Pool boiling heat transfer of CNT/water nanofluids

The effects of carbon nanotubes structures and different functional groups were studied on the pool boiling heat transfer coefficients (HTC) and critical heat fluxes (CHF). In order to enhance the dispersion and stability in the aqueous media, multi-walled carbon nanotubes (CNT) were functionalized using two methods. So, covalent functionalization with cysteine and silver nano-particles and non-covalent functionalization via Gum Arabic (GA) were employed. Then, three nanofluids including GA-, Cysteine- and Ag treated CNT were prepared in different weight concentrations and their thermal performance were investigated nearly up to the CHF. In agreement with the results, while the pool boiling HTC of the non-covalent nanofluids were lower than that of the deionized water, the covalent nanofluids demonstrated significant increases. In addition, the CHF of the nanofluids exhibited significant enhancement in all concentrations. The CHF and HTC were also measured in the presence of different diameters. As the size of CNT decreased, the specific surface area increased, implying higher CHF and HTC. [Display omitted] •CNT are functionalized via cysteine and silver nanoparticles.•Covalent and non-covalent nanofluids are utilized to investigate the effects of functional groups.•The pool boiling HTC and CHF of the covalent and non-covalent nanofluids are studied experimentally.•The effect of CNT diameter on the pool boiling HTC and CHF is studied.