The stability, viscosity and thermal conductivity of carbon nanotubes nanofluids with high particle concentration: A surface modification approach

This study demonstrated a novel approach to formulating nanofluids with high mass concentration, good colloidal stability, enhanced thermal conductivity and moderate viscosity increase from the β-Cyclodextrin (β-CD) modified carbon nanotubes. This method could be applied to a variety of functional nanomaterials and make use of the liquid properties and functions of dispersed nanoparticles to make nanofluids become more efficient heat transfer fluids and industrial application media. A scalable improved two-step method based on mechanical milling technique for the preparation of nanofluids was demonstrated. Highly stable nanofluids with up to 5 wt% of surface-modified multiwalled carbon nanotubes (CD-CNTs) in deionized water were successfully obtained. It was demonstrated that the preparation method could effectively disperse the carbon nanotube aggregates, providing relatively small increases in viscosity (the viscosity of 5 wt% nanofluids was 31 mPa·s averagely). The thermal values of CD-CNTs/water nanofluids reached to their maximum values (1.013 W/(m·K) and 69.68%, respectively) at 5 wt%. Heat was more easily transferred along the carbon nanotubes, which was more efficient than thermal conduction through solid-liquid-solid paths. This study has demonstrated that the proposed surface modification technique and preparation method could together ensure the requirements for achieving MWCNTs nanofluids with high mass concentration and desired properties.