Seven important parameters (temperature, concentration, average primary particle size, pH of nanofluid, density of nanoparticle, elapsed and sonication time) which are responsible for the change of the thermal conductivity of nanofluids were experimentally investigated on CuO/water nanofluid and were statistically surveyed by factorial design method. In order to investigate the main effects and their interactions on the thermal conductivity ratio a 2_III^(7-4) fractional factorial design (FFD) with three other experiments at the center of the design for analysis of variance were applied. Also, the factorial model was statistically validated by analysis of variance (ANOVA). The predicted response was compared with the experimental ones. Generally, the predicted values were in reasonable agreement with the experimental data, further confirming the high predictability of the models.

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