Response surface methodology-based optimization of Al 2 O 3 -CuO hybrid nanofluid synthesis parameters for enhanced stability in thermal energy storage applications

Zeta potential and particle size (PS) are highly influential parameters in determining the stability of the nanofluids. Therefore, in the present article, the influence of synthesis parameters on the stability of the hybrid nanofluid (hNF) prepared from two dissimilar nanoparticles, CuO and Al 2 O 3 , has been investigated by implementing response surface methodology (RSM). Furthermore, three input factors (nanoparticle concentration, sonication speed and sonication time), three levels and a face-centred central composite design technique were utilized in the study. Furthermore, to relate the variable parameters to the developed model through analysis of variance (ANOVA), a regression analysis was applied. ANOVA results confirmed the statistical significance of the model; the Predicted R 2 of 0.9589 is in reasonable agreement with the adjusted R 2 of 0.9832 having difference of less than 0.2. For zeta potential, the predicted R 2 of 0.9334 and adjusted R 2 of 0.9826 were observed for PS. Finding suggests, and it is reasonable to state, that sonication speed has a great impact on the zeta potential and PS of the hNF, followed by concentration and sonication time. The zeta potential improves while PS reduces with an increase in the sonication speed. Higher concentration and sonication time have a negative impact on the response parameters. The optimum operating conditions were obtained at a nanoparticle concentration of 0.110043% (∼0.1%), sonication time of 89.2426 (∼90) min, and sonication speed of 1482.07 (∼1500) r/min. Under these conditions, the model predicted a zeta potential of 35.0277 mV and a PS of 72.3068 nm. The predicted optimum factors were confirmed experimentally with an error of less than 10%. Lastly, the results confirmed that the models were consistent with the data, indicating the importance and reliability of the models in predicting the studied responses.