Application of three-level general factorial design approach for thermal conductivity of MgO/water nanofluids

In this study, a three-level general factorial design was employed to evaluate the effect of parameters of temperature, volume fraction and nanoparticle diameter on thermal conductivity coefficient of MgO/water nanofluids. The reason of investigating MgO/water nanofluid is because of there is no certain defined relationship between thermal conductivity of MgO/Water nanofluid and temperature, volume fraction and particle size parameters. The factors under investigation were selected based on previous experiences and also the restrictions existing in the process. Also, the range of each variable was selected in a way that the effect of each one on the response of process is noticeable as much as possible. The nanofluid thermal conductivity coefficient was evaluated in different volume fractions ranging from 0.01 to 0.03. Regression analysis indicated good fit of the experimental data to the third-order polynomial model with coefficient of determination (R-2) value of 0.9994 and F-value of 2570.57. The results revealed that all three parameters of temperature, nanoparticle volume fraction, and nanoparticle size and the interaction between them affect the nanofluid thermal conductivity coefficient. The optimum value of temperature, nanoparticle size and volume fractions for thermal conductivity of MgO/water nanofluid were 25 degrees C, 40 nm and 0.03, respectively. Also, the results show that the effect of an increase in nanoparticle diameter on thermal conductivity coefficient is low and it has a decreasing influence. (C) 2017 Elsevier Ltd. All rights reserved.