In this work, the effects of carbon nanotubes and an amphoteric surfactant, namely lauryl betaine, on the absorbance, contact angle, surface tension, and thermal conductivity of DW were experimentally investigated. The concentration of the carbon nanotubes was 0.5 wt% and that of lauryl betaine was 100, 500, and 1000 ppm in distilled water. From the absorbance measurement results, the addition of lauryl betaine could increase the absorbance in the wavelength range of UV and visible rays (200~1000 nm). In addition, the higher the surfactant concentration, the higher the dispersibility. The contact angle of the distilled water showed a monotonic decreasing trend with an increase in the surfactant blending ratio, while there were no significant changes in that of the carbon nanotube nanofluid. Analogous behaviors were observed in the surface tension measurements. The surface tension of the distilled water dramatically decreased with an increase in the surfactant blending ratio. The highest decrement was 46.05% at the surfactant concentration of 1000 ppm. In contrast, there were no significant changes in the case of the carbon nanotube nanofluid. Adding 0.5 wt% of the carbon nanotubes to distilled water could substantially enhance the thermal conductivity up to approximately 3%. The degradation effect of the amphoteric surfactant on the thermal conductivity of the fluids was observed in both distilled water and nanofluids.
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