest temperature (50°C), and highest solid concentration (1%). In addition, a new and accurate correlation function for this phenomenon was established. By using linear regression and MANOVA analysis, the correlation function achieved an R 2 of 0.99 with a difference of at most 1.15%, reflecting its high accuracy of prediction. It is clear that the values of all three variables—nanoparticle size, temperature, and volume fraction—played a highly important and interdependent role in the determination of the values of the thermal conductivity of the nanofluid. By performing a sensitivity analysis on the results of interest, the significant role of thermal conductivity in the variation of the variables at the extremes of the experimental range—20 nm, 50°C, and 1%—was established.