Comparing the effect of single and mixture surfactants on the improvement in stability and thermal conductivity of CuO nanofluid: an experimental study

Abstract

In the present study, the effect of single and mixed surfactants, including SDS and CTAB, on the stability and thermal conductivity of CuO nanofluid is studied. By using a standard two-step method, the nanofluids are prepared. The mass fraction of single surfactants and the CTAB-to-SDS mass fraction ratio of mixture surfactants are considered the parameters of this study. The visual sedimentation technique and zeta potential analysis are employed to evaluate the stability of nanofluid, and the DLS analysis is used to measure the mean diameter of particles. Also, the nanofluid’s thermal conductivity coefficient is measured using the KD2 apparatus and compared with the theoretical models. The results show that the nanofluid containing mixed surfactants has more stability than that of the single one so that the maximum stability is observed at a 95:5 mixture of CTAB–SDS. Also, it is observed that the thermal conductivity of the most stable mixture surfactant is lower than the single one at lower temperatures (20, 25, 30 °C), while at higher temperatures (35, 40, 45 °C), the mixture surfactant demonstrates higher thermal conductivity than the single one. The increases in thermal conductivity of CuO–water nanofluid containing mixture surfactant at 35 °C, 40 °C, and 45 °C are 13.476%, 16.381%, and 16.432%, respectively.